Metacommunity Dynamics and Environmental Filtering of Aquatic Macroinvertebrates Across a River Network in Benue State, North Central Nigeria

Metacommunity theory provides a powerful conceptual framework for understanding how local and regional processes jointly determine species distributions across interconnected habitat patches, yet its empirical application to tropical African river networks is almost entirely absent from the literature. This study applies a metacommunity analytical framework to aquatic macroinvertebrate communities across a dendritic river network in Benue State, encompassing main channel, tributary, and headwater habitats of the Katsina-Ala and Donga river systems. Macroinvertebrates were sampled at seventy-two sites using standardised methods, and local environmental variables, spatial connectivity variables, and regional dispersal limitation metrics were quantified simultaneously. Variation partitioning, multiple regression on distance matrices, and element of metacommunity structure analysis were applied to decompose the relative contributions of environmental filtering, spatial processes, and their interactions to community composition variation. Results show that environmental filtering, primarily mediated by current velocity, substrate type, and water temperature, accounted for the largest unique fraction of community variation (31 percent), while spatial processes contributed a smaller but significant fraction (14 percent) consistent with limited dispersal effects in headwater taxa. Interaction fractions were substantial, indicating scale-dependent coupling of environmental and dispersal processes. Headwater communities showed stronger dispersal limitation than main channel communities. The study provides the first metacommunity analysis for a Nigerian river network, advancing fundamental ecological understanding and identifying implications for bioassessment design that must account for spatial autocorrelation in macroinvertebrate data interpretation. Keywords: metacommunity, macroinvertebrates, river network, Benue State, environmental filtering.