The effects of network shape and perturbation on food web persistence

Abstract

Global change is altering ecological communities and the food webs they support, reducing food web persistence. While a variety of features likely impact the dynamics of perturbed food webs, the relative importance of intrinsic factors (i.e. characteristics of the food web itself) and extrinsic factors (i.e. the type of perturbation experienced) is still unclear. Food web shape, which I define jointly by the species richness distribution and the biomass distribution across trophic levels, may be a useful tool in understanding persistence dynamics. I use a size-based food web model to investigate how 1) persistence dynamics vary across different food web shapes, and 2) how food web shape interacts with perturbation type (pulse, press, and periodic pulse) to influence species loss and biomass change over time. I show that while food webs in the natural world can take on all forms of biomass and species richness distribution, these shapes aren’t likely stable without external forcing on the system, and that food webs with bottom-heavy species distributions are the most persistent. In addition, I show that when perturbed, the number of species lost and magnitude of change in biomass is driven jointly by endogenous mechanisms (i.e. food web shape), and exogenous mechanisms such as the trophic level of the perturbed species. These findings can be useful when forecasting how communities of interest may react to increasingly turbulent perturbation regimes caused by anthropogenic global change.