ALBERT

Description: ABSTRACT A reactive transport modeling framework is presented that allows simultaneous assessment of groundwater flow, water quality evolution including δ 13 C, and 14 C activity or “age”. Through application of this framework, simulated 14 C activities can be directly compared with measured 14 C activities. This bypasses the need for interpretation of a 14 C age prior to flow simulation through factoring out processes other than radioactive decay, which typically involves simplifying assumptions regarding spatial and temporal variability in reactions, flow, and mixing. The utility of the approach is demonstrated for an aquifer system with spatially variable carbonate mineral distribution, multiple organic carbon sources, and transient boundary conditions for 14 C activity in the recharge water. In this case the simulated 14 C age was shown to be relatively insensitive to isotopic fractionation during DOC oxidation and variations in assumed DOC degradation behaviour. We demonstrate that the model allows quantitative testing of hypotheses regarding controls on groundwater age and water quality evolution for all three carbon isotopes. The approach also facilitates incorporation of multiple environmental tracers and combination with parameter optimization techniques. This article is protected by copyright. All rights reserved.

Description: Water scarcity is likely to increase in the coming years, making improvements in irrigation efficiency increasingly important. An emerging technology that promises to increase irrigation efficiency substantially is a wireless irrigation sensor network that uploads sensor data into irrigation management software, creating an integrated system that allows real-time monitoring and control of moisture status that has been shown in experimental settings to reduce irrigation costs, lower plant loss rates, shorten production times, decrease pesticide application, and increase yield, quality, and profit. We use an original survey to investigate likely initial acceptance, ceiling adoption rates, and profitability of this new sensor network technology in the nursery and greenhouse industry. We find that adoption rates for a base system and demand for expansion components are decreasing in price, as expected. The price elasticity of the probability of adoption suggests that sensor networks are likely to diffuse at a rate somewhat greater than that of drip irrigation. Adoption rates for a base system and demand for expansion components are increasing in specialization in ornamental production: Growers earning greater shares of revenue from greenhouse and nursery operations are willing to pay more for a base system and are willing to purchase larger numbers of expansion components at any given price. We estimate that growers who are willing to purchase a sensor network expect investment in this technology to generate significant profit, consistent with findings from experimental studies. This article is protected by copyright. All rights reserved.

Description: This technical note presents a useful methodology for studying how the variance of hydraulic and/or reactive attributes of an aquifer are linked to the multi-scaled and hierarchical sedimentary architecture of the aquifer. A new recursive equation is derived which quantitatively describes how the variance is related to sedimentary facies defined at all scales across an entire stratal hierarchy. As compared to prior published equations that emphasize differences in means among facies populations within a hierarchical level, it emphasizes differences across levels. Because of the hierarchical relationships among the terms of the equation, we find it to be useful for conducting a holistic analysis of the relative contributions to the variance arising from all facies types defined across all scales. The methodology is demonstrated using appropriate field data, and is shown to be useful in defining parsimonious classification systems.

Description: ABSTRACT A primary concern for geologic carbon storage is the potential for leakage of stored carbon dioxide (CO 2 ) into the shallow subsurface where it could degrade the quality of groundwater and surface water. In order to predict and mitigate the potentially negative impacts of CO 2 leakage, it is important to understand the physical processes that CO 2 will undergo as it moves through naturally heterogeneous porous media formations. Previous studies have shown that heterogeneity can enhance the evolution of gas phase CO 2 in some cases, but the conditions under which this occurs have not yet been quantitatively defined, nor tested through laboratory experiments. This study quantitatively investigates the effects of geologic heterogeneity on the process of gas phase CO 2 evolution in shallow aquifers through an extensive set of experiments conducted in a column that was packed with layers of various test sands. Soil moisture sensors were utilized to observe the formation of gas phase near the porous media interfaces. Results indicate that the conditions under which heterogeneity controls gas phase evolution can be successfully predicted through analysis of simple parameters, including the dissolved CO 2 concentration in the flowing water, the distance between the heterogeneity and the leakage location, and some fundamental properties of the porous media. Results also show that interfaces where a less permeable material overlies a more permeable material affect gas phase evolution more significantly than interfaces with the opposite layering.

Description: To study how an impacting plume modifies the mantle lithosphere, we analyzed the microstructures and crystal preferred orientations (CPO) of 29 peridotites and 37 pyroxenites that sample the mantle root of the Ontong Java Plateau (OJP) from 60 to 120 km depth. The peridotites show a strong compositional variability, but homogeneous coarse-granular to tabular microstructures, except for those equilibrated at the shallowest and deepest depths, which are porphyroclastic. All peridotites have clear olivine CPO, with dominant fiber-[010] patterns. Low intragranular misorientations and straight grain boundaries in olivine suggest that, above 100 km depth, annealing often followed deformation. Calculated density and P-wave velocities of the peridotites decrease weakly with depth. S-wave velocities decrease faster, resulting in increasing Vp/Vs ratio with depth. Calculated densities and seismic velocity profiles are consistent with those estimated for normal mantle compositions under a cold oceanic geotherm. Enrichment in pyroxenites may further increase seismic velocities. The calculated seismic properties cannot therefore explain the low S-waves velocities predicted by Rayleigh wave tomography and ScS data in the mantle beneath the OJP. Calculated P- and S-wave anisotropy is variable (2-12%). It is higher on average in the deeper section of the lithosphere. Because olivine has dominantly [010]-fiber CPO patterns, if foliations are horizontal, vertically propagating S-waves and Rayleigh waves will sample very weak anisotropy in the OJP mantle lithosphere. Moreover, if the orientation of the lineation changes with depth, the anisotropy-induced contrast in seismic properties might produce an intralithospheric reflector marking the stratification of the OJP mantle root.

Description: The quantification of heat and mass flow between deep reservoirs and the surface is important for understanding magmatic and hydrothermal systems. Here, we use high-resolution measurement of carbon dioxide flux (ϕCO 2 ) and heat flow at the surface to characterize the mass (CO 2 and steam) and heat released to the atmosphere from two magma-hydrothermal systems. Our soil gas and heat flow surveys at Rotokawa and White Island in the Taupō Volcanic Zone, New Zealand, include over 3,000 direct measurements of ϕCO 2 and soil temperature and 60 carbon isotopic values on soil gases. Carbon dioxide flux was separated into background and magmatic/hydrothermal populations based on the measured values and isotopic characterization. Total CO 2 emission rates (ΣCO 2 ) of 441 ± 84 t d -1 and 124 ± 18 t d -1 were calculated for Rotokawa (2.9 km 2 ) and for the crater floor at White Island (0.3 km 2 ), respectively. The total CO 2 emissions differ from previously published values by +386 t d -1 at Rotokawa and +25 t d -1 at White Island, demonstrating that earlier research underestimated emissions by 700% (Rotokawa) and 25% (White Island). These differences suggest that soil CO 2 emissions facilitate more robust estimates of the thermal energy and mass flux in geothermal systems than traditional approaches. Combining the magmatic/hydrothermal-sourced CO 2 emission (constrained using stable isotopes) with reservoir H 2 O:CO 2 mass ratios and the enthalpy of evaporation, the surface expression of thermal energy release for the Rotokawa hydrothermal system (226 MW t ) is 10 times greater than the White Island crater floor (22.5 MW t ).

Description: Fluvial sediment loads are frequently calculated with rating curves fit to measured sediment transport rates. Rating curves are often treated as statistical representations in which the fitted parameters have little or no physical meaning. Such models, however, may produce large errors when extrapolation is needed, and they provide no insight into the sediment transport process. It is shown that log-linear least squares, the usual method for fitting rating curves, does not generally produce physically meaningful parameter values. In addition, it cannot accommodate data that include zero-transport samples. Alternative fitting methods based non-linear least squares and on maximum likelihood parameter estimation are described and evaluated. The maximum likelihood approach is shown to fit synthetic data better than linear or non-linear least squares, and to perform well with data that include zero-transport samples. In contrast, non-linear least squares methods produce large errors in the parameter estimates when zero-transport samples are present or when the variance structure of the data is incorrectly specified. Analyses with fractional bedload data from a mountain stream suggest that bedload transport rates are gamma distributed, that the arrivals of bedload particles in a sampler conform to a Poisson distribution, and that the variance of non-zero samples can be expressed as a power function of the mean. Preliminary physical interpretations of variations in the rating curve parameters fit to fractional bedload data with the maximum likelihood method are proposed, and their relation to some previous interpretations of rating curve parameters are briefly discussed. This article is protected by copyright. All rights reserved.

Description: To better constrain the mechanical behavior of sediments accreted to accretionary prism, we conducted triaxial mechanical tests on natural samples from the Miura-Boso paleo-accretionary prism (Japan) in drained conditions with confining pressures up to 200 MPa as well as post-experiments P-wave velocity (V p ) measurements. During experiments, deformation is principally non-coaxial and accommodated by two successive modes of deformation, both associated with strain-hardening and velocity-strengthening behavior: (1) compaction-assisted shearing, distributed in a several mm-wide shear zone and (2) faulting, localized within a few tens of µm-wide, dilatant fault zone. Deformation is also associated with (1) a decrease in Young's modulus all over the tests, (2) anomalously low V p in the deformed samples compared to their porosity and (3) an increase in sensitivity of V p to effective pressure. We interpret this evolution of the poroelastic properties of the material as reflecting the progressive breakage of intergrain cement and the formation of microcracks along with macroscopic deformation. When applied to natural conditions, these results suggest that the deformation style (localized vs distributed) of shallow (z 〈 a few km) sediments is mainly controlled by the variations in stress/strain rate during the seismic cycle and is therefore independent of the porosity of sediments. Finally, we show that the effect of strain, through cement breakage and microcracks formation, may lower V p for effective pressure up to 40 MPa. As a consequence, the low V p anomalies observed in Nankai accretionary prisms by seismic imaging between 2 and 4km depth [ Kitajima and Saffer , 2012] could reflect sediment deformation rather than porosity anomalies. This article is protected by copyright. All rights reserved.

Description: This study presents a new thermodynamic model for the calculation of phase relations during the melting of anhydrous spinel lherzolite at pressures of 1–2.5 GPa. The model is based on the total energy minimization algorithm for calculating phase equilibria within multicomponent systems and the thermodynamic configuration of Ueki and Iwamori [2013]. The model is based on a SiO 2 – Al 2 O 3 – FeO–Fe 3 O 4 –MgO–CaO system that includes silicate melt, olivine, clinopyroxene, orthopyroxene, and spinel as possible phases. The molar Gibbs free energy of the melt phase is modeled quasi-empirically, and the thermodynamic parameters for silicate melt end-member components are calibrated with a polybaric calibration database. The temperatures and pressures used in this newly compiled calibration dataset are 1230–1600 ∘ C and 0.9–3 GPa, corresponding to the stability range of spinel lherzolite. The modeling undertaken during this study reproduces the general features of experimentally determined melting phase relations of spinel lherzolite at 1–2.5 GPa, including the solidus temperature, the melt composition, the chemical reaction during melting and the degree of melting. This new thermodynamic modeling also reproduces phase relations of various bulk compositions from fertile to deplete spinel lherzolite and can be used in the modeling of polybaric mantle melting within various natural settings. Comparing the results derived from this new modeling with those produced using previous models indicates that the new approach outlined here, involving a combination of total energy minimization and the direct calibration of melt thermodynamic parameters at pressure and temperature conditions corresponding to mantle melting with a relatively simple melt thermodynamic equation, can accurately model polybaric melting phase relations. This article is protected by copyright. All rights reserved.

Description: Knowledge on the behavior of Mg isotopes during metamorphic dehydration is the prerequisite for applying Mg isotopes as tracers for crustal recycling. Here, we report Mg isotopic compositions of metapelites from the Onawa contact aureole, Maine. Except one sample, all metapelites across the aureole, from the wall-rock regional metamorphic rocks to the partially melted rocks adjacent to the pluton, have similar Mg isotopic compositions (δ 26 Mg = -0.09 to +0.12‰). This observation indicates limited Mg isotope fractionation during metamorphic dehydration and fluid-rock interaction, due to the low Mg concentration in fluids relative to rocks. Our results suggest that Mg isotopic compositions of metapelites can record those of their protoliths and, hence, recycled clastic sedimentary materials may preserve their low-temperature Mg isotopic signatures through subduction zones. Therefore, Mg isotopes may serve as new tracers for crustal recycling, for example, tracing components experienced weathering cycles within granite sources.

Description: This paper presents the results of a comprehensive model-based analysis of a uranyl [U(VI)] tracer test conducted at the U.S. DOE Hanford 300 Area (300A) IFRC. Despite the highly complex field conditions the numerical three-dimensional multi-component reactive transport model was able to capture most of the spatiotemporal variations of the observed U(VI) concentrations. A multi-model analysis was performed to interrogate the relative importance of various processes and factors for controlling field-scale reactive transport during the uranyl tracer test. The results indicate that multi-rate sorption/desorption, surface complexation reactions, and initial concentrations were the most important processes and factors controlling U(VI) migration. On the other hand, cation exchange reactions, the choice of the surface complexation model, and dual-domain mass transfer processes played less important roles under the prevailing field-test condition. Further analysis of the modeling results demonstrates that these findings are conditioned to the relatively stable groundwater chemistry and the selected length of the field experimental duration (16 days). The model analysis also revealed the crucial role of the intraborehole flow that occurred within the long-screened monitoring wells and thus affected both field measurements and simulated U(VI) concentrations as a combined effect of aquifer heterogeneity and dynamic flow conditions. This study provides the first highly data-constrained uranium transport simulations under highly dynamic flow conditions. It illustrates the value of reactive transport modeling for elucidating the relative importance of individual processes in controlling uranium transport under specific field-scale conditions.

Description: The dynamics of drying processes from porous media are critically influenced by the intensity of an adjacent free flow and by processes at the interface between free flow and the porous medium. In this paper, the influence of hydraulic properties of a porous medium and of the interaction between fluids and porous medium on the drying dynamics during the capillary-flow dominated stage-1 and transition to the diffusion-dominated stage-2 are studied using a coupled free-flow - porous-medium flow model on the REV scale. We present a detailed model concept that considers mass balance equations, an energy balance equation and the coupling to the adjacent free flow. Key microscale processes are identified and incorporated in the macroscale description of the evaporation process. Own experimental results are used to illustrate main features of the modeling framework. We demonstrate that the use of a homogeneous distribution of soil parameters without consideration of pore-scale induced nonlinearities in the numerical simulations results in a rather constant drying rate in stage-1, which was not observed for the high evaporative demand in the experiments. To account for the dependency of the drying rate on the surface moisture content, special conditions based on the work of Haghighi et al. [2013] and Schlünder [1988] are analyzed for their applicability on the REV scale. Typical features of a drying process, such as different stages of the drying rate, could be reproduced.

Description: Making useful predictions in ungauged basins is an incredibly difficult task given the limitations of hydrologic models to represent physical processes appropriately across the heterogeneity within and among different catchments. Here, we introduce a new method for this challenge, Bayes empirical Bayes, that allows for the statistical pooling of information from multiple donor catchments and provides the ability to transfer parametric distributions rather than single parameter sets to the ungauged catchment. Further, the methodology provides an efficient framework with which to formally assess predictive uncertainty at the ungauged catchment. We investigated the utility of the methodology under both synthetic and real data conditions, and with respect to its sensitivity to the number and quality of the donor catchments used. This study highlighted the ability of the hierarchical Bayes empirical Bayes approach to produce expected outcomes in both the synthetic and real data applications. The method was found to be sensitive to the quality (hydrologic similarity) of the donor catchments used. Results were less sensitive to the number of donor catchments, but indicated that predictive uncertainty was best constrained with larger numbers of donor catchments (but still adequate with fewer donors)

Description: Autumn is a season of dynamic change in forest streams of the northeastern USA due to effects of leaf fall on both hydrology and biogeochemistry. Few studies have explored how interactions of biogeochemical transformations, various nitrogen sources, and catchment flowpaths affect stream nitrogen variation during autumn. To provide more information on this critical period, we studied 1) the timing, duration, and magnitude of changes to stream nitrate, dissolved organic nitrogen (DON), and ammonium concentrations; 2) changes in nitrate sources and cycling; and 3) source areas of the landscape that most influence stream nitrogen. We collected samples at higher temporal resolution for a longer duration than typical studies of stream nitrogen during autumn. This sampling scheme encompassed the patterns and extremes that occurred during baseflow and stormflow events of autumn. Baseflow nitrate concentrations decreased by an order of magnitude from 5.4 to 0.7 μmol L -1 during the week when most leaves fell from deciduous trees. Changes to rates of biogeochemical transformations during autumn baseflow explained the low nitrate concentrations; in-stream transformations retained up to 72% of the nitrate that entered a stream reach. A decrease of in-stream nitrification coupled with assimilatory nitrate uptake was a primary factor in the seasonal nitrate decline. The period of low nitrate concentrations ended with a storm event in which stream nitrate concentrations increased by 25 fold. In the ensuing weeks, stormflow nitrate concentrations progressively decreased over closely-spaced, yet similarly sized events. Most stormflow nitrate originated from nitrification in near-stream areas with occasional, large inputs of unprocessed atmospheric nitrate, which has rarely been reported for non-snowmelt events. A maximum input of 33% unprocessed atmospheric nitrate to the stream occurred during one event. The large inputs of unprocessed atmospheric nitrate show direct and rapid effects on forest streams that may be widespread, although undocumented, throughout nitrogen-polluted temperate forests. In contrast to a week-long nitrate decline during peak autumn litterfall, baseflow DON concentrations increased after leaf fall and remained high for two months. Dissolved organic nitrogen was hydrologically flushed to the stream from riparian soils during stormflow. In contrast to distinct seasonal changes in baseflow nitrate and DON concentrations, ammonium concentrations were typically at or below detection limit, similar to the rest of the year. Our findings reveal couplings among catchment flow paths, nutrient sources and transformations that control seasonal extremes of stream nitrogen in forested landscapes.

Description: During the recent years there has been an increasing interest in multivariate frequency analysis of hydrological variables, e.g. those describing extreme events like rainfall, floods or droughts. The multivariate analysis provides a better understanding of the phenomena under investigation and an additional insight about the interrelationships between the different variables (e.g. peak, volume and duration of the flood), exploiting the complete structure of the problem and making a full use of the available data. However, while the developments on multivariate analysis of hydrological data has produced a large body of literature, a clear assessment of the use of these methods in the design and risk assessment of hydraulic structures is still a matter of debate. In the present work we illustrate a general, structure-based framework for the design and/or risk assessment of hydraulic structures in a bivariate environment; we also compare it to recently proposed methods which are based on the assumption of hydrological design events (as is customary in the univariate context). For illustration purposes, both the structure-based and the design event-based approaches are applied to the design of an idealized structure, thus exploring the differences among the methods as function of the parameters involved. Our work highlights that the return period of structure failure in a multivariate environment strictly depends on the particular structure under design, and in most cases the design of an hydraulic structure cannot be based on a single, hydrological multivariate design event. This acts as a warning for practitioners against the use of design methods based on single hydrological events, as usually done in the context of univariate hydrology, thus neglecting the interplay between the structure and the hydrological loads acting on it.

Description: Proliferation of evapotranspiration (ET) products warrants comparison of these products. The study objective was to assess uncertainty in ET output from four land surface models (LSMs), Noah, Mosaic, VIC, and SAC in NLDAS-2, two remote sensing-based products, MODIS and AVHRR, and GRACE-inferred ET from a water budget with precipitation from PRISM, monitored runoff, and total water storage change (TWSC) from GRACE satellites. The three cornered hat method, which does not require a priori knowledge of the true ET value, was used to estimate ET uncertainties. In addition, TWSC or total water storage anomaly (TWSA) from GRACE was compared with water budget estimates of TWSC from a flux-based approach or TWSA from a storage-based approach. The analyses were conducted using data from three regions (humid – arid) in the South Central US as case studies. Uncertainties in ET are lowest in LSM ET (~5 mm/month), moderate in MODIS- or AVHRR-based ET (10 – 15 mm/month), and highest in GRACE-inferred ET (20 – 30 mm/month). There is a tradeoff between spatial resolution and uncertainty, with lower uncertainty in the coarser-resolution LSM ET (~14 km) relative to higher uncertainty in the finer-resolution (~ 1 ‒ 8 km) RS ET. Root-mean-square (RMS) of uncertainties in water budget estimates of TWSC is about half of RMS of uncertainties in GRACE-derived TWSC for each of the regions. Future ET estimation should consider a hybrid approach that integrates strengths of LSMs and satellite-based products to constrain uncertainties.

Description: It is well documented that deforestation results in an increase in landslide frequency due to the control that forest roots have on slope stability. The loss of forest vegetation leads to a reduction in soil cohesion and a decrease in the shear strength of the soil profile. As a result, the slope becomes more susceptible to landsliding and the return time of landslides decreases. When a landslide removes the soil profile, there may not be adequate time for seedlings to grow and enhance soil stability. In this study, we investigate whether bistable dynamics emerge from the interaction of forest vegetation with the formation and accumulation of colluvial deposits in soil-mantled landscapes. To that end, we develop deterministic and stochastic models of landslide occurrence with a dynamic vegetation component. Results show that bistability exists for the deterministic case for both steep and shallow hollows under event and supply limited conditions. However, for the stochastic case, the randomness of landslide occurrence largely changed the states of the system such that the system only exhibited one stable state, which was the fully vegetated condition. Examining different management practices under stochastic conditions showed that the system eventually recovered; however, management practices influenced the recovery time of the forest. Thus, different management practices could render the land in a state of low vegetation over economically significant time periods.

Description: Seepage flux from ephemeral streams can be an important component of the water balance in arid and semi-arid regions. An emerging technique for quantifying this flux involves the measurement and simulation of a flood wave as it moves along an initially dry channel. This study investigates the usefulness of including surface water and groundwater data to improve model calibration when using this technique. We trialed this approach using a controlled flow event along a 1387 m reach of artificial stream channel. Observations were then simulated using a numerical model that combines the diffusion wave approximation of the Saint-Vénant equations for streamflow routing, with Philips’ infiltration equation and the groundwater flow equation. Model estimates of seepage flux for the upstream segments of the study reach, where streambed hydraulic conductivities were approximately 10 1 m d -1 , were on the order of 10 -4 m 3 d -1 m -2 . In the downstream segments, streambed hydraulic conductivities were generally much lower but highly variable (~10 -3 – 10 -7 m d -1 ). The Latin Hypercube Monte Carlo sensitivity analysis showed that the flood front timing, surface water stage, groundwater heads and the predicted stream flow seepage were most influenced by specific yield. Furthermore, inclusion of groundwater data resulted in a higher estimate of total seepage estimates than if the flood front timing were used alone.

Description: Ecology, Volume 95, Issue 1, Page 68-77, January 2014. Delayed life history effects (DLHEs) occur when fitness in one life stage affects fitness in subsequent life stages. Given their biphasic life cycle, pond-breeding amphibians provide a natural system for studying DLHEs, although these effects are not restricted to species with biphasic life histories. In this study, we used multiple mark–recapture techniques enabled by a large trapping array to monitor components of fitness and resulting DLHEs in a population of the endangered California tiger salamander (Ambystoma californiense). We found that DLHEs are prominent across all life stage transitions and that there is variation in whether selection acts primarily at the individual or cohort level. We also demonstrated that there is more than an order of magnitude variation in mean cohort fitness, providing tremendous variation for DLHEs to act upon. We documented an evolutionary trade-off between mass at emergence and date of emergence, which may play a role in maintaining the variation in mass (fitness) at emergence. A literature review revealed that such high levels of intercohort variation occur in many other pond-breeding amphibians, and that appropriately documenting the magnitude of intercohort variation requires long-term studies (roughly two population turnovers). Given the profound effect that DLHEs can have on population dynamics, quantifying intercohort variation in mean fitness and the level(s) at which selection acts will be very important for developing accurate models of population dynamics. In general, when developing models of population dynamics, more attention should be paid to variation in mean fitness and not just variation in total numbers.

Description: Ecology, Volume 95, Issue 1, Page 30-36, January 2014. Competition plays an important role in structuring the community dynamics of phytophagous insects. As the number and impact of biological invasions increase, it has become increasingly important to determine whether competitive differences exist between native and exotic insects. We conducted a meta-analysis to test the hypothesis that native/exotic status affects the outcome of herbivore competition. Specifically, we used data from 160 published studies to assess plant-mediated competition in phytophagous insects. For each pair of competing herbivores, we determined the native range and coevolutionary history of each herbivore and host plant. Plant-mediated competition occurred frequently, but neither native nor exotic insects were consistently better competitors. Spatial separation reduced competition in native insects but showed little effect on exotics. Temporal separation negatively impacted native insects but did not affect competition in exotics. Insects that coevolved with their host plant were more affected by interspecific competition than herbivores that lacked a coevolutionary history. Insects that have not coevolved with their host plant may be at a competitive advantage if they overcome plant defenses. As native/exotic status does not consistently predict outcomes of competitive interactions, plant–insect coevolutionary history should be considered in studies of competition.

Description: Magnetic anomaly identifications underpin plate tectonic reconstructions and form the primary dataset from which age of the oceanic lithosphere and seafloor spreading regimes in the ocean basins can be determined. Although these identifications are an invaluable resource, their usefulness to the wider scientific community has been limited due to the lack of a central community infrastructure to organize, host and update these interpretations. We have developed an open-source, community-driven online infrastructure as a repository for quality-checked magnetic anomaly identifications from all ocean basins. We provide a global sample dataset that comprises 96,733 individually picked magnetic anomaly identifications organized by ocean basin and publication reference, and provide accompanying Hellinger-format files, where available. Our infrastructure is designed to facilitate research in plate tectonic reconstructions or research that relies on an assessment of plate reconstructions, for both experts and non-experts alike. To further enhance the existing repository and strengthen its value, we encourage others in the community to contribute to this effort.

Description: We present a probabilistic sediment cascade model to simulate sediment transfer in a mountain basin (Illgraben, Switzerland) where sediment is produced by hillslope landslides and rockfalls and exported out of the basin by debris flows and floods. The model conceptualizes the fluvial system as a spatially lumped cascade of connected reservoirs representing hillslope and channel storages where sediment goes through cycles of storage and remobilization by surface runoff. The model includes all relevant hydrological processes that lead to runoff formation in an Alpine basin, such as precipitation, snow accumulation, snow melt, evapotranspiration, and soil water storage. Although the processes of sediment transfer and debris flow generation are described in a simplified manner, the model produces complex sediment discharge behavior which is driven by the availability of sediment and antecedent wetness conditions (system memory) as well as the triggering potential (climatic forcing). The observed probability distribution of debris flow volumes and their seasonality in 2000-2009 are reproduced. The stochasticity of hillslope sediment input is important for reproducing realistic sediment storage variability, although many details of the hillslope landslide triggering procedures are filtered out by the sediment transfer system. The model allows us to explicitly quantify the division into transport and supply-limited sediment discharge events. We show that debris flows may be generated for a wide range of rainfall intensities because of variable antecedent basin wetness and snowmelt contribution to runoff, which helps to understand the limitations of methods based on a single rainfall threshold for debris flow initiation in Alpine basins.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Predicting the future trend and viability of populations is an essential task in ecology. Because many populations respond to changing environments, uncertainty surrounding environmental responses must be incorporated into population assessments. However, understanding the effects of environmental variation on population dynamics requires information on several important demographic parameters which are often difficult to estimate. Integrated population models facilitate the integration of time-series data on population size and all existing demographic information from a species, allowing the estimation of demographic parameters for which limited or no empirical data exist. Although these models are ideal for assessments of population viability, they have so far not included environmental uncertainty. We incorporated environmental variation in an integrated population model to account for both demographic and environmental uncertainty in an assessment of population viability. In addition, we used this model to estimate true juvenile survival, an important demographic parameter for population dynamics that is difficult to estimate empirically. We applied this model to assess the past and future population trend of a rare island endemic songbird, the Montserrat Oriole Icterus oberi, which is threatened by volcanic activity. Montserrat Orioles experienced lower survival in years with volcanic ash-fall, causing periodic population declines that were compensated by higher seasonal fecundity in years with high pre-breeding season rainfall. Due to the inclusion of both demographic and environmental uncertainty in the model, the estimated population growth rate in the immediate future was highly imprecise (95% credible interval 0.844 - 1.105), and the probability of extinction after three generations (in the year 2028) was low (2.1%). This projection demonstrates that accounting for both demographic and environmental sources of uncertainty provides a more realistic assessment of the viability of populations under unknown future environmental conditions.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Evidence of age-dependent changes in foraging behavior of free-ranging individuals is scarce, especially at older stages. Using the isotopic niche as a proxy of the trophic niche during both the breeding (blood) and inter-nesting (feather) periods, we report here empirical evidence for age-, gender- and breeding status-dependent foraging ecology and examine its potential consequences on subsequent reproduction and survival in an extremely long-lived species, the wandering albatross. Immature wandering albatrosses of both sexes forage in the subtropics (δ13C) and feed at the same trophic position (δ15N) than the adults. In contrast to immature birds, adult females forage on average at northern latitudes than males, with both sexes feeding in the subtropics during the inter-nesting period, and males, not females, favouring subantartic waters during incubation. In contrast to adult females, males showed a unique pattern among birds and mammals of a continuous change with age in their main feeding habitat by foraging progressively further south in colder waters during both the breeding and inter-nesting periods. In males, foraging at higher latitudes (lower feather δ13C values) is associated with a lower probability to breed during the following years compared to other birds, but with no effect on their probability to survive. Foraging in cold and windy waters may be linked to foraging impairment that might explain different life history trade-offs and lower investment in reproduction with age. This key point requires further longitudinal investigations and/or studies examining foraging success and energy budget of birds feeding in different water masses.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Interactions between plants and scatterhoarding animals may shift from mutualism to predation as a function of resources available to those animals. Because seed species differ in their nutrient content and defenses to predation, resource selection and cache management by scatterhoarders, and thus seed fate, may also depend on the relative availability of different seed types. We tracked the fates of tagged Castanea dentata, Quercus alba, and Q. rubra seeds presented to rodents in pairwise combinations and found that C. dentata, which has moderate dormancy prior to germination, survived better in the presence of Q. alba (no dormancy) than with Q. rubra (longer dormancy). Decisions made by scatterhoarders in response to the composition of available seed resources can alter the relationship between masting and seed dispersal effectiveness in individual tree species and may have influenced the evolution of asynchrony among species-specific masting patterns in temperate forests. In theory, preferential allocation of certain seed species to storage or consumption may also result in indirect apparent predation by one seed species on another.

Description: Characterizing the complex geometries and the heterogeneity of the deposits in meandering river systems is a long-standing issue for the 3D modeling of alluvial formations. Such deposits are important sources of accessible groundwater in alluvial aquifers throughout the world and also play a major role as hydrocarbons reservoirs. In this paper we present a method to generate meandering river centerlines that are stochastic, geologically realistic, connected and conditioned to local observations or global geomorphological characteristics. The method is based on fast 1D multiple-point statistics in a transformed curvilinear domain: the succession in directions observed in a real world meandering river (the analog) is considered as statistical model for multiple-point statistics simulation. The integration of local data is accomplished by an inverse procedure ensuring that the channels pass through a given set of locations while conserving the high-order spatial characteristics of an analog. The methodology is applied on seven real world case studies. This work demonstrates the flexibility and the applicability of multiple-point statistics outside the standard paradigm that considers the simulation of a 2D or 3D variable with spatial coordinates.

Description: Large asymmetric bedforms commonly develop in rivers. The turbulence associated with flow separation that develops over their steep lee side is responsible for the form shear stress which can represent a substantial part of total shear stress in rivers. This paper uses the Delft3D modeling system to investigate the effects of bedform geometry and forcing conditions on flow separation length and associated turbulence, and bedform shear stress over angle-of-repose (30° lee side angle) bedforms. The model was validated with laboratory measurements that showed sufficient agreement to be used for a systematic analysis. The influence of flow velocity, bed roughness, relative height (bedform height / water depth) and aspect ratio (bedform height / length) on the variations of the normalized length of the flow separation zone, the extent of the wake region (where the turbulent kinetic energy (TKE) was more than 70% of the maximum TKE), the average TKE within the wake region and the form shear stress were investigated. Form shear stress was found not to scale with the size of the flow separation zone but to be related to the product of the normalized extent of the wake region (extent of the wake region / extent of water body above the bedform) and the average TKE within the wake region. The results add to understanding of the hydrodynamics of bedforms and may be used for the development of better parameterizations of small-scale processes for application in large-scale studies.

Description: We explore the bankfull width ( W bf ) vs. drainage area ( A da ) relationship across a range of climatic and geologic environments, and ask (1) is the relationship between ln ( W bf ) and ln ( A da ) best described by a linear function and (2) can a reliable relationship be developed for predicting W bf with A da as the only independent variable. The principal dataset for this study was compiled from regional curve studies and other reports that represent 1,018 sites (1 m ≤ W bf ≤ 110 m and 0.50 km 2 ≤ A da ≤ 22,000 km 2 ) in the continental U.S. Two additional datasets were used for validation. After dividing the data into small-, medium-, and large-size basins which, respectfully, correspond to A da 〈 4.95 km 2 , 4.95 km 2 ≤ A da 〈 337 km 2 , and A da ≥ 337 km 2 , regression lines from each dataset were compared using one-way analysis of covariance (ANCOVA). A second ANCOVA was performed to determine if mean annual precipitation ( P ) is an extraneous factor in the W bf vs. A da relationship. The ANCOVA results reveal that using A da alone does not yield a reliable W bf vs. A da relationship that is applicable across a wide range of environments and that P is a significant extraneous factor in the relationship. Considering data for very small basins ( A da ≤ 0.49 km 2 ) and very large basins ( A da ≥ 1.0×10 5 km 2 ) we conclude that a two-segment linear model is the most probable form of the ln ( W bf ) vs. ln ( A da ) relationship. This study provides useful information for building complex multivariate models for predicting W bf .

Description: We present an efficient method for high-volume heavy mineral separation from clay-rich rocks using an ultrasonic probe. The ultrasonic clay separator (UCS) is an easily constructed device that allows for the recovery of high-density minerals, as small as 10 microns, with a minimum of sample preparation. Heavy mineral recovery from clay-rich material with the UCS yields a greater number of small (〈100 micron) grains and approximately double the amount of material from that of gravity settling and decanting. Despite development with heavy mineral recovery in mind, the UCS should suitable for recovering small grain size geologic materials from flocculating clay-rich material.

Description: Recent studies show that multimodel combinations improve hydroclimatic predictions by reducing model uncertainty. Given that climate forecasts are available from multiple climate models, which could be ingested with multiple watershed models, what is the best strategy to reduce the uncertainty in streamflow forecasts? To address this question, we consider three possible strategies: (1) reduce the input uncertainty first by combining climate models and then use the multimodel climate forecasts with multiple watershed models (MM-P) (2) ingest the individual climate forecasts (without multimodel combination) with various watershed models and then combine the streamflow predictions that arise from all possible combinations of climate and watershed models (MM-Q)(3) combine the streamflow forecasts obtained from multiple watershed models based on strategy (1) to develop a single streamflow prediction that reduces uncertainty in both climate forecasts and watershed models (MM-PQ) . For this purpose, we consider synthetic schemes that generate streamflow and climate forecasts, for comparing the performance of three strategies with the true streamflow generated by a given hydrologic model. Results from the synthetic study show that reducing input uncertainty first ( MM-P ) by combining climate forecasts results in reduced error in predicting the true streamflow compared to the error of multimodel streamflow forecasts obtained by combining streamflow forecasts from all-possible combination of individual climate model with various hydrologic models ( MM-Q ). Since the true hydrologic model structure is unknown, it is desirable to consider MM-PQ as an alternate choice that reduces both input uncertainty and hydrologic model uncertainty. Application on two watersheds in NC also indicates that reducing the input uncertainty first is critical before reducing the hydrologic model uncertainty.

Description: The understanding of reasons leading to non-uniqueness of soil erosion susceptibility is still inadequate, yet indispensable for establishing general relations between runoff volume and sediment yield. To obtain relevant insights, we performed a series of numerical simulations with a detailed hydrodynamic model using synthetic storms of varying intensity, duration, and lag time between events as representations of different hydrologic response conditions in a zero-order catchment. The design targeted to generate surface flow and ‘perturb’ soil substrate by a first rainfall event, creating a set of initial conditions in terms of flow and deposited sediment prior to the onset of a subsequent rainfall event. Due to the differential effect of (re)detachment and (re)entrainment processes on soil particles of varying sizes, the deposited sediment mass formed shielding layer. One of the essential results is that unless the initial condition of flow and sediment is identical, the same volume of runoff can generate different total sediment yields and their variation can reach up to ~200%. The effect is attributed to two major conflicting effects exerted by the deposited ‘initialization’ (soil antecedent condition) sediment mass: erosion enhancement, because of supply of highly erodible sediment, and erosion impediment, because of constrain on the availability of lighter particles by heavier sediment. Consistently with this inference, long-term simulations with continuous rainfall show that a peculiar feature of sediment yield series is the existence of maximum before the steady-state is reached. The two characteristic time scales, the time to peak and the time to steady-state, separate three characteristic periods that correspond to flow-limited, source-limited, and steady-state regimes. These time scales are log-linearly and negatively related to the spatially averaged Shields parameter: the smaller the rainfall input and the heavier a given particle is, the larger the two scales are. The results provide insights on how the existence of shield operates on erosion processes, possibly implying that accurate short-term predictions of geomorphic events from headwater areas may never become a tractable problem: the latter would require a detailed spatial characterization of particle size distribution prior to precipitation events.

Description: In the detachment mode of slow seafloor spreading, convex-upward detachment faults take up a high proportion of the plate separation velocity exposing gabbro and serpentinized peridotite on the seafloor. Large, long-lived hydrothermal systems such as TAG are situated off-axis and may be controlled by fluid flow up a detachment fault, with the source of magmatic heat being as deep as 7 kmbsf. The consequences of such deep circulation for the evolution of fluid temperature and salinity have not previously been investigated. Microthermometry on fluid inclusions trapped in diabase, gabbro and trondjhemite, recovered at the Atlantis Massif Oceanic Core Complex (30° N, mid-Atlantic Ridge), reveals evidence for magmatic exsolution, phase separation, and mixing between hydrothermal fluids and previously phase separated fluids. Four types of fluid inclusions were identified, ranging in salinity from 1.4 wt.% NaCl to 35 wt.% NaCl, although the most common inclusions have salinities close to seawater (3.4 wt.% NaCl). Homogenization temperatures range from 160 to 〉400 °C, with the highest temperatures in hypersaline inclusions trapped in trondjhemite and the lowest temperatures in low salinity inclusions trapped in quartz veins. The fluid history of the Atlantis Massif is interpreted in the context of published thermochronometric data from the Massif, and a comparison with the inferred circulation pattern beneath the TAG hydrothermal field, to better constrain the pressure temperature conditions of trapping and when in the history of exhumation of the rocks sampled by IODP Hole U1309D fluids have been trapped.

Description: Ecology, Volume 95, Issue 1, Page 98-109, January 2014. Grazing, fire, and climate shape mesic grassland communities. With global change altering all three factors, understanding how grasslands respond to changes in these combined drivers may aid in projecting future changes in grassland ecosystems. We manipulated rainfall and simulated grazing (clipping) in two long-term fire experiments in mesic grasslands in North America (NA) and South Africa (SA). Despite their common drivers, grasslands in NA and SA differ in evolutionary history. Therefore, we expected community structure and production in NA and SA to respond differently to fire, grazing, and drought. Specifically, we hypothesized that NA plant community composition and production would be more responsive than the SA plant communities to changes in the drivers and their interactions, and that despite this expected stability of SA grasslands, drought would be the dominant factor controlling production, but grazing would play the primary role in determining community composition at both sites. Contrary to our hypothesis, NA and SA grasslands generally responded similarly to grazing, drought, and fire. Grazing increased diversity, decreased grass cover and production, and decreased belowground biomass at both sites. Drought alone minimally impacted plant community structure, and we saw similar treatment interactions at the two sites. Drought was not the primary driver of grassland productivity, but instead drought effects were similar to or less than grazing and fire. Even though these grasslands differed in evolutionary history, they responded similarly to our fire, grazing, and climate manipulations. Overall, we found community and ecosystem convergence in NA and SA grasslands. Grazing and fire are as important as climate in controlling mesic grassland ecosystems on both continents.

Description: Ecology, Volume 95, Issue 1, Page 173-184, January 2014. Biodiversity has been shown to increase the temporal stability of community and ecosystem attributes through multiple mechanisms, but these same mechanisms make less consistent predictions about the effects of richness on population stability. The overall effects of biodiversity on population and community stability will therefore depend on the dominant mechanisms that are likely to vary with the nature of biodiversity loss and the degree of environmental variability. We conducted a mesocosm experiment in which we generated a gradient in zooplankton species richness by directly manipulating dominant species and by allowing/preventing immigration from a metacommunity. The mesocosms were maintained under either constant or variable nutrient environments. Population, community, and ecosystem data were collected for five months. We found that zooplankton population and community stability is enhanced in species-rich communities in both constant and variable environments. Species richness increased primarily through the addition of species with low abundance. The communities that were connected to a metacommunity via immigration were the most diverse and the most stable, indicating the importance of both metacommunity dynamics and rare species for stability. We found little evidence for selection effects or overyielding as stabilizing forces. We did find support for asynchronous dynamics and statistical averaging, both of which predict destabilizing effects at the population level. We also found support for weak interactions, which predicts that both populations and communities will become more stable as richness increases. In order to understand the effects of biodiversity loss on stability, we will need to understand when different stabilizing mechanisms tend to operate but also how multiple mechanisms interact.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Theory of invasion ecology indicates that the number of invading individuals (propagule size) and the timing of invasion are important for invasion success. Propagule size affects establishment success due to an Allee effect and the effect of demographic stochasticity, whereas the timing of invasion does so via niche opportunity produced by fluctuating predation pressure and resource abundance. We propose a synthesis of these two mechanisms by a time-varying dose-response curve where the dose is propagule size and the response is establishment probability. We show an example of the synthesis in a simple predator-prey model where successful invasion occurs as a demographic regime shift because of the bistability of the system. The two mechanisms are not independent, but simultaneously determine invasion success in our model. We found that positive growth rate of an invading species does not ensure its establishment, especially when its propagule size is small or when its growth rate is in a decreasing trend. We suggest the difficulty of understanding invasion process based on a dose-response curve of propagule size as no unique curve can be determined due to the effects of invasion timing (i.e., the threshold of demographic regime shift is time-varying). The results of our model analysis also have an implication on the phase relationship between population cycles of predators and prey.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Grasslands have been lost and degraded in the USA since Euro-American settlement due to agriculture, development, introduced invasive species, and changes in fire regimes. Fire is frequently used in prairie restoration to control invasion by trees and shrubs, but may have additional consequences. For example, fire might reduce damage by herbivore and pathogen enemies by eliminating litter, which harbors eggs and spores. Less obviously, fire might influence enemy loads differently for native and introduced plant hosts. We used a controlled burn in a Willamette Valley (Oregon) prairie to examine these questions. We expected that without fire, introduced host plants should have less damage than native host plants because the introduced species are likely to have left many of their enemies behind when they were transported to their new range (the enemy release hypothesis, or ERH). If the ERH holds, then fire, which should temporarily reduce enemies on all species, should give an advantage to the natives because they should see greater total reduction in damage by enemies. Prior to the burn, we censused herbivore and pathogen attack on eight plant species (five of non-native origin: Bromus hordaceous, Cynosuros echinatus, Galium divaricatum, Schedonorus arundinaceus (=Festuca arundinacea), Sherardia arvensis; and three natives: Danthonia californica, Epilobium minutum, and Lomatium nudicale). The same plots were monitored for two years post-fire. Prior to the burn, native plants had more kinds of damage and more pathogen damage than introduced plants, consistent with the ERH. Fire reduced pathogen damage relative to the controls more for the native than the introduced species, but the effects on herbivory were negligible. Pathogen attack was correlated with plant reproductive fitness, whereas herbivory was not. These results suggest that fire may be useful for promoting some native plants in prairies due to its negative effects on their pathogens.

Description: Aquifer hydraulic properties such as hydraulic conductivity ( K ) are ubiquitously heterogeneous and typically only a statistical characterization can be sought. Additionally statistical anisotropy at typical characterization scales is the rule. Thus, regardless of the processes governing solute transport at the local (pore) scale, transport becomes non-Fickian. Mass-transfer models provide an efficient tool that reproduces observed anomalous transport; in some cases though, these models lack predictability as model parameters cannot readily be connected to the physical properties of aquifers. In this study we focus on a multi-rate mass-transfer model (MRMT), and in particular the apparent capacity coefficient (β), which is a strong indicator of the potential of immobile zones to capture moving solute. We aim to find if the choice of an apparent β can be phenomenologically related to measures of statistical anisotropy. We analyzed an ensemble of random simulations of three-dimensional log-transformed multi-Gaussian permeability fields with stationary anisotropic correlation under convergent flow conditions. It was found that apparent β also displays an anisotropic behavior, physically controlled by the aquifer directional connectivity, which in turn is controlled by the anisotropic correlation model. A high hydraulic connectivity results in large β values. These results provide new insights into the practical use of mass-transfer models for predictive purposes.

Description: In this paper, an operational algorithm is proposed for the mapping of surface moisture over the northern and central parts of Tunisia, in North Africa. A change detection approach is applied, using 160 multi-incidence Envisat ASAR Wide Swath images acquired in the horizontal polarization over a 7-year period. Parameterization of this algorithm is considered for three classes of vegetation cover density (NDVI〈0.25, 0.25〈NDVI〈0.5 and NDVI〉0.5), retrieved from SPOT-VGT decadal images. A relative soil moisture index, ranging between 0 (for the driest surfaces) and 1 (for saturated soils), is proposed for each date, with a resolution of 1 km. The retrieved soil moistures are validated by means of ground measurements based on continuous thetaprobe measurements, as well as low resolution (25 km) ERS and ASCAT soil moisture products from the Vienna University of Technology (TU Wien). A qualitative relationship between spatio-temporal variations of moisture and precipitation is also discussed.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Complementary resource use and redundancy of species that fulfill the same ecological role are two mechanisms that can respectively increase and stabilize process rates in ecosystems. For example, predator complementarity and redundancy can determine prey consumption rates and their stability, yet few studies take into account the multiple predator species attacking multiple prey at different rates in natural communities. Thus, it remains unclear whether these biodiversity mechanisms are important determinants of consumption in entire predator-prey assemblages, such that food-web interaction structure determines community-wide consumption and stability. Here, we use empirical quantitative food-webs to study the community-wide effects of functional complementarity and redundancy of consumers (parasitoids) on herbivore control in temperate forests. We find that complementarity in host resource use by parasitoids was a strong predictor of absolute parasitism rates at the community level, and that redundancy in host-use patterns stabilised community-wide parasitism rates in space, but not through time. These effects can potentially explain previous contradictory results from predator diversity research. Phylogenetic diversity (measured using taxonomic distance) did not explain functional complementarity or parasitism rates, so could not serve as a surrogate measure for functional complementarity. Our study shows that known mechanisms underpinning predator diversity effects on both functioning and stability can easily be extended to link food webs to ecosystem functioning.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Floral nectar of many plant species is prone to colonization by microbial organisms such as yeasts. Their presence and metabolism of nectar chemical components have the potential to modify a suite of floral traits important for pollinator attraction, including nectar quality and scent. However, studies on the direct and indirect effects of nectar-inhabiting microogranisms on pollinator behavior and plant reproductive success remain rare. To determine their potential to affect pollinator behavior and plant fitness, we experimentally manipulated the common nectar-inhabiting yeast Metschnikowia reukaufii in the nectar of Delphinium nuttallianum, a short-lived montane perennial herb. We detected positive indirect, pollinator-mediated effects of yeasts on male plant fitness measured as pollen donation using powdered fluorescent dyes. However, we detected no direct or indirect effects on components of female fitness. Matching effects on male plant fitness, pollinators responded positively to the presence of yeasts, removing more nectar from flowers treated with M. reukaufii. Our results provide evidence of effects of nectar-inhabiting yeasts on male plant fitness and highlight the importance of microorganisms in mediating plant-pollinator interactions and subsequent plant fitness.

Description: We study the elastic wave speed structure of the crust and the uppermost mantle in western Tibet using P and S-wave arrival times from regional earthquakes recorded by a temporary seismic network. We relocate the earthquakes, and subsequently invert travel time residuals for 3D distributions of wave speed. Resolution tests with a variety of input structures are used to verify the reliability of our results. The crust beneath western Tibet has low P-wave speed (5.9 - 6.3 km/s) throughout its nearly 80 km thickness, with lower values in this range concentrated within the Lhasa block. Beneath the Himalaya wave speeds are higher. Southern and western limits of the slow material beneath the Tibetan Plateau correlate with the Karakoram fault, and dip beneath the plateau at ~40° angle. We find no evidence of a sub-horizontal low velocity zone in the crust. In the uppermost mantle we find a long and narrow region of fast (up to 8.4 km/s) P-wave speed extending from the Karakoram fault in NE direction, and crossing the Bangong-Nujiang suture. In a north-south cross-section, the distribution of relatively fast P-wave speed suggests a ramp-flat geometry consistent with India underthrusting the Tibetan Plateau at least as far as 32.5°N. A plausible interpretation of the upper mantle fast feature is the formation of eclogite from the mafic lower-crustal material of India after it is underthrust beneath Tibet. Notably, in western Tibet this process only takes place in a narrow region.

Description: We have employed shear wave splitting techniques to image anisotropy beneath the D'Entrecasteaux Islands, in southeastern Papua New Guinea. Our results provide a detailed picture of the extending continent that lies immediately ahead of a propagating mid-ocean ridge tip; we image the transition from continental to oceanic extension. A dense shear wave splitting dataset from a 2010-11 passive-source seismic deployment is analyzed using single- and multi-channel methods. Splitting delay times of 1-1.5 s are observed and fast axes of anisotropy trending N-S, parallel to rifting direction, predominate the results. This trend is linked to lattice-preferred orientation of olivine, primarily in the shallow convecting mantle, driven by up to 200 km of N-S continental extension ahead of the westward-propagating Woodlark Rift. This pattern differs from several other continental rifts that evince rift-strike-parallel fast axes and is evident despite the complex recent tectonic history. We contend that across most of this rift, the unusually high rate and magnitude of extension has been sufficient to produce a regime change to a mid-ocean-ridge-like mantle fabric. Stations in the south of our array show more complex splitting that might be related to melt or to complex inherited structure at the edge of the extended region.

Description: From April 2010 through February 2011, CO 2 flux surveys were performed on Lake Rotomahana, New Zealand. The area has been hydrothermally active with fumaroles and sublacustrine hydrothermal activity before and since the eruption of Mt Tarawera in 1886. The total CO 2 emission from the lake calculated by sequential Gaussian simulation is 549 ± 72 t day -1 . Two different mechanisms of degassing, diffusion through the water-air interface and bubbling, are distinguished using a graphical statistical approach. The carbon dioxide budget calculated for the lake confirms that the main source of CO 2 to the atmosphere is by diffusion covering 94.5 % of the lake area (mean CO 2 flux 25 g m -2 day -1 ) and to a lesser extent, bubbling (mean CO 2 flux 1297 g m -2 day -1 ). Mapping of the CO 2 flux over the entire lake, including over lakefloor vents detected during the survey, correlates with eruption craters formed during the 1886 eruption. These surveys also follow regional tectonic patterns present in the southeastern sector of Lake Rotomahana suggesting a deep magmatic source (~ 10 km) for CO 2 and different pathways for the gas to escape to the surface. The values of δ 13 C CO2 (-2.88 and -2.39 ‰) confirm the magmatic origin of CO 2 .

Description: Ecology, Volume 95, Issue 1, Page 3-8, January 2014. Periodical cicadas (Magicicada spp.) mature in 13 or 17 years, the longest development times for any non-diapausing insects. Selection may favor prolonged development since nymphs experience little mortality and individuals taking 17 years have been shown to have greater fecundity than those taking 13 years. Why don't periodical cicadas take even longer to develop? Nymphs feed on root xylem fluid and move little. Ovipositing females prefer fast-growing trees at forest edges. I hypothesized that (1) adults emerging at edges would be heavier than those from forest interiors and (2) habitat changes could limit development time. I collected newly eclosed females that had neither fed as adults nor moved from their site of development. For M. septendecim, females from edges were 4.9% heavier than those from the interior. I assumed that emergence density indicated habitat quality and measured density at eight sites in 1979, 1996, and 2013. Over three generations, variation in densities was great; densities at two sites crashed, and at one site they exploded to 579/m2. Habitat transience may limit development time because only adults can reassess habitats and reposition offspring. In conclusion, cicadas are affected by habitat characteristics, habitats change over 17 years, and cicadas may emerge, mate, and redistribute their offspring to track habitat dynamics.

Description: Ecology, Volume 95, Issue 1, Page 56-67, January 2014. Predation has been suggested to be especially important in simple food webs and less productive ecosystems such as the arctic tundra, but very few data are available to evaluate this hypothesis. We examined the hypothesis that avian predators could drive the population dynamics of two cyclic lemming species in the Canadian Arctic. A dense and diverse suite of predatory birds, including the Snowy Owl (Bubo scandiacus), the Rough-legged Hawk (Buteo lagopus), and the Long-tailed Jaeger (Stercorarius longicaudus), inhabits the arctic tundra and prey on collared (Dicrostonyx groenlandicus) and brown (Lemmus trimucronatus) lemmings during the snow-free period. We evaluated the predation pressure exerted by these predators by combining their numerical (variation in breeding and fledgling numbers) and functional (variation in diet and daily consumption rates) responses to variations in lemming densities over the 2004–2010 period. Breeding density and number of fledglings produced by the three main avian predators increased sharply without delay in response to increasing lemming densities. The proportion of collared lemmings in the diet of those predators was high at low lemming density (both species) but decreased as lemming density increased. However, we found little evidence that their daily consumption rates vary in relation to changes in lemming density. Total consumption rate by avian predators initially increased more rapidly for collared lemming but eventually leveled off at a much higher value for brown lemmings, the most abundant species at our site. The combined daily predation rate of avian predators exceeded the maximum daily potential growth rates of both lemming species except at the highest recorded densities for brown lemmings. We thus show, for the first time, that predation pressure exerted without delay by avian predators can limit populations of coexisting lemming species during the snow-free period, and thus, that predation could play a role in the cyclic dynamic of these species in the tundra.

Description: Ecology, Volume 95, Issue 1, Page 238-239, January 2014.

Description: Ecology, Volume 95, Issue 1, Page 238-239, January 2014.

Description: This paper presents the results of a data based comparative study of several hundred catchments across continental United States belonging to the MOPEX dataset to systematically explore the connection between the flood frequency curve and mean annual water balance. Mean annual water balance is expressed in terms of two similarity measures: (i) the climatic aridity index, AI , which is a measure of the competition between energy and water availability; and (ii) the baseflow index, BFI , which is a measure of total runoff partitioning into surface and subsurface components at the annual time scale. The data analyses showed that the aridity index, AI , has a first order control on the shape of the flood frequency curve (also known as the growth curve), as expressed in terms of both the mean and coefficient of variation ( C v ) of the annual maximum floods, once normalized by catchment size (i.e., specific flood discharge) While the mean annual (specific) flood discharge decreases with increasing aridity, C v increases with increasing aridity. On the other hand, the BFI was found to be a second order control on the flood frequency curve. Higher BFI , meaning higher contributions of subsurface flow to total streamflow, leads to a decrease of the mean annual (specific) flood discharge, and vice versa. The statistically significant relationship between AI and the flood frequency curve and the consistent shift of the growth curves with AI support the use of AI as a similarity measure for regionalization of flood frequency.

Description: The performance of glacio-hydrological models which simulate catchment response to climate variability depends to a large degree on the data used to force the models. The forcing data become increasingly important in high elevation, glacierised catchments where the interplay between extreme topography, climate and the cryosphere is complex. It is challenging to generate a reliable forcing dataset that captures this spatial heterogeneity. In this paper, we analyze the results of a one year field campaign focusing on air temperature and precipitation observations in the Langtang Valley in the Nepalese Himalayas. We use the observed time series to characterize both temperature lapse rates (LRs) and precipitation gradients (PGs). We study their spatial and temporal variability, and we attempt to identify possible controlling factors. We show that very clear LRs exist in the valley and that there are strong seasonal differences related to the water vapor content in the atmosphere. Results also show that the LRs are generally shallower than the commonly used environmental lapse rates. The analysis of the precipitation observations reveal that there is great variability in precipitation over short horizontal distances. A uniform valley wide PG cannot be established and several scale-dependent mechanisms may explain our observations. We complete our analysis by showing the impact of the observed LRs and PGs on the outputs of the TOPKAPI-ETH glacio-hydrological model. We conclude that LRs and PGs have a very large impact on the water balance composition and that short-term monitoring campaigns have the potential to improve model quality considerably.

Description: Regional-scale geologic structures characteristic of mantle lithosphere within cratons found in continent interiors are interpreted using geo-registered diverse data sets from the Slave craton of northwest Canada. We developed and applied a new method for mapping seismic discontinuities in three dimensions using multi-year observations at sparse, individual broadband receivers. New, fully 3-D conductivity models used all available magnetotelluric data. Discontinuity surfaces and conductivity models were geo-registered with previously published P-wave and surface wave velocity models to confirm first-order structures such as a mid-lithosphere discontinuity. Our 3-D model to 400 km depth was calibrated by ‘drill hole’ observations derived from xenolith suites extracted from kimberlites. A number of new structural discontinuities emerge from direct comparison of co-registered data sets and models. Importantly we distinguish primary mantle layers from secondary features related to younger metasomatism. Sub-horizontal Slave craton layers with tapered, wedge-shaped margins indicate construction of the craton core at 2.7 Ga by underthrusting and flat stacking of lithosphere. Mapping of conductivity and metasomatism in 3-D, the latter inferred via mineral recrystallization and resetting of isotopic ages in xenoliths, indicates overprinting of the primary layered structures. The observed distribution of relatively conductive mantle at 100–200 km depths is consistent with pervasive metasomatism; vertical ‘chimneys’ reaching to crustal depths in locations where kimberlites erupted or where Au mineralization is known.

Description: Many physically-based hydrological/hydrogeological models used for predicting groundwater seepage areas, including topography-based index models such as TOPMODEL, rely on the Dupuit assumption. To ensure the sound use of these simplified models, knowledge of the conditions under which they provide a reasonable approximation is critical. In this study, a Dupuit solution for the seepage length in hillslope cross-sections is tested against a full-depth solution of saturated groundwater flow. In homogeneous hillslopes with horizontal impervious base and constant-slope topography, the comparison reveals that the validity of the Dupuit solution depends not only on the ratio of depth to hillslope length d/L (as might be expected), but also on the ratio of hydraulic conductivity to recharge K/R and on the topographic slope s . The validity of the Dupuit solution is shown to be in fact a unique function of another ratio, the ratio of depth to seepage length d/L S . For d/L S 〈 0.2, the relative difference between the two solutions is quite small (〈 14% for the wide range of parameter values tested), whereas for d/L S 〉 0.2, it increases dramatically. In practice, this criterion can be used to test the validity of Dupuit solutions. When d/L S increases beyond that cut-off, the ratio of seepage length to hillslope length L S /L given by the full-depth solution tends towards a non-zero asymptotic value. This asymptotic value is shown to be controlled by (and in many cases equal to) the parameter R/sK . Generalization of the findings to cases featuring heterogeneity, non-horizontal impervious base and variable-slope topography is discussed.

Description: Isothermal compositional flow models require coupling transient compressible flows and advective transport systems of various chemical species in subsurface porous media. Building such numerical models is quite challenging and may be subject to many sources of uncertainties because of possible incomplete representation of some geological parameters that characterize the system's processes. Advanced data assimilation methods, such as the ensemble Kalman filter (EnKF), can be used to calibrate these models by incorporating available data. In this work, we consider the problem of estimating reservoir permeability using information about phase pressure as well as the chemical properties of fluid components. We carry out state-parameter estimation experiments using joint and dual updating schemes in the context of the EnKF with a two-dimensional single-phase compositional flow model (CFM). Quantitative and statistical analyses are performed to evaluate and compare the performance of the assimilation schemes. Our results indicate that including chemical composition data significantly enhances the accuracy of the permeability estimates. In addition, composition data provide more information to estimate system states and parameters than do standard pressure data. The dual state-parameter estimation scheme provides about 10% more accurate permeability estimates on average than the joint scheme when implemented with the same ensemble members, at the cost of twice more forward model integrations. At similar computational cost, the dual approach becomes only beneficial after using large enough ensembles.

Description: Groundwater-fed irrigation has been shown to deplete groundwater storage, decrease surface water runoff and increase evapotranspiration. Here we simulate soil moisture dependent groundwater-fed irrigation with an integrated hydrologic model. This allows for direct consideration of feedbacks between irrigation demand and groundwater depth. Special attention is paid to system dynamics in order to characterized spatial variability in irrigation demand and response to increased irrigation stress. A total of 80 years of simulation are completed for the Little Washita Basin in Southwestern Oklahoma, USA spanning a range of agricultural development scenarios and management practices. Results show regionally aggregated irrigation impacts consistent with other studies. However, here a spectral analysis reveals that groundwater-fed irrigation is also shown to amplify the annual streamflow cycle while dampening longer-term cyclical behavior with increased irrigation during climatological dry periods. Feedbacks between the managed and natural system are clearly observed with respect to both irrigation demand and utilization when water table depths are within a critical range. Although the model domain is heterogeneous with respect to both surface and subsurface parameters, relationships between irrigation demand, water table depth and irrigation utilization are consistent across space and between scenarios. Still, significant local heterogeneities are observed both with respect to transient behavior and response to stress. Spatial analysis of transient behavior shows that farms with groundwater depths within a critical depth range are most sensitive to management changes. Differences in behavior highlight the importance of groundwater's role in system dynamics in addition to water availability.

Description: Including positive feedbacks in hydrological models has recently been shown to result in complex behavior with multiple steady states. When a large disturbance, say a major drought, is simulated within such models the hydrology changes. Once the disturbance ends the hydrology does not return to that prior to the disturbance, but rather, persists within an alternate state. These multiple steady states (henceforth attractors ) exist for a single model parameterization and cause the system to have a finite resilience to such transient disturbances. A limitation of past hydrological resilience studies is that multiple attractors have been identified using mean annual or mean monthly forcing. Considering that most hydrological fluxes are subject to significant forcing stochasticity and do not operate at such large time scales, it remains an open question whether multiple hydrological attractors can exist when a catchment is subject to stochastic daily forcing. This question is the focus of this paper and it needs to be addressed prior to searching for multiple hydrological attractors in the field. To investigate this, a previously developed semi-distributed hill-slope ecohydrological model was adopted which exhibited multiple steady states under average monthly climate forcing. In this paper, the ecohydrological model was used to explore if feedbacks between the vegetation and a saline water table result in two attractors existing under daily stochastic forcing. The attractors and the threshold between them (henceforth repellor ) were quantified using a new limit cycle continuation technique that up-scaled climate forcing from daily to monthly (model and limit cycle code is freely available). The method was used to determine the values of saturated lateral hydraulic conductivity at which multiple attractors exist. These estimates were then assessed against time-integration estimates, which they agreed with. Overall, multiple attractors where found to exist under stochastic daily forcing. However, changing the climate forcing from monthly to daily did significantly reduce the parameter range over which two attractors existed. This suggests fewer catchments may have multiple attractors than previously considered.

Description: The companion paper showed that multiple steady state groundwater levels can exist within a hill-slope Boussinesq-vegetation model under daily stochastic forcing. Using a numerical limit-cycle continuation algorithm, the steady states (henceforth attractors ) and the threshold between them (henceforth repellor ) were quantified at a range of saturated lateral conductivity values, . This paper investigates if stochastic daily forcing can switch the catchment between both of the attractors. That is, an attractor may exist under average forcing conditions but can stochastic forcing switch the catchment into and out of each of the attractor basins?; i.e. making the attractor emerge . This was undertaken using the model of the companion paper and by completing daily time-integration simulations at six values of the saturated lateral hydraulic conductivity, ; three having two attractors and three having only a deep water table attractor. By graphically analyzing the simulations, and comparing against simulations from a model modified to have only one attractor, multiple attractors were found to emerge under stochastic daily forcing. However, the emergence of attractors was significantly more subtle and complex than that suggested by the companion paper. That is, an attractor may exist but never emerge; both attractors may exist and both may emerge but identifying the switching between attractors was often ambiguous; and only one attractor may exist and but a second temporary attractor may exist and emerge during periods of high precipitation. This subtle and complex emergence of attractors was explained using continuation analysis of the climate forcing rate, and not a model parameter such as . It showed that the temporary attractor existed over a large range of values and this suggests that more catchments may have multiple attractors than suggested by the companion paper. By combining this continuation analysis with the time-integration simulations, hydrological signatures indicative of a switch of multiple attractors were proposed. These signatures may provide a means for identifying actual catchments that have switched between multiple attractors.

Description: ABSTRACT A large-time analytical solution is proposed for the spatial variance and coefficient of variation of the depth-averaged concentration due to instantaneous, cross-sectionally uniform solute sources in pseudo-rectangular open channel flows. The mathematical approach is based on the use of the Green functions and on the Fourier decomposition of the depth-averaged velocities, coupled with the method of the images. The variance spatial trend is characterized by a minimum at the center of the mass and two mobile, decaying symmetrical peaks which, at very large times, are located at the inflexion points of the average Gaussian distribution. The coefficient of variation, which provides an estimate of the expected percentage deviation of the depth-averaged point concentrations about the section-average, exhibits a minimum at the center which decays like t -1 and only depends on the river diffusive time-scale. The defect of cross-sectional mixing quickly increases with the distance from the center, and almost linearly at large times. Accurate numerical Lagrangian simulations were performed to validate the analytical results in pre-asymptotic and asymptotic conditions, referring to a particularly representative sample case for which cross-sectional depth and velocity measurements were known from a field survey. In addition, in order to discuss the practical usefulness of computing large-time concentration spatial moments in river flows, and resorting to directly measured input data, the order of magnitude of section-averaged concentrations and corresponding coefficients of variation was estimated in field conditions and for hypothetical contamination scenarios, considering a unit normalized mass impulsively injected across the transverse section of 81 U.S. rivers.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Successful dispersal can enhance both individual fitness and population persistence, but the process of dispersal is often inherently risky. The interplay between the costs and benefits of dispersal are poorly documented for species with complex life-histories due to the difficulty of tracking dispersing individuals. Here we investigate variability in dispersal histories of a freshwater fish, Awaous stamineus, across the species' entire geographic range in the Hawaiian archipelago. Like many animals endemic to tropical island streams, these gobies have an amphidromous life cycle in which a brief marine larval phase enables dispersal among isolated freshwater habitats. Using otolith microchemistry, we document three distinct marine dispersal pathways, all of which are observed on every island. Surprisingly, we also find that 62% of individuals complete their life cycle entirely within freshwater, in contrast to the assumption that amphidromy is obligate in Hawaiian stream gobies. Comparing early life history outcomes based on daily otolith growth rings, we find that individuals with marine dispersal have shorter larval durations and faster larval growth, and their growth advantage over purely-freshwater counterparts continues to some degree into adult life. These individual benefits of maintaining a marine dispersal phase presumably balance against the challenge of finding and re-entering an island stream from the ocean. The facultative nature of amphidromy in this species highlights the selective balance between costs and benefits of dispersal in life history evolution. Accounting for alternative dispersal strategies will be essential for conservation of the amphidromous species that often dominate tropical island streams, many of which are at risk of extinction.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Climate change forecasts of more frequent climate extremes suggest that such events will become increasingly important drivers of future ecosystem dynamics and function. Because the rarity and unpredictability of naturally occurring climate extremes limits assessment of their ecological impacts, we experimentally imposed extreme drought and a mid-summer heat wave over two years in a central US grassland. While the ecosystem was resistant to heat waves, it was not resistant to extreme drought, which reduced aboveground net primary productivity (ANPP) below the lowest level measured in this grassland in almost thirty years. This extreme reduction in ecosystem function was a consequence of reduced productivity of both C4 grasses and C3 forbs. However, the dominant forb was negatively impacted by the drought more than the dominant grass, and this led to a reordering of species abundances within the plant community. Although this change in community composition persisted post-drought, ANPP recovered completely the year after drought due to rapid demographic responses by the dominant grass, compensating for loss of the dominant forb. Overall, these results show that an extreme reduction in ecosystem function attributable to climate extremes (e.g., low resistance) does not preclude rapid ecosystem recovery. Given that dominance by a few species is characteristic of most ecosystems, knowledge of the traits of these species and their responses to climate extremes will be key for predicting future ecosystem dynamics and function.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. The resource quality of the host has been shown to affect parasite transmission success, prevalence and virulence. Seasonal availability of environmental nutrients alters density and stoichiometric quality (carbon-nutrient ratios) of both producers and consumers, suggesting that nutrient availability may drive fluctuations in parasite prevalence patterns observed in nature. We examined the interactions between the population dynamics of a keystone herbivore Daphnia and its parasites, and their associations with water nutrient concentrations, resource quantity and quality and other environmental variables (temperature, pH, oxygen concentration) in a small lake, using general linear models. We found that the prevalence of two gut endoparasites were positively related to food source and quality as well as nitrogen content of Daphnia - whereas the prevalence of an epibiont and overall parasite species richness were negatively related to phosphorus content of Daphnia. When only endoparasite species richness was considered, no connections to nutrients were found. Daphnia density was not connected to parasites, but we found interactions between Daphnia fecundity and parasite prevalence. Overall, our results suggest that environmental nutrient concentrations and stoichiometric quality of the host have a potential to affect seasonality in parasite epidemics, but the connections between environmental carbon:nutrient ratios and parasite prevalence patterns are diverse and species-specific.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. The Tibetan Plateau (TP) is experiencing high rates of climatic change. We present a novel combined mechanistic-bioclimatic modeling approach to determine (i) how changes in precipitation and temperature on the TP may impact net primary production (NPP) in four major biomes (forest, shrub, grass, desert); and (ii) if there exists a maximum rain use efficiency (RUEMAX) that represents a "boundary that constrain(s) site-level productivity and efficiency" (Huxman et al. 2004). We used a daily mechanistic ecosystem model to generate 40-y outputs using observed climatic data for scenarios of (i) decreased precipitation (25 to 100%); (ii) increased air temperature (1 to 6°C); (iii) simultaneous changes in both precipitation ( ± 50%, ± 25%) and air temperature (+1 to +6°C); and (iv) increased interannual variability (IAV) of precipitation (+1σ to +3σ, with fixed means). We fitted model output from these scenarios to Huxman et al.'s RUEMAX bioclimatic model, NPP = α +RUE•PPT (where α = intercept, RUE is rain use efficiency and PPT is annual precipitation). Based on these analyses we conclude that: (i) there is strong support (when not explicit, then trend-wise) for Huxman et al.'s assertion that biomes converge to a common RUEMAX during the driest years at a site, thus representing the boundary for highest rain use efficiency; (ii) the interactive effects of simultaneously decreasing precipitation and increasing temperature on NPP for the TP is smaller than might be expected from additive, single-factor changes in these drivers; and (iii) that increasing IAV of precipitation may ultimately have a larger impact on biomes of the Tibetan Plateau than changing amounts of rainfall and air temperature alone.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Niche differentiation is a major hypothesized determinant of species distributions, but its practical importance is heavily debated and underlying mechanisms are poorly understood. Trait-based approaches have been used to infer niche differentiation and predict species distributions. For understanding underlying mechanisms, individual traits should be scaled up to whole-plant performance, which hardly has been done. We measured seven key traits that are important for carbon and water balance for 37 tropical tree species. We used a process-based plant physiological model to simulate the carbon budget of saplings along gradients of light and water availability, and quantified the performance of the species in terms of their light compensation points (a proxy for shade tolerance), water compensation points (proxy for drought tolerance) and maximum carbon gain rates (proxy for potential growth rate). We linked species performances to their observed distributions (the realized niches) at two spatial scales in Bolivian lowland forests: along a canopy openness gradient at local scale (~1 km2) and along a rainfall gradient (1100-2200 mm/y) at regional (~1000 km) scale. We show that the water compensation point was the best predictor of species distributions along water and light resource gradients within and across tropical forests. A sensitivity analysis suggests that the stomatal regulation of minimum leaf water potentials, rather than stem hydraulic traits (sapwood area and specific conductivity), contributed to the species differences in the water compensation point of saplings. The light compensation point and maximum carbon gain - both driven by leaf area index and the leaf nitrogen concentration - also contributed to differential species distributions at the local scale, but not or only marginally at the regional scale. Trait-and-physiology-based simulations of whole-plant performance thus help to evaluate the possible roles of individual traits in physiological processes underlying species performance along environmental gradients. The development of such whole plant concepts will improve our ability to understand responses of plant communities to shifts in resource availability and stress under global change.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Birds and their population dynamics are often used to understand and document anthropogenic effects on biodiversity. Nest success is a critical component of the breeding output of birds in different environments; but to obtain the complete picture of how bird populations respond to perturbations, we also need an estimate of nest abundance or density. The problem is that raw counts generally underestimate actual nest numbers because detection is imperfect and because some nests may fail or fledge before being subjected to detection efforts. Here we develop a state-space superpopulation capture-recapture approach in which inference about detection probability is based on the age at first detection, as opposed to the sequence of re-detections in standard capture-recapture models. We apply the method to ducks in which 1) the age of the nests and their initiation dates can be determined upon detection and 2) the duration of the different stages of the breeding cycle is a priori known. We fit three model variants with or without assumptions about the phenology of nest initiation dates, and use simulations to evaluate the performance of the approach in challenging situations. In an application to blue-winged teal Anas discors breeding at study sites in North and South Dakota, USA, nesting stage (egg-laying or incubation) markedly influenced nest survival and detection probabilities. Two individual covariates (one binary covariate: presence of grazing cattle at the nest site, and one continuous covariate: Robel index of vegetation) had only weak effects. We estimated that 5-10% of the total number of nests were available for detection but missed by field crews. An additional 6-15% were never available for detection. These proportions are expected to be larger in less intense, more typical sampling designs. User-friendly software nestAbund is provided to assist users in implementing the method.

Description: Understanding the nature of the crust has long been a goal for seismologists when imaging the Earth. This is particularly true in volcanic regions where imaging melt storage and migration can have important implications for the size and nature of an eruption. Receiver functions and the H- κ stacking (H κ ) technique are often used to constrain crustal thickness (H) and the ratio of P- to S-wave velocities ( κ ). In this paper I show that it is essential to consider anisotropy when performing H κ . I show that in a medium with horizontally transverse isotropy a strong variation in κ with back azimuth is present which characterises the anisotropic medium. In a vertically transverse isotropic medium no variation in κ with back azimuth is observed, but κ is increased across all back azimuths. Thus, estimates of κ are more difficult to relate to composition than previously thought. I extend these models to melt induced anisotropy and show that similar patterns are observed, but with more significant variations and increases in κ . Based on these observations I develop a new anisotropic H- κ stacking technique which inverts H κ data for melt fraction, aspect ratio and orientation of melt inclusions. I apply this to data for the Afar Depression and show that melt is stored in interconnected stacked sills in the lower crust, which likely supply the recent volcanic eruptions and dike intrusions. This new technique can be applied to any anisotropic medium where it can provide constraints on the average crustal anisotropy.

Description: A Fortran 90 program to visualize data on the Yin-Yang grid system is developed. The purpose of this study is to provide simulation researchers with a source code as a starting point of their own custom-made visualization tools. A basic but sufficiently diverse set of visualization methods are implemented using a Fortran 90 binding for OpenGL for scalar and vector fields defined or simulated on the Yin-Yang grid.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Disease is often expected to limit host populations, but diseases do not always dramatically reduce host numbers and often have no effect. The impact of a fungal pathogen (Entomophaga grylli pathotype 1) on grasshopper (Camnula pellucida) populations was studied in a field experiment. We tested whether the effects of disease on grasshopper survival were 1) additive, with disease mortality summing with other mortality sources to determine the total population mortality rate or 2) compensatory, where disease mortality simply replaces mortality from other sources so that the total population mortality rate remains unchanged. We examined grasshopper survival in relation to differences in disease exposure, host density levels, and host developmental stage. The effects of disease varied with grasshopper developmental stage and density. Disease mortality increased by 60% at high grasshopper density compared to low density treatments, and decreased when grasshoppers fully matured. Despite increased rates of disease mortality at high densities, the total mortality rate was not notably higher in diseased grasshoppers (87%) compared to disease-free counterparts at high densities (83%), indicating that a large proportion of disease mortality simply replaced mortality from food limitation. Additive responses were supported in early and late instars, with disease exposure resulting in decreased grasshopper survival. In contrast, the effect of disease on adults was inconclusive. Yet, the disease did not affect adult survival suggesting that adult disease mortality is compensatory. Therefore, disease reduction of grasshopper populations (additive mortality) is more likely to occur during earlier developmental stages when hosts are most vulnerable to disease and at low host densities when food is abundant. Combined, our results emphasize the importance of host dynamics and food availability in how this host-pathogen system responds to disease. Accordingly, compensatory versus additive mortality may need to be considered when examining how disease ultimately affects host population dynamics.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Urbanization and global climate change can profoundly alter biological systems, yet scientists often analyze their effects separately. We test how the timing of life cycle events (phenology) is jointly influenced by these two components of global change. To do so, we use a long-term phenological dataset of 20 common butterfly species from 83 sites across the state of Ohio, USA, with sites that range from rural undeveloped areas to moderately sized cities. These sites span a several °C latitudinal gradient in mean temperature, mimicking the range of projected global climate warming effects through the end of the century. Although shifts toward earlier phenology are typical of species' responses to either global climate change or urbanization, we found that their interaction delayed several Ohio butterfly species' first appearance and peak abundance phenology. Exploitative species exhibited smaller delays in first appearance and peak abundance phenology in areas that were urbanized and geographically warm. Our results show that phenological responses to urbanization are contingent upon geographic variation in temperature, and that the impacts of urbanization and global climate change should be considered simultaneously when developing forecasts of biological responses to environmental change.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Fertilization via agricultural inputs and nutrient deposition is one of the major threats to global terrestrial plant richness, yet we still do not fully understand the mechanisms by which fertilization decreases plant richness. Tall clonal species have recently been proposed to cause declines in plant species richness by increasing in abundance in response to fertilization and competing strongly with other species. We tested this hypothesis in a fertilization experiment in a low productivity grassland by using a novel experimental manipulation of the presence vs. absence of clonal species and by examining the role of height within these treatments. We found that fertilization decreased species richness more in the presence than absence of clonal species. We also found that only tall species increased in biomass in response to fertilization. In the absence of clonal species, fertilization increased biomass of tall non-clonal species. However, in the presence of clonal species, fertilization decreased tall non-clonal biomass and only tall clonal biomass increased. Fertilization caused almost all short species to be lost in the presence, but not the absence, of clonal species and caused greater declines in the mean and variance of light levels in the presence of clonal species. These results show that the traits of species in a community can determine the magnitude of species loss due to fertilization. The strongly negative effect of tall clonals on species richness in fertilized plots is likely a result of their capacity to decrease light levels to a greater extent and more uniformly than non-clonal species, and thereby drive the exclusion of short species. These results help clarify the mechanisms whereby fertilization decreases grassland plant species richness and suggest that efforts to prevent the loss of species under fertilized conditions may be most effective when they focus on controlling the biomass of tall clonal species.

Description: Two major causes of salt marsh loss are vertical drowning, when sediment accumulation on the platform cannot keep vertical pace with sea level rise, and horizontal retreat, associated with wave-induced marsh boundary erosion. Despite these processes having been extensively documented and modeled, is unclear which loss modality dominates given a set of environmental parameters. A three-point dynamic model was developed to predict marsh loss as a function of sea level rise, allochthonous sediment supply, wind regime, tidal range, and marsh bank and mudflat erodability. Marsh horizontal and vertical evolution was found to respond in opposing ways to wave induced erosion processes. Marsh horizontal retreat was triggered by large mudflats, strong winds, high erodability of marsh bank and mudflat, whereas the opposite conditions acted to reduce the sediment supply to the marsh platform, promoting marsh loss to drowning. With low and moderate rates of sea level rise (~ 5 mm/yr), retreat was found to be a more likely marsh loss modality than drowning. However, conditions associated with marsh retreat also increase the system resilience by transferring sediment on the marsh platform and preventing drowning. Our results suggest the use of a modular strategy for short-term marsh management: selectively protect extensive salt marsh regions by maintaining healthy vegetation on the platform, while allowing other areas to retreat, leveraging the natural resilience embedded in the lateral loss of marsh extent.

Description: Observational data and the Princeton Urban Canopy Model, with its detailed representation of urban heterogeneity and hydrological processes, are combined to study evaporation and turbulent water vapor transport over urban areas. The analyses focus on periods before and after precipitation events, at two sites in the Northeastern United States. Our results indicate that while evaporation from concrete pavements, building rooftops and asphalt surfaces is discontinuous and intermittent, overall these surfaces accounted for nearly 18% of total latent heat fluxes (LE) during a relatively wet 10-day period. More importantly, these evaporative fluxes have a significant impact on the urban surface energy balance, particularly during the 48 hours following a rain event when impervious evaporation is the highest. Thus, their accurate representation in urban models is critical. Impervious evaporation after rainfall is also shown to correlate the sources of heat and water at the earth surface, resulting in a conditional scalar transport similarity over urban terrain following rain events.

Description: The spatial and temporal dynamics of seasonal snow covers play a critical role for many hydrological, ecological, and climatic processes. This paper presents a new, innovative approach to continuously monitor these dynamics using numerous low-cost, standalone snow monitoring stations (SnoMoS). These stations provide snow and related meteorological data with a high temporal and spatial resolution. Data collected by SnoMoS include: snow depth, surface temperature, air temperature and humidity, total precipitation, global radiation, wind speed, and barometric pressure. A total of 99 sensors were placed over the winters 2010/11 and 2011/12 at multiple locations within three 40 - 180 km² basins in the Black Forest region of Southern Germany. The locations were chosen to cover a wide range of slopes, elevations, and expositions in a stratified sampling design. Furthermore, “paired stations” located in close proximity to each other, one in the open and one underneath various forest canopies, were set up to investigate the influence of vegetation on snow dynamics. The results showed that considerable differences in snow depth and, therefore, snow water equivalent (SWE) are present within the study area despite its moderate temperatures and medium elevation range (400 - 1500 m). The relative impact of topographical factors like elevation, aspect, and of different types of forest vegetation were quantified continuously and were found to change considerably over the winter period. The recorded differences in SWE and snow cover duration were large enough that they should be considered in hydrologic and climate models.

Description: Integrated land surface-groundwater models are valuable tools in simulating the terrestrial hydrologic cycle as a continuous system and exploring the extent of land surface–subsurface interactions from catchment to regional scales. However, the fidelity of model simulations is impacted not only by the vegetation and subsurface parameterizations, but also by the antecedent condition of model state variables, such as the initial soil moisture, depth to groundwater and ground temperature. In land surface modeling, a given model is often run repeatedly over a single year of forcing data until it reaches an equilibrium state: the point at which there is minimal artificial drift in the model state or prognostic variables (most often the soil moisture). For more complex coupled and integrated systems, where there is an increased computational cost of simulation and the number of variables sensitive to initialization is greater than in traditional uncoupled land surface modeling schemes, the challenge is to minimize the impact of initialization while using the smallest spin-up time possible. In this study, multi-criteria analysis was performed to assess the spin-up behavior of the ParFlow.CLM integrated groundwater-surface water-land surface model over a 208 km 2 sub-catchment of the Ringkobing Fjord catchment in Denmark. Various measures of spin-up performance were computed for model state variables such as the soil moisture and groundwater storage, as well as for diagnostic variables such as the latent and sensible heat fluxes. The impacts of initial conditions on surface water–groundwater interactions were then explored. Our analysis illustrates that the determination of an equilibrium state depends strongly on the variable and performance measure used. Choosing an improper initialization of the model can generate simulations that lead to a misinterpretation of land surface-subsurface feedback processes and result in large biases in simulated discharge. Estimated spin-up time from a series of spin-up functions revealed that 20 (or 21) years of simulation were sufficient for the catchment to equilibrate according to at least one criterion at the 0.1% (0.01%) threshold level. Amongst a range of convergence metrics examined, percentage changes in monthly values of groundwater and unsaturated zone storages produced a slow system convergence to equilibrium, whereas criteria based on ground temperature allowed a more rapid spin-up. Slow convergence of unsaturated and saturated zone storages is a result of the dynamic adjustment of the water table in response to a physically arbitrary or inconsistent initialization of a spatially uniform water table. Achieving equilibrium in subsurface storage ensured equilibrium across a spectrum of other variables, hence providing a good measure of system-wide equilibrium. Overall, results highlight the importance of correctly identifying the key variable affecting model equilibrium and also the need to use a multi-criteria approach to achieve a rapid and stable model spin-up.

Description: In this paper, we perform a detailed regional analysis of the link between meteorological drought indices and streamflow for a comprehensive Austrian dataset of 47 small to medium-size catchments in humid-temperate climate. Four drought indices considering different components of the catchment water balance are tested. We assess the quality of the link using rank correlation analysis, and the probability of detecting low flow events by hit-scores. Overall, correlations range between 0.4 and 0.8 and differ significantly between regions. A stratified analysis shows that the link is much stronger (i) for summer low flows and droughts than for anomalies in general, and (ii) for more humid than more arid conditions. Under more humid conditions streamflow droughts of small to medium-size catchments are to a large extent generated by climate forcing and therefore well represented by a simple meteorological index. Under increasingly dry conditions, the climate signal gets less predictive and storage properties of the underground become more important. A simple soil moisture accounting scheme (such as those of the Palmer index) can considerably improve the correlations. Overall, we conclude there is a significant link between meteorological drought and streamflow drought, except for catchments where groundwater storage and snow processes are important. The results are encouraging and provide a wealth of information which can profitably be used to set up statistical prediction models to estimate low flows from meteorological time series.

Description: Water resources in the western United States are contingent on interannual variations in snowpack. Interannual snowpack variability has been attributed to large-scale climate patterns including the El Niño-Southern Oscillation (ENSO), however the contribution of snowfall frequency and extreme snowfall events to this variability are less well quantified. Long term records from Snowpack Telemetry and Cooperative Observer Program stations in the eleven western states were used to investigate these relationships by considering the number of snowfall days and snowfall water equivalent (SFE) of extreme snowfall events. The top decile of snowfall events contributed 20-38% of annual SFE, depending on the region. An average of 65% and 69% of the interannual variability in annual SFE was explained by snowfall days and SFE of top decile snowfall events, respectively, with extreme events being a more significant predictor at most stations. The latitudinal dipole in SFE during ENSO phases results from changes in snowfall frequency and extreme events. In the Pacific Northwest, above normal SFE during La Niña winters was a product of both larger contributions from extremes and more snowfall days, while below normal SFE during El Niño winters was primarily associated with a substantial reduction in extremes. Conversely, annual SFE during ENSO phases in the mountains of Arizona was more closely linked to fluctuations in snowfall days than extremes. Results indicate the importance of extreme snowfall events in shaping interannual variability in water resources and suggest that improved predictive ability may inform better water resource management now and in the coming decades.

Description: Cell-centered finite volume methods are prevailing in numerical simulation of flow in porous media. However, due to the lack of cell-centered finite volume methods for mechanics, coupled flow and deformation is usually treated either by coupled finite-volume-finite element discretizations, or within a finite element setting. The former approach is unfavorable as it introduces two separate grid structures, while the latter approach loses the advantages of finite volume methods for the flow equation. Recently we proposed a cell-centered finite volume method for elasticity. Herein we explore the applicability of this novel method to provide a compatible finite volume discretization for coupled hydro-mechanic flows in porous media. We detail in particular the issue of coupling terms, and show how this is naturally handled. Furthermore, we observe how the cell-centered finite volume framework naturally allows for modeling fractured and fracturing porous media through internal boundary conditions. We support the discussion with a set of numerical examples: The convergence properties of the coupled scheme are first investigated; Secondly, we illustrate the practical applicability of the method both for fractured and heterogeneous media.

Description: The spatiotemporal distribution of Land Surface Temperature (LST) is linked to the partitioning of the coupled surface water and energy budgets. In watersheds with a strong seasonality in precipitation and vegetation cover, the temporal evolution of LST patterns are a signature of the interactions between the land surface and atmosphere. Nevertheless, few studies have sought to understand the topographical and ecohydrological controls on LST in regions of complex terrain. Numerical watershed models, tested against spatially-distributed field and remote sensing data, can aid in linking the seasonal evolution of LST to meteorology, terrain, soil and vegetation. In this study, we use a distributed hydrologic model to explore LST patterns in a semiarid mountain basin during the transition from a dry spring to the wetter North American monsoon (NAM). By accounting for vegetation greening through remotely-sensed parameters, the model reproduces LST and surface soil moisture observations derived from ground, aircraft and satellite platforms with good accuracy at individual sites and as spatial basin patterns. Distributed simulations reveal how LST varies with elevation, slope and aspect and the role played by the seasonal vegetation canopy in cooling the land surface and increasing the spatial variability in LST. As a result, LST is shown to track well with ecosystem-specific changes in vegetation cover, evapotranspiration and soil moisture during the NAM. Furthermore, vegetation greening is shown to modulate the spatial heterogeneity of LST during the NAM that should be considered in subsequent atmospheric studies in regions of complex terrain.

Description: Models of landscape evolution or hydrological processes typically depend on the accurate determination of upslope drainage area from digital elevation data, but such calculations can be very computationally demanding when applied to high-resolution topographic data. To overcome this limitation, we propose calculating drainage area in an implicit, iterative manner using linear solvers. The basis of this method is a recasting of the flow routing problem as a sparse system of linear equations, which can be solved using established computational techniques. This approach is highly parallelizable, enabling data to be spread over multiple computer processors. Good scalability is exhibited, rendering it suitable for contemporary high-performance computing architectures with many processors, such as graphics processing units (GPUs). In addition, the iterative nature of the computational algorithms we use to solve the linear system creates the possibility of accelerating the solution by providing an initial guess, making the method well suited to iterative calculations such as numerical landscape evolution models. We compare this method with a previously proposed parallel drainage area algorithm and present several examples illustrating its advantages, including a continent-scale flow routing calculation at 3 arcsecond resolution, improvements to models of fluvial sediment yield, and acceleration of drainage area calculations in a landscape evolution model. We additionally describe a modification that allows the method to be used for parallel basin delineation.

Description: Ecology, Ahead of Print. Predicting the future trend and viability of populations is an essential task in ecology. Because many populations respond to changing environments, uncertainty surrounding environmental responses must be incorporated into population assessments. However, understanding the effects of environmental variation on population dynamics requires information on several important demographic parameters which are often difficult to estimate. Integrated population models facilitate the integration of time-series data on population size and all existing demographic information from a species, allowing the estimation of demographic parameters for which limited or no empirical data exist. Although these models are ideal for assessments of population viability, they have so far not included environmental uncertainty. We incorporated environmental variation in an integrated population model to account for both demographic and environmental uncertainty in an assessment of population viability. In addition, we used this model to estimate true juvenile survival, an important demographic parameter for population dynamics that is difficult to estimate empirically. We applied this model to assess the past and future population trend of a rare island endemic songbird, the Montserrat Oriole Icterus oberi, which is threatened by volcanic activity. Montserrat Orioles experienced lower survival in years with volcanic ash-fall, causing periodic population declines that were compensated by higher seasonal fecundity in years with high pre-breeding season rainfall. Due to the inclusion of both demographic and environmental uncertainty in the model, the estimated population growth rate in the immediate future was highly imprecise (95% credible interval 0.844 - 1.105), and the probability of extinction after three generations (in the year 2028) was low (2.1%). This projection demonstrates that accounting for both demographic and environmental sources of uncertainty provides a more realistic assessment of the viability of populations under unknown future environmental conditions.

Description: Ecology, Ahead of Print. Grasslands have been lost and degraded in the USA since Euro-American settlement due to agriculture, development, introduced invasive species, and changes in fire regimes. Fire is frequently used in prairie restoration to control invasion by trees and shrubs, but may have additional consequences. For example, fire might reduce damage by herbivore and pathogen enemies by eliminating litter, which harbors eggs and spores. Less obviously, fire might influence enemy loads differently for native and introduced plant hosts. We used a controlled burn in a Willamette Valley (Oregon) prairie to examine these questions. We expected that without fire, introduced host plants should have less damage than native host plants because the introduced species are likely to have left many of their enemies behind when they were transported to their new range (the enemy release hypothesis, or ERH). If the ERH holds, then fire, which should temporarily reduce enemies on all species, should give an advantage to the natives because they should see greater total reduction in damage by enemies. Prior to the burn, we censused herbivore and pathogen attack on eight plant species (five of non-native origin: Bromus hordaceous, Cynosuros echinatus, Galium divaricatum, Schedonorus arundinaceus (=Festuca arundinacea), Sherardia arvensis; and three natives: Danthonia californica, Epilobium minutum, and Lomatium nudicale). The same plots were monitored for two years post-fire. Prior to the burn, native plants had more kinds of damage and more pathogen damage than introduced plants, consistent with the ERH. Fire reduced pathogen damage relative to the controls more for the native than the introduced species, but the effects on herbivory were negligible. Pathogen attack was correlated with plant reproductive fitness, whereas herbivory was not. These results suggest that fire may be useful for promoting some native plants in prairies due to its negative effects on their pathogens.

Description: Ecology, Ahead of Print. Floral nectar of many plant species is prone to colonization by microbial organisms such as yeasts. Their presence and metabolism of nectar chemical components have the potential to modify a suite of floral traits important for pollinator attraction, including nectar quality and scent. However, studies on the direct and indirect effects of nectar-inhabiting microogranisms on pollinator behavior and plant reproductive success remain rare. To determine their potential to affect pollinator behavior and plant fitness, we experimentally manipulated the common nectar-inhabiting yeast Metschnikowia reukaufii in the nectar of Delphinium nuttallianum, a short-lived montane perennial herb. We detected positive indirect, pollinator-mediated effects of yeasts on male plant fitness measured as pollen donation using powdered fluorescent dyes. However, we detected no direct or indirect effects on components of female fitness. Matching effects on male plant fitness, pollinators responded positively to the presence of yeasts, removing more nectar from flowers treated with M. reukaufii. Our results provide evidence of effects of nectar-inhabiting yeasts on male plant fitness and highlight the importance of microorganisms in mediating plant-pollinator interactions and subsequent plant fitness.

Description: Ecology, Ahead of Print. Complementary resource use and redundancy of species that fulfill the same ecological role are two mechanisms that can respectively increase and stabilize process rates in ecosystems. For example, predator complementarity and redundancy can determine prey consumption rates and their stability, yet few studies take into account the multiple predator species attacking multiple prey at different rates in natural communities. Thus, it remains unclear whether these biodiversity mechanisms are important determinants of consumption in entire predator-prey assemblages, such that food-web interaction structure determines community-wide consumption and stability. Here, we use empirical quantitative food-webs to study the community-wide effects of functional complementarity and redundancy of consumers (parasitoids) on herbivore control in temperate forests. We find that complementarity in host resource use by parasitoids was a strong predictor of absolute parasitism rates at the community level, and that redundancy in host-use patterns stabilised community-wide parasitism rates in space, but not through time. These effects can potentially explain previous contradictory results from predator diversity research. Phylogenetic diversity (measured using taxonomic distance) did not explain functional complementarity or parasitism rates, so could not serve as a surrogate measure for functional complementarity. Our study shows that known mechanisms underpinning predator diversity effects on both functioning and stability can easily be extended to link food webs to ecosystem functioning.

Description: Ecology, Ahead of Print. Understanding the way in which species are associated in communities is a fundamental question in ecology. Yet there remains a tension between communities as highly structured units or as coincidental collections of individualistic species. We explore these ideas using a new statistical approach that clusters species based on their environmental response- a species archetype, rather than clustering sites based on their species composition. We find that there are groups of species, which are consistently highly correlated, but that these groups are not unique to any set of locations and overlap spatially. The species present at a single site are a realisation of species from the (multiple) archetype groups that are likely to be present at that location based on their response to the environment.

Description: Ecology, Ahead of Print. Invasive alien predators can impose strong selection on native prey populations and induce rapid evolutionary change in the invaded communities. However, studies on evolutionary responses to invasive predators are often complicated by the lack of replicate populations differing in coexistence time with the predator, which would allow determining how prey traits change during the invasion. The red swamp crayfish Procambarus clarkii has invaded many freshwater areas worldwide, with negative impacts for native fauna. Here, we examined how coexistence time shapes antipredator responses of the Iberian waterfrog (Pelophylax perezi) to the invasive crayfish by raising tadpoles from five populations differing in historical exposure to P. clarkii (30 years, 20 years or no coexistence). Tadpoles from non-invaded populations responded to the presence of P. clarkii with behavioral plasticity (reduced activity), whereas long-term invaded populations showed canalized antipredator behavior (constant low activity level). Tadpoles from one of the long-term invaded populations responded to the crayfish with inducible morphological defenses (deeper tails), reflecting the use of both constitutive and inducible antipredator defenses against the exotic predator by this population. Our results suggest that, while naive P. perezi populations responded behaviorally to P. clarkii, the strong predation pressure imposed by the crayfish has induced the evolution of qualitatively different antipredator defenses in populations with longer coexistence time. These responses suggest that strong selection by invasive predators may drive rapid evolutionary change in invaded communities. Examining responses of prey species to biological invasions using multiple populations will help us better forecast the impact of invasive predators in natural communities.

Description: Ecology, Ahead of Print. Imbalances in phosphorus (P) intake relative to demand negatively affect animal growth, but their consequences are less understood for vertebrates, in which bone represents a significant and potentially flexible pool of P. Flexibility in body-P content could buffer vertebrates from the effects of imbalances between P intake and demand, reducing the likelihood of a sharp stoichiometric "knife-edge" in the relationship between growth rate and diet-P level. We conducted a meta-analysis of published aquaculture experiments that tested effects of diet %P on fish growth rate (49 studies, 28 species) and body-P content (27 of the studies in the main data set, 20 species). Our meta-analysis revealed significant P limitation of growth, as well as significant negative effects of excess P on growth rate. Diet-P thresholds for these effects occurred at ecologically relevant levels (mean ± SD optimal diet-P of 1.2 ± 0.45% under experimental conditions of high ration). Finally, the analysis also suggested a pattern of relatively shallow relationships between growth rate and diet-P level, coupled with surprisingly flexible body-P content in fishes. This result is consistent with fish using flexible body-P content (presumably mediated through bone P) to buffer imbalances between P intake and demand. Together, our results provide evidence for a relatively "dull" stoichiometric "knife-edge" in fishes, driven in part by flexible body-P content.

Description: Ecology, Ahead of Print. Community ecologists use functional groups based on the rarely tested assumption that within-group responses to ecological processes are similar and thus members are functionally equivalent. However, recent research suggests functional equivalency may break down with human impacts. We tested the equivalency assumption and model predictions of responses to simulated human alterations in nutrients and large herbivores for two models of coral reef algae, the Relative Dominance Model (RDM) and the Functional Group Model (FGM). Results of both mesocosm and field experiments using assembled communities were compared to model predictions and within- and between-group variability were assessed. Both models' predictions of group response to herbivory matched experimental outcomes, but only the RDM predicted response to nutrients. However, within-group variability was dramatic, as the RDM grouped species with opposite responses to herbivory and the FGM grouped species with unique responses to nutrients. These heterogeneous responses resulted in loss of information and masked strong interactions between herbivory and nutrients that were not included in the models. As humans continue to impact major ecological processes in ecosystems globally, we postulate that functional-group models may need to be reformulated to account for shifting baselines.

Description: Ecology, Ahead of Print. Flowering plants often occur in mixed-species groups where interactions between them can occur both pre- and post-pollination. In post-pollination interactions conspecific (CP) and heterospecific pollen (HP) interact on the style and previous work indicates that these interactions, often, but not always, lead to reduced fitness. However, over half of insect-pollinated species display a mixed mating system, where both self and outcross CP could interact with HP, yet no study has evaluated the effects on both types of CP. We present and test hypotheses for the differential effects of HP depending on CP source and timing of HP arrival with a mixed-mating plant, M. guttatus, and one of its HP donors (Helianthus exilis). We found H. exilis pollen reduced tube growth and fertilization success of M. guttatus self pollen to a greater degree than outcross pollen, but only when CP and HP were applied simultaneously. Our results indicate that for mixed-mating plants the fitness consequences of HP receipt can be more detrimental than previously thought. Furthermore, our findings suggest that HP receipt, which can be high in biodiverse areas, has the potential to influence mating system and genetic diversity of the plant populations within them.

Description: Ecology, Ahead of Print. Factors that control tree seedling dynamics are critical determinants of forest diversity. We examined the role of density-dependent mortality and abiotic factors in the differential establishment and survival of tree seedlings at three large mapped forest plots in Indiana, Virginia and Wisconsin, USA. We tested whether seedling densities and seedling survival are related to local biotic and abiotic factors with generalized linear mixed models. Spatial point pattern analyses were utilized to determine if the distribution patterns of seedlings and saplings are consistent with a pattern generated by negative density-dependent mortality with respect to conspecific trees. Initial sampled seedling density for nearly a third of species showed a positive correlation with increasing conspecific basal area indicating dispersal limitation, but few had any association with abiotic variables. By contrast, survival of seedlings over one year significantly declined with increasing conspecific basal area. Point pattern analyses indicated that nearly one third of tree species had significantly over-dispersed point patterns of conspecific seedlings and saplings relative to adult densities; the majority of other species exhibited random spatial arrangements. Our results demonstrate that negative conspecific density-dependent mortality of seedlings could generate the spatial patterns observed at later life stages. By differentially favoring seedlings of other species, this process may contribute to the maintenance of tree diversity in temperate forests, just as others have demonstrated for tropical forests.

Description: Ecology, Ahead of Print. Communities are comprised of individual species that respond to changes in their environment depending in part on their niche requirements. These species comprise the biodiversity of any given community. Common biodiversity metrics such as richness, evenness, and the species abundance distribution are frequently used to describe biodiversity across ecosystems and taxonomic groups. While it is increasingly clear that researchers will need to forecast changes in biodiversity, ecology currently lacks a framework for understanding the natural background variability in biodiversity or how biodiversity patterns will respond to environmental change. We predict that while species populations depend on local ecological mechanisms (e.g., niche processes) and should respond strongly to disturbance, community-level properties that emerge from these species should generally be less sensitive to disturbance because they depend on regional mechanisms (e.g., compensatory dynamics). Using published data from terrestrial animal communities, we show that community-level properties were generally resilient under a suite of artificial and natural manipulations. In contrast, species responded readily to manipulation. Our results suggest that community-level measures are poor indicators of change, perhaps because many systems display strong compensatory dynamics maintaining community-level properties. We suggest that ecologists consider using multiple metrics that measure composition and structure in biodiversity response studies.

Description: Ecology, Ahead of Print. In colonial-breeding species, prebreeders often emigrate temporarily from natal reproductive colonies then subsequently return for one or more years before producing young. Variation in attendance/nonattendance patterns can have implications for subsequent recruitment. We used open robust-design multi-state models and 27 years of encounter data for prebreeding female Weddell seals (Leptonychotes weddellii Lesson) to evaluate hypotheses about (1) the relationships of temporary emigration (TE) probabilities to environmental and population size covariates, (2) motivations for attendance and consequences of nonattendance for subsequent probability of recruitment to the breeding population. TE probabilities were density-dependent (= 0.66, = 0.17) (βBPOP = 0.66, SE = 0.17)and increased when the fast-ice edge was distant from the breeding colonies (βDIST = 0.75, SE = 0.04), and were strongly age- and state-dependent. These results suggest that tradeoffs between potential benefits and costs of colony attendance vary annually and might influence motivation to attend colonies. Recruitment probabilities were greatest for seals that consistently attended colonies in 2 or more years (e.g.,ψage10 = 0.56, sd = 0.17) and lowest for seals that never or inconsistently attended prior to recruitment (e.g., ψage10 = 0.32, sd = 0.15). In colonial-breeding seabirds repeated colony attendance increases subsequent probability of recruitment to the adult breeding population; our results suggest similar implications for a marine mammal and are consistent with the hypothesis that prebreeders were motivated to attend reproductive colonies to gain reproductive skills or perhaps to optimally synchronize estrus through close association with mature breeding females.

Description: Ecology, Ahead of Print. Fertilization via agricultural inputs and nutrient deposition is one of the major threats to global terrestrial plant richness, yet we still do not fully understand the mechanisms by which fertilization decreases plant richness. Tall clonal species have recently been proposed to cause declines in plant species richness by increasing in abundance in response to fertilization and competing strongly with other species. We tested this hypothesis in a fertilization experiment in a low productivity grassland by using a novel experimental manipulation of the presence vs. absence of clonal species and by examining the role of height within these treatments. We found that fertilization decreased species richness more in the presence than absence of clonal species. We also found that only tall species increased in biomass in response to fertilization. In the absence of clonal species, fertilization increased biomass of tall non-clonal species. However, in the presence of clonal species, fertilization decreased tall non-clonal biomass and only tall clonal biomass increased. Fertilization caused almost all short species to be lost in the presence, but not the absence, of clonal species and caused greater declines in the mean and variance of light levels in the presence of clonal species. These results show that the traits of species in a community can determine the magnitude of species loss due to fertilization. The strongly negative effect of tall clonals on species richness in fertilized plots is likely a result of their capacity to decrease light levels to a greater extent and more uniformly than non-clonal species, and thereby drive the exclusion of short species. These results help clarify the mechanisms whereby fertilization decreases grassland plant species richness and suggest that efforts to prevent the loss of species under fertilized conditions may be most effective when they focus on controlling the biomass of tall clonal species.

Description: Ecology, Ahead of Print. Nutrient pollution constitutes a major threat to biodiversity - one whose magnitude is predicted to increase greatly in the near future. While the negative effects of excessive nitrogen and phosphorus loading on local species diversity are widely appreciated, a growing body of evidence indicates that increases in productivity (a correlate of nutrient supply) can also reduce predictability in community composition by driving community divergence and increases in beta diversity (or compositional dissimilarity among communities). Stochastic variation in dispersal history has frequently been cited as a cause of such patterns. However, underlying mechanisms have not received strong experimental scrutiny. I present results of a microcosm experiment testing the effects of enrichment and dispersal mode on zooplankton community structure. I show that beta diversity increases with enrichment but only in the presence of sequential dispersal and variation in dispersal history. Sequential dispersal and enrichment enhanced beta diversity by driving increases in temporal compositional turnover (or beta diversity in time). These results suggest that nutrient enrichment and dispersal may have interactive effects on community organization by facilitating persistent compositional flux and reducing our ability to predict the structure of communities in both space and time.

Description: Ecology, Ahead of Print. Climate change forecasts of more frequent climate extremes suggest that such events will become increasingly important drivers of future ecosystem dynamics and function. Because the rarity and unpredictability of naturally occurring climate extremes limits assessment of their ecological impacts, we experimentally imposed extreme drought and a mid-summer heat wave over two years in a central US grassland. While the ecosystem was resistant to heat waves, it was not resistant to extreme drought, which reduced aboveground net primary productivity (ANPP) below the lowest level measured in this grassland in almost thirty years. This extreme reduction in ecosystem function was a consequence of reduced productivity of both C4 grasses and C3 forbs. However, the dominant forb was negatively impacted by the drought more than the dominant grass, and this led to a reordering of species abundances within the plant community. Although this change in community composition persisted post-drought, ANPP recovered completely the year after drought due to rapid demographic responses by the dominant grass, compensating for loss of the dominant forb. Overall, these results show that an extreme reduction in ecosystem function attributable to climate extremes (e.g., low resistance) does not preclude rapid ecosystem recovery. Given that dominance by a few species is characteristic of most ecosystems, knowledge of the traits of these species and their responses to climate extremes will be key for predicting future ecosystem dynamics and function.

Description: Ecology, Ahead of Print. Thresholds profoundly affect our understanding and management of ecosystem dynamics, but we have yet to develop practical techniques to assess the risk that thresholds will be crossed. Combining ecological knowledge of critical system interdependencies with a large-scale experiment we tested for breaks in the ecosystem interaction network to identify threshold potential in real world ecosystem dynamics. Our experiment on marine sandflats demonstrated that reductions in incident sunlight changed the interaction network between sediment biogeochemical fluxes, productivity and macrofauna. By demonstrating loss of positive feedbacks and changes in the architecture of the network, we provide mechanistic evidence that stressors lead to breakpoints in dynamics, which theory predicts pre-dispose a system to a critical transition.

Description: Ecology, Ahead of Print. Pendulous lichens dominate canopies of boreal forests, with dark Bryoria species in upper versus light Alectoria and Usnea species in lower canopy. These genera offer important ecosystem services like winter forage for reindeer and caribou. The mechanism behind this niche separation is poorly understood. We tested the hypothesis that species-specific sun-screening fungal pigments protect underlying symbiotic algae differently against high light, and thus shape the vertical canopy gradient of epiphytes. Three pale species with the reflecting pigment usnic acid (Alectoria sarmentosa, Usnea dasypoga, U. longissima) and three with dark, absorbing melanins (Bryoria capillaris, B. fremontii, B. fuscescens) were compared. We subjected the lichens to desiccation stress with and without light, and assessed their performance with chlorophyll fluorescence. Desiccation alone only affected U. longissima. By contrast, light in combination with desiccation caused photoinhibitory damage in all species. Usnic lichens were significantly more susceptible to light during desiccation than melanic ones. Thus, melanin is a more efficient light-screening pigment than usnic acid. Thereby, the vertical gradient of pendulous lichens in forest canopies is consistent with a shift in type and functioning of sun-screening pigments, from high-light tolerant Bryoria in the upper to susceptible Alectoria and Usnea in the lower canopy.

Description: Ecology, Ahead of Print. Predicting the effects of climate change on ecological communities requires an understanding of how environmental factors influence both physiological processes and species interactions. Specifically, the net impact of temperature on community structure depends on the relative response of physiological energetic costs (metabolism) and energetic gains (ingestion of resources) that mediate the flow of energy throughout a food web. However, the relative temperature scaling of metabolic and ingestion rates have rarely been measured for multiple species within an ecological assemblage and it is not known how, and to what extent, these relative scaling differences vary among species. To investigate the relative influence of these processes, I measured the temperature scaling of metabolic and ingestion rates for a suite of rocky intertidal species using a multiple regression experimental design. I compared oxygen consumption rates (as a proxy for metabolic rate) and ingestion rates by estimating the temperature scaling parameter of the 'universal temperature dependence' (UTD) model, a theoretical model derived from first principles of biochemical kinetics and allometry. The results show that consumer metabolic rates (energetic costs) tend to be more sensitive to temperature than ingestion rates (energetic gains). Thus, as temperature increases, metabolic rates tend to increase faster relative to ingestion rates, causing the overall energetic efficiencies of these rocky intertidal invertebrates to decline. Metabolic and ingestion rates largely scaled in accordance with the UTD model; however, non-linearity was evident in several cases, particularly at higher temperatures, in which alternative models were more appropriate. There are few studies where multiple rate dependencies are measured on multiple species from the same ecological community. These results indicate that there may be general patterns across species in the temperature scaling of biological rates, with important implications for forecasting temperature effects on ecological communities.

Description: Ecology, Ahead of Print. Metacommunity theory generally predicts that regional dispersal of organisms among local habitat patches should influence spatial patterns of species diversity. In particular, increased dispersal rates are generally expected to increase local (α) diversity, yet homogenize local communities across the region (decreasing β-diversity), resulting in no change in regional (γ) diversity. Although the effect of dispersal on α-diversity has garnered much experimental attention, the influence of dispersal rates on diversity at larger spatial scales (β and γ) is poorly understood. Furthermore, these theoretical predictions are not well tested in the field, where other environmental factors (e.g., habitat size, resource density) likely also influence species diversity. Here, we use a system of freshwater rock pools on Appledore Island, Maine, USA to test the effects of dispersal rate on species diversity in metacommunities. The pools exist in clusters (metacommunities) that experience different levels of dispersal imposed by gulls (Larus spp.), which we show to be frequent passive dispersers of rock-pool invertebrates. Although previous research has suggested that waterbirds may disperse aquatic invertebrates, our study is the first to quantify the rate at which such dispersal occurs and determine its effects on species diversity. In accordance with theory, we found that metacommunities experiencing higher dispersal rates had significantly more homogeneous local communities (reduced β-diversity) and that γ-diversity was not influenced by dispersal rate. Contrary to theoretical predictions, however, α-diversity in the rock pools was not significantly influenced by dispersal. Rather, local diversity was significantly positively related to local habitat size and both α- and γ-diversity were influenced by the physicochemical environment of the pools. These results provide an important field test of metacommunity theory, highlighting how local and regional factors interact to drive patterns of species diversity in metacommunities, and demonstrate that waterbirds are indeed important dispersal vectors for aquatic invertebrates.

Description: Ecology, Ahead of Print. Given the health and economic burden associated with the widespread occurrence of co-infections in human and agricultural animals, understanding how co-infections contribute to host heterogeneity to infection and transmission is critical if we are to assess risk of infection based on host characteristics. Here, we examine whether host heterogeneity to infection leads to similar heterogeneity in transmission in a population of rabbits single and co-infected with two helminths and monitored monthly for eight years. Compared to single infections, co-infected rabbits carried higher Trichostrongylus retortaeformis intensities, longer worms with fewer eggs in utero and shed a similar numbers of parasite eggs. In contrast, the same co-infected rabbits harbored fewer Graphidium strigosum with longer bodies and more eggs in utero, and shed more eggs of this helminth. A positive density-dependent relationship between fecundity and intensity was found for T. retortaeformis but not G. strigosum in co-infected rabbits. Juvenile rabbits contributed to most of the infection and shedding of T. retortaeformis while adult hosts were more important for G. strigosum dynamics of infection and transmission, and this pattern was consistent in single and co-infected individuals. This host-parasite system suggests that we cannot predict pattern of parasite shedding during co-infections based on intensity of infection alone. We suggest that a mismatching between susceptibility and infectiousness should be expected in helminth co-infections and should not be overlooked.

Description: Ecology, Ahead of Print. Large pelagic predators play important roles in oceanic ecosystems and may migrate vast distances to utilize resources in different marine ecoregions. Understanding movement patterns of migratory marine animals is critical for effective management, but often challenging due to the cryptic habitat of pelagic migrators and the difficulty of assessing past movements. Chemical tracers can partially circumvent these challenges by reconstructing recent migration patterns. Pacific bluefin tuna (Thunnus orientalis; PBFT) inhabit the western and eastern Pacific Ocean and are in steep decline due to overfishing. Understanding age-specific eastward trans-Pacific migration patterns can improve management practices but these migratory dynamics remain largely unquantified. Here, we combine a Fukushima-derived radiotracer (134Cs) with bulk tissue- and amino acid-stable isotope analyses of PBFT to distinguish recent migrants from residents of the eastern Pacific Ocean. The proportion of recent migrants to residents decreased in older year classes, though the proportion of older PBFT that recently migrated across the Pacific was greater than previous estimates. This novel toolbox of biogeochemical tracers can be applied to any species that crosses the North Pacific Ocean.

Description: Ecology, Ahead of Print. The emission of volatile monoterpenes from coniferous trees impacts the oxidative state of the troposphere and multi-trophic signaling between plants and animals. Previous laboratory studies have revealed that climate anomalies and herbivory alter the rate of tree monoterpene emissions. However, no studies to date have been conducted to test these relations in situ. We conducted a two-year field experiment at two semi-arid sites dominated by pinyon pine (Pinus edulis) during outbreaks of a specialist herbivore, the southwestern tiger moth (Lophocampa ingens: Arctiidae). We discovered that during the early spring, when herbivory rates were highest, monoterpene emission rates were approximately two to six times higher from undamaged needles on damaged trees, with this increase in emissions due to α-pinene, β-pinene, and camphene at both sites. During mid-summer, emission rates did not differ between previously damaged and undamaged trees at the site on the Western Slope of the Rocky Mountains, but rather tracked changes in the temperature and precipitation regime characteristic of the region. As the mid-summer drought progressed at the Eastern Slope site, emission rates were low but differences between previously damaged and undamaged trees were not statistically significant. Despite no difference in emissions, mid-summer tissue monoterpene concentrations were significantly lower in previously damaged trees at both sites. With the onset of monsoon rains during late summer, emission rates from previously damaged trees increased to levels higher than those of undamaged trees despite the lack of herbivory. We conclude (1) herbivory systemically increases the flux of terpenes to the atmosphere during the spring, (2) drought overrides the effect of past herbivory as the primary control over emissions during the mid-summer, and (3) that a release from drought and the onset of late-summer rains is correlated with a secondary increase in emissions, particularly from herbivore-damaged trees, possibly due to a drought-delayed stimulation of induced monoterpene synthesis and/or increases in stomatal conductance. A greater understanding of the interactive effects of seasonality and herbivory on monoterpene emissions provides much needed information regarding the atmospheric and ecological consequences these compounds will have on semi-arid ecosystems.

Description: Ecology, Ahead of Print. Fires are the major natural disturbance in the boreal forest, and their frequency and intensity will likely increase as the climate warms. Terrestrial nutrients released by fires may be transported to boreal lakes, stimulating increased primary productivity, which may radiate through multiple trophic levels. Using a before-after-control-impact (BACI) design, with pre- and post-fire data from burned and unburned areas, we examined effects of a natural fire across several trophic levels of boreal lakes, from nutrient and chlorophyll levels to macroinvertebrates to waterbirds. Concentrations of total nitrogen and phosphorus were not affected by the fire. Chlorophyll a levels were also unaffected, likely reflecting the stable nutrient concentrations. For aquatic invertebrates, we found that densities of 3 functional feeding groups did not respond to the fire (filterers, gatherers, scrapers), while 2 groups increased (shredders, predators). Amphipods accounted for 98% of shredder numbers, and we hypothesize that fire-mediated habitat changes may have favored their generalist feeding and habitat ecology. This increase in amphipods may have in turn driven increased predator densities, as amphipods were the most numerous invertebrate in our lakes and are commonly taken as prey. Finally, abundance of waterbird young, which feed primarily on aquatic invertebrates, was not affected by the fire. Overall, ecosystems of our study lakes were largely resilient to forest fires, likely due to their high initial nutrient concentrations and small catchment sizes. Moreover, this resilience spanned multiple trophic levels, a significant result for ecologically similar boreal regions, especially given the high potential for increased fires with future climate change.