Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Pamela K. Diggle

Second Advisor

Yan B. Linhart

Third Advisor

Deane Bowers

Abstract

The diversity of flower structure and flowering characteristics in angiosperms has long inspired researchers to study evolutionary mechanisms that have produced it. Darwin's recognition of many apparent flower adaptations to pollinators led to a focus on animal pollinators as selective forces, but recently, the importance of simultaneously considering other selective agents has been recognized. Particularly, herbivores can select for plant traits, and can interact with or limit selection by pollinators in complex ways. Assemblages of pollinators and herbivores can vary greatly among plant populations. In plants with generalized pollination systems and multiple herbivores, the potentially complex effects of these biotic selective forces may lead to local adaptation. Conversely, conflicting selection by multiple herbivores and pollinators may limit local adaptation and maintain variation within populations. Erysimum capitatum (Brassicaceae) is a widespread and variable plant species with generalized pollination that is attacked by a number of herbivores. I studied interactions of E. capitatum with pollinators and herbivores in four populations over an elevational gradient in the Rocky Mountains, and tested for local adaptation to suites of pollinators and herbivores. I used observational and experimental methods in natural populations, and performed a common garden experiment using plants grown from two of the original four source populations. Plant traits varied among natural populations, and individuals of E. capitatum were visited by diverse groups of pollinators and herbivores that shifted in abundance and importance in time and space. Both pollinators and herbivores preferentially visited plants with more flowers, and herbivory reduced pollinator visitation in some populations and years. Pollinators did not select on plant traits in any year or population, but herbivores sometimes selected for plant traits. These results suggest that plant plasticity may mediate interactions with both pollinators and herbivores. Pollination and herbivory both changed plant fitness, but I found no signs of local adaptation to pollinators and herbivores in the common garden experiment. However, non-local plants did have lower reproductive success than local ones, and may be locally adapted to other factors.

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