Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

M. Deane Bowers

Second Advisor

William D. Bowman

Third Advisor

Michael Breed

Fourth Advisor

Alexander Cruz

Fifth Advisor

Lee A. Dyer

Abstract

Ripe, fleshy fruits function primarily to attract mutualist animals; however, many wild fruits contain secondary metabolites that are distasteful or toxic to consumers. A number of hypotheses have been proposed to explain this apparent evolutionary paradox, but few have been tested experimentally. The goal of my dissertation research was to investigate the evolutionary ecology of fruit chemical traits, integrating quantitative chemical analyses with experiments to elucidate the functional significance of fruit secondary metabolites in natural populations. I conducted a series of field studies using three groups of plants, one temperate and two tropical. First, using the tropical shrub Hamelia patens (Rubiaceae), I investigated the potential for leaf herbivory to affect seed dispersal and showed that plant responses to herbivory can alter fruit chemistry and reduce fruit removal by seed-dispersing birds. Next, using detailed chemical analyses and field observations of fruit-frugivore interactions in the temperate shrub Lonicera x bella (Caprifoliaceae), I showed that fruits can contain higher levels of secondary metabolites than leaves, and that these metabolites serve an important role in defense against insects and pathogens. Finally, using additional chemical analyses and controlled experiments with the tropical plant genus Piper (Piperaceae), I showed that fruit secondary metabolites can be explained as a trade-off between defense against antagonists and attraction of seed-dispersing bats. Together, this dissertation demonstrates the importance of fruit chemical traits in mediating interactions between plants and diverse antagonistic and mutualistic consumers and represents a significant contribution to our understanding of both seed dispersal and plant defense.

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