An analysis of homogenization and differentiation of Canadian freshwater fish faunas with an emphasis on British Columbia

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Abstract
Faunal homogenization and differentiation occur when geographic regions show increased or decreased, respectively, similarity to each other in species composition owing to introductions and extinctions or extirpations. I used species presence–absence data for "native" (i.e., estimated species compositions before European settlement) and "total" (i.e., including nonnative fishes and extinctions) faunas to examine faunal similarity of freshwater fishes among aquatic ecoregions of British Columbia and among Canadian provinces and territories. British Columbia ecoregions showed faunal differentiation as the mean Jaccard's faunal similarity coefficient for total faunas was significantly less than that for native faunas (31.4% versus 34.9%), but some ecoregions showed homogenization (e.g., Vancouver Island and Columbia River ecoregions). Comparisons across Canada showed low but significant homogenization; average pairwise Jaccard's coefficient was higher in total versus native faunas (29.1% similarity versus 27.8%, respectively). British Columbia's fish fauna increased the most in similarity to other areas (except the three territories), with an average increase of 4.9%. Native faunal similarity patterns are part of Canada's natural heritage but are threatened by human-mediated increases in nonnative species and extinctions. This analysis provides a baseline to track changes in inter regional faunal relationships at different geographic scales.

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