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The evolutionary response of plants to root herbivory.
Watts, Sean*,1, Reichman, O. 1, 1 University of California, Santa Barbara, Santa Barbara, CA, USA
ABSTRACT- Most work conducted on plant-herbivore interactions has focused on aboveground herbivory. Plants, however, suffer greater negative consequences from belowground herbivory. We investigated the capacity for plants to evolve in response to root herbivory by comparing populations of two grassland forbs (Eschscholzia californica and Hemizonia fasciculate) on the California Channel Islands, which have no record of gophers, and mainland areas with high densities of gophers. We used this system to test the hypothesis that, due to the absence of root herbivory, island plant species have a reduced capacity to both deter and tolerate root loss. Island and mainland plants were collected to determine if island plant forms contain less defensive compounds than mainland conspecifics. In addition, we censused island and mainland populations to determine if island plant forms exhibit lower fecundity and greater mortality in response to simulated belowground herbivory. Results from the 2002 field season indicate that the roots of mainland Eschscholzia californica are defended by a greater amount and greater variety of alkaloid compounds. Censuses conducted after simulated root herbivory showed greater mortality among island Hemizonia fasciculat and a delayed recovery in island Eschscholzia californica which translated to lower total annual reproduction relative to mainland populations. In addition to characterizing the evolutionary responses of island and mainland plants to root herbivory, this set of experiments should contribute to a comprehensive, understanding of the ecological tradeoffs between growth, defense and reproduction in plants.
Key words: gophers, roots, herbivory