Determining the effects of exotic warm-season grass invasion on small mammal communities of North Central Oklahoma, USA

Background/Question/Methods

Old World Bluestems (OWBs) are invasive warm-season grasses that have been planted onto millions of hectares of marginal farmland in the southern and central Great Plains to reduce soil erosion and to increase forage production. These grasses are currently of major management concern due to their rapid invasion into native prairies. Invasions of OWBs into native prairies have negative ecological and economical consequences, and may have  profound impacts on the small mammal communities of these grasslands. Previous studies have shown that as native plant communities lose their high biodiversity to monocultures of exotic species, small mammal diversity, richness, and abundances decline. We hypothesize that as these invasions progress towards monocultures, they will provide fewer microhabitats and resource bases, compared to the highly diverse native rangelands, with a concomitant reduction in abundance and richness of small mammals. We assessed the effects of OWB invasions on small mammal communities in Oklahoma, USA. We conducted small mammal trapping at 4 replicate sites in  grasslands with 40-60% OWB cover, and native, non-invaded grasslands. Plant species composition, visual obstruction, areial cover, and litter detph were assessed at each trapping site to allow for development of species-specific habitat modeling.

Results/Conclusions

Over the course of our 2 year study, we completed 5,120 trap days (24 hr/day). Current analysis is based on 3,840 trap days and 225 total captures consisting of 8 species. We captured 74 individuals in the native grasslands and 151 individuals in the OWB invaded grasslands. Our preliminary data indicate that invasion of OWB into the native grasslands lowered species richenss and increased the relative abundance of hispid cotton rats (Sigmodon hispidus). However, invasion by this warm-season grass lowered the relative abundance of deer mice (Peromyscus maniculatus), compared to the native grassland controls. Further analysis is being conducted on all captures for all 5,120 trap days. Species-specific responses to vegetative structure will also be modeld. Because small mammals are a vital part of grassland ecosystems, influencing all trophic levels, alterations to these small mammal communities may have profound effects on ecosystem functioning.