Date of Award

Spring 1-1-2011

Document Type

Thesis

Degree Name

Master of Arts (MA)

Department

Ecology & Evolutionary Biology

First Advisor

Samuel M. Flaxman

Second Advisor

Christy M. McCain

Abstract

This study examined predator-prey interactions to determine which sources of information available to individuals influenced their movement and habitat selection across a heterogeneous landscape. I tested observed spatial distributions of organisms against predictions of a general interference ideal free distribution model to determine whether mobile predators, prey, or both achieve optimal distributions. To do so, I incorporated habitat selection treatments in which there were (1) prey but no predators, (2) predators but no prey, and (3) predators and prey simultaneously. For these experiments, I used a tritrophic system in which seven-spotted lady beetles (Coccinella septempunctata L., Coleoptera: Coccinellidae), pea aphids (Acyrthosiphon pisum (Harris), Hemiptera: Aphididae), and tic bean plants (Vicia faba L., Fabaceae) were, respectively, the predators, prey, and prey's resource. In microcosms, I created and quantified patches of varying quality (from the perspective of the prey) among which predators and prey were allowed to move freely. I also examined intraspecific competition between beetle predators by determining the coefficient of interference for the beetles. Theoretical studies of tritrophic systems have given rise to the general prediction that predators should aggregate where prey's resource is of the highest quality, not necessarily where prey are most abundant. This suggests a general adaptive strategy of information use for predators: assess the quality of the prey's resource and spend more time where those resources are better. Empirically testing this and other predictions of models is important for advancing understanding of how spatial distributions are impacted by trophic interactions. My research quantified measures of individual fitness, intra-specific competition, and inter-species interactions in order to test predictions of a general interference model with mobile predators and prey. For this model, I integrate and systematically assess qualities important within a natural system, such as competition and intrinsic growth rates across patches. My results show that predators were able to detect and respond to the quality of their prey's resource. Furthermore, both predators and prey followed predicted spatial distributions of simultaneous ideal free distribution. The joining of theoretical and empirical studies is critical for improving understanding of distributions and abundances of organisms in nature.

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