Abstract
Many 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.
Highlights
Spatial variation in habitat quality is the basic factor that structures source–sink dynamics in heterogeneous landscapes (Pulliam 1988; Dias 1996)
Rapid extinction precluded analysis of this specific scenario, but of those that reached steady state, the weakest source–sink dynamics were produced by systems with the lowest fecundity and patch quality disparity
In an effort to help identify the characteristics of systems that are likely to exhibit strong source–sink dynamics, we compared the roles of influential factors in strengthening source–sink dynamics in a series of controlled simulation experiments to generate hypotheses for future exploration with empirical data
Summary
Spatial variation in habitat quality is the basic factor that structures source–sink dynamics in heterogeneous landscapes (Pulliam 1988; Dias 1996). Demographic surpluses in higher-quality habitats (e.g., sources) and deficits in lower-quality habitats (e.g., sinks) commonly arise, and movement among local populations can stabilize dynamics at regional scales (Dias 1996). Species and population factors such as growth rates, dispersal abilities, and demographic responses to environmental variability can affect the severity of source–sink dynamics, driving sources, and sinks to become more or less extreme. These habitat and population factors have been individually
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