Document: NOR-3-23-9

Diversity in plant quality, herbivore movement, and herbivore population dynamics.

UNDERWOOD, N.*

University of California, Davis, CA 95616 USA ¹

Abstract:
Many empirical studies have examined how plant diversity (mono- versus polyculture) affects herbivore population size. Most of these studies have focused on how the number of non-host plant species in a community affects herbivore populations on a host-plant. However, the suitability of plants as hosts can vary continuously among species and especially within species (among genotypes or ecotypes). A more general question about the effect of plant diversity on herbivores is thus how the amount and kind of variation in quality among plant types affects the dynamics of herbivore populations. Many aspects of diversity in plant quality may affect herbivore populations, including the range (coefficient of variation) and distribution (skewness and kurtosis) of variation in quality among types. I use mathematical modeling to explore how these and other aspects of plant diversity affect herbivore dynamics. Results show that the degree and distribution of variability among plants, and the pattern of herbivore movement should affect the way that plant types combine in their effects on herbivore populations. Even when herbivores move at random, herbivore dynamics on mixtures are not equal to the average of their dynamics on individual plant types (monocultures). Low-quality plants contribute disproportionately to the size of herbivore populations on plant mixtures, so that as the variation among plants increases herbivore populations are more strongly influenced by low-quality plants.

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This abstract is being presented at: 1:05 PM in session:
Symposium # 23: Why Variation is Not Just Noise: The Influence of Variability on Plant-Herbivore and Plant-Pathogen Interactions.