Patterns in the diversity of the world's land vertebrate genera

Background: The number of species of terrestrial vertebrate in one of the world's great zoological regions fits a linear combination of area (A) and one climatic variable - either annual actual evapotranspiration (AE) or mean annual temperature (T) - with an R2 of 0.97. The same is true of species diversity in the four separate classes of terrestrial vertebrate; their R2-values range from 0.90 to 0.95. Goals: Determine whether the number of genera, G, fits the same or a similar pattern. Measure the relationship between G and S (the number of species). Estimate the effect of total breakdown of biogeographical barriers on G. Data: The global terrestrial vertebrate data sets of the World Wildlife Fund. We used 755 of their 825 ecoregions and all 24,992 species in those 755 ecoregions. The WWF ecoregion data sets have names, locations, ID numbers, areas, and 102 climatic variables. Results: The patterns for area, temperature, AE, and genera closely follow the patterns for species. Area, by itself, significantly fit the number of genera in the zoological regions. But a linear combination of log A and log AE significantly improved that fit. It closely and significantly fit log G (R20.972). The same was true of a linear combination of log A and T (R20.964). Each of the separate classes of vertebrate exhibited the same patterns as total G, although their R2-values were slightly less. Neither climate variable was significant by itself in any case. G also fit the number of species very closely (R20.99). The fit is a power function with a coefficient of 0.77, so that there are more species per genus in provinces with high than low diversity. The Neotropics (most diverse) have 5.22 species per genus; Hawaii (least diverse) has 1.74 species per genus. The advent of the Homogocene (complete homogenization of the world's zoological regions) would cause the extinction of 49% of her terrestrial vertebrate genera, leaving sustainable only 2239 of the 4416 now sustainable. In addition, loss of natural terrestrial area would further reduce sustainable G. For example, loss of 80% of the area (the currently sanctioned international hope is to protect 20%) would lead to the extinction of 54% more genera, leaving only 1021.