Nestedness patterns and dispersal dynamics in tropical central Indian stream fish metacommunities

Abstract

Dispersal processes, such as immigration and extinction rates, and habitat properties play a crucial role in determining species composition and nestedness patterns within communities. In the current global scenario of changing environmental conditions and habitat fragmentation, information on the role of natural dispersal mechanisms and disturbance factors are especially important for understanding dynamics of species composition changes in stream ecosystems. We investigated spatial and temporal patterns of nestedness of fish communities in tropical stream systems of central India and the relationship of various dispersal factors (immigration–extinction rates and their variability) with habitat properties (habitat size and heterogeneity) and anthropogenic disturbances. We tested predictions of the classical model by Schlosser on immigration–extinction dynamics along longitudinal gradients in stream community composition for these streams. The results revealed significant patterns of nestedness for all study sites. Sites exposed to varying degrees of disturbance (induced by human activities) showed lower nestedness than undisturbed ones. Immigration rates did not show strong relations with nestedness but extinction rates were significantly related (negatively) to nestedness. In addition, disturbance played an important role in determining immigration rates and variability in immigration rates. Stream characteristics, such as habitat-size and habitat-variability gradients, were not statistically significant predictors of immigration and extinction rates. Our results demonstrate the influence of local anthropogenic disturbances on dispersal dynamics of species. A reduction in availability of suitable habitats could lower immigrations.