Effects of Smooth Brome on Brewer's Sparrow Nest Survival in Sagebrush Steppe

Abstract

Abstract. Invasive plants represent a serious threat to native biodiversity worldwide through direct competition with native species and indirect effects resulting in ecosystem-level changes. In the western U.S., the sagebrush ecosystem has been seriously altered by the invasion of cheatgrass (Bromus tectorum), an exotic annual, and other species including smooth brome (B. inermis), an exotic perennial. We monitored 112 Brewer's Sparrow (Spizella breweri) nests (2006 and 2007) in Grand Teton National Park, Wyoming, to assess the potential effects of a smooth brome vs. native understory on nest survival in sagebrush steppe. Brewer's Sparrows settled earlier and clutch size was larger in native habitat, but indices of nest success were higher in the exotic habitat. Rates of failure and nest predation were higher in the native habitat. Using the logistic-exposure method, we compared estimates of survival in the two habitats. The model with the greatest support, according to AICc model-selection criteria, con...