Date of Award

Fall 12-1-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Advisor

Steven L. Lima

Second Advisor

Michael J. Angilletta

Third Advisor

William A. Mitchell

Abstract

Despite its ecological importance, the concept of prey naivete has become a biological truism that receives little study. I explored the evolution of naivete and its likely influence on two major ecological patterns: a) the historically greater destructiveness of freshwater predator introductions, and b) the greater strength of aquatic trophic cascades. In a review of the ecological literature, I demonstrate that the conditions for the evolution of naivete (isolation) exist in freshwater habitats at multiple spatial scales. In addition, I show that freshwater prey exhibit naivete which could be responsible for the high impacts of freshwater predator introductions. I then construct theoretical models which show that, when vulnerability to predators is involved in tradeoffs with foraging ability, prey naivete can result in strong trophic cascades. Thus, the relative strength of freshwater cascades could be due to the presence of na'ive freshwater herbivores. I then conducted a meta-analysis oflog response ratios of 76 trophic cascade studies. I show that greater species turnover is generally associated with stronger trophic cascades. In addition, I demonstrate that density-mediated indirect effects appear to be unimportant in dictating cascade strength in diverse systems. Lastly, I conducted a mesocosm experiment to explore the capacity of species turnover to enhance trophic cascades. I established 32 floating, 1000 liter mesocosms and manipulated herbivore community heterogeneity in three separate treatments. I found that homogenous herbivore communities produce inva1iant trophic cascades. In summary, it appears that prey naivete is an important factor in driving ecological differences between freshwater and terrestrial systems.

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