Overcompensation in Response to Mammalian Herbivory: Measure of True Fitness, Alternative Selection Pressures, Compara- tive Responses, and the Genetics of Overcompensation

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Over the past decade, there has been a heated debate surrounding the potential beneficial effects of herbivores on plants. Up to now, the problem of resolving the question as to whether herbivory could ever be good for plants has been that convincing data have not been published. However, recent experimental and observational studies showed that when mule deer and elk browsed the monocarpic biennial, scarlet gillia, Ipomopsis aggregata, relative fitness in terms of seed production and subsequent seedling survival averaged 2.4 times that of the uneaten contols. In light of these results, over compensation cannot be easily dismissed, although more information is needed on potential beneficial effects of herbivores on plants. It is necessary to understand the interactions between plants and their herbivores at many levels in much greater detail. The goals of this project are: 1. To examine the long-term fitness effects of herbivory; 2. To examine the effects of secondary herbivory on plant growth and reproduction; 3. To determine if there are selection pressures other than herbivory potentially involved in producing the observed response patterns (e.g., fire and frost damage); 4. To initiate molecular genetic studies in an effort to understand some of the potential genetic mechanisms involved in overcompensation; and 5. To begin comparative studies on two additional diverse sites to see how common overcompensation by scarlet gilia is and to begin to understand something of the evolution of such a response. The results of these studies have the potential for making important contributions to both basic and applied fields of ecology, evolutionary biology and agriculture.