PARENT SESSION
Oral Session #14: Invasive species: Effects.
Presiding: S. DeSimone
Monday, August 5. 1:00 PM to 3:45 PM. Greenlee Meeting Room, TCC.
Effects of nonnative grasses on small mammal populations and communities .
Litt, Andrea*,1, Steidl, Robert1, 1 University of Arizona, Tucson, AZ
ABSTRACT- Invasions of nonnative species are an increasing problem in most ecosystems, with approximately 50,000 nonnative plant and animal species established in the U. S. A series of effects has been attributed to these invasions, including local extinctions, reductions in diversity, and decreases in population sizes of native species. In the southwestern U.S., Lehmann lovegrass (Eragrostis lehmanniana) has continued to increase in abundance and distribution, which likely has far-reaching consequences across a range of ecological scales. We quantified the influence of this nonnative grass on the diversity and abundance of small mammals in grasslands of southern Arizona by examining a suite of population and community characteristics of small mammals along three points of a gradient of nonnative grass invasion: no nonnative grass, a mix of nonnative and native grasses, and complete dominance by nonnative grasses. We live-trapped small mammals for during spring, summer, and winter 2000-2002. We found that small mammal populations varied little along the invasion gradient, which contrasts with previous observations. In summer 2001, for example, species richness (mean ± SE species) was similar along the invasion gradient, from 5.6 ± 0.47 for areas dominated by native grasses, 6.8 ± 0.46 for areas composed of both nonnative and nonnative grasses, and 6.1 ± 0.53 for areas dominated by exotic grasses. Relative abundance (no. individuals) of all small mammal species combined averaged 27 ± 2.9 for areas dominated by native grasses, 19 ± 1.5 for areas composed of both nonnative and nonnative grasses, and 25 ± 3.1 areas plots dominated by nonnative grasses. Although these dramatic changes in vegetation explained little with regards to general patterns of small-mammal abundance and richness, composition of the small mammal community changed appreciably in response to the changes in vegetation structure and cover.
KEY WORDS: exotic plants, small mammals, Lehmann lovegrass