Spatiotemporal Variation in Dispersal as a Driver of Macroinvertebrate Metacommunity Dynamics

Abstract

Across taxa, community assembly has traditionally been attributed to local processes such as species competition and environmental filtering. Metacommunity theory, however, highlights regional drivers such as dispersal and connectivity as key structuring forces. The mechanisms governing freshwater macroinvertebrates community assemblage have long been studied due these organism's ubiquity, diversity, and sensitivity to environmental stressors. Macroinvertebrates reliance on river networks for their larval stages also makes their dispersal complex, and therefore crucial to frame their assemblages in a metacommunity context. While metacommunity theory has been widely applied to macroinvertebrate community ecology within the last 15 years, the spatial and temporal variability of dispersal across networks is still poorly understood. To address this gap, we conducted a year-long survey of the macroinvertebrate communities in the Little Stoney Creek watershed of Giles County, Virginia. Macroinvertebrates were sampled once a month for 12 months from the benthos and drift at eight sites across a gradient from headwaters to mainstem to discover if there was any difference in community dynamics between poorly connected sites (headwaters) and well connected sites (mainstems) across seasons. Broadly, we hypothesized that mainstem sites would have less temporal variability in community dynamics compared to headwater sites due to mass effects and high dispersal rates. We found high temporal variability in dispersal and the subsequent correlation of dispersal assemblages with the resident benthic community across sites, but only weak evidence to suggest that this variation varies between headwaters and mainstems. However, considering the stochastic and difficult to model nature of macroinvertebrate drift dispersal, we consider the existence of even weak evidence of spatial differences to be promising. Further study of macroinvertebrate dispersal in metacommunities is needed to better understand the complex mechanisms governing macroinvertebrate communities, particularly in the context of biomonitoring applications.