Historical, abiotic, and biotic drivers influence contemporary lacustrine fish community composition in the glacial Lake Agassiz basin

Historical determinants and local ecological filters tend to drive community assembly at large and smaller spatiotemporal scales, respectively. We examined the effects of differential contact to the Wisconsinan deglaciation dispersal corridor, Lake Agassiz, and habitat heterogeneity and species interactions on contemporary lacustrine fish community composition in 261 northwestern Ontario lakes. Species composition varied significantly across lakes grouped by their most recent glacial lake coverage, driven by turnover, and the number of connections (not-covered, single, and secondary contact) to the dispersal corridor over time, explained by nestedness. Maximum lake depth, elevation, and most recent stage of glacial lake coverage were dominant drivers of community composition patterns; and most of the significant species co-occurrence relationships were positive. While the dominant environmental variables reflect the effects of habitat heterogeneity and isolation from the dispersal corridor, the species co-occurrence analysis results reflect the influence of environmental niche filtering and biotic interactions in shaping lacustrine fish communities. The spatiotemporal evolution of Lake Agassiz played a role as a historical determinant, and habitat heterogeneity and local species interactions were ecological determinants.