Density-dependence and stability in stochastic environments: Shaky-ball vs. shaky-bowl

Background/Question/Methods

Understanding how ecological systems respond to environmental perturbations is a primary focus of contemporary ecology. The characteristic return rate, intuitively the ability of a system to return to its equilibrium after perturbations, is often synonymous or a proxy to the stability of a system. Although theoretical and numerous empirical studies support that relationship, it is based on the same structural assumption: the influence of perturbations on growth rate is additive, i.e., perturbations are x-multiplicative. In this work, we explored the influence of perturbation on the carrying capacity, i.e., K-multiplicative.

Results/Conclusions

We found that as the characteristic return rate increases, stability decreases. The reverse relationship holds for most theoretical models and is illustrated with two empirical example of population (Euphranta connexa) and tritrophic aquatic foodweb dynamics--strong density-dependence can increase the variability of the system. Our results underscore the complex interactions between deterministic and stochastic drivers in a system and the need of a diverse approach to implement stochasticity in ecological modeling.