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SummaryMany factors affect the presence and exchange of individuals among subpopulations and influence not only the emergence, but the strength of ensuing source–sink dynamics within metapopulations. Yet their relative contributions remain largely unexplored. To help identify the characteristics of empirical systems that are likely to exhibit strong versus weak source–sink dynamics and inform their differential management, we compared the relative roles of influential factors in strengthening source–sink dynamics. In a series of controlled experiments within a spatially explicit individual‐based model framework, we varied patch quality, patch size, the dispersion of high‐ and low‐quality patches, population growth rates, dispersal distances, and environmental stochasticity in a factorial design. We then recorded source–sink dynamics that emerged from the simulated habitat and population factors. Long‐term differences in births and deaths were quantified for sources and sinks in each system and used in a statistical model to rank the influences of key factors. Our results suggest that systems with species capable of rapid growth, occupying habitat patches with more disparate qualities, with interspersed higher‐ and lower‐quality habitats, and that experience relatively stable environments (i.e., fewer negative perturbations) are more likely to exhibit strong source–sink dynamics. Strong source–sink dynamics emerged under diverse combinations of factors, suggesting that simple inferences of process from pattern will likely be inadequate to predict and assess the strength of source–sink dynamics. Our results also suggest that it may be more difficult to detect and accurately measure source–sink dynamics in slow‐growing populations, highly variable environments, and where a subtle gradient of habitat quality exists.

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Contemporary climate change is causing large shifts in biotic distributions 1 , which has the potential to bring previously isolated, closely related species into contact 2 . This has led to concern that hybridization and competition could threaten species persistence 3 . Here, we use bioclimatic models to show that future range overlap by the end of the century is predicted for only 6.4% of isolated, congeneric species pairs of New World birds, mammals and amphibians. Projected rates of climate-induced overlap are higher for birds (11.6%) than for mammals (4.4%) or amphibians (3.6%). As many species will have di culty tracking shifting climates 4 , actual rates of future overlap are likely to be far lower, suggesting that hybridization and competition impacts may be relatively modest.Widespread changes in species distributions due to climate change are documented for diverse taxa and are expected to become more pronounced over the coming century as rates of warming increase 1 . One expected outcome of climate change-induced range shifts is the establishment of geographic range overlap among previously isolated taxa, leading to novel species interactions and assemblages 5,6 . The potential for climate change to result in new interactions among closely related species has given rise to conservation concern, as these may have negative consequences for species persistence. Climate-induced range contact between ecologically similar species may introduce high levels of interspecific competition to populations already stressed by changing climatic conditions 7,8 . In addition, recently diverged species with incomplete reproductive barriers may hybridize, reducing population fitness through genetic admixture or leading to species extinctions through asymmetric hybridization 9,10 . Although few studies have empirically documented climate-induced contact among closely related species 2 , many have expressed concern that it could lead to a significant loss of biodiversity 3,11 .Despite potential for negative impacts, no attempt has yet been made to estimate future rates of climate-induced geographic overlap among previously isolated, closely related species. We used bioclimatic models to predict potential end-of-century (2071-2100) areas of climatic suitability for 9,577 congeneric species pairs, including New World birds (n = 3,858), mammals (n = 1,661) and amphibians (n = 4,058). From this data set, we calculated the number of nonoverlapping (that is, allopatric), congeneric species pairs with ranges projected to come into contact (that is, sympatry) in the coming century. We accounted for variability among estimates by including in our results only species pairs projected to come into contact under a majority (>5) of 10 general circulation models (GCMs).We found that 6.4% of 4,796 allopatric species pairs are projected to come into geographic contact by the end of the century (Fig. 1). Rates of future contact for species pairs were significantly greater for birds than mammals or amphibians (generalized linear mixed mode...

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Population sinks present unique conservation challenges. The loss of individuals in sinks can compromise persistence; but conversely, sinks can improve viability by improving connectivity and facilitating the recolonization of vacant sources. To assess the contribution of sinks to regional population persistence of declining populations, we simulated source-sink dynamics for 3 very different endangered species: Black-capped Vireos (Vireo atricapilla) at Fort Hood, Texas, Ord's kangaroo rats (Dipodomys ordii) in Alberta, and Northern Spotted Owls (Strix occidentalis caurina) in the northwestern United States. We used empirical data from these case studies to parameterize spatially explicit individual-based models. We then used the models to quantify population abundance and persistence with and without long-term sinks. The contributions of sink habitats varied widely. Sinks were detrimental, particularly when they functioned as strong sinks with few emigrants in declining populations (e.g., Alberta's Ord's kangaroo rat) and benign in robust populations (e.g., Black-capped Vireos) when Brown-headed Cowbird (Molothrus ater) parasitism was controlled. Sinks, including ecological traps, were also crucial in delaying declines when there were few sources (e.g., in Black-capped Vireo populations with no Cowbird control). Sink contributions were also nuanced. For example, sinks that supported large, variable populations were subject to greater extinction risk (e.g., Northern Spotted Owls). In each of our case studies, new context-dependent sinks emerged, underscoring the dynamic nature of sources and sinks and the need for frequent re-assessment. Our results imply that management actions based on assumptions that sink habitats are generally harmful or helpful risk undermining conservation efforts for declining populations.

Wildfires change plant community structure and impact wildlife habitat and population dynamics. Recent wildfire-induced losses of big sagebrush (Artemisia tridentata) in North American shrublands are outpacing natural recovery and leading to substantial losses in habitat for sagebrush-obligate species such as greater sage-grouse. Managers are considering restoration strategies that include planting container-grown sagebrush to improve establishment within areas using more conventional seeding methods. Although it is thought that planting sagebrush provides initial structural advantages over seeding, empirical comparisons of sagebrush growth are lacking between individuals established postfire using both methods. Using a Bayesian hierarchical approach, we evaluated sagebrush height and canopy area growth rates for plants established in 26 seeded and 20 planted locations within the Great Basin. We then related recovery rates to previously published nesting habitat requirements for sagegrouse. Under average weather conditions, planted or seeded sagebrush will require 3 or 4 years, respectively, and a relatively high density (≥2 plants/m 2) to achieve the minimum recommended canopy cover for sage-grouse (15%). Sagebrush grown in warmer and drier conditions met this cover goal months earlier. Although planted sagebrush reached heights to meet sagegrouse nesting requirements (30 cm) 1 year earlier than seeded plants, seeded individuals were approximately 19 cm taller with 410 cm 2 more canopy area than planted sagebrush after 8 years. However, big sagebrush establishment from seed is unreliable. Strategically planting small, high-density patches of container-grown sagebrush in historic sage-grouse nesting habitat combined with lower density seedings in larger surrounding areas may accelerate sage-grouse habitat restoration.