Quantifying the effects of multiple processes on local abundance: a cohortapproach for open populations

A challenge for species with demographically open populations is to evaluat e the relative importance of various processes that together set local abun dance. We developed a cohere-based framework for quantifying the influence of an external supply of colonists and subsequent density-independent and d ensity-dependent mortality on local abundance. Two complementary approaches - based on limitation and elasticity - revealed the nature of interactions and nonlinearities among these processes. Data for an Indo-Pacific reef fi sh were used to document the settler-survivor relationship and to quantify natural variation in settlement. Limitation by density-dependence was two-f old and 20-fold greater than by supply or density-independent mortality, re spectively. Elasticity analyses showed that adult abundance was 40% more se nsitive to small proportionate changes in supply than in density-dependence . These techniques provide a way to compare across systems, which could enh ance our ability to draw general conclusions regarding the processes that s hape local abundance of species with open populations.