Impacts of Cheatgrass (Bromus tectorum) on Western Fence Lizard (Sceloporus occidentalis) Populations in Nevada

Abstract

The encroachment of cheatgrass (Bromus tectorum) has become a major crisis for ecosystems in the western United States. Very little research has been conducted on the impacts of cheatgrass on small vertebrates, including lizard species. This study was conducted to evaluate whether cheatgrass impacts western fence lizard (Sceloporus occidentalis) populations, and to explore possible causal mechanisms. Visual encounter surveys in this study displayed a strong relationship of lizard encounters in sagebrush areas in contrast to cheatgrass-dominated zones. Potential mechanisms reducing lizard populations in cheatgrass environments (or causing emigration away from cheatgrass sites) are reductions in lizard mobility, altered micro-site temperatures, and altered plant and insect diversity. Experiments on lizard mobility showed that smaller lizards are significantly impacted by the physical resistance imposed by thick blankets of cheatgrass, compared to larger lizards. Temperatures of cheatgrass areas have a larger temperature range than sagebrush areas. For plant diversity, data were insufficient for analyses. Cheatgrass areas were not found to support high insect diversity, in terms of insect richness (number of species) and abundance (number of individuals). Sagebrush areas did not support higher insect richness, but contained higher insect abundance. Overall, conclusions from this study, among other supporting research, warns that cheatgrass negatively impacts lizard populations and threaten other obligate species as well. Serious considerations should be taken on how to prevent cheatgrass’ influences on lizard populations and the native habitat that the populations depend on. KEYWORDS: