Autocorrelated exogenous factors and the detection of delayed density dependence

Abstract

Coupled trophic interactions with specialist predators or resources are thought to be primarily responsible for generating delayed density dependence. Previous theoretical studies suggest that autocorrelation in exogenous factors could generate apparent negative delayed density dependence in populations regulated only by direct density dependence. Using both linear and nonlinear models, we show that autocorrelated exogenous factors can generate the spurious appearance of not only negative, but also positive, delayed density dependence in populations regulated only by direct density dependence. Evidence for negative delayed density dependence is found mainly in populations exhibiting monotonic deterministic stability, whereas evidence for positive delayed density dependence is found mainly in populations exhibiting damped or persistent two-point cycles, or more complex deterministic dynamics. We argue that fluctuating resources (e.g., mast seeding) in bottom-up controlled communities could qualify as autocorrelated exogenous factors and cause apparent delayed density dependence in the population of their consumers.