TESTING MODELS OF SOURCE-SINK DYNAMICS AND BALANCED DISPERSAL

I discuss two classes of models that predict patterns of dispersal acr oss heterogeneous environments: the source-sink and balanced dispersal models. Data collected during a long-term study of small mammals in a n experimentally fragmented landscape support the predictions of the b alanced dispersal model. In addition, a literature review indicates th at for 28 species, Few empirical studies have enough detailed demograp hic data to distinguish between assumptions of the two models and to t est their predictions. The review indicates both models are poorly sup ported by empirical studies and many of the studies cited as evidence for source-sink dynamics cannot distinguish a sink habitat from a habi tat with a low carrying capacity. I conclude that a continuum should e xist between species vagility and the dispersal patterns seen in heter ogeneous landscapes. Species with high vagility and the ability to ass ess habitat quality should lend towards balanced dispersal. In species with low vagility or where dispersal is controlled by abiotic factors (wind, or water currents), source-sink dynamics will be more common. Investigators must collect detailed demographic and movement data if t hey hope to test these models and further our understanding of the rol e of spatial dynamics in ecology.