Extinctions in simple and complex communities

Disagreement exists between the results of theoretical and empirical exploration into the effect of increasing community complexity on the stability of multispecies ecosystems. A recent return to interest in this area suggests previous results should be re-assessed, from both experimental studies and models, to understand where this discrepancy arises from. Here we propose various simple extensions to a standard multispecies community model that each increase the complexity of the system in a different way. We find that increasing the number of species in a community leads to a decrease in community persistence after the system is perturbed, and go on to show that increasing the dynamical diversity of the community members leads to an increase in stability through a reduction in extinction events, relative to the less complex form of the model. Our results suggest that different forms of complexity lead to different outcomes in the stability properties of the community. While aspects of this work agree with previous empirical findings that more complex communities are more robust to perturbation, we stress that the type of complexity included and the measure of stability used in community models must be properly defined, to allow objective comparisons to be made with previous and future work.