The effect of density dependence on community structure

The effect of population density controls on the relationship between stability and species richness was explored by constructing Monte Carlo community models with density dependent population controls. Simulated communities with more initial species exhibit proportionally fewer extinctions. This form of stability is greatest at low interaction strengths and intermediate connectivities. Stability appeared to be related to the fact that species with more interactions were less likely to be driven to extinction by negative interactions. Species with mutualistic (+ / +) and commensal (0/ +) interactions survive at greater than expected proportions, while those with relatively more competitive (− / −) and amensal (0 / −) interactions tend toward extinction. Incorporation of density dependent population control thus leads to features that previous community models have not exhibited. It is suggested that communities with many of the populations controlled by abiotic factors in a density dependent fashion should exhibit increased stability with more species.