Prey heterogeneity and the presence of weak trophic interactions are commonly thought to stabilize predator-prey interactions and promote community persistence. Prior theoretical explorations of such processes have focused largely on long-term community dynamics and effects on point/nonpoint equilibria. However, most ecologists recognize that many natural systems experience temporally varying environmental conditions that can buffet populations and drive population trajectories far from equilibrial conditions. The effects of prey heterogeneity on such transitory dynamics have received much less attention. Here we present a mathematical and experimental exploration of the effects of prey heterogeneity and enrichment on the transitory dynamics and persistence of predator-prey interactions. We first parameterized a nonlinear predator-prey model using a laboratory-based zooplankton-phytoplankton system composed of a rotifer as top predator, an edible alga (as its prey) and an inedible alga (as a weakly interacting prey species) . We then numerically explored the short-term and long-term dynamics of this system for a range of enrichment and dilution levels in the presence or absence of the inedible prey species. Predictions were then tested experimentally under controlled laboratory conditions.
Results/Conclusions
Model results generated contrasting predictions of the effects of prey heterogeneity on transitory dynamics and the probability of system persistence. Presence of the inedible prey stabilized the dynamics of the edible prey, reducing the amplitude of transitory fluctuations. However, inedible prey also created long transitory periods of low abundance of the edible prey. Consequently, predators experienced long periods of low abundance following initial population peaks, increasing the probability of predator extinction. This effect was particularly pronounced under high enrichment levels and low dilution rates. When exploring long-term dynamics of the system, model results were similar to previous studies, with the presence of inedible prey reducing the amplitude of predator and edible prey population oscillations. The magnitude of this stabilizing effect was reduced at higher levels of enrichment. Experimental results largely supported model predictions. Edible prey experienced smaller amplitude transitory oscillations in the presence of the inedible alga. However, presence of the inedible alga increased the probability of extinction of the zooplankton-predator; extinctions after initial predator population peaks occurred in all replicates at low enrichment levels and in two of three replicates at high enrichment levels. As predicted, higher dilution rates decreased the probability of predator extinction.
