Patch spatial attributes and time to disturbance affect the emergence of source local populations within ephemeral habitats

Abstract

Understanding the demography of local populations within ephemeral habitat patches is crucial for effective local (site-based) conservation management in spatially and temporally heterogeneous environments. Evidence suggests that species persisting in networks of ephemeral patches often exhibit source-sink dynamics, where certain local populations act as temporary sources at some time between initial colonization and patch disappearance due to disturbance. Here we present an individual-based demographic model inspired by Cabrera voles (Microtus cabrerae) in dynamic agricultural mosaics to test the hypothesis that the emergence of a source local population within an ephemeral habitat patch is largely driven by the combined effects of the patch spatial attributes (size, internal quality and connectivity to other hypothetical patches) and the time to disturbance (i.e. the patch lifespan). We focused on two key emergent demographic metrics quantifying the source-sink status of local populations based on their self-sustainability and potential contribution to other patches. We used sensitivity analyses to estimate the strength of linear associations between these metrics and the patch spatial attributes, and to quantify the main and interaction effects across different patch lifespans since initial colonization. Our model revealed that considerable spatial and temporal variation may emerge in local populations’ source-sink status based on differences in patch size, internal quality, connectivity, and lifespan. According to predictions, patch internal quality correlated positively with local population self-sustainability and potential contribution to other patches, though the strength of these relationships was mostly relevant only after about three vole generation times (ca. one year) since initial colonization, and only in combination with the positive effects of patch size and connectivity. Accordingly, results also supported the prediction that the emergence of a temporary source local population is conditional to the longevity of the habitat patch, with short patch lifespans (less than about three vole generation times) greatly limiting local population self-sustainability and potential contribution to other patches. While empirical testing is needed to confirm these findings, our study strengthens the view that local management efforts focusing on reducing or mitigating disturbance (e.g. severe droughts, human farming activities) at large and well-connected high-quality patches will likely promote the occurrence of temporary source local populations, which should be crucial for long-term species persistence over larger spatial scales.