Regional Species Pools and the Assembly of Local Ecological Communities

We model the sequential assembly of species into communities, using a notion of permanence from dynamical-systems theory, to investigate effects of species pools on the development of local communities. The results show that communities built from species-rich pools develop more slowly to invasion-resistant states. Fewer basal species are found locally where species are rich in consumers, although specialization by the consumers for different kinds of prey enables more basal species to exist locally. The invasion-resistant states eventually achieved by such an assembly process may be single communities or cyclic sequences of communities uninvadable by species not in the cycle. These endstates of assembly are properties of the species pool, and the form they take depends on the nature of the pool. If made rich enough, species pools cause saturation of local communities such that the number of species present locally becomes uncoupled from the richness of the pool.