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 Riv er, Oklahoma. In a macroecological analysis that controlled for phylogeneti c relationships among the 41 species, we used body size, average population size, area of geographic range and distance to the centre of the geographi c range as correlates of colonization and extinction probabilities. Average population size was the single best predictor of both colonization and ext inction probabilities. Additionally, extinction probabilities were marginal ly greater for large-bodied than small-bodied species, and larger for speci es 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 siz e effects on extinction. Overall, our results confirm that species-level tr aits are correlated with standardized estimates of extinction and colonizat ion probabilities within large assemblages of species. These analyses may b e useful in applied conservation problems where direct estimates of extinct ion and colonization probabilities cannot be obtained.