Abstract

Ecologists know that simple nonlinear models can generate fixed points, periodic cycles, and aperiodic oscillations in population abundance without any external environmental variation. Another familiar theoretical result is that shifts in demographic parameters (such as survival or fecundity) can move a population from one of these behaviors to another. Unfortunately, empirical evidence to support these theoretical possibilities is scarce. We designed a joint theoretical and experimental study to test the hypothesis that changes in demographic parameters cause predictable changes in the nature of population fluctuations. Specifically, we developed a simple model describing population growth in the flour beetle Tribolium. We then predicted, using standard mathematical techniques to analyze the model, that changes in adult mortality would produce substantial shifts in population dynamic behavior. Finally, by experimentally manipulating the adult mortality rate we observed changes in the dynamics from stable fixed points, to periodic cycles, to aperiodic oscillations that corresponded to the transitions forecast by the mathematical model.