Dispersal drives changes in fish community abundance in intermittent stream networks

Abstract

Increasing trends in fragmentation and dewatering of streams warrants research on how populations and communities respond to varying water levels and barriers to movement. Although these responses are complicated by many spatial and temporal processes, long‐term datasets might help reveal complex patterns and processes driving variability in species abundances. The objective of this study was to develop a predictive framework for fish community and population responses to varying levels of water availability across six sites in two intermittent stream networks sampled >10 years. We predicted that fishes would emigrate into intermittent reaches during wet conditions; thus, overall abundances within perennial source locations will decline. Accordingly, when intermittent reaches dry, fishes will contract to wetted habitats resulting in high abundance. Observed fish community abundances were highly variable within and among study sites, but four of six sites matched our predictions. A tagging study confirmed these results and demonstrated a substantial proportion of individuals moved away from perennial reaches and into newly wetted intermittent reaches. However, site and species‐specific relationships were variable and likely depended on the habitat, metacommunity dynamics, and life history strategies. Findings suggest that species dispersal dynamics, in addition to recruitment and mortality, should be carefully considered when interpreting species responses to varying water lev…