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Humans are dominant global drivers of ecological and evolutionary change, rearranging ecosystems and natural selection. In the present article, we show increasing evidence that human activity also plays a disproportionate role in shaping the eco-evolutionary potential of systems—the likelihood of ecological change generating evolutionary change and vice versa. We suggest that the net outcome of human influences on trait change, ecology, and the feedback loops that link them will often (but not always) be to increase eco-evolutionary potential, with important consequences for stability and resilience of populations, communities, and ecosystems. We also integrate existing ecological and evolutionary metrics to predict and manage the eco-evolutionary dynamics of human-affected systems. To support this framework, we use a simple eco–evo feedback model to show that factors affecting eco-evolutionary potential are major determinants of eco-evolutionary dynamics. Our framework suggests that proper management of anthropogenic effects requires a science of human effects on eco-evolutionary potential.

Natural hybrid zones can be used to dissect the mechanisms driving key evolutionary processes by allowing us to identify genomic regions important for establishing reproductive isolation and that allow for transfer of adaptive variation. We leverage wholegenome data in a system where two bird species, the saltmarsh (Ammospiza caudacuta) and Nelson’s (A. nelsoni) sparrow, hybridize despite their relatively high background genetic differentiation and past ecological divergence. Adaptive introgression is plausible in this system because Nelson’s sparrows are recent colonists of saltwater marshes, compared to the specialized saltmarsh sparrow that has a longer history of saltmarsh adaptation. Comparisons among whole-genome sequences of 34 individuals from allopatric and sympatric populations show that ongoing gene flow is shaping the genomic landscape, with allopatric populations exhibiting genome-wide F ST estimates close to double of that observed in sympatry. We characterized patterns of introgression across the genome and identify regions that exhibit biased introgression into hybrids from one parental species. These regions offer compelling candidates for genes related to tidal marsh adaptations suggesting that adaptive introgression may be an important consequence of hybridization. These findings highlight the value of considering the landscapes of both genome-wide introgression and divergence when characterizing the evolutionary forces that drive speciation.

While foraging, animals often trade off between food and safety, reducing feeding in response to increased predation risk. This response, however, may not be a viable option for animals that are energetically compromised. Many single-species studies have shown that hungry animals select habitats within which foraging opportunities are greater even if predation pressures are higher, but it is unclear whether these patterns can be extrapolated to entire communities. Here, we examined the stopover habitat use of 28 frugivorous landbird species along the coast of Maine, USA, during an energetically demanding period of the annual cycle, fall migration. Across 6 stopover sites, we determined whether or not a tradeoff existed between using safe habitat patches (patches with high woody plant stem density) and patches with high food resources (patches with high fruit abundance). Controlling for raptor abundance at a site, landbird migrants were captured at higher rates in sites where no tradeoff existed, suggesting that birds avoided staying in sites where there was a predation risk–foraging tradeoff. At all sites, regardless of the presence or absence of a tradeoff, longer-distance migrants used patches with high food availability more frequently than shorter-distance migrants; patch use by shorter-distance migrants was explained by habitat cover alone. Our findings suggest that, for the Gulf of Maine, birds reduce predation risk at the scale of a stopover site, and differences in habitat selection at finer patch scales are mediated by migration strategy.

Primary and secondary male sexual traits can influence the interspecific interactions of hybridizing populations, yielding fitness consequences and either promoting or restricting gene flow. In this study, we evaluated the relative male fitness of two species of hybridizing tidal marsh endemics: saltmarsh (Ammospiza caudacutus) and Nelson's sparrows (A. nelsoni) and assessed the effects of male condition and competitive ability on resulting patterns of paternity and gene flow. We compared reproductive success (number of offspring sired) among saltmarsh, Nelson's, and hybrid sparrow males (n = 125) and modeled male fitness in relation to measured pre‐copulatory (body size, fat scores, and muscle scores) and post‐copulatory (cloacal protuberance (CP) volume and sperm length) male sexual traits across two sites within the center of the hybrid zone. We found saltmarsh sparrows had higher levels of skew in fertilization success than Nelson's and greater reproductive output than both Nelson's and hybrids, suggesting interspecific competition may occur. Body size was the best predictor of reproductive success, independent of male genotypes, providing evidence for a role of pre‐copulatory sexual selection. We also found evidence of post‐copulatory sexual selection and sperm competition contributing to patterns of hybridization, with CP volume and sperm length increasing with number of offspring sired. Differential mean fitness by species may influence patterns of hybridization and has the potential to drive asymmetrical introgression; however, the drivers of male fitness differed between species and sites, suggesting the level of sexual selection and resulting patterns of gene flow are context dependent and not stable across a small sptatial scale within the center of this mosaic hybrid zone. Overall, few interspecific offspring and nearly equal backcrossing in both parental species within the center of the hybrid zone suggest mechanisms such as reinforcement exist to limit hybridization and minimize asymmetric introgression. We used SNP genotypes to assess and compare male reproductive success in two inter‐breeding species of marsh sparrow—saltmarsh and Nelson's sparrow—and their hybrids. Saltmarsh sparrow males had higher reproductive output, greater variance in reproductive success, and higher levels of multiple paternity than Nelson's sparrows and hybrids. We found evidence for both pre‐copulatory (body size) and post‐copulatory (sperm competition) sexual selection, with drivers of fitness differing between the two species. Photo shows a pair of mating saltmarsh sparrows (credit: Grace McCulloch).

Many bird species nest in precarious, unpredictable locations to decrease the risk of predation. Although it is likely that many species have adapted behaviors to deal with stochastic habitats, there is currently limited evidence of plastic behavior increasing avian fecundity in the wild. Virginia Rails (Rallus limicola) and Soras (Porzana carolina) live in the littoral zones of wetlands that experience high hydrologic variability. During the summers of 2010 and 2011, we tested for the effects of hydrology and behavioral plasticity on the survival of Virginia Rail (n = 75) and Sora (n = 22) nests across 10 wetlands in Maine, USA. We identified the best predictors of both (1) nesting success at individual nests and (2) mean nesting success at the site level, using logistic-exposure models and an information-theoretic approach. Daily nesting survival was 98% for both species, and apparent nest survival was 31 of 85 nests, or 63.5%. Ninety percent of all nesting failures was from predation. Hydrology had a positive effect on nesting survival, and deeper, more variable water levels increased both individual nesting survival and mean site-level nest survival. Both species added material to their nests throughout the season in response to water-level increases, and we found that this behavioral plasticity had a positive effect on nesting survival. We caution that more variable water depths than those observed during our 2 yr of study could lead to increases in flood-related nest loss, because these birds require a delicate balance: the water must be deep enough to deter predators, yet shallow enough that they can build up their nests to prevent flooding during rain events. More information is needed on the extent of this behavior across marsh birds and other bird species.

While it is clear that many migratory behaviors are shared across taxa, generalizable models that predict the distribution and abundance of migrating taxa at the landscape scale are rare. In migratory landbirds, ephemeral concentrations of refueling birds indicate that individual behaviors sometimes produce large epiphenomena in particular geographic locations. Identifying landscape factors that predict the distribution and abundance of birds during migratory stopover will both improve our understanding of the migratory process and assist in broad, regionally relevant conservation. In this study we used autumnal passerine stopover data from a five‐year period and eleven stopover sites across coastal Maine, USA, to test four broad hypotheses of migrant distribution and abundance that have been supported in other regions: a) the community characteristics of the pool of potential migrants, b) a site's local geography, c) landscape composition and configuration measured at different spatial scales, and d) interactions between these factors. Our final model revealed that birds concentrate at ‘habitat islands’, sites that possess a disproportionate percentage of the vegetated habitat in the 4‐km surrounding landscape. The strength of this pattern, however, was inversely proportional to a species' remaining migratory distance. Our results corroborate several studies that emphasize the importance of land cover composition at finer spatial scales (< 80 km²) for predicting the stopover distribution and abundances of migratory birds. This suggests that different migrants likely assess stopover sites with similar mechanisms along their migratory route, and these commonalities may be broadly applied to identify stopover locations of conservation importance across the continent.

Background Exploring hybrid zone dynamics at different spatial scales allows for better understanding of local factors that influence hybrid zone structure. In this study, we tested hypotheses about drivers of introgression at two spatial scales within the Saltmarsh Sparrow ( Ammospiza caudacuta ) and Nelson’s Sparrow ( A. nelsoni ) hybrid zone. Specifically, we evaluated the influence of neutral demographic processes (relative species abundance), natural selection (exogenous environmental factors and genetic incompatibilities), and sexual selection (assortative mating) in this mosaic hybrid zone. By intensively sampling adults (n = 218) and chicks (n = 326) at two geographically proximate locations in the center of the hybrid zone, we determined patterns of introgression on a fine scale across sites of differing habitat. We made broadscale comparisons of patterns from the center with those of prior studies in the southern edge of the hybrid zone. Results A panel of fixed SNPs (135) identified from ddRAD sequencing was used to calculate a hybrid index and determine genotypic composition/admixture level of the populations. Another panel of polymorphic SNPs (589) was used to assign paternity and reconstruct mating pairs to test for sexual selection. On a broad-scale, patterns of introgression were not explained by random mating within marshes. We found high rates of back-crossing and similarly low rates of recent-generation (F1/F2) hybrids in the center and south of the zone. Offspring genotypic proportions did not meet those expected from random mating within the parental genotypic distribution. Additionally, we observed half as many F1/F2 hybrid female adults than nestlings, while respective male groups showed no difference, in support of Haldane’s Rule. The observed proportion of interspecific mating was lower than expected when accounting for mate availability, indicating assortative mating was limiting widespread hybridization. On a fine spatial scale, we found variation in the relative influence of neutral and selective forces between inland and coastal habitats, with the smaller, inland marsh influenced primarily by neutral demographic processes, and the expansive, coastal marsh experiencing higher selective pressures in the form of natural (exogenous and endogenous) and sexual selection. Conclusions Multiple drivers of introgression, including neutral and selective pressures (exogenous, endogenous, and sexual selection), are structuring this hybrid zone, and their relative influence is site and context-dependent.

Diversification rates vary greatly among taxa. Understanding how species-specific traits influence speciation rates will help elucidate mechanisms driving biodiversity over broad spatio-temporal scales. Ecological specialization and range size are two hypothesized drivers of speciation rates, yet each mechanism predicts both increases and decreases in speciation. We constructed a continuous index of specialization using avian bill morphology to determine the relative effect of specialization and range size and shape on speciation rates across 559 species within the Emberizoidea superfamily, a morphologically diverse New World clade. We found a significant positive correlation between specialization and speciation rate and a negative correlation with range size. Only the effect of specialization persisted after removing island endemics, however, suggesting that ecological specialization is an important driver of diversity across large macroevolutionary scales, and the relative importance of specific drivers may differ between islands and continents.

Linking genotype to phenotype is a primary goal for understanding the genomic underpinnings of evolution. However, little work has explored whether patterns of linked genomic and phenotypic differentiation are congruent across natural study systems and traits. Here, we investigate such patterns with a meta‐analysis of studies examining population‐level differentiation at subsets of loci and traits putatively responding to divergent selection. We show that across the 31 studies (88 natural population‐level comparisons) we examined, there was a moderate (R2 = 0.39) relationship between genomic differentiation (FST) and phenotypic differentiation (PST) for loci and traits putatively under selection. This quantitative relationship between PST and FST for loci under selection in diverse taxa provides broad context and cross‐system predictions for genomic and phenotypic adaptation by natural selection in natural populations. This context may eventually allow for more precise ideas of what constitutes “strong” differentiation, predictions about the effect size of loci, comparisons of taxa evolving in nonparallel ways, and more. On the other hand, links between PST and FST within studies were very weak, suggesting that much work remains in linking genomic differentiation to phenotypic differentiation at specific phenotypes. We suggest that linking genotypes to specific phenotypes can be improved by correlating genomic and phenotypic differentiation across a spectrum of diverging populations within a taxon and including wide coverage of both genomes and phenomes.

Demographic rates are rarely estimated over an entire species range, limiting empirical tests of ecological patterns and theories, and raising questions about the representativeness of studies that use data from a small part of a range. The uncertainty that results from using demographic rates from just a few sites is especially pervasive in population projections, which are critical for a wide range of questions in ecology and conservation. We developed a simple simulation to quantify how this lack of geographic representativeness can affect inferences about the global mean and variance of growth rates, which has implications for the robust design of a wide range of population studies. Using a coastal songbird, saltmarsh sparrow Ammodramus caudacutus, as a case study, we first estimated survival, fecundity, and population growth rates at 21 sites distributed across much of their breeding range. We then subsampled this large, representative dataset according to five sampling scenarios in order to simulate a variety of geographic biases in study design. We found spatial variation in demographic rates, but no large systematic patterns. Estimating the global mean and variance of growth rates using subsets of the data suggested that at least 10–15 sites were required for reasonably unbiased estimates, highlighting how relying on demographic data from just a few sites can lead to biased results when extrapolating across a species range. Sampling at the full 21 sites, however, offered diminishing returns, raising the possibility that for some species accepting some geographical bias in sampling can still allow for robust range-wide inferences. The subsampling approach presented here, while conceptually simple, could be used with both new and existing data to encourage efficiency in the design of long-term or large-scale ecological studies.