Developing an Original Metacommunity Theory Framework for Freshwater Fish Assemblages in Nigerian River Basins: Patch Dynamics, Species Sorting, and Dispersal Limitation

This dissertation develops and empirically tests an original metacommunity theory framework for freshwater fish assemblages across four major Nigerian river basins spanning the North Central, South East, and South South geopolitical zones. Existing metacommunity frameworks were developed predominantly in temperate contexts, and their applicability to tropical African rivers with distinctive hydrological regimes, degradation gradients, and seasonality is untested. The dissertation employs a three-phase methodological design: a comprehensive fish community survey across 60 sites in the Cross, Anambra, Benue, and lower Niger basins using standardised electrofishing and netting; genetic connectivity analysis using population-level microsatellite genotyping to quantify dispersal among sites; and a modelling phase integrating community, environmental, and dispersal data under variation partitioning and spatially explicit metacommunity simulation frameworks. The dissertation proposes the Nigerian River Metacommunity Model (NRMM) as an original theoretical contribution, which identifies species sorting as the dominant assembly process at the within-basin scale and dispersal limitation as dominant across basin divides, with a context-dependent transition zone along major confluence systems. This finding diverges from patch dynamics predictions applied to temperate rivers. The NRMM further demonstrates that human-modified sites exhibit metacommunity decoupling, where community-environment relationships are disrupted by non-random anthropogenic filters. Original contributions include the NRMM theoretical framework, the 60-site multi-basin survey dataset, and a dispersal-informed conservation prioritisation algorithm for Nigerian freshwater biodiversity management. Keywords: metacommunity theory, freshwater fish, Nigerian river basins, species sorting, dispersal limitation.