Testing macroecology models with stream-fish assemblages

We measured species-level probabilities of colonization and extinction from a decade (1976–86) of stream-fish censuses at 10 sites on the Cimarron River, Oklahoma. In a macroecological analysis that controlled for phylogenetic relationships among the 41 species, we used body size, average population size, area of geographic range and distance to the centre of the geographic range as correlates of colonization and extinction probabilities. Average population size was the single best predictor of both colonization and extinction probabilities. Additionally, extinction probabilities were marginally greater for large-bodied than small-bodied species, and larger for species in which the census sites were closer to the edge than the centre of the geographic range. Ignoring phylogeny masked the edge-of-range and body size effects on extinction. Overall, our results confirm that species-level traits are correlated with standardized estimates of extinction and colonization probabilities within large assemblages of species. These analyses may be useful in applied conservation problems where direct estimates of extinction and colonization probabilities cannot be obtained.