ALBERT

Description: Bacteria are essential for many ecosystem services but our understanding of factors controlling their functioning is incomplete. While biodiversity has been identified as an important driver of ecosystem processes in macrobiotic communities, we know much less about bacterial communities. Due to the high diversity of bacterial communities, high functional redundancy is commonly proposed as explanation for a lack of clear effects of diversity. The generality of this claim has, however, been questioned. We present the results of an outdoor dilution-to-extinction experiment with four lake bacterial communities. The consequences of changes in bacterial diversity in terms of effective number of species, phylogenetic diversity and functional diversity were studied for (i) bacterial abundance, (ii) temporal stability of abundance, (iii) nitrogen concentration, and (iv) multifunctionality. We observed a richness gradient ranging from 15 to 280 operational taxonomic units. Individual relationships between diversity and functioning ranged from negative to positive depending on lake, diversity dimension and aspect of functioning. Only between phylogenetic diversity and abundance did we find a statistically consistent positive relationship across lakes. A literature review of 24 peer-reviewed studies that used dilution-to-extinction to manipulate bacterial diversity corroborated our findings: about 25% found positive relationships. Combined, these results suggest that bacteria-driven community functioning is relatively resistant to reductions in diversity. This article is protected by copyright. All rights reserved.

Description: The degree of ecological specialization plays a crucial role in shaping the structure and functioning of communities. However, comparing specialization within and among groups of organisms is complicated due to methodological issues but also by conceptual and terminological inconsistencies. Environmental predictability has been considered a key determinant of specialization though empirical evidence is still limited. Fungi and their insect consumers provide a poorly studied but promising system to measure host specialization and test the predictability hypothesis. In this study we systematically sampled mushrooms in North European boreal forest, and reared total samples of fungivores colonizing the fruitbodies. Due to the unpredictable nature of mushrooms as a resource, low levels of host specialization can be predicted for these insects which have indeed widely been considered polyphagous. Contrary to expectations, majority of the studied fungus gnats were found not to exploit their host taxa indiscriminately. Not only were some mushroom taxa never colonised, but also the infestation rate of acceptable hosts differed in most of these fungivores. Gnat species themselves formed continua with respect to the estimates of the degree of specialization, derived from parametric individual-based analyses of presence-absence data. In most cases, host use was best explained by models in which the hosts were classified at genus level, with limited support to specialization to particular host species, families or orders. Indeed, most of the common fungivores appeared to preferentially use various species from one or a few mushroom genera while occasionally feeding on members of other host taxa. This pattern has likely evolved as a compromise between selective forces stemming from host unpredictability, and taxon-specific chemical profiles of the mushrooms. Our study highlights the multidimensional nature of ecological specialization: a high number of acceptable hosts does not preclude considerable discrimination among members of the available resource pool. Such situations can only be revealed by individual-based analyses capable of capturing differences in partner-to-partner interaction intensities. This article is protected by copyright. All rights reserved.

Description: Prey at risk of predation may experience stress and respond physiologically by altering their metabolic rates. Theory predicts that such physiological changes should alter prey nutrient demands from N-rich to C-rich macronutrients and shift the balance between maintenance and growth/reproduction. Theory further suggests that for ectotherms, temperature stands to exacerbate this stress. Yet, the interactive effects of predation stress and temperature stress on diet, metabolism, and survival of ectotherms are not well known. This knowledge gap was addressed with a laboratory study in which wild juvenile grasshoppers were collected, assigned to one of three groups, and raised at three different temperatures. All grasshoppers had access to equal quantities of two diets composed of opposite carbohydrate:protein ratios. Half of the individuals in each temperature group were exposed to predation risk cues from spider predators, while the other half were kept in risk free conditions. Grasshoppers consumed more carbohydrates when exposed to predation risk, but consumption favored greater protein intake as temperature increased. Moreover, the difference in carbohydrate intake between risk cue and risk free treatments diminished as temperature increased. Furthermore, variability between individual consumption patterns both within and between treatments decreased markedly as temperature increased, suggesting that higher temperatures promote more consistent individual consumption behaviors. Grasshoppers grew faster and larger as temperature increased, which translated into higher survival rates at higher temperatures. Warmer grasshoppers also did not alter their metabolic rates in response to predation risk cues, in contrast to colder grasshoppers. Digestive efficiency increased with temperature as well, further indicating that lower temperatures were much more stressful than higher temperatures for grasshoppers. The study shows that physiological responses of ectothermic herbivores to predation stress are highly plastic and temperature dependent, with higher temperatures promoting increased protein intake, growth, development, survival, and digestive efficiency relative to colder temperatures. These findings help to reconcile why dietary responses (proportion of protein vs. carbohydrate intake) to predation stress may vary among different prey taxa studied previously. This article is protected by copyright. All rights reserved.

Description: Contradictory evidence from biogeomorphological studies has increased the debate on the extent of lichen contribution to differential rock surface weathering in both natural and cultural settings. This study, undertaken in Côa Valley Archaeological Park, aimed at evaluating the effect of rock surface orientation on the weathering ability of dominant lichens. Hyphal penetration and oxalate formation at the lichen-rock interface were evaluated as proxies of physical and chemical weathering, respectively. A new protocol of pixel-based supervised image classification for the analysis of periodic acid-Schiff stained cross-sections of colonized schist revealed that hyphal spread of individual species was not influenced by surface orientation. However, hyphal spread was significantly higher in species dominant on north-west facing surfaces. An apparently opposite effect was noticed in terms of calcium oxalate accumulation at the lichen-rock interface, detected by Raman spectroscopy and complementary X-ray microdiffraction on south-east facing surfaces only. These results suggest that lichen-induced physical weathering may be most severe on north-west facing surfaces by means of an indirect effect of surface orientation on species abundance, and thus dependent on the species, whereas lichen-induced chemical weathering is apparently higher on south-east facing surfaces and dependent on micro-environmental conditions, giving only weak support to the hypothesis that lichens are responsible for the currently observed pattern of rock-art distribution in Côa Valley. Assumptions about the drivers of open-air rock-art distribution patterns elsewhere should also consider the micro-environmental controls of lichen-induced weathering, to avoid biased measures of lichen contribution to rock-art deterioration. This article is protected by copyright. All rights reserved.

Description: The majority of humanity now lives in cities or towns, with this proportion expected to continue increasing for the foreseeable future. As novel ecosystems, urban areas offer an ideal opportunity to examine multi-scalar processes involved in community assembly as well as the role of human activities in modulating environmental drivers of biodiversity. Although ecologists have made great strides in recent decades at documenting ecological relationships in urban areas, much remains unknown, and we still need to identify the major ecological factors, aside from habitat loss, behind the persistence or extinction of species and guilds of species in cities. Given this paucity of knowledge, there is an immediate need to facilitate collaborative, interdisciplinary research on the patterns and drivers of biodiversity in cities at multiple spatial scales. In this review, we introduce a new conceptual framework for understanding the filtering processes that mold diversity of urban floras and faunas. We hypothesize that the following hierarchical series of filters influence species distributions in cities: 1) regional climatic and biogeographical factors; 2) human facilitation; 3) urban form and development history; 4) socioeconomic and cultural factors; and 5) species interactions. In addition to these filters, life history and functional traits of species are important in determining community assembly and act at multiple spatial scales. Using these filters as a conceptual framework can help frame future research needed to elucidate processes of community assembly in urban areas. Understanding how humans influence community structure and processes will aid in the management, design, and planning of our cities to best support biodiversity. This article is protected by copyright. All rights reserved.

Description: The main goal of this study is to create a database that ultimately serves further studies on riparian vegetation and flow response guilds in the boreal region and on transferability of results across different regions. For this aim we compiled traits for all woody riparian species in northern Sweden that, directly or indirectly, underlie their responses to hydrological and hydraulic conditions, between October 2012 and April 2015. Consulted sources of information were diverse, ranging from scientific to informative and whose accuracy might or might not be verified. They were focused on particular or several traits and species from concrete areas to a worldwide perspective. Sources were characterized by different degrees of accessibility and showed a wide variety of descriptions, categorical and ordinal classifications, and numerical information for each trait. Our effort was to synthesize information for each trait from all sources into the common frame of our own database, following own defined criteria so that comparisons between species are congruent. Therefore, this data set is unique in that it comprehensively combines and homogenizes morphological, phenological, reproductive and ecological data for 59 woody, riparian, boreal species and from 118 sources of information, that would otherwise be scattered and hardly available. This article is protected by copyright. All rights reserved.

Description: Size variation within a population can influence the structure of ecosystem interactions, because ecological performance differs between individuals of different sizes. Although the impact of size variation in a predator species on the structure of interactions is well understood, our knowledge about how size variation in a prey species might modify the interactions between predators and prey is very limited. Here, by examining the interactions between predatory Hynobius retardatus salamander larvae and their prey, Rana pirica frog tadpoles, we investigated how large prey individuals affect the predation mortality of small prey conspecifics. First, in an experiment conducted in a field pond in which we manipulated the presence of salamanders and large tadpoles (i.e., large enough to protect them against salamander predation) with small tadpoles, we showed that in the presence of large tadpoles the mortality of small tadpoles from salamander predation was increased. On the basis of our observations of the activity of individuals, we hypothesized that active large tadpoles caused physical disturbances, which in turn caused the small tadpoles to move, and thus increased their encounter frequency with the predatory salamanders. To test this hypothesis, we conducted a laboratory experiment in small tanks with three players (i.e., one salamander as predator, one small tadpole as focal prey, and either a small or a large tadpole as the prospective movement inducer). In each tank, we manipulated the presence or absence of a movement inducer, and, when present, its size (large or small) and access (caged or uncaged) to the focal prey. In the presence of a large, uncaged movement inducer, the focal prey was more active and suffered from higher predation mortality compared with the other treatments, because the large movement inducer (unlike a small movement inducer) moved actively and, when uncaged, could stimulate movement of the focal prey through direct contact. The results indicated that high activity of large prey individuals and the resulting behavioral interactions with small conspecifics via direct contact indirectly increased the mortality of the small prey. This article is protected by copyright. All rights reserved.

Description: The phyllosphere (comprising the leaf surface and interior) is one of the world's largest microbial habitats and is host to an abundant and diverse array of bacteria. Nonetheless, the degree to which bacterial communities are benign, harmful, or beneficial to plants in situ is unknown. We tested the hypothesis that the net effect of reducing bacterial abundance and diversity would vary substantially among host species (from harmful to beneficial) and this would be strongly mediated by soil resource availability. To test this, we monitored tree seedling growth responses to commercial antibiotics among replicated resource supply treatments (N, P, K) in a tropical forest in Panama for 29 months. We applied either antibiotics or control water to replicated seedlings of five common tree species ( Alseis blackiana , Desmopsis panamensis , Heisteria concinna , Sorocea affinis , and Tetragastris panamensis ). These antibiotic treatments significantly reduced both the abundance and diversity of bacteria epiphytically as well as endophytically. Overall, the effect of antibiotics on performance was highly host specific. Applying antibiotics increased growth for three species by as much as 49% ( Alseis , Heisteria , and Tetragastris ), decreased growth for a fourth species by nearly 20% ( Sorocea ), and had no impact on a fifth species ( Desmopsis ). Perhaps more importantly, the degree to which foliar bacteria were harmful or not varied with soil resource supply. Specifically, applying antibiotics had no effect when potassium was added but increased growth rate by almost 40% in the absence of potassium. Alternatively, phosphorus enrichment caused the effect of bacteria to switch from being primarily beneficial to harmful or vice versa, but this depended entirely on the presence or absence of nitrogen enrichment ( i.e ., important and significant interactions). Our results are the first to demonstrate that the net effect of reducing the abundance and diversity of bacteria can have very strong positive and negative effects on seedling performance. Moreover, these effects were clearly mediated by soil resource availability. Though speculative, we suggest that foliar bacteria may interact with soil fertility to comprise an important, yet cryptic dimension of niche differentiation, which can have important implications for species coexistence. This article is protected by copyright. All rights reserved.

Description: Emerging aquatic insects from streams are important food sources for riparian predators, yet their availability is seasonally limited. Spatial heterogeneity in stream water temperature was found to spatially desynchronize the emergence timing of aquatic insects, and prolong their flight period, potentially enhancing consumer growth. While a mayfly Ephemerella maculata emergence lasted for 12-22 days in local sites along a river, mayflies emerged 19 days earlier from warmer than cooler sites. Therefore, the overall emergence of E. maculata from the river lasted for 37 days, and adult swarms were observed over that same period in an adjacent reproductive habitat. A feeding experiment with the riparian spider Tetragnatha versicolor showed that a prolonged subsidy, as would occur in a heterogeneous river, led to higher juvenile growth than a synchronous pulsed subsidy of equal total biomass, as would typify a more homogeneous river. Since larger female adult spiders produce more eggs, spiders that received prolonged subsidy as juveniles should achieve higher fecundity. Restoring spatial heterogeneity in streams may benefit not only stream communities but also riparian predators. This article is protected by copyright. All rights reserved.

Description: Mixing models are statistical tools that use biotracers to probabilistically estimate the contribution of multiple sources to a mixture. These biotracers may include contaminants, fatty acids, or stable isotopes, the latter of which are widely used in trophic ecology to estimate the mixed diet of consumers. Bayesian implementations of mixing models using stable isotopes (e.g. MixSIR, SIAR) are regularly used by ecologists for this purpose, but basic questions remain about when each is most appropriate. In this study, we describe the structural differences between common mixing model error formulations in terms of their assumptions about the predation process. We then introduce a new parameterization that unifies these mixing model error structures, as well as implicitly estimates the rate at which consumers sample from source populations (i.e. consumption rate). Using simulations and previously published mixing model datasets, we demonstrate that the new error parameterization outperforms existing models and provides an estimate of consumption. Our results suggest that the error structure introduced here will improve future mixing model estimates of animal diet. This article is protected by copyright. All rights reserved.

Description: Contagious seed dispersal refers to the tendency for some sites to receive many dispersed seeds while other sites receive few dispersed seeds. Contagious dispersal can lead to interspecific associations in seed arrival, and this in turn might lead to interspecific associations in seedling recruitment. We evaluate the extent of spatially contagious seed arrival, the frequency of positive interspecific associations in seed arrival, and their consequences for seedling recruitment at the community level in a tropical moist forest. We quantified seed arrival to 200 passive seed traps for 28 years of weekly censuses and seedling recruitment to 600 1-m 2 quadrats for 21 years of annual censuses on Barro Colorado Island, Panama. We assessed whether spatially contagious seed dispersal was more important among zoochorous species than among anemochorous species, increased in importance with similarity in fruiting times, and led to interspecific associations in seed arrival and seedling recruitment. We controlled adult seed source associations statistically to evaluate predicted relationships. We found that spatially contagious seed arrival was widespread among zoochorous species, but also occurred among anemochorous species when the strong, consistent trade winds were present. Significant interspecific associations in seed arrival were more likely for pairs of species with zoochorous seeds and similar fruiting times and persisted through seedling recruitment. Thus, interspecifically contagious seed dispersal affects local species composition and alters the mixture of interspecific interactions through the seed, germination and early seedling stages in this forest. Future investigations should consider the implications of interspecific association at the regeneration stages documented here for later life stages and species coexistence. This article is protected by copyright. All rights reserved.

Description: Understanding processes that may stabilize ecological systems confronted with rapidly changing environmental conditions is a key issue in ecology. We studied a system of highly fluctuating populations, the moth Achyra rantalis feeding on the plant Sesuvium portulacastrum in a group of small subtropical islands of the Bahamas. The plant is a prostrate inhabitant of shorelines, and consequently moths are highly vulnerable to being consumed by the ground-foraging lizard Anolis sagrei . We measured the percent ground cover of Sesuvium and abundance of Achyra on 11 islands with lizards present and 21 islands without lizards annually for 10 consecutive years. Overall abundance of Achyra was 4.6 times higher on no-lizard islands than on lizard islands. The percent cover of Sesuvium exhibited lower temporal variability on lizard islands when the study site was undisturbed by hurricanes, and higher recovery rate on lizard islands following hurricanes. We suggest that both of these stabilizing phenomena are linked to a trophic cascade in which predatory lizards control herbivore populations, thereby suppressing outbreaks and enhancing plant recovery following physical disturbance. This article is protected by copyright. All rights reserved.

Description: Seed dispersal effectiveness, which measures the number of adult plant individuals produced by seed dispersal, is the product of the number of seeds dispersed and the probability a seed produces an adult. Directed dispersal to certain habitat types may enhance some stages of recruitment but disfavor others, generating demographic conflicts in plant ontogeny. We asked whether temporal changes in habitat features may affect the distribution of seedlings recruited from dispersed acorns, and whether this could induce shifts in the life-stage conflicts experienced by successive cohorts of naturally recruited plants. As early successional habitats are characterized by rapid change, we used a burnt pine stand in southern Spain to monitor the recruitment and performance of a major tree species ( Quercus ilex ) across seven years in four types of post-fire habitats. These differed in structure and included patches of unburnt forest and three management alternatives of burnt trees: logging, partial cutting, and non-intervention. Young oaks that resprouted after the fire were mainly located near acorn sources, while new seedlings initially emerged mostly in habitats with standing snags due to habitat selection by European jays, Garrulus glandarius, for dispersal. The dead pines gradually collapsed and attracted less dispersal, so subsequent seedling cohorts mainly recruited within patches of unburnt pines. These live pines enhanced the survival of the oaks located beneath their canopy but greatly reduced their growth as compared to the other post-fire habitats, thus representing a demographic conflict that was absent elsewhere. As a consequence of the directional shift in the habitat where seedlings recruited, successive seedling cohorts experienced a gradual improvement in their likelihood of survival but a reduction in growth. The progressive intensification of this life-stage conflict hinged on the reduction of vertical structures in the habitat with standing burnt pines. Recruitment success thus involved temporal variation in the habitat where recruitment occurred, likely resulting from changes in the direction of seed dispersal, and spatial variation in habitat suitability for seedling establishment and growth. Temporal changes in habitat structure can indirectly change the environment in which recruitment occurs, and consequently seed dispersal effectiveness, by shifting the direction of seed dispersal. This article is protected by copyright. All rights reserved.

Description: Long-term experiments provide a way to test presumed causes of successional or environmentally driven vegetation changes. Early-successional nitrogen (N)-fixing plants are widely thought to facilitate productivity and vegetation development on N-poor sites, thus accounting for observed vegetation patterns later in succession. We tested this facilitative impact on vegetation development in a 23-year field experiment on an Interior Alaska (U.S.A.) floodplain. On three replicate early-successional silt bars, we planted late-successional white spruce ( Picea glauca ) seedlings in the presence and absence of planted seedlings of an early-successional N-fixing shrub—thinleaf alder ( Alnus incana ). Alder initially facilitated survivorship and growth of white spruce. Within six years, however, after canopy closure, alder negatively affected spruce survivorship and growth. Our three replicate sites followed different successional trajectories. One site was eliminated by erosion and supported no vegetation development during our study. The other two sites, which differed in site moisture, diverged in vegetation composition. Structural equation modeling (SEM) suggested that, in the drier of these two sites, alder inhibited spruce growth directly (presumably by competition) and indirectly through effects mediated by competition with other woody species. However at the wetter site alder had both positive and negative effects on spruce growth, with negative effects predominating. Snowshoe hares ( Lepus americanus ) in alder thickets further reduced height growth of spruce in the wetter site. We conclude that net effects of alder on white spruce, the late-successional dominant, were primarily inhibitory and indirect, with the mechanisms depending on initial site moisture. Our results highlight the importance of long-term research showing that small differences among initial replicate sites can cause divergence in successional trajectories–consistent with individualistic distributions of species and communities along environmental gradients. This divergence was detectable only decades later. This article is protected by copyright. All rights reserved.

Description: Decades of ecological study have demonstrated the importance of top-down and bottom-up controls on food webs, yet few studies within this context have quantified the magnitude of energy and material fluxes at the whole-ecosystem scale. We examined top-down and bottom-up effects on food web fluxes using a field experiment that manipulated the presence of a consumer, the Trinidadian guppy Poecilia reticulata , and the production of basal resources by thinning the riparian forest canopy to increase incident light. To gauge the effects of these reach-scale manipulations on food web fluxes, we used a nitrogen ( 15 N) stable isotope tracer to compare basal resource treatments (thinned canopy vs. control) and consumer treatments (guppy introduction vs. control). The thinned canopy stream had higher primary production than the natural canopy control, leading to increased N fluxes to invertebrates that feed on benthic biofilms (grazers), fine benthic organic matter (collector-gatherers), and organic particles suspended in the water column (filter-feeders). Stream reaches with guppies also had higher primary productivity and higher N fluxes to grazers and filter feeders. In contrast, N fluxes to collector-gatherers were reduced in guppy introduction reaches relative to upstream controls. N fluxes to leaf shredding invertebrates, predatory invertebrates and the other fish species present (Hart's killifish, Anablepsoides hartii ) did not differ across light or guppy treatments, suggesting that effects on detritus-based linkages and upper trophic levels were not as strong. Effect sizes of guppy and canopy treatments on N flux rates were similar for most taxa, though guppy effects were the strongest for filter feeding invertebrates while canopy effects were the strongest for collector-gatherer invertebrates. Combined, these results extend previous knowledge about top-down and bottom-up controls on ecosystems by providing experimental, reach-scale evidence that both pathways can act simultaneously and have equally strong influence on nutrient fluxes from inorganic pools through primary consumers. This article is protected by copyright. All rights reserved.

Description: Fifty years ago, Ehrlich and Raven proposed that insect herbivores have driven much of plant speciation, particularly at tropical latitudes. There have been no explicit tests of their hypotheses. Indeed there were no proposed mechanisms either at the time or since by which herbivores might generate new plant species. Here we outline two main classes of mechanisms, pre-zygotic and post-zygotic, with a number of scenarios in each by which herbivore-driven changes in host plant secondary chemistry might lead to new plant lineage production. The former apply mainly to a sympatric model of speciation while the latter apply to a parapatric or allopatric model. Our review suggests that the steps of each mechanism are known to occur individually in many different systems, but no scenario has been thoroughly investigated in any one system. Nevertheless, studies of Dalechampia and its herbivores and pollinators, and patterns of defense tradeoffs in trees on different soil types in the Peruvian Amazon provide evidence consistent with the original hypotheses of Ehrlich and Raven. For herbivores to drive sympatric speciation, our findings suggest that interactions with both their herbivores and their pollinators should be considered. In contrast, herbivores may drive speciation allopatrically without any influence by pollinators. Finally, there is evidence that these mechanisms are more likely to occur at low latitudes, and thus more likely to produce new species in the tropics. The mechanisms we outline provide a predictive framework for further study of the general role that herbivores play in diversification of their host plants. This article is protected by copyright. All rights reserved.

Description: Community ecologists have strived to find mechanisms that mediate the assembly of natural communities. Recent evidence suggests that natural enemies could play an important role in the assembly of hyper-diverse tropical plant systems. Classic ecological theory predicts that in order for coexistence to occur, species differences must be maximized across biologically important niche dimensions. For plant-herbivore interactions, it has been recently suggested that, within a particular community, plant species that maximize the difference in chemical defense profiles compared to neighboring taxa will have a relative competitive advantage. Here we tested the hypothesis that plant chemical diversity can affect local community composition in the hyper-diverse genus Piper at a lowland wet forest location in Costa Rica. We first characterized the chemical composition of 27 of the most locally abundant species of Piper . We then tested whether species with different chemical compositions were more likely to coexist. Finally, we assessed the degree to which Piper phylogenetic relationships are related to differences in secondary chemical composition and community assembly. We found that, on average, co-occurring species were more likely to differ in chemical composition than expected by chance. Contrary to expectations, there was no phylogenetic signal for overall secondary chemical composition. In addition we found that species in local communities were, on average, more phylogenetically closely related than expected by chance, suggesting that functional traits other than those measured here also influence local assembly. We propose that selection by herbivores for divergent chemistries between closely related species facilitates the coexistence of a high diversity of congeneric taxa via apparent competition. This article is protected by copyright. All rights reserved.

Description: Invasive alien predators (IAP) are spreading on a global scale and often with devastating ecological effects. One reason for their success may be that prey species fail to recognize them due to a lack of co-evolutionary history. We performed a comprehensive test of this ‘prey naiveté’ hypothesis using a novel approach: we tested whether predator-naive tadpoles of the agile frog ( Rana dalmatina ) display antipredator behaviour upon encountering chemical cues produced by native, invasive (established or recent) or allopatric fishes (four perciforms, four siluriforms and two cypriniforms). We studied the influence of population origin on predator-detection ability by presenting chemical cues to predator-naive tadpoles that originated from fishless hill-ponds or fish-infested floodplain populations. Before trials, we fed fishes with tadpoles or an alternative food to test whether direct chemical cues from the predator's diet influences the tadpoles’ recognition of potential predators. Tadpoles reduced their activity upon exposure to cues from native and long-established invasive perciforms, but not in response to recent invaders, allopatric predators or to any siluriforms. Also, predators that were previously fed with tadpoles did not universally induce behavioural defences upon first encounter. Finally, tadpoles originating from isolated hill-ponds exhibited higher baseline activity and responded weaker than their conspecifics from floodplain populations, which co-exist with predatory fishes. Our results indicate that tadpoles may be vulnerable to invading predatory fishes due to their inability to recognize them as dangerous, though their ability to recognize invasive IAP may evolve rapidly, in less than 30 generations. This article is protected by copyright. All rights reserved.

Description: Chronic wasting disease (CWD) is a fatal neurodegenerative disease affecting free-ranging and captive cervids that now occurs in 24 US States and two Canadian provinces. Despite the potential threat of CWD to deer populations little is known about the rates of infection and mortality caused by this disease. We used epidemiological models to estimate the force-of-infection and disease-associated mortality for white-tailed deer in the Wisconsin and Illinois CWD outbreaks. Models were based on age-prevalence data corrected for bias in aging deer using the tooth wear and replacement method. Both male and female deer in the Illinois outbreak had higher corrected age-specific prevalence with slightly higher female infection than deer in the Wisconsin outbreak. Corrected ages produced more complex models with different infection and mortality parameters than those based on apparent prevalence. We found that adult male deer have 〉 3 fold higher risk of CWD infection than female deer. Males also had higher disease mortality than female deer. As a result CWD prevalence was 2 fold higher in adult males than females. We also evaluated the potential impacts of alternative contact structures on transmission dynamics in Wisconsin deer. Results suggested that transmission of CWD among male deer during the nonbreeding season may be a potential mechanism for producing higher rates of infection and prevalence characteristically found in males. However, alternatives based on high environmental transmission and transmission from females to males during the breeding season may also play a role. This article is protected by copyright. All rights reserved.

Description: Extinctions have no simple determinism, but rather result from complex interplays between environmental factors and demographic-genetic feedback that occur at small population size. Inbreeding depression has been assumed to be a major trigger of extinction vortices, yet very few models have studied its consequences in dynamic populations with realistic population structure. Here we investigate the impact of Complementary Sex Determination (CSD) on extinction in parasitoid wasps and other insects of the order Hymenoptera. CSD is believed to induce enough inbreeding depression to doom simple small populations to extinction, but we suggest that in parasitoids CSD may have the opposite effect. Using a theoretical model combining the genetics of CSD and the population dynamics of host-parasitoid systems, we show that CSD can reduce the risk of parasitoid extinction by reducing fluctuations in population size. Our result suggests that inbreeding depression is not always a threat to population survival, and that considering trophic interactions may reverse some pervasive hypotheses on its demographic impact. This article is protected by copyright. All rights reserved.

Description: Stability in population dynamics is an emergent property of the interaction between direct and delayed density dependence, the strengths of which vary with environmental covariates. Analysis of variation across populations in the strength of direct and delayed density dependence can reveal variation in stability properties of populations at the species level. We examined the stability properties of 22 elk/red deer populations in a two-stage analysis. First, we estimated direct and delayed density dependence applying an AR(2) model in a Bayesian hierarchical framework. Second, we plotted the coefficients of direct and delayed density dependence in the Royama parameter plane. We then used a hierarchical approach to test the significance of environmental covariates of direct and delayed density dependence. Three populations exhibited highly stable and convergent dynamics with strong direct, and weak delayed, density dependence. The remaining 19 populations exhibited more complex dynamics characterized by multi-annual fluctuations. Most (15 of 19) of these exhibited a combination of weak to moderate direct and delayed density dependence. Best-fit models included environmental covariates in 17 populations (77% of the total). Of these, interannual variation in growing-season primary productivity and interannual variation in winter temperature were the most common, performing as the best-fit covariate in six and five populations, respectively. Interannual variation in growing-season primary productivity was associated with the weakest combination of direct and delayed density dependence, while interannual variation in winter temperature was associated with the strongest combination of direct and delayed density dependence. These results accord with a classic theoretical prediction that environmental variability should weaken population stability. They furthermore suggest that two forms of environmental variability, one related to forage resources and the other related to abiotic conditions, both reduce stability but in opposing fashion: one through weakened direct density dependence and the other through strengthened delayed density dependence. Importantly, however, no single abiotic or biotic environmental factor emerged as generally predictive of the strengths of direct or delayed density dependence, nor of the stability properties emerging from their interaction. Our results emphasize the challenges inherent to ascribing primacy to drivers of such parameters at the species level and distribution scale. This article is protected by copyright. All rights reserved.

Description: Ecosystem multifunctionality – the simultaneous production of multiple ecosystem functions – depends on community diversity, composition, productivity and spatial scale. In metacommunities, each of these community properties is affected by how species disperse between local patches to track environmental change. Here we use a consumer-resource metacommunity model of resource competition to show how dispersal affects the link between diversity, composition, and ecosystem multifunctionality. When species differ in their functional traits, and environmental niche, metacommunity multifunctionality becomes highly dependent upon dispersal, which allows community diversity to be maintained when environmental conditions change. Dispersal promotes multifunctionality in two ways: 1) species sorting – whereby species track local environmental changes by shifting in space, thus preserving diversity and ensuring high biomass productivity, and 2) mass effects – whereby source sink dynamics allow species to persist in sub-optimal environments, thus increasing local diversity. Changing the rate at which species disperse affects the strength of these metacommunity processes, and so metacommunity multifunctionality exhibits a unimodal relationship with dispersal, peaking when dispersal is intermediate. Species sorting dynamics also provide spatial insurance whereby compensatory dynamics stabilize the fluctuations of each function through time at the regional scale. However, this does not extend to the local scale, where species sorting results in high temporal variability for each function, even though the overall rates of multifunctionality are high. Our results suggest that metacommunity processes are important determinants of ecosystem multifunctionality, and thus effective management of multiple ecosystem functions requires consideration of landscape connectivity. This article is protected by copyright. All rights reserved.

Description: The cost and difficulty of manipulative field studies makes low statistical power a pervasive issue throughout most sub-disciplines in ecology. Ecologists are already aware that small sample sizes increase the probability of committing Type II errors. In this article, we address a relatively unknown problem with low power: underpowered studies must overestimate small effect sizes in order to achieve statistical significance. First, we describe how low replication coupled with weak effect sizes leads to Type M errors, or exaggerated effect sizes. We then conduct a meta-analysis to determine the average statistical power and Type M error rate for manipulative field experiments that address important questions related to global change; global warming, biodiversity loss, and drought. Finally, we provide recommendations for avoiding Type M errors and constraining estimates of effect size from underpowered studies. This article is protected by copyright. All rights reserved.

Description: Although the functional basis of variable and synchronous seed production (masting behavior) has been extensively investigated, only recently has attention been focused on the proximate mechanisms driving this phenomenon. We analyzed the relationship between weather and acorn production in 15 species of oaks (genus Quercus ) from three geographic regions on two continents with the goals of determining the extent to which similar sets of weather factors affect masting behavior across species and to explore the ecological basis for the similarities detected. Lag-1 temporal autocorrelations were predominantly negative, supporting the hypothesis that stored resources play a role in masting behavior across this genus, and we were able to determine environmental variables correlating with acorn production in all but one of the species. Standard weather variables outperformed “differential-cue” variables based on the difference between successive years in a majority of species, consistent with the hypothesis that weather is linked directly to the proximate mechanism driving seed production and that masting in these species is likely to be sensitive to climate change. Based on the correlations between weather variables and acorn production, cluster analysis failed to generate any obvious groups of species corresponding to phylogeny or life-history. Discriminant function analyses were, however, able to identify the phylogenetic section to which the species belonged and, controlling for phylogeny, the length of time species required to mature acorns, whether they were evergreen or deciduous, and, to a lesser extent, the geographic region to which they are endemic. These results indicate that similar proximate mechanisms are driving acorn production in these species of oaks, that the environmental factors driving seed production in oaks are to some extent phylogenetically conserved, and that the shared mechanisms driving acorn production result in some degree of synchrony among coexisting species in a way that potentially enhances predator satiation, at least when they have acorns requiring the same length of time to mature. This article is protected by copyright. All rights reserved.

Description: Many studies suggest that biodiversity may be particularly important for ecosystem multi functionality, because different species with different traits can contribute to different functions. Support, however, comes mostly from experimental studies conducted at small spatial scales in low-diversity systems. Here, we test whether different species contribute to different ecosystem functions that are important for carbon cycling in a high-diversity human-modified tropical forest landscape in Southern Mexico. We quantified aboveground standing biomass, primary productivity, litter production, and wood decomposition at the landscape level, and evaluated the extent to which tree species contribute to these ecosystem functions. We used simulations to tease apart the effects of species richness, species dominance and species functional traits on ecosystem functions. We found that dominance was more important than species traits in determining a species’ contribution to ecosystem functions. As a consequence of the high dominance in human-modified landscapes, the same small subset of species mattered across different functions. In human-modified landscapes in the tropics, biodiversity may play a limited role for ecosystem multifunctionality due to the potentially large effect of species dominance on biogeochemical functions. However, given the spatial and temporal turnover in species dominance, biodiversity may be critically important for the maintenance and resilience of ecosystem functions. This article is protected by copyright. All rights reserved.

Description: A number of ecological factors have been shown to influence the importance of positive interactions (i.e. facilitation) in nature, including environmental stress and ontogenetic effects, and many more are likely to emerge as facilitation research expands to new ecosystems and taxa. In this study, I used a combination of field surveys and experiments to explore the roles of stress, ontogeny, and organismal movement in determining the importance of mussel ( Mytilus californianus) recruit facilitation in central California. Results indicate that interactions between mussel recruits (shell length 〈 20 mm) and habitat ameliorating neighbors shift from neutral to positive from the low to high mussel zone. I also observed ontogenetic shifts in recruit survival and growth in the upper mussel zone that suggest mussel recruits migrate from algal substrate to adult mussel beds. This type of habitat shift, where an organism moves sequentially from one facilitator to another, may be common in nature and presents an exciting new area for research. This article is protected by copyright. All rights reserved.

Description: Tropical savannas are hypothesized to be hot spots of nitrogen fixer diversity and activity because of the high disturbance and low nitrogen characteristic of savanna landscapes. Here we compare the abundances of nitrogen-fixing and non-fixing trees in both tropical savannas and tropical forests under climatically equivalent conditions, using plant inventory studies across 566 plots in South America and Africa. A single factor – aridity – explained 19-54% of the variance in fixer abundance, and unexpectedly was more important than fire frequency, biome, and continent. Nitrogen fixers were more abundant in arid environments; as a result, African savannas, which tend to be drier, were richer in nitrogen fixers than South American savannas. Fixer abundance converged on similar levels in forests in both continents. We conclude that climate plays a greater role than fire in determining the distribution of nitrogen fixers across tropical savanna and forest biomes. This article is protected by copyright. All rights reserved.

Description: The timing of the fruit-set stage (i.e. start and end of fruit set) is crucial in a plant's life cycle, but its response to temperature change is still unclear. We investigated the timing of seven phenological events, including fruit-set dates during 3 years for six alpine plants transplanted to warmer (+ ~3.5 °C in soils) and cooler (- ~3.5 °C in soils) locations along an altitudinal gradient in the Tibetan area. We found that fruit-set dates remained relatively stable under both warming and cooling during the 3-years transplant experiment. Three earlier phenological events (emergence of first leaf, first bud set, and first flowering) and two later phenological events (first leaf coloring and complete leaf coloring) were earlier by 4.8-8.2 days °C −1 and later by 3.2-7.1 days °C −1 in response to warming. Conversely, cooling delayed the three earlier events by 3.8-6.9 days °C −1 and advanced the two later events by 3.2-8.1 days °C −1 for all plant species. The timing of the first and/or last fruit-set dates, however, did not change significantly compared to earlier and later phenological events. Statistical analyses also showed that the dates of fruit set were not significantly correlated or had lower correlations with changes of soil temperature relative to the earlier and later phenological events. Alpine plants may thus acclimate to changes in temperature for their fruiting function by maintaining relatively stable timings of fruit set compared with other phenological events to maximize the success of seed maturation and dispersal in response to short-term warming or cooling. This article is protected by copyright. All rights reserved.

Description: Statistical models of habitat preference and species distribution (e.g., Resource Selection Functions and Maximum Entropy approaches) perform a quantitative comparison of the use of space with the availability of all habitats in an animal's environment. However, not all of space is accessible all of the time to all individuals, so availability is in fact determined by limitations in animal perception and mobility. Therefore, measuring habitat availability at biologically relevant scales is essential for understanding preference, but herein lies a trade-off: Models fitted at large spatial scales, will tend to average across the responses of different individuals that happen to be in regions with contrasting habitat compositions. We suggest that such models may fail to capture local extremes (hotspots and coldspots) in animal usage and call this potential problem, homogenization . In contrast, models fitted at smaller scales will vary stochastically depending on the particular habitat composition of their narrow spatial neighborhood, and hence fail to describe responses when predicting for different sampling instances. This is the now well-documented issue of non-transferability of habitat models. We illustrate this tradeoff, using a range of simulated experiments, incorporating variations in environmental gradients, richness and fragmentation. We propose diagnostics for detecting the two issues of homogenization and non-transferability and show that these scale-related symptoms are likely to be more pronounced in highly fragmented or steeply graded landscapes. Further, we address these problems by treating the neighborhood of each cell in the landscape grid as an individual sampling instance (with its own neighborhood), hence allowing coefficients to respond to the local expectations of environmental variables according to a Generalized Functional Response (GFR). Under simulation this approach is consistently better at estimating robust (i.e., transferable) habitat models at smaller scales, and less susceptible to homogenization at larger scales. At the same time, it represents the first application of a GFR to continuous space (rather than multiple, spatially distinct datasets), allowing the predictive advantages of this extension of species distribution models to become available to data from large-scale but single-site field studies.

Description: Conspecific negative density dependence (CNDD) has been recognized as a key mechanism underlying species coexistence, especially in tropical forests. Recently, some studies have reported that seedling survival is also negatively correlated with the phylogenetic relatedness between neighbors and focal individuals, termed phylogenetic negative density dependence (PNDD). In contrast to CNDD or PNDD, shared habitat requirements between closely related individuals are thought to be a cause of observed positive effects of closely related neighbors, which may affect the strength and detectability of CNDD or PNDD. In order to investigate the relative importance of these mechanisms for tropical tree seedling survival, we used generalized linear mixed models to analyze how the survival of more than 10 000 seedlings of woody plant species related to neighborhood and habitat variables in a tropical rainforest in southwest China. By comparing models with and without habitat variables, we tested how habitat filtering affected the detection of CNDD and PNDD. The best-fitting model suggested that CNDD and habitat filtering played key roles in seedling survival, but that, contrary to our expectations, phylogenetic positive density dependence (PPDD) had a distinct and important effect. While habitat filtering affected the detection of CNDD by decreasing its apparent strength, it did not explain the positive effects of closely related neighbors. Our results demonstrate that a failure to control for habitat variables and phylogenetic relationships may obscure the importance of conspecific and heterospecific neighbor densities for seedling survival.

Description: Time can be a limiting constraint for consumers, particularly when resource phenology mediates foraging opportunity. Though a large body of research has explored how resource phenology influences trophic interactions, this work has focused on the topics of trophic mismatch or predator swamping, which typically occur over short periods, at small spatial extents or coarse resolutions. In contrast many consumers integrate across landscape heterogeneity in resource phenology, moving to track ephemeral food sources that propagate across space as resource waves. Here we provide a conceptual framework to advance the study of phenological diversity and resource waves. We define resource waves, review evidence of their importance in recent case studies, and demonstrate their broader ecological significance with a simulation model. We found that consumers ranging from fig wasps ( Chalcidoidea) to grizzly bears ( Ursus arctos ) exploit resource waves, integrating across phenological diversity to make resource aggregates available for much longer than their component parts. In model simulations, phenological diversity was often more important to consumer energy gain than resource abundance per se. Current ecosystem-based management assumes that species abundance mediates the strength of trophic interactions. Our results challenge this assumption and highlight new opportunities for conservation and management. Resource waves are an emergent property of consumer–resource interactions and are broadly significant in ecology and conservation.

Description: Essential fatty acids (EFAs) are primarily generated by phytoplankton in aquatic ecosystems, and can limit the growth, development, and reproduction of higher consumers. Among the most critical of the EFAs are highly unsaturated fatty acids (HUFAs), which are only produced by certain groups of phytoplankton. Changing environmental conditions can alter phytoplankton community and fatty acid composition and affect the HUFA content of higher trophic levels. Almost no research has addressed intraspecific variation in HUFAs in zooplankton, nor intraspecific relationships of HUFAs with body size and fecundity. This is despite that intraspecific variation in HUFAs can exceed interspecific variation and that intraspecific trait variation in body size and fecundity is increasingly recognized to have an important role in food web ecology (effect traits). Our study addressed the relative influences of abiotic selection and food web effects associated with climate change on intraspecific differences and interrelationships between HUFA content, body size, and fecundity of freshwater copepods. We applied structural equation modeling and regression analyses to intraspecific variation in a dominant calanoid copepod, Leptodiatomus minutus , among a series of shallow north-temperate ponds. Climate-driven diurnal temperature fluctuations favored the coexistence of diversity of phytoplankton groups with different temperature optima and nutritive quality. This resulted in unexpected positive relationships between temperature, copepod DHA content and body size. Temperature correlated positively with diatom biovolume, and mediated relationships between copepod HUFA content and body size, and between copepod body size and fecundity. The presence of brook trout further accentuated these positive effects in warm ponds, likely through nutrient cycling and stimulation of phytoplankton resources. Climate change may have previously unrecognized positive effects on freshwater copepod DHA content, body size, and fecundity in the small, shallow bodies of inland waters that are commonly found in north-temperate landscapes.

Description: Understanding the impacts of biodiversity loss on ecosystem functioning and services has been a central issue in ecology. Experiments in synthetic communities suggest that biodiversity loss may erode a set of ecosystem functions, but studies in natural communities indicate that the effects of biodiversity loss are usually weak and that multiple functions can be sustained by relatively few species. Yet, the mechanisms by which natural ecosystems are able to maintain multiple functions in the face of diversity loss remain poorly understood. With a long-term and large-scale removal experiment in the Inner Mongolian grassland, here we showed that losses of plant functional groups (PFGs) can reduce multiple ecosystem functions, including biomass production, soil NO 3 -N use, net ecosystem carbon exchange, gross ecosystem productivity, and ecosystem respiration, but the magnitudes of these effects depended largely on which PFGs were removed. Removing the two dominant PFGs (perennial rhizomatous grasses and perennial bunchgrasses) simultaneously resulted in dramatic declines in all examined functions, but such declines were circumvented when either dominant PFG was present. We identify the major mechanism for this as a compensation effect by which each dominant PFG can mitigate the losses of others. This study provides evidence that compensation ensuing from PFG losses can mitigate their negative consequence, and thus natural communities may be more resilient to biodiversity loss than currently thought if the remaining PFGs have strong compensation capabilities. On the other hand, ecosystems without well-developed compensatory functional diversity may be much more vulnerable to biodiversity loss. This article is protected by copyright. All rights reserved.

Description: Understanding processes that promote species coexistence is integral to diversity maintenance. In hyperdiverse tropical forests, local conspecific density (LCD) and light are influential to woody seedling recruitment and soil nutrients are often limiting, yet the simultaneous effects of these factors on seedling survival across time remain unknown. We fit species- and age-specific models to census and resource data of seedlings of 68 woody species from a Costa Rican wet tropical forest. In decreasing order of prevalence, seedling survivorship was related to LCD, soil base cations, irradiance, nitrogen, and phosphorus. Species–specific responses to factors did not covary, providing evidence that species life history strategies have not converged to one continuum of high-surviving stress tolerant to low-surviving stress intolerant species. Survival responses to all factors varied over the average seedling's lifetime, indicating seedling requirements change with age and conclusions drawn about processes important to species coexistence depend on temporal resolution. This article is protected by copyright. All rights reserved.

Description: Sea-to-land nutrient transfers can connect marine food webs to those on land, creating a dependence on marine webs by opportunistic species. We show how nitrogen, imported by grey seals, Halichoerus grypus , and traced through stable isotope (δ 15 N) measurements in marram grass , Ammophila breviligulata , significantly alters foraging behavior of a free-roaming megaherbivore (feral horses, Equus ferus caballus ) on Sable Island, Canada. Values of δ 15 N correlated with protein content of marram and strongly related to pupping-seal densities, and positively influenced selective foraging by horses. The latter was density-dependent consistent with optimal foraging theory. We present the first demonstration of how sea-to-land nutrient transfers can affect the behavioral process of resource selection (resource use relative to availability) of terrestrial consumers. We hypothesize that persistence of horses on Sable Island is being facilitated by N subsidies. Our results have relevance to advancing theory on trophic dynamics in island biogeography and metaecosystem ecology. This article is protected by copyright. All rights reserved.

Description: The “landscape of fear” model, recently advanced in research on the non-lethal effects of carnivores on ungulates, predicts that prey will exhibit detectable antipredator behavior not only during risky times (i.e., predators in close proximity) but also in risky places (i.e., habitat where predators kill prey or tend to occur). Aggregation is an important antipredator response in numerous ungulate species, making it a useful metric to evaluate the strength and scope of the landscape of fear in a multi-carnivore, multi-ungulate system. We conducted ungulate surveys over a 2-year period in South Africa to test the influence of three broad-scale sources of variation in the landscape on spatial patterns in aggregation: (1) habitat structure, (2) where carnivores tended to occur (i.e., population-level utilization distributions), and (3) where carnivores tended to kill ungulate prey (i.e., probabilistic kill site maps). We analyzed spatial variation in aggregation for six ungulate species exposed to predation from recently reintroduced lion ( Panthera leo ) and spotted hyena ( Crocuta crocuta ). Although we did detect larger aggregations of ungulates in “risky places,” these effects existed primarily for smaller-bodied (〈150 kg) ungulates and were relatively moderate (change of ≤4 individuals across all habitats). In comparison, ungulate aggregations tended to increase at a slightly lower rate in habitat that was more open. The lion, an ambush (stalking) carnivore, had stronger influence on ungulate aggregation than the hyena, an active (coursing) carnivore. In addition, places where lions tended to kill prey had a greater effect on ungulate aggregation than places where lions tended to occur, but an opposing pattern existed for hyena. Our study reveals heterogeneity in the landscape of fear and suggests broad-scale risk effects following carnivore reintroduction only moderately influence ungulate aggregation size and vary considerably by predator hunting mode, type of predation risk, and prey species.

Description: Many insect parasitoids are highly specialized and thus develop on only one or a few related host species, yet some hosts are attacked by many different parasitoid species in nature. For this reason, they have been often used to examine the consequences of competitive interactions. Hosts represent limited resources for larval parasitoid development and thus one competitor usually excludes all others. Although parasitoid competition has been debated and studied over the past several decades, understanding the factors that allow for coexistence among species sharing the same host in the field remains elusive. Parasitoids may be able to coexist on the same host species if they partition host resources according to size, age, or stage, or if their dynamics vary at spatial and temporal scales. One area that has thus far received little experimental attention is if competition can alter host usage strategies in parasitoids that in the absence of competitors attack hosts of the same size in the field. Here, we test this hypothesis with two parasitoid species in the genus Aphytis , both of which are specialized on the citrus pest California red scale Aonidiella aurantii . These parasitoids prefer large scales as hosts and yet coexist in sympatry in eastern parts of Spain. Parasitoids and hosts were sampled in 12 replicated orange groves. When host exploitation by the stronger competitor, A. melinus , was high the poorer competitor, A. chrysomphali , changed its foraging strategy to prefer alternative plant substrates where it parasitized hosts of smaller size. Consequently, the inferior parasitoid species shifted both its habitat and host size as a result of competition. Our results suggest that density-dependent size-mediated asymmetric competition is the likely mechanism allowing for the coexistence of these two species, and that the use of suboptimal (small) hosts can be advantageous under conditions imposed by competition where survival in higher quality larger hosts may be greatly reduced.

Description: Long-distance breeding and natal dispersal play central roles in many ecological and evolutionary processes, including gene flow, population dynamics, range expansion, and individual responses to fluctuating biotic and abiotic conditions. However, the relative contribution of long-distance dispersal to these processes depends on the ability of dispersing individuals to successfully reproduce in their new environment. Unfortunately, due to the difficulties associated with tracking dispersal in the field, relatively little is known about its reproductive consequences. Furthermore, because reproductive success is influenced by a variety of processes, disentangling the influence of each of these processes is critical to understanding the direct consequences of dispersal. In this study, we used stable hydrogen and carbon isotopes to estimate long-distance dispersal and winter territory quality in a migratory bird, the American Redstart ( Setophaga ruticilla ). We then applied Aster life-history models to quantify the strength of influence of these factors on apparent reproductive success. We found no evidence that male or female reproductive success was lower for long-distance dispersers relative to non-dispersing individuals. In contrast, carry-over effects from the winter season did influence male, but not female, reproductive success. Use of Aster models further revealed that for adult males, winter territory quality influenced the number of offspring produced whereas for yearling males, high-quality winter territories were associated with higher mating and nesting success. These results suggest that although long-distance natal and breeding dispersal carry no immediate reproductive cost for American Redstarts, reproductive success in this species may ultimately be limited by the quality of winter habitat.

Description: Ecological patterns arise from the interplay of many different processes, and yet the emergence of consistent phenomena across a diverse range of ecological systems suggests that many patterns may in part be determined by statistical or numerical constraints. Differentiating the extent to which patterns in a given system are determined statistically, and where it requires explicit ecological processes, has been difficult. We tackled this challenge by directly comparing models from a constraint-based theory, the Maximum Entropy Theory of Ecology (METE) and models from a process-based theory, the size-structured neutral theory (SSNT). Models from both theories were capable of characterizing the distribution of individuals among species and the distribution of body size among individuals across 76 forest communities. However, the SSNT models consistently yielded higher overall likelihood, as well as more realistic characterizations of the relationship between species abundance and average body size of conspecific individuals. This suggests that the details of the biological processes contain additional information for understanding community structure that are not fully captured by the METE constraints in these systems. Our approach provides a first step towards differentiating between process- and constraint-based models of ecological systems and a general methodology for comparing ecological models that make predictions for multiple patterns.

Description: In the coming century, climate change is projected to impact precipitation and temperature regimes worldwide, with especially large effects in drylands. We use big sagebrush ecosystems as a model dryland ecosystem to explore the impacts of altered climate on ecohydrology and the implications of those changes for big sagebrush plant communities using output from 10 Global Circulation Models (GCMs) for two representative concentration pathways (RCPs). We ask: 1) What is the magnitude of variability in future temperature and precipitation regimes among GCMs and RCPs for big sagebrush ecosystems and 2) How will altered climate and uncertainty in climate forecasts influence key aspects of big sagebrush water balance? We explored these questions across 1980-2010, 2030-2060, and 2070-2100 to determine how changes in water balance might develop through the 21 st century. We assessed ecohydrological variables at 898 sagebrush sites across the western US using a process-based soil water model, SOILWAT to model all components of daily water balance using site-specific vegetation parameters and site-specific soil properties for multiple soil layers. Our modeling approach allowed for changes in vegetation based on climate. Temperature increased across all GCMs and RCPs, while changes in precipitation were more variable across GCMs. Winter and spring precipitation was predicted to increase in the future (7% by 2030-2060, 12% by 2070-2100), resulting in slight increases in soil water potential (SWP) in winter. Despite wetter winter soil conditions, SWP decreased in late spring and summer due to increased evapotranspiration (6% by 2030-2060, 10% by 2070-2100) and groundwater recharge (26% and 30% increase by 2030-2060 and 2070-2100). Thus, despite increased precipitation in the cold season, soils may dry out earlier in the year, resulting in potentially longer drier summer conditions. If winter precipitation cannot offset drier summer conditions in the future, we expect big sagebrush regeneration and survival will be negatively impacted, potentially resulting in shifts in the relative abundance of big sagebrush plant functional groups. Our results also highlight the importance of assessing multiple GCMs to understand the range of climate change outcomes on ecohydrology, which was contingent on the GCM chosen. This article is protected by copyright. All rights reserved.

Description: Mass mortality of the sea urchin Diadema antillarum due to disease outbreaks in 1983 and 1991 decimated populations in the Florida Keys, and they have yet to recover. Here, we use a coupled advection-diffusion and fertilization-kinetics model to test the hypothesis that these populations are fertilization-limited. We found that fertilization success was ≥ 96% prior to the first disease outbreak, decreased substantially following recurrent disease to 3%, and has since remained low. By investigating the combined effects of physical factors (population spatial extent and current velocity) and sea urchin behavior (aggregation) on density-dependent fertilization success, we show that fertilization success at a given density increases with increasing population spatial extent and decreasing current velocity, and is greater under simulated aggregation behavior of D. antillarum . However, at present population densities, the increase in fertilization success due to aggregation is 〈 1%, even under the most favorable physical conditions. These results indicate that populations are severely fertilization-limited, and that Allee effects at low population density will continue to limit recovery. Our results can serve as a practical guide to managers in the development of coral reef restoration strategies, including the design of a D. antillarum restocking program to obtain reproductively viable populations. This article is protected by copyright. All rights reserved.

Description: Theory suggests that high activity levels in animals increase growth at the cost of increased mortality. This growth-mortality trade-off has recently been incorporated into the wider framework of the pace-of-life syndrome (POLS) hypothesis. However, activity is often quantified only in the laboratory and on a diurnal basis, leaving open the possibility that animals manage predation risk and feeding efficiency in the wild by modulating their circadian activity rhythms. Here we investigate how laboratory activity in wild brown trout parr ( Salmo trutta L.) associates with circadian activity, growth, and mortality in their natal stream. We found that individuals with high activity in the laboratory displayed high dispersal and cathemeral activity in their natal stream. In contrast, trout with low laboratory activity showed variation of activity in the wild, which was negatively related to the light intensity. Our results do not support the growth-mortality trade-off of the POLS hypothesis as highly active, fast-growing individuals showed higher survival than inactive conspecifics. These novel results show for the first time that active and inactive individuals, as scored in the lab, can show different circadian patterns of behaviour in the wild driven by light intensity. This implies that studies conducted under a narrow range of light conditions can bias our understanding of individual behavioural variation and its fitness consequences in the wild. This article is protected by copyright. All rights reserved.

Description: Encounter competition is interference competition in which animals directly contend for resources. Ecological theory predicts the trait that determines the resource holding potential (RHP), and hence the winner of encounter competition, is most often body size or mass. The difficulties of observing encounter competition in complex organisms in natural environments, however, has limited opportunities to test this theory across diverse species. We studied the outcome of encounter competition contests among mesocarnivores at deer carcasses in California to determine the most important variables for winning these contests. We found some support for current theory in that body mass is important in determining the winner of encounter competition, but we found that other factors including hunger and species-specific traits were also important. In particular, our top models were ‘strength and hunger’ and ‘size and hunger,’ with models emphasizing the complexity of variables influencing outcomes of encounter competition. In addition, our wins above predicted (WAP) statistic suggests that an important aspect that determines the winner of encounter competition is species-specific advantages that increase their RHP, as bobcats ( Lynx rufus ) and spotted skunks ( Spilogale gracilis ) won more often than predicted based on mass. In complex organisms, such as mesocarnivores, species-specific adaptations, including strategic behaviors, aggressiveness, and weapons, contribute to competitive advantages and may allow certain species to take control or defend resources better than others. Our results help explain how interspecific competition shapes the occurrence patterns of species in ecological communities. This article is protected by copyright. All rights reserved.

Description: Ecological theory suggests that pathogens are capable of regulating or limiting host population dynamics, and this relationship has been empirically established in several settings. However, although studies of childhood diseases were integral to the development of disease ecology, few studies show population limitation by a disease affecting juveniles. Here, we present empirical evidence that disease in lambs constrains population growth in bighorn sheep ( Ovis canadensis ) based on 45 years of population-level and 18 years of individual-level monitoring across 12 populations. While populations generally increased (lambda =1.11) prior to disease introduction, most of these same populations experienced an abrupt change in trajectory at the time of disease invasion, usually followed by stagnant-to-declining growth rates (lambda = 0.98) over the next twenty years. Disease-induced juvenile mortality imposed strong constraints on population growth that were not observed prior to disease introduction, even as adult survival returned to pre-invasion levels. Simulations suggested that models including persistent disease-induced mortality in juveniles qualitatively matched observed population trajectories, whereas models that only incorporated all-age disease events did not. We use these results to argue that pathogen persistence may pose a lasting, but under-recognized, threat to host populations, particularly in cases where clinical disease manifests primarily in juveniles. This article is protected by copyright. All rights reserved.

Description: Global environmental change (GEC) is affecting species interactions and causing a rapid decline in biodiversity. In this study, I present a new Ecosystem Disruption Index (EDI) to quantify the impacts of simulated nitrogen (N) deposition (0, 10, 20 and 50 kg N ha -1 yr -1 + 6-7 kg N ha -1 yr -1 background) on abiotic and biotic ecological interactions. This comparative index is based on pairwise linear and quadratic regression matrices. These matrices, calculated at the N treatment level, were constructed using a range of abiotic and biotic ecosystem constituents: soil pH, shrub cover, and the first component of several separate principal component analyses using soil fertility data (total carbon and N) and community data (annual plants; microorganisms; biocrusts; edaphic fauna) for a total of seven ecosystem constituents. Four years of N fertilization in a semiarid shrubland completely disrupted the network of ecological interactions, with a greater proportional increase in ecosystem disruption at low-N addition levels. Biotic interactions, particularly those involving microbes, shrubs and edaphic fauna, were more prone to be lost in response to N, whereas interactions involving soil properties were more resilient. In contrast, edaphic fauna was the only group directly affected by N addition, with mites and collembolans increasing their abundance with up to 20 kg N ha -1 yr -1 and then decreasing, which supports the idea of higher-trophic level organisms being more sensitive to disturbance due to more complex links with other ecosystem constituents. Future experimental studies evaluating the impacts of N deposition, and possibly other GEC drivers, on biodiversity and biotic and abiotic interactions may be able to explain results more effectively in the context of ecological networks as a key feature of ecosystem sensitivity. This article is protected by copyright. All rights reserved.

Description: Edaphic variation in plant community composition is widespread, yet its underlying mechanisms are rarely understood and often assumed to be physiological. In East African savannas, Acacia tree species segregate sharply across soils of differing parent material: the ant-defended whistling thorn, A. drepanolobium (ACDR), is monodominant on clay vertisols that are nutrient rich but physically stressful, whereas poorly defended species such as A. brevispica (ACBR) dominate on nutrient-poor but otherwise less-stressful sandy loams. Using a series of field experiments, we show that large-mammal herbivory interacts with soil properties to maintain this pattern. In the absence of large herbivores, transplanted saplings of both species established on both soil types. Browsers strongly suppressed survival and growth of ACDR saplings on sandy soil, where resource limitation constrained defensive investment. On clay soil, ACBR saplings established regardless of herbivory regime, but elephants prevented recruitment to maturity, apparently because trees could not tolerate the combination of biotic and abiotic stressors. Hence, each tree species was filtered out of one habitat by browsing in conjunction with different edaphic factors and at different ontogenetic stages. Browser abundance was greater on sandy soil, where trees were less defended, consistent with predicted feedbacks between plant community assembly and herbivore distributions. By exploring two inversely related axes of soil “quality” (abiotic stress and nutrient content), our study extends the range of mechanisms by which herbivores are known to promote edaphic specialization, illustrates how the high cost of a protection mutualism can constrain the realized niche of host trees, and shows that large-scale properties of savanna ecosystems are shaped by species interactions in cryptic ways that mimic simple abiotic determinism. These results suggest that ongoing declines in large-herbivore populations may relax spatial heterogeneity in plant assemblages and reduce the beta diversity of communities. This article is protected by copyright. All rights reserved.

Description: Controversy exists over the cause and timing of the extinction of the Pleistocene megafauna. In the tropical Andes, deglaciation and associated rapid climate change began c. 8000 years before human arrival, providing an opportunity to separate the effects of climate change from human hunting on megafaunal extinction. We present a paleoecological record spanning the last 25,000 years from Lake Pacucha, Peru (3100 m elevation). Fossil pollen, charcoal, diatoms, and the dung fungus Sporormiella, chronicle a two-stage megaherbivore population collapse. Sporormiella abundance, the proxy for megafaunal presence, fell sharply at c. 21,000 years ago, but rebounded prior to a permanent decline between c. 16,800 and 15,800 years ago. This two-stage decline in megaherbivores resulted in a functional extinction by c. 15,800 years ago, 3000 years earlier than human occupation of the high Andes. Declining megaherbivore populations coincided with warm, wet intervals. Climatic instability and megafaunal population collapse triggered an ecological cascade that resulted in novel floral assemblages, and increases in woody species, fire frequency, and plant species that were sensitive to trampling. Our data revealed that Andean megafaunal populations collapsed due to positive feedbacks between habitat quality and climate change rather than human activity. This article is protected by copyright. All rights reserved.

Description: Increasing temperatures and a reduction in the frequency and severity of freezing events have been linked to species distribution shifts. Across the globe, mangrove ranges are expanding towards higher latitudes, likely due to diminishing frequency of freezing events associated with climate change. Continued warming will alter coastal wetland plant dynamics both above- and belowground, potentially altering plant capacity to keep up with sea level rise. We conducted an in-situ warming experiment, in Northeast Florida, to determine how increased temperature (+2°C) influences co-occurring mangrove and salt marsh plants. Warming was achieved using passive warming with three treatment levels (ambient, shade control, warmed). Avicennia germinans , the black mangrove , exhibited no differences in growth or height due to experimental warming but displayed a warming-induced increase in leaf production (48%). Surprisingly, Distichlis spicata, the dominant salt marsh grass , increased in biomass (53% in 2013 and 70% in 2014), density (41%) and height (18%) with warming during summer months. Warming decreased plant root mass at depth and changed abundances of anaerobic bacterial taxa. Even while the poleward shift of mangroves is clearly controlled by the occurrences of severe freezes, chronic warming between these freeze events may slow the progression of mangrove dominance within ecotones. This article is protected by copyright. All rights reserved.

Description: In terrestrial ecosystems, a large portion (20-80%) of the dissolved Si (DSi) in soil solution has passed through vegetation. While the importance of this ‘terrestrial Si filter’ is generally accepted, few data exist on the pools and fluxes of Si in forest vegetation and the rate of release of Si from decomposing plant tissues. We quantified the pools and fluxes of Si through vegetation and coarse woody debris (CWD) in a northern hardwood forest ecosystem (Watershed 6, W6) at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire, USA. Previous work suggested that the decomposition of CWD may have significantly contributed to an excess of DSi reported in stream-waters following experimental deforestation of Watershed 2 (W2) at the HBEF. We found that woody biomass (wood + bark) and foliage account for approximately 65% and 31%, respectively, of the total Si in biomass at the HBEF. During the decay of American beech ( Fagus grandifolia ) boles, Si loss tracked the whole-bole mass loss, while yellow birch ( Betula alleghaniensis ) and sugar maple ( Acer saccharum ) decomposition resulted in a preferential Si retention of up to 30% after 16 years. A power-law model for the changes in wood and bark Si concentrations during decomposition, in combination with an exponential model for whole-bole mass loss, successfully reproduced Si dynamics in decaying boles. Our data suggest that a minimum of 50% of the DSi annually produced in the soil of a biogeochemical reference watershed (W6) derives from biogenic Si (BSi) dissolution. The major source is fresh litter, while only ~2% comes from the decay of CWD. Decay of tree boles could only account for 9% of the excess DSi release observed following the experimental deforestation of W2. Therefore, elevated DSi concentrations after forest disturbance are largely derived from other sources (e.g., dissolution of BSi from forest floor soils and/or mineral weathering). This article is protected by copyright. All rights reserved.

Description: Temperature can play an important role in determining the feeding preferences of ectotherms. In light of the warmer temperatures arising with the current climatic changes omnivorous ectotherms may perform diet shifts towards higher herbivory to optimize energetic intake. Such diet shifts may also occur during heat waves, which are projected to become more frequent, intense and longer lasting in the future. Here, we investigated how heat waves of different duration affect feeding preferences in omnivorous anuran tadpoles and how these choices affect larval life history. In laboratory experiments, we fed tadpoles of three species on animal, plant or mixed diet and exposed them to short heat waves (similar to the heat waves these species experience currently) or long heat waves (predicted to increase under climate change). We estimated the dietary choices of tadpoles fed on the mixed diet using stable isotopes and recorded tadpole survival and growth, larval period and mass at metamorphosis. Tadpole feeding preferences were associated with their thermal background, herbivory increasing with breeding temperature in nature. Patterns in survival, growth and development generally support decreased efficiency of carnivorous diets and increased efficiency or higher relative quality of herbivorous diets at higher temperatures. All three species increased herbivory in at least one of the heat wave treatments, but the responses varied among species. Diet shifts towards higher herbivory were maladaptive in one species, but beneficial in the other two. Higher herbivory in omnivorous ectotherms under warmer temperatures may impact species differently and further contribute to changes in the structure and function of freshwater environments. This article is protected by copyright. All rights reserved.

Description: Environmental filtering, including the influence of environmental constraints and biological interactions on species’ survival, is known to significantly affect patterns of community assembly in terrestrial ecosystems. However, its role in regulating patterns and processes of community assembly in deep-sea environments is poorly studied. Here, we investigated the role of wood characteristics in the assembly of deep-sea wood fall communities. Ten different wood species (substrata) that varied in structural complexity were sunk to a depth of 3,100 m near Monterey Bay, CA. In total, 28 wood parcels were deployed on the deep-sea bed. After 2 years, the wood parcels were recovered with over 7,000 attached or colonizing macroinvertebrates. All macroinvertebrates were identified to the lowest taxonomic level possible, and included several undescribed species. Diversity indices and multivariate analyses of variance detected significant variation in the colonizing community assemblages among different wood substrata. Structural complexity seemed to be the primary factor altering community composition between wood substrata. For example, wood-boring clams were most abundant on solid logs, while small arthropods and limpets were more abundant on bundles of branches that provided more surface area and small, protected spaces to occupy. Other factors such as chemical defenses, the presence of bark, and wood hardness likely also played a role. Our finding that characteristics of woody debris entering the marine realm can have significant effects on community assembly supports the notion of ecological and perhaps evolutionarily significant links between land and sea. This article is protected by copyright. All rights reserved.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. The evolutionary pressures that drive long larval planktonic durations in some coastal marine organisms, while allowing direct development in others, have been vigorously debated. We introduce into the argument the asymmetric dispersal of larvae by coastal currents and find that the strength of the currents helps determine which dispersal strategies are evolutionarily stable. In a spatially and temporally uniform coastal ocean of finite extent, direct development is always evolutionarily stable. For passively drifting larvae, long planktonic durations are stable when the ratio of mean to fluctuating currents is small and the rate at which larvae increase in size in the plankton is greater than the mortality rate (both in units of per time). However, larval behavior that reduces downstream larval dispersal for a given time in plankton will be selected for, consistent with widespread observations of behaviors that reduce dispersal of marine larvae. Larvae with long planktonic durations are shown to be favored not for the additional dispersal they allow, but for the additional fecundity that larval feeding in the plankton enables. We analyze the spatial distribution of larval life histories in a large database of coastal marine benthic invertebrates and document a link between ocean circulation and the frequency of planktotrophy in the coastal ocean. The spatial variation in the frequency of species with planktotrophic larvae is largely consistent with our theory; increases in mean currents lead to a decrease in the fraction of species with planktotrophic larvae over a broad range of temperatures.

Description: Ecology, Volume 94, Issue 9, Page 1955-1965, September 2013. Laboratory studies have demonstrated that the microscopic stages of kelps can rapidly resume development from a delayed state. Like terrestrial seeds or aquatic resting eggs, banks of delayed kelp stages may supplement population recovery after periods of stress, playing an important role for kelp populations that experience adult sporophyte absences due to seasonal or interannual disturbances. We found that removing the microscopic stages from natural rock substratum could prevent the appearance of juvenile kelp sporophytes for three months and the establishment of a diverse kelp assemblage for over four months within a southern California kelp forest. Juveniles were observed within one month in plots where microscopic stages were left intact, which may confer an advantage for the resulting sporophytes as they attain larger sizes before later recruiting neighbors. Microsatellite diversity was high (expected heterozygosity HE ≈ 0.9) for juveniles and adults within our sites. Using a microsatellite-based parentage analysis for the dominant kelp, Macrocystis pyrifera, we estimated that a portion of the new M. pyrifera sporophyte recruits had originated from their parents at least seven months after their parents had disappeared. Similar delay durations have been demonstrated in recent laboratory studies. Additionally, our results suggest that zoospore dispersal distances 〉50 m may be supported by including additional microsatellite loci in the analysis. We propose a mixed-age and, potentially, a mixed-origin bank of M. pyrifera gametophytes promotes maximal genetic diversity in recovering populations and reduces population genetic subdivision and self-fertilization rates for intact populations by promoting the survival of zoospores dispersed 〉10 m and during inhospitable environmental conditions.

Description: Ecology, Volume 94, Issue 9, Page 2109-2110, September 2013. Abstract Total body size, mass or linear measurements, and gonad mass or volumes have been recorded for the North American Pacific coast sea urchins Strongylocentrotus purpuratus, Mesocentrotus (Strongylocentrotus) franciscanus, and Lytechinus pictus by various workers at diverse sites and for varying lengths of time from 1954 to 2009. Some dissections included other body components such as the gut, body wall, and Aristotle's lantern, and some dissections included both wet and dry mass. There are numerous peer-reviewed publications that have used some of these data, but some data have appeared only in graduate theses or in the gray literature. There also are data that have never appeared outside the original data sheets. Historically, data were used to describe reproductive cycles and then to compare responses to stressors such as food limitation or pollution. Differences in temperature among sites also have been explored. More recently, dissection data have linked gonad development to ocean conditions, so called bottom-up forcing. The data set presented here is a historical record of gonad development for a common group of marine invertebrates in intertidal and nearshore environments, which can be used to test hypotheses concerning future changes associated with climate change and ocean acidification along the Pacific Coast of North America.

Description: Ecology, Volume 94, Issue 9, Page 2108-2111, September 2013. Abstract Chytridiomycosis caused by the fungal invasive pathogen Batrachochytrium dendrobatidis (Bd) was first detected in 1999 in Christchurch, New Zealand, in the Australian introduced frog species Litoria raniformis. It was detected in wild native frogs in the critically endangered Leiopelma archeyi in 2001 on the Coromandel Peninsula and has been suggested as responsible for a mass decline (88%) in that population between 1994 and 2002. We report the current distribution, host species and prevalence, where known, of Bd in New Zealand, which is essential for conservation management of New Zealand native frogs (Leiopelma spp.). The data set is structured so that it can be readily added to the Australian Bd database for further analyses. Our data included all regions in New Zealand and six offshore islands at 135 sites with 704 records from 23 contributors spanning collection dates 1930–2010. We report 54 positive sites from 132 positive individuals. We also detail negative findings, but declaring an area free from disease should consider the sensitivity of the test used and numbers of individuals tested. The data also included a comprehensive museum survey testing 152 individuals from five species (20 L. archeyi, 50 L. hochstetteri, 15 L. aurea, 40 L. ewingii, and 27 L. raniformis) from 1930–1999 using histology and Bd-specific immunohistochemistry. All museum specimens were negative, so the 1999 positive result is still the earliest record. In the L. archeyi Coromandel Ranges population, the period prevalence of Bd from 2006 to 2010 was relatively stable at 16%, but the number of animals tested remains low (up to N = 19) due to the now depleted population numbers. The period prevalence of Bd in the L. archeyi Whareorino population has remained both consistent and low (6%) between 2005 and 2010. In L. hochstetteri, L. hamiltoni, and L. pakeka all sampling for Bd has been negative. Positive Bd results have been found in all three Litoria spp., but Bd has not been found in the six offshore areas tested. Most data have been previously unpublished and represent the first confirmed reports of Bd in many regions and species in New Zealand.

Description: Ecology, Volume 94, Issue 9, Page 2055-2065, September 2013. A growing body of research documents the importance of plant genetic effects on arthropod community structure. However, the mechanisms underlying these effects are often unclear. Additionally, plant genetic effects have largely been quantified in common gardens, thus inflating the estimates of their importance by minimizing levels of natural variation. Using Valeriana edulis, a dioecious plant with genetically based sex determination, we conducted surveys and experiments on wild-grown individuals to document field patterns of arthropod association between the sexes and the mechanisms underlying these plant genetic effects. Three years of surveys revealed strong and consistent sex-biased arthropod association in wild-grown plants: female plants supported 4-fold, 1.5-fold, and 4-fold higher densities of aphids, aphid predators, and aphid-tending ants, respectively, compared to males. There was mixed evidence that the female bias for aphids was due to higher plant quality, while we found no difference between plant sexes in aphid preference or the top-down effects of predators and tending ants. Female bias for ants was due to both the greater attractiveness of female plants (direct effect mediated by floral nectar) and an independent, weaker effect of higher aphid abundance on females (density-mediated indirect effect). Conversely, the female bias for predators was driven solely by the greater attractiveness of female plants. We did not find interaction modification, i.e., ant–aphid and predator–aphid interactions were equivalent between plant sexes. Plant sex explained 0.24%, 2.28%, and 4.42% of the variance in aphids, predators, and ants, respectively, values comparable to but slightly weaker than those previously reported from common-garden studies. In contrast to the prediction of diminished plant genetic effects with increasing trophic level, we show how weak indirect effects on predators and parasitoids (via herbivores) can be complemented by strong direct effects via common plant traits (floral resources). In summary, we document direct and indirect effects of genetically based sex on a multi-trophic arthropod community that were expressed in wild-grown plants across multiple years.

Description: Ecology, Volume 94, Issue 9, Page 1893-1897, September 2013. The leaf economics spectrum (LES) has revolutionized the way many ecologists think about quantifying plant ecological trade-offs. In particular, the LES has connected a clear functional trade-off (long-lived leaves with slow carbon capture vs. short-lived leaves with fast carbon capture) to a handful of easily measured leaf traits. Building on this work, community ecologists are now able to quickly assess species carbon-capture strategies, which may have implications for community-level patterns such as competition or succession. However, there are a number of steps in this logic that require careful examination, and a potential danger arises when interpreting leaf-trait variation among species within communities where trait relationships are weak. Using data from 22 diverse communities, we show that relationships among three common functional traits (photosynthetic rate, leaf nitrogen concentration per mass, leaf mass per area) are weak in communities with low variation in leaf life span (LLS), especially communities dominated by herbaceous or deciduous woody species. However, globally there are few LLS data sets for communities dominated by herbaceous or deciduous species, and more data are needed to confirm this pattern. The context-dependent nature of trait relationships at the community level suggests that leaf-trait variation within communities, especially those dominated by herbaceous and deciduous woody species, should be interpreted with caution.

Description: Ecology, Volume 94, Issue 9, Page 2111-2112, September 2013. Abstract We present data from the first five years (2008–2012) of the establishment of the 25.6-ha Smithsonian Conservation Biology Institute (SCBI) Large Forest Dynamics Plot, comprising the initial woody stem census, woody seedling plot surveys, seed rain, and dendrochronological data. The plot is in mature secondary mixed deciduous forest 5 km south of Front Royal, Virginia, USA. The initial plot census enumerated 38 932 free-standing living stems and 29 991 living individuals ≥1 cm dbh comprising 62 species, 38 genera, and 26 families, along with an additional 1248 dead/missing standing stems, for a total of 40 180 stems. Dominant canopy trees include tulip poplar (Liriodendron tulipifera), hickories (Carya spp.), oaks (Quercus spp.), white ash (Fraxinus americana), and black gum (Nyssa sylvatica). Prominent understory components include spicebush (Lindera benzoin), pawpaw (Asimina triloba), American hornbeam (Carpinus caroliniana), witchhazel (Hamamelis virginiana), and eastern redbud (Cercis canadensis). Few species predominate numerically on the plot; seven species have 〉1000 individuals (71.3% of the total). Mean stand density was 1179 living individuals/ha, while mean basal area was 34.1 m2/ha. Of the total plot area, 4 ha have had white-tailed deer (Odocoileus virginianus) exclusion since 1990. Woody seedling surveys from 2010–2012 in 354 1-m2 plots measured 19 415 seedlings of 47 species, from new germinants up to 1 cm dbh. Community-wide seed rain data from 200 0.5-m2 litterfall traps yielded a total of 9197 records from 37 species. Long-term seed data collected from 1986–2011 for Quercus and Carya within the exclosure and two replicate sites are also presented, documenting considerable annual variation in mast production. Dendrochronological data from 492 tree cores suggested the major canopy trees established circa 1900, but scattered trees of several species existed earlier. Large-scale forest dynamics plots employing standardized methodology have a long, rich history in the tropics. Similar plots in the temperate zone have been largely lacking, however. The SCBI plot represents one of the first of its kind in the Smithsonian Global Earth Observatory's recently established network of such plots, complementing its well-known network of tropical forest plots and enabling comparative studies on forest ecology and climate change at the global scale.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. The installation of green roofs, defined here as rooftops with a shallow soil cover and extensive vegetation, has been proposed as a possible measure to mitigate the loss of green space caused by the steady growth of cities. However, the effectiveness of green roofs in supporting arthropod communities, and the extent to which they facilitate connectivity of these communities within the urban environment is currently largely unknown. We investigated the variation of species community composition (β-diversity) of four arthropod groups with contrasting mobility (Carabidae, Araneae, Curculionidae and Apidae) on 40 green roofs and 40 extensively managed green sites on the ground in the city of Zurich, Switzerland. With redundancy analysis and variation partitioning i) we disentangled the relative importance of local environmental conditions, the surrounding land-cover composition, and habitat connectivity on species community composition. ii) We searched for specific spatial scales of habitat connectivity for the different arthropod groups. iii) Finally, we discussed the ecological and functional value of green roofs in cities. Our study revealed that on green roofs community composition of highly mobile arthropod groups (bees and weevils) were mainly shaped by habitat connectivity while low mobile arthropod groups (carabids and spiders) were more influenced by local environmental conditions. A similar but less pronounced pattern was found for ground communities. The high importance of habitat connectivity in shaping highly mobile species community composition indicates that these green roof communities are substantially connected by the frequent exchange of individuals among surrounding green roofs. On the other hand, low mobile species communities on green roofs are more likely connected to ground sites than to other green roofs. The integration of green roofs in urban spatial planning strategies has great potential to enable higher connectivity among green spaces, so that eventually even communities of low mobile species become connected. Furthermore, improving the design of green roofs (composition and configuration of vegetation and soil types) could enhance the ecological value especially for low mobile species.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Assessing trait responses to environmental gradients requires the simultaneous analysis of the information contained in three tables: L (species distribution across samples), R (environmental characteristics of samples) and Q (species traits). Among the available methods, the so-called fourth-corner and RLQ methods are two appealing alternatives that provide a direct way to test and estimate trait-environment relationships. Both methods are based on the analysis of the fourth-corner matrix which crosses traits and environmental variables weighted by species abundances. However, they greatly differ in their outputs: RLQ is a multivariate technique that provides ordination scores to summarize the joint structure among the three tables, whereas the fourth-corner method mainly tests for individual trait-environment relationships (i.e. one trait and one environmental variable at a time). Here, we illustrate how the complementarity between these two methods can be exploited to promote new ecological knowledge and to improve the study of trait-environment relationships. After a short description of each method, we apply them to real ecological data to present their different outputs and provide hints about the gain resulting from their combined use.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Insect mutualisms can have disproportionately large impacts on local arthropod and plant communities and their responses to climatic change. The objective of this study was to determine if the presence of insect mutualisms affects host plant and herbivore responses to warming. Using open-top warming chambers at Harvard Forest, MA, USA, we manipulated temperature and presence of ants and Chaitophorus populicola aphids on Populus tremuloides host plants and monitored ant attendance and persistence of C. populicola, predator abundance, plant stress, and abundance of Myzus persicae, a pest aphid that colonized plants during the experiment. We found that, regardless of warming, C. populicola persistence was higher when tended by ants, and some ant species increased aphid persistence more than others. Warming had negligible direct but strong indirect effects on plant stress. Plant stress decreased with warming only when both ants and C. populicola aphids were present and engaged in mutualism. Plant stress was increased by warming- induced reductions in predator abundance and increases in M. persicae aphid abundance. Altogether, these findings suggest that insect mutualisms could buffer the effects of warming on specialist herbivores and plants, but, when mutualisms are not intact, the direct effects of warming on predators and generalist herbivores yield strong indirect effects of warming on plants.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. The processes that structure assemblages of species in hyper-diverse genera, such as Ficus (Moraceae), are not well understood. Functional diversity of co-occurring species can reveal evidence for assembly processes; however, intraspecific variation may weaken species-level patterns. We studied whether functional and phylogenetic diversity of Ficus species indicated the effects of spatial variation in filters associated with topography or niche partitioning related to resource use and biotic interactions. We also asked whether individual trait patterns supported species-level patterns. We studied six traits (leaf area, succulence, specific leaf area: SLA, maximum DBH, fruit size, and latex exudation) for 22 Ficus species and 335 individuals {greater than or equal to} 10 cm DBH on a 20-ha forest plot in China. We found that higher elevation was correlated to changes in mean and reduced diversity of five traits, possibly due to frequent disturbances at higher elevations that favored fast-growing, poorly defended species with high SLA. Maximum DBH showed phylogenetic conservatism but high diversity among co-occurring species, suggesting adult stature is an important axis of within-quadrat niche partitioning. At the individual level, trait patterns were qualitatively consistent but were stronger than species-level patterns, especially for the leaf traits with the greatest intraspecific variation (SLA and succulence). Individual-level SLA exhibited the strongest evidence for both among and within-quadrat niche partitioning and indicated elevational filtering. Local niche partitioning and elevational filtering likely play an important role in maintaining species and functional diversity in the most speciose genus at our study site. Our results highlight the importance of individual variation, as it may reveal otherwise obscured niche effects.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Inputs of terrestrial organic carbon (t-OC) into lakes are often considered a resource subsidy for aquatic consumer production. Although there is evidence that terrestrial carbon can be incorporated into the tissues of aquatic consumers, its ability to enhance consumer production has been debated. Our research aims to evaluate the net effect of t-OC input on zooplankton. We used a survey of zooplankton production and resource use in ten lakes along a naturally occurring gradient of t-OC concentration to address these questions. Total and group-specific zooplankton production was negatively related to t-OC. Residual variation in zooplankton production that was not explained by t-OC was negatively related to terrestrial resource use (allochthony) by zooplankton. These results challenge the designation of terrestrial carbon as a resource subsidy; rather, the negative effect of reduced light penetration on the amount of suitable habitat and the low resource quality of t-OC appear to diminish zooplankton production. Our findings suggest that ongoing continental-scale increases in t-OC concentrations of lakes will likely have negative impacts on the productivity of aquatic food webs.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Ecological structures and processes occur at specific spatio-temporal scales, and interactions that occur across multiple scales mediate scale-specific (e.g. individual, community, local or regional) responses to disturbance. Despite the importance of scale, explicitly incorporating a multi-scale perspective into research and management actions remains a challenge. The discontinuity hypothesis provides a fertile avenue for addressing this problem, by linking measureable proxies to inherent scales of structure within ecosystems. Here we outline the conceptual framework underlying discontinuities, and review the evidence supporting the discontinuity hypothesis in ecological systems. Next we explore the utility of this approach for understanding cross-scale patterns and the organization of ecosystems by describing recent advances for examining non-linear responses to disturbance, and phenomena such as extinctions, invasions, and resilience. To stimulate new research, we present methods for performing discontinuity analysis, detail outstanding knowledge gaps, and discuss potential approaches for addressing these gaps.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Cross-ecosystem fluxes can intertwine otherwise disparate food webs, but the effects of biodiversity at the genotypic level on fluxes across ecosystems boundaries is not known. Fresh leaves, which vary in traits such as defensive compounds against terrestrial herbivores, drop off trees and enter streams, providing a vital resource for riverine organisms. We demonstrate substantial variation in decomposition rates among individual trees in four different rivers in the Olympic Peninsula of Washington State, USA. We show that locally derived red alder leaf litter decomposes on average 24% faster than red alder leaf litter introduced from other riparian zones. Within rivers, leaves downstream of their parent trees decompose nearly as quickly as leaves from local trees. Leaves upstream of the parent tree decomposed as slowly as leaves from trees growing alongside different rivers. Over time, aquatic decomposer communities have locally adapted to the specific trees supplying the riparian subsidies. In energy-limited environments, such as small shaded streams, consumers must be efficient foragers. Our results indicate that this pressure for efficiency has led to adaptation at a particularly fine scale. More broadly, these results illustrate how genetic diversity and the effects of selection in one ecosystem can indirectly shape the structure of other ecosystems through ecological fluxes across boundaries.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Environmental conditions and individual strategies in early life may have a profound effect on fitness. A critical moment in the life of an organism occurs when an individual reaches independence and stops receiving benefits from its relatives. Understanding the consequences of individual strategies at the time of independence requires quantification of their fitness effects. We explored this period in the red grouse (Lagopus lagopus scoticus). In this system, testosterone and parasite (Trichostrongylus tenuis) levels are known to influence survival and reproduction; the two key components of individual fitness. We experimentally and simultaneously manipulated testosterone and parasites at three levels (high, intermediate, and control levels for both factors) in 195 young males in 5 populations using a factorial experimental design. We explored the effects of our treatments on fitness by monitoring reproduction and survival throughout the life of all males and estimating λind, a rate-sensitive index of fitness. Parasite challenges increased the number of worms with a time lag, as previously found. However, we did not find significant effects of parasite manipulations on fitness, possibly because parasite abundance did not increase to harmful levels. Our hormone manipulation was successful at increasing testosterone at three different levels. Such increases in hormone levels decreased overall fitness. This was caused by reduced offspring production in the first breeding attempt rather than by any effect of the treatment on bird survival. Our results highlight that investing in high testosterone levels at independence, a strategy that might enhance short-term recruitment probability in territorial species such as red grouse, has a fitness cost, and can influence the resolution of the trade-off between reproduction and survival later in life.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. The study of population dynamics requires unbiased, precise estimates of abundance and vital rates that account for the demographic structure inherent in all wildlife and plant populations. Traditionally, these estimates have only been available through approaches that rely on intensive capture-recapture data. We extend recently developed N-mixture models to demonstrate how demographic parameters and abundance can be estimated for structured populations using only stage-structured count data. Our modeling framework can be used to make reliable inferences on abundance as well as recruitment, immigration, stage-specific survival, and detection rates during sampling. We present a range of simulations to illustrate the data requirements, including the number of years and locations necessary for accurate and precise parameter estimates. We apply our modeling framework to a population of northern dusky salamanders (Desmognathus fuscus) in the mid-Atlantic region and find that the population is unexpectedly declining. Our approach represents a valuable advance in the estimation of population dynamics using multi-state data from unmarked individuals and should additionally be useful in the development of integrated models that combine data from intensive (e.g., capture-recapture) and extensive (e.g., counts) data sources.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Long distance seed dispersal (LDD) is considered a crucial determinant of tree distributions, but its effects depend on demographic processes that enable seeds to establish into adults and that remain poorly understood at large spatial scales. We estimated rates of seed arrival, germination, and survival and growth for a canopy tree species (Miliusa horsfieldii), in a landscape spanning evergreen forest where the species' abundance is high to deciduous forest where it is extremely low. We then used an individual-based model (IBM) to predict sapling establishment and compare the relative importance of seed arrival and establishment in explaining the observed distribution of seedlings. Individuals in deciduous forest, far from the source population, experienced multiple benefits -- increased germination rate, new recruit height, seedling survival and growth -- from being in a habitat where conspecifics were almost absent. The net effect of these spatial differences in demographic processes was significantly higher estimated sapling establishment probabilities for seeds dispersed long distances into deciduous forest. Despite the high rate of establishment in this habitat, Miliusa is rare in the deciduous forest because arrival of seeds at long distances from the source population is extremely low. Across the entire landscape, the spatial pattern of seed arrival is much more important than the spatial pattern of establishment for explaining observed seedling distributions. By using dynamic models to link demographic data to spatial patterns, we conclude that LDD plays a pivotal role in the distribution of this tree in its native habitat.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Individual growth rates and survival are major determinants of individual fitness, population size structure and community dynamics. The relationships between growth rate, survival and temperature may thus be important for predicting biological responses to climate change. Although it is well known that growth rates and survival are affected by competition and predation in addition to temperature, the combined effect of these factors on growth rates, survival and size structure has rarely been investigated simultaneously in the same ecological system. To address this question, we conducted experiments on the larvae of two species of damselflies and determined the temperature-dependence of growth rates and survival and the resulting cohort size structure under three scenarios of increasing ecological complexity: no competition, intraspecific competition and interspecific competition. In one species, the relationship between growth rate and temperature became steeper in the presence of competitors whereas that of survival remained unchanged. In the other species, the relationship between growth rate and temperature was unaffected by competitive interactions but survival was greatly reduced at high temperatures in the presence of interspecific competitors. We also found that the combined effect of competitive interactions and temperature on cohort size structure differed from the effects of these factors in isolation. Together, these findings suggest that it will be challenging to scale up information from traditional, single-species laboratory studies to the population and community level.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Invasive pathogen - insect symbioses have been extensively studied in many different ecological niches. Whether the damage of symbioses in different introduced regions might be influenced by other microorganisms has, however, received little attention. Eight years of field data showed that the varied levels of the nematode and beetle populations and infested trees of the invasive Bursaphelenchus xylophilus-Monochamus alternatus symbiosis were correlated with patterns in the isolation frequencies of ophiostomatoid fungi at six sites, while the laboratory experiments showed that the nematode produced greater numbers of offspring with a female biased sex ratio and developed faster in the presence of one native symbiotic ophiostomatoid fungus Sporothrix sp.1. Diacetone alcohol (DAA) from xylem inoculated with Sporothrix sp.1 induced B. xylophilus to produce greater numbers of offspring. Its presence also significantly increased the growth and survival rate of M. alternatus, and possibly explains the prevalence of the nematode-vector symbiosis when Sporothrix sp.1 was dominant in the fungal communities. Studying the means by which multispecies interactions underlying biogeographical dynamics allowed us to better understanding the varied levels of damage caused by biological invasion across the invaded range.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. In various terrestrial and aquatic ecosystems, predators affect resources indirectly via intermediate prey. Such indirect interactions involve reducing the density of the prey (density-mediated indirect interactions, DMIIs) or changing the behavioral, morphological or life history traits of the prey (trait-mediated indirect interactions, TMIIs). Although the importance of TMIIs has been highlighted recently, the strengths of both DMIIs and TMIIs under natural conditions have rarely been evaluated, especially in the context of resource community structure. We studied a three-level marine food chain involving the carnivorous snail Thais clavigera, its limpet prey Siphonaria sirius and the limpet's food sources, the algae Lithoderma sp. and Ulva sp. We measured the strengths of DMIIs and TMIIs and observed how the algal community changes under the pressure of natural predation by T. clavigera on S. sirius. Neither DMIIs nor TMIIs affected the total algal cover or chlorophyll content per unit area. However, both types of indirect interactions caused similar changes in algal composition by increasing the cover of Ulva and decreasing the cover of Lithoderma. This change in the algal community was caused by a reduction in the limpet's preferential consumption of the competitively dominant Ulva over Lithoderma. These results suggest that both DMIIs and TMIIs have similar effects on the changes in resource community structure under natural conditions.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Classifying the states of an individual and quantifying transitions between states is crucial while modeling animal behavior, movement and physiologic status. When these states are hidden or imperfectly known, it is particularly convenient to relate them to appropriate quantitative measurements taken on the individual. This task is however challenging when quantitative measurements are not available at each sampling occasion. For capture-recapture data, various ways of incorporating such non-discrete information have been used, but they are either ad hoc and/or use a fraction of the available information by relying on a priori thresholds to assign individual states. Here we propose to assign discrete states based on a continuous measurement and then model survival and transition probabilities based on these assignments. The main advantage of this new approach is that a more informative use of the non-discrete information is done. As an illustrative working example, we applied this approach to eco-epidemiological data collected accross a series of years and in which individuals of a long-lived seabird, the black-legged kittiwake (Rissa tridactyla), could either be visually detected or physically recaptured and blood sampled for subsequent immunological analyses. We discuss how this approach opens many perspectives in eco-epidemiology but also more broadly in population ecology.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Knowledge from basic plant ecology suggests that impact of one plant species on another is driven by either competition for the same limiting resources, or by unique plant traits. These processes might be context specific, explaining a differential impact of exotic plant invaders in the native vs. introduced range. With the help of a conceptual framework, we aimed at identifying the relationship between invader biomass and impact in the invasive Centaurea stoebe by conducting pairwise competition experiments with 15 European (old) and 15 North American (new) neighboring species. Old neighbors grew larger and could use available soil moisture more efficiently for growth than new neighbors. Interestingly, biomass of C. stoebe explained a substantial amount of the variation in biomass of the co-evolved neighbors, but not of the new "naïve" neighbors. Thus, impact in the home range appears to be driven by competition for the same limiting resources, but by other factors in the introduced range, possibly by exploitation of resources that are not used by the new neighbors or by interference competition. This distinction has important consequences for the management of invasive species; as in our study ecosystem recovery is less likely after simple biomass reduction.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. The giant panda (Ailuropoda melanoleuca) was taken to the brink of extinction in the 1980s through a combination of deforestation, large-scale loss of bamboo in the core of its range, poaching, and zoo collection, causing over 1,000 deaths from the 1950s. It was thought that the drastic population decline was likely to impose a severe impact on population viability. Here, based on temporal genotyping of individuals we show that this rapid decline did not significantly reduce the overall effective population size and genetic variation of this species, or of the two focal populations (Minshan and Qionglai) that declined the most. These results are contrary to previously assumptions, probably because the population decline has not produced the expected negative impact because of the short time scale involved (at most 10 generations), or because previous surveys underestimated the population size at the time of decline. However, if present-day habitat fragmentation and limited migration of giant pandas remains, we predict a loss of genetic diversity across the giant pandas' range in the near future. Thus, our findings highlight the substantial resilience of this species when facing demographic and environmental stochasticity, but key conservation strategies, such as enhancing habitat connectivity and habitat restoration should be immediately implemented to retain the extant genetic variation and maintain long-term evolutionary potential of this endangered species.

Description: Ecology, Volume 0, Issue 0, Ahead of Print. Habitat loss can have a negative effect on the number, abundance, and composition of species in plant-pollinator communities. Although we have a general understanding of the negative consequences of habitat loss for biodiversity, much less is known about the resulting effects on the pattern of interactions in mutualistic networks. Ecological networks formed by mutualistic interactions often exhibit a highly nested architecture with low modularity, especially in comparison with antagonistic networks. These patterns of interaction are thought to confer stability on mutualistic communities. With the growing threat of environmental change, it is important to expand our understanding of the factors that affect biodiversity and the stability of the communities that provide critical ecosystem functions and services. We studied the effects of habitat loss on plant-pollinator network architecture and found that regional habitat loss contributes directly to species loss and indirectly to the re-organization of interspecific interactions in a local community. Networks became more highly connected and more modular with habitat loss. Species richness and abundance were the primary drivers of variation in network architecture, though species composition affected modularity. Theory suggests that an increase in modularity with habitat loss will threaten community stability, which may contribute to an extinction debt in communities already affected by habitat loss.