Wednesday, August 8, 2007 - 8:40 AM

COS 71-3: Herbivore dynamics facilitate invasive plants in coastal meadows

Emily K. Gonzales1, Peter Arcese1, and David R. Clements2. (1) University of British Columbia, (2) Trinity Western University

Plant communities around the world are becoming dominated by nonnative species. While the dominance of non-native plants suggests that competitive displacement is driving community structure, we present comparative and experimental evidence that native herbivores reduce the abundance of native species and facilitate non-native species through selective herbivory and seed dispersal. To do so, we:

1. Quantified the demographic success of focal native species under herbivory and competition treatments crossed in a 4-yr, 2x2 factorial experiment; 2. Compared general measures of native and non-native species in the plant community; 3. Tested whether forage preferences of black-tailed deer were consistent with the relative abundance of native and non-native plant functional groups; and 4. Collected deer pellets and examined the composition of species that could be dispersed via endozoochory. The positive feedback dynamics of non-native species and selective herbivory, competition, and endozoochory had yet to be demonstrated for native herbivores and we found that: 1. Herbivory dramatically reduced the demographic success of native herbaceous and woody species while competition had no measurable effect; 2. Some extant native forbs exhibited herbivore-avoidance strategies while sexual reproduction was nearly eliminated by herbivory for other native species; 3. Deer foraged selectively on native perennial forbs; and 4. Non-native annual forbs germinated in abundance from deer pellets. Our results suggest that native deer can have profound local and community level effects on plant community structure and control measures will play a major role in the restoration and conservation of endangered coastal plant communities in western North America.