Date of Award
Exotic invasive species can alter ecosystem health. Cheatgrass (Bromus tectorum), Russian thistle (Salsola kali) and tall tumble mustard (Sisymbrium altissimum) are widely distributed invasive plants occurring throughout desert and shrub-steppe communities in the western United States. Due to the relative ease of capture, small mammal community metrics are often used to quantify overall ecosystem health. Studies examining small mammal communities are numerous but few have specifically examined the effects of invasive plants at the community level in arid ecosystems. In this study I examined community level small mammal responses to changes in microhabitat features, with an emphasis on levels of invasive species dominance. In the summers of 2010-2013, small mammals were sampled using Sherman live traps and vegetation structure was measured using the line-point intercept method. Using estimates of species richness and number of captures (relative abundance), I developed generalized linear mixed models (GLMMs) to test the predictor variables: percent invasive species cover, plant species richness, percent shrub cover, percent bare ground, mean plant height, moon illumination, and percent litter cover. Findings revealed a significant negative relationship between percent invasive species cover and small mammal species richness and a significant nonlinear relationship between percent invasive species cover and small mammal relative abundance, where total capture rates and cover of invasive plants exhibited a positive relationship, reached a threshold, and then exhibited a negative relationship. This non-linear finding provides support for the intermediate disturbance hypothesis and suggests that intermediate levels of exotic plant invasions may positively affect organisms that are members of higher trophic levels that consume primarily small mammals. Overall, this study suggests that if maintaining high levels of total small mammal abundance (e.g., biomass) is important for higher trophic level species (e.g., the kit fox), the importance of invasive species eradication and native species restoration should be carefully considered if invasive species have not completely displaced the native flora community. However, if maintaining small mammal diversity is a higher priority, eradication of invasives and native species restoration should be a top priority. Further, maintaining intermediate levels of invasive species in order to strengthen small mammal biomass could prove both challenging and risky.
Smith, Trinity N., "The Influence of Invasive Plants on the Small Mammal Community in a Cold Desert" (2015). Undergraduate Honors Capstone Projects. 627.
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Eric M. Gese
Departmental Honors Advisor
Eugene W. Schupp
Capstone Committee Member