While the effects of resource pulses are well-studied in the ecological literature, and the effects of pulses are often quite different from those of constant resource input. In the light of the large effects of bottom-up pulses, it is surprising that top-down pulses, such as those originating from temporal variation in predation, have been largely ignored. Temporal variability in predation can stem from movement among patches by mobile predators, consumer aggregations, burst breeding events or life-history transitions by predators with complex life histories. This variability in predation pressure could have important implications for our understanding of the direct and indirect effects of predator-prey interactions on food webs. Here, we explore the effects of pulsatile consumption on both consumer population dynamics and the strength of trophic cascades. Using a simple logistic growth model, we compared the population size, extinction risk, and time until extinction for populations with predation occurring constantly, stochastically, or cyclically. We then expanded our model to three trophic levels and tested the effects of these three types of temporal variability in predation on the strength of trophic cascades and contrasts them with the effects of resource pulses.
Results/Conclusions
We found that pulsed predation resulted in lower population sizes, and that differences in prey population size between constant and pulsed predation was greatest when predation events were large, infrequent, and when the prey population growth rate was low. Additionally, when predation pulses were stochastically timed, prey population sizes were lower than cyclically spaced predation events. Similarly, prey populations were more likely to go extinct when predation events were large and infrequent. In our three trophic-level model, predator pulses decreased the strength of trophic cascades. Pulsed predation also altered oscillations among all trophic levels, and for comparable magnitudes, had similar effects on changes in equilibrium population size as resource pulses. These findings indicate that the inclusion of temporal variability in predator-prey dynamics can have important effects on species interactions and should be incorporated into studies of population dynamics and trophic cascades.