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A Mechanistic and Landscape Scale Approach Quantifying Habitat Suitability of Cheatgrass (Bromus tectorum) Engineered Habitats for Great Basin Reptiles
AdvisorFeldman, Chris R.
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Invasive species are recognized as key drivers of global change and can have significant impacts on ecosystem functioning and biodiversity. Yet, a detailed understanding of the impacts of invasion on native wildlife is lacking. Furthermore, the driving mechanisms behind those adverse impacts of invasion that have been quantified are rarely investigated. An understanding of such mechanisms is needed to predict wildlife responses to plant invasion and to design targeted ecological restoration practices. In the Great Basin Desert of North America, habitat degradation has led to widespread invasion by a highly successful plant species, cheatgrass (Bromus tectorum). The result has been the alteration of landscape structure and ecosystem function. This novel habitat has been implicated in biodiversity losses for multiple wildlife taxa in the Great Basin. Yet, an understanding of the mechanisms driving these losses is lacking. Reptiles are an important component of this system and model organisms for elucidating the impacts of desert habitat modification. We established six paired study sites across three heavily invaded landscapes of northwest Nevada to quantify differences between cheatgrass invaded habitat and the adjacent native shrub habitat. All cheatgrass habitats had a depauperate or non-existent reptile community as compared to shrub habitat. We then assessed four possible mechanisms driving these differences in reptile biodiversity: 1) plant community composition, 2) physical habitat structure, 3) arthropod prey community composition and 4) the thermal environment. Cheatgrass habitats had significantly less plant diversity, a homogenized habitat structure and a significantly less diverse arthropod prey base. Lastly, cheatgrass invasion has likely rendered vast expanses of the Great Basin Desert thermally unsuitable for at least one reptile species, Sceloporus occidentalis. We suggest that suitable habitat for Great Basin Desert reptiles is altered, or wholly erased, by cheatgrass invasion. Our mechanistic approach to understanding biodiversity loss in the Great Basin Desert will provide a knowledge base that is urgently needed to help mitigate the rapidly advancing invasion of Bromus tectorum and other detrimental invasives across the globe.