Effects of stream topology on ecological community results from neutral models

While neutral theory and models have stimulated considerable literature, less well investigated is the effect of topology on neutral metacommunity model simulations. We implemented a neutral metacommunity model using two different stream network topologies, a widely branched network (wide tree) and a narrowly branched network (high tree), both represented as binary trees. The wide tree had fewer exceedances of carrying capacity, higher final number of individuals per community, and greater community (α) diversity than the high tree. The difference in diversity increased with increasing dispersal rate. We infer that the greater connectivity of the wide tree facilitated more even spatial dispersal, which limited carrying capacity exceedances and associated random deletions, which, in turn, resulted in higher diversity. Effects specifically due to topology should be considered in analyses of community patterns for mobile aquatic species.