Monday, August 3, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Background/Question/Methods To test the hypotheses that the North American beaver, Castor canadensis, changes arthropod communities on Fremont cottonwood (Populus fremontii) and also induces increased shoot growth as a result of herbivory, I conducted arthropod surveys and measured shoot elongation on trees which had been cut by beavers as well as those which had not in 4 riparian areas of Northern Arizona. This is important because no known published studies have addressed the effects of a large mammalian herbivore on a diverse arthropod community. Results/Conclusions I found five major patterns: 1) species total abundance and richness did not differ significantly between beaver felled and control trees, which may be due to small sample size or timing of surveys. 2) Species indicator analyses revealed one significant arthropod species indicative of browsed trees and 5 species (2 significant) which were indicators of specific sites. This suggests that there are at least some arthropod species which show fidelity to each site and one which prefers some aspect of browsed trees over control trees. 3) Species accumulation curves showed that control trees accumulate species more slowly than browsed trees, suggesting that browsed trees may be preferable to a larger variety of species than control trees. 4) Differences in arthropod community composition were significant between sites, but not between treatments. Site differences are likely due to differing hydrology, stress and other environmental factors between sites, and 5) shoot elongation was nearly 2 times greater on resprout than on unbrowsed trees, a finding supported by previous research and indicative of both architectural and nutritional differences between resprout and control trees. These findings suggest that, as a result of herbivory, beavers are changing the structure of the arthropod communities on, possibly by increasing habitat heterogeneity through the creation of greater diversity in architecture and nutrient availability within this foundation tree species.
