Dissertation Research: Examining Anti-predator Cascades Over Four Trophic Levels

Purdue University, West Lafayette IN

Investigators

Abstract

Predators can affect prey populations in complex ways. Predators that eat herbivores, for example, can reduce herbivore pressure on plant communities directly by consuming the herbivores or indirectly through what is known as "non-consumptive effects". Non-consumptive effects often occur when the mere presence of a predator causes prey species to reduce feeding activity to avoid being eaten, themselves. This anti-predator behavior has important impacts on herbivore survival and likely on the plants that would otherwise be eaten by the herbivores. Such effects on plants are further complicated by the fact that many predators are omnivorous, feeding on both plants and animals. This project examines how ground beetles, which eat seeds, and mice, which eat both seeds and ground beetles, influence each other and affect the abundance of a common plant (lambsquarters), whose seeds they consume. Because lambsquarters is a weed species of agricultural importance, results of this study have direct implications for weed management by farmers. This project will provide interdisciplinary training for a graduate student and will involve mentorship of an undergraduate researcher. Concepts and results of this project are being integrated into Purdue's teaching curriculum, and will be presented at scientific conferences, as well as at farmer-focused agricultural conferences. This work will also be interpreted for the public at various outreach events including farm tours, Master Gardener courses, and educational webinars. More specifically, this project will use a seed predator food web to examine the environmental and behavioral factors that drive complex predator-prey interactions over multiple trophic levels. Preliminary data suggest that predator-mediated use of refuge by rodents interferes with beetle activity and seed removal. Reductions in seed removal by beetles in the presence of mice could be attributed to intra-guild predation (consumptive effects) or anti-predator vigilance (non-consumptive effects; NCEs). These two distinct, but non-mutually exclusive trophic pathways have different long-term implications for plant population dynamics. This project will build on these concepts with an experiment on seed-foragers' responses to predation risk. It will address three specific questions: 1) Is seed predation affected by NCEs of intra-guild predators? 2) Do structural refuges mediate NCEs on seed predation? 3) Does refuge habitat affect the frequency of vertebrate/invertebrate predation events? The experiment will examine how granivore foraging behavior on seeds of lambsquarters is impacted by the presence of predators and the availability of protective cover.