Spatial Heterogeneity and Biogeographical Division of the Ichthyofauna of Northern Eurasia

A biogeographical division of northern Eurasia (within the USSR borders as of 1991) based on cluster analysis of the cyclostome and fish fauna composition at 597 sites listed in the Biodat database has been performed. The classification based on the Jaccard similarity coefficients included two regions, 12 subregions, eight provinces, and 11 districts. The division performed explained 67% of the variance of the similarity coefficients, this being 21% higher than the respective value for an earlier scheme (Berg, 1962) that covered a significantly greater territory. Correlation with the climatic regimes and environmental factors identified could explain 82% of fish fauna heterogeneity (the multiple coefficient of correlation was 0.91). The nonorthogonal relations with the temperature regime (67% of the variance of similarity coefficients), landscape and climatic zoning (58%), location within a specific river basin (57%), and provinciality (30%) were the most important factors.