Understanding the processes that shape colonization is central to explaining the distribution of organisms in the environment. In order for passively dispersing organisms to colonize new habitats a physical mode of transport is required. In aquatic systems flowing water can alter dispersal rates by providing a mechanism for passive dispersers to overcome physical barriers. We test flooding effects in system of hundreds of riverine rock pools to determine its impact on community structure. This study aimed to determine whether rock pool communities are distinct from those found in the adjacent river channel and the degree to which within-year variation in inundation increases similarity of community composition. We hypothesized that river flooding events increase dispersal of organisms into pools and that those inundated with higher frequency are more similar to river communities and each other than those more isolated from the river. We randomly sampled macroinvertebrate communities in both the pools and river channel, and categorized pools by their elevation to estimate frequency of flooding. We examined species composition, alpha diversity, and used a test of homogeneity of multivariate dispersions to assess differences in beta diversity among groups.
Results/Conclusions
We observed 39 taxa in pools versus 15 in river samples. Abundant taxa differed between pools and the river. The most abundant organisms found in the pools were larval mosquitoes and non-biting midges, pulmonated pond snails, and amphipods; while the river samples were dominated by gilled snails, amphipods and flatworms. All taxa observed in the river samples were also present in rock pools, i.e., the river community was a nested subset of the regional rock pool community. These differences in composition suggest rock pool communities are colonized from both lentic and lotic regional species pools. Preliminary results show there was no significant difference in alpha diversity between the river sites and pools. However, there was a significant difference between the river channel samples and the rock pools in their multivariate dispersion, indicating that community composition was more variable in pools than the river channel. However, beta diversity was similar across rock pools from different elevations. Collectively, these data suggest that while flooding is necessary for passive dispersal of river taxa into pools, dispersal of river organisms is not sensitive to finer-scale temporal variation in rock pool flooding frequency.