ALBERT

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: Abstract 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. This article is protected by copyright. All rights reserved.

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. This article is protected by copyright. All rights reserved.

Description: Abstract The elasticity of hcp‐Fe‐5wt%Si has been investigated by synchrotron X‐ray diffraction up to 110 GPa and 2100 K, and by picosecond acoustics measurements at ambient temperature up to 115 GPa. The established Pressure‐Volume‐Temperature (PVT) equation of state shows that the density of the Earth's inner core can be matched by an Fe‐Si alloy with 5wt% Si for all reasonable core temperatures, but that its compressional and shear velocities remain too high with respect to seismological observations. On the other hand, Fe‐Si alloys whose velocities are expected to get close to seismological observations are too dense at relevant temperatures. Thus, based on these combined velocity‐density measurements, silicon is not likely to be the sole light element in the inner core.

Description: Untangling the spatial and temporal processes that influence population dynamics of migratory species is challenging, because changes in abundance are shaped by variation in vital rates across heterogeneous habitats and throughout the annual cycle. We developed a full-annual-cycle, integrated population model and used demographic data collected between 2011 and 2014 in southern Indiana and Belize to estimate stage-specific vital rates of a declining migratory songbird, the Wood Thrush ( Hylocichla mustelina ). Our primary objective was to understand how spatial and temporal variation in demography contributes to local and regional population growth. Our full-annual-cycle model allowed us to estimate: 1) age-specific, seasonal survival probabilities, including latent survival during both spring and autumn migration, and 2) how the relative contribution of vital rates to population growth differed among habitats. Wood Thrushes in our study populations experienced the lowest apparent survival rates during migration and apparent survival was lower during spring migration than during fall migration. Both mortality and high dispersal likely contributed to low apparent survival during spring migration. Population growth in high-quality habitat was most sensitive to variation in fecundity and apparent survival of juveniles during spring migration, whereas population growth in low-quality sites was most sensitive to adult apparent breeding-season survival. These results elucidate how full-annual-cycle vital rates, particularly apparent survival during migration, interact with spatial variation in habitat quality to influence population dynamics in migratory species.

Description: Determining the geographic connections between breeding and nonbreeding populations, termed migratory connectivity, is critical to advancing our understanding of the ecology and conservation of migratory species. Assignment models based on stable isotopes historically have been an important tool for studying migratory connectivity of small-bodied species, but the low resolution of these assignments has generated interest into combining isotopes with other sources in information. Abundance is one of the most appealing data sources to include in isotope-based assignments, but there are currently no statistical methods or guidelines for optimizing the contribution of stable isotopes and abundance for inferring migratory connectivity. Using known-origin stable-hydrogen isotope samples of six Neotropical migratory bird species, we rigorously assessed the performance of assignment models that differentially weight the contribution of the isotope and abundance data. For two species with adequate sample sizes, we used Pareto optimality to determine the set of models that simultaneously minimized both assignment error rate and assignment area. We then assessed the ability of the top models from these two species to improve assignments of the remaining four species compared to assignments based on isotopes alone. We show that the increased precision of models that include abundance is often offset by a large increase in assignment error. However, models that optimally weigh the abundance data relative to the isotope data can result in higher precision and, in some cases, lower error than models based on isotopes alone. The top models, however, depended on the distribution of relative breeding abundance, with patchier distributions requiring stronger downweighting of abundance, and we present general guidelines for future studies. These results confirm that breeding abundance can be an important source of information for studies investigating broad-scale movements of migratory birds and potentially other taxa. Stable isotopes are critical tools for determining the migratory connectivity of small migratory species, and they are increasingly combined with data on breeding abundance under the assumption that this improves prediction. Unfortunately, this assumption is unfounded: Abundance data nearly always dominate migratory connectivity predictions, reducing the contribution of the useful isotope data and inflating error. Using known-origin stable hydrogen isotopes samples for six Neotropical migratory bird species, we show that weighting abundance data can improve assignment performance but that the spatial distribution of abundance influences the optimal weighting combinations.

Description: ABSTRACT The southernmost terrestrial extent of the Irish Sea Ice Stream (ISIS), which drained a large proportion of the last British–Irish Ice Sheet, impinged on to the Isles of Scilly during Marine Isotope Stage 2. However, the age of this ice limit has been contested and the interpretation that this occurred during the Last Glacial Maximum (LGM) remains controversial. This study reports new ages using optically stimulated luminescence (OSL) dating of outwash sediments at Battery, Tresco (25.5 ± 1.5 ka), and terrestrial cosmogenic nuclide exposure dating of boulders overlying till on Scilly Rock (25.9 ± 1.6 ka), which confirm that the ISIS reached the Isles of Scilly during the LGM. The ages demonstrate this ice advance on to the northern Isles of Scilly occurred at ∼26 ka around the time of increased ice-rafted debris in the adjacent marine record from the continental margin, which coincided with Heinrich Event 2 at ∼24 ka. OSL dating (19.6 ± 1.5 ka) of the post-glacial Hell Bay Gravel at Battery suggests there was then an ∼5-ka delay between primary deposition and aeolian reworking of the glacigenic sediment, during a time when the ISIS ice front was oscillating on and around the Llŷn Peninsula, ∼390 km to the north. Copyright © 2017 The Authors. Journal of Quaternary Science Published by John Wiley & Sons, Ltd.

Description: The Yellowknife Bay formation represents a ~5 m thick stratigraphic section of lithified fluvial and lacustrine sediments analyzed by the Curiosity rover in Gale crater, Mars [ Grotzinger et al ., 2014 ]. Previous works have mainly focused on the mudstones that were drilled by the rover at two locations. The present study focuses on the sedimentary rocks stratigraphically above the mudstones by studying their chemical variations in parallel with rock textures. Results show that differences in composition correlate with textures and both manifest subtle but significant variations through the stratigraphic column. Though the chemistry of the sediments does not vary much in the lower part of the stratigraphy, the variations in alkali elements indicate variations in the source material and/or physical sorting. as shown by the identification of alkali feldspars. The sandstones contain similar relative proportions of hydrogen to the mudstones below, suggesting the presence of hydrous minerals that may have contributed to their cementation. Slight variations in magnesium correlate with changes in textures suggesting that diagenesis, through cementation and dissolution modified the initial rock composition and texture simultaneously. The upper part of the stratigraphy (~1m thick) displays rocks with different compositions suggesting a strong change in the depositional system. The presence of float rocks with similar compositions found along the rover traverse suggests some of these outcrops extend further away in the nearby hummocky plains.