Occupancy modeling of non-native mountain goats in the greater Yellowstone area
DeVoe, Jesse Daniel
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Non-native species can have adverse impacts on native species; however, coexistence may be possible if their ecological niches minimally overlap. Fine spatial scale information is needed to understand these niches but can be challenging to obtain for rare, imperfectly detected species inhabiting difficult to survey landscapes. Non-native mountain goats (Oreamnos americanus) in the greater Yellowstone area (GYA) are such a species and have substantial potential to expand in distribution and occupy similar habitats to native Rocky Mountain bighorn sheep (Ovis canadensis canadensis). To understand the niche and potential for expansion of mountain goats in the GYA, this study used a unique, fine spatial scale method to collect detection-nondetection data from two study areas with established mountain goat populations over three summer seasons (2011-2013). Relationships between scale-specific habitat covariates and mountain goat selection were evaluated using a single-species, single-season occupancy analysis to model occupancy and detection probabilities based on 505 mountain goat detections from 53,098 surveyed sampling units. Habitat selection was most strongly associated with terrain covariates, including mean slope and slope variance, at a spatial scale of 500 x 500 m, and canopy cover, heat load, and normalized difference vegetation index at a spatial scale of 100 x 100 m. These results provide new insight into multi-scale patterns of mountain goat habitat selection, as well as evidence that mean slope and slope variance are superior terrain covariates to distance to escape terrain that has dominated published mountain goat habitat models. The model predicted 10,745 km2 of suitable habitat within the GYA, of which 57% is currently un-colonized. Throughout the GYA, suitable habitat appears to generally overlap extensively with areas occupied by bighorn sheep. I also estimated the GYA may have the potential to support 5,372-8,918 mountain goats when all predicted habitat is occupied, or approximately 2.5-4.2 times the most recent abundance estimate of 2,104.