Citation:

Heinrichs, J., J. Lawler, AND N. Schumaker. Intrinsic and extrinsic drivers of source-sink dynamics. Ecology and Evolution. Wiley-Blackwell Publishing, Hoboken, NJ, 6:892-904, (2016).

Impact/Purpose:

Human activities impact plant and animal populations. Researchers explore how these anthropogenic disturbances alter the viability of valued species, but there are too many such systems for every one to be studied independently. This complexity creates a need for general principles that can be applied in cases where system-specific research is not available to inform decision making. This paper develops such general principles by relating landscape structure, disturbance, and species’ life history in the context of demographic source-sink models. The results show that the importance of individual habitat patches can start to become predictable when only basic information about species and disturbance are known.

Description:

1. 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. 2. 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. 3. 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 the spatial source-sink dynamics that emerged from the simulated population and habitat parameters. Long-term differences in births and deaths among sources and sinks in each system were measured and used in a statistical model to rank the influences of key factors. 4. 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, that also experience relatively stable environments (i.e., fewer negative perturbations), are more likely to exhibit strong source-sink dynamics. 5. 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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