EFFECTS OF CHRONIC PESTICIDE STRESS ON WILDLIFE POPULATIONS IN COMPLEX LANDSCAPES: PROCESSES AT MULTIPLE SCALES

摘要

Populations exposed to pesticides may often be divided into subpopulations, where some subpopulations are exposed to pesticides and others are not. We consider three models for such populations. The first is a simple discrete time model with no density-dependent reproduction. The second is a continuous time model that includes density- dependence for populations not exposed to pesticides. In both models, populations exposed to pesticides are assumed to decline geometrically (exponentially in the continuous time model). Migration between exposed and safe habitat patches is symmetric, so that all individuals leaving safe patches enter exposed patches and vice versa. The rate is assumed to be the same for both kinds of patches. The conditions for persistence of the population in the landscape are the same for both models. Increasing migration rate between patches decreases the ability of the population to persist. Populations that have low rates of increase in safe habitat patches have greater difficulty persisting than those with high rates of increase in safe patches. The toxicity of the pesticide also affects population persistence. More toxic pesticides that result in higher rates of death and/or lower rates of birth in exposed habitat patches lower the ability of the population to persist in the landscape. We consider an additional set of models of a metapopulations that persist because of a balance between colonization and local extinction. In such systems, pesticides may endanger regional persistence by reducing the pool of sites available for colonization. We conclude with an outline of important future directions for theoretical research intended to elucidate the impact of pesticides on populations spatially complex landscapes.