PULSED PREDATION DETERMINES FRESHWATER POND COMMUNITY ASSEMBLY

Abstract

Historically, community ecologists have assumed constant consumer pressure when modeling predator-prey interactions, however, we know that interactions in most natural systems are dynamic. Inconstant predation may account for some discrepancies between natural ecosystems and model predictions and recent theoretical work shows that episodic pulsed predation events can have strong, destabilizing effects on the persistence and equilibrium densities of prey populations. In this study we conducted an experiment modeled after natural systems (such as intermittent streams, temporary ponds, and periodically flooded riverine rock pools) that experience episodic introductions and removals of predators. Specifically we created 32 artificial freshwater ponds and applied one of four different bluegill sunfish predation treatments: no predation, constant predation, and two magnitudes of stochastically pulsed predation (one or five fish). Pulses consisted of 24-hour introductions of predators to pools, and by the end of the experiment constant predation and large pulses had experienced equivalent predator exposure. We compared both macroinvertebrate diversity and several metrics estimating microbial function to determine the effects of pulsed predation on assembly and structure of communities. We found that pulsed predation resulted in communities with different overall abundance and diversity when compared to constant predation. In addition, the magnitude of predation pulses in environments appears to be key in determining their effect on communities, as the small pulse of fish resulted in communities more similar to control treatments while large pulse treatments resulted in communities more similar to constant fish presence. Microbial community function was high in all tanks, resulting in low free nitrogen in this experiment and thus we cannot conclusively link microbial community function to pulsed fish predation. Understanding how predation pulses structure ecosystems and invertebrate communities improves our general understanding of processes regulating consumer-resource interactions and can improve our ability to predict community responses to increasingly unpredictable environmental change.