Testing metapopulation models with stream-fish assemblages

We assessed the utility of simple metapopulation models in an analysis of a decade (1976-86) of stream-fish censuses at 10 sites on the Cimarron River , Oklahoma. This assemblage is a good candidate for metapopulation analysis because there was substantial annual turnover of population, with frequent local extinctions and recolonizations. However, annual probabilities of co lonization and extinction were usually not correlated with the fraction of sites occupied, a key prediction of many Levins-style metapopulation models . Instead, these probabilities were related to position in the stream gradi ent. For most species, colonization was less likely and extinction more lik ely in upstream than downstream sites. Consequently, the simple Levins-styl e metapopulation models failed to accurately predict the dynamics of most s pecies. Metapopulation models that incorporate spatial variability in colon ization and extinction probabilities may be more successful for populations that are distributed across environmental gradients.