Abstract
Non‐native species can have adverse impacts on native species. Predicting the potential extent of distributional expansion and abundance of an invading non‐native species can inform appropriate conservation and management actions. Non‐native mountain goats (Oreamnos americanus) in the greater Yellowstone area (GYA) have substantial potential to occupy similar habitats to native Rocky Mountain bighorn sheep (Ovis canadensis canadensis). To understand the potential for expansion of mountain goats in the GYA, this study evaluated detection‐nondetection data derived from ground‐based occupancy surveys of viewsheds partitioned into a grid of 100 × 100 m sampling units. Surveys were conducted over three summer seasons (2011–2013) in two study areas with well‐established mountain goat populations. Relationships between scale‐specific habitat covariates and mountain goat selection were evaluated to model occupancy and detection probabilities based on mountain goat detections in 505 of the 53,098 sampling units surveyed. Habitat selection was most strongly associated with terrain covariates, including mean slope and slope variance, at a spatial scale of 500 × 500 m, and canopy cover, heat load, and normalized difference vegetation index at a spatial scale of 100 × 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 more informative terrain covariates than distance to escape terrain, which has been commonly used in published mountain goat habitat models. The model predicted 9,035 km2 of suitable habitat within the GYA, of which 57% is currently un‐colonized. Seventy‐five percent of all bighorn observations recorded in the GYA fall within predicted suitable mountain goat habitat. We also estimated that the GYA might have the potential to support 5,331–8,854 mountain goats when all predicted habitat is occupied, or approximately 2.5–4.2 times the most recent abundance estimate of 2,354.
Highlights
Introductions and expanding distributions of non-native species are globally common and considered to be a significant component of human-caused global environmental change (Vitousek et al 1997)
Model suites The model from Akaike’s information criterion (AIC) model selection used for estimating cincluded SLP500, SLP5002, SLPv500ps, RCK300, RCK3002, COV100, NDVI100, and GRAD100 (Appendix C: Table C1), resulting in c 1⁄4 3.46 from 1,200 simulations
Through analysis of detection and non-detection observations collected from two mountain ranges across three summer seasons, we found evidence that mountain goat habitat selection occurred at two distinct spatial scales
Summary
Introductions and expanding distributions of non-native species are globally common and considered to be a significant component of human-caused global environmental change (Vitousek et al 1997). Understanding invasive species’ patterns of habitat selection and predicting their range expansion is important for developing appropriate conservation and management actions (Lodge et al 2006, Gormley et al 2011). This can be challenging when species are rare on the landscape and inhabit heterogeneous, difficult-to-survey terrain. The more recent development of occupancy methods has provided the ability to incorporate estimates of detection into evaluations of habitat selection for rare species (MacKenzie et al 2005, 2006), and may provide a means to understand selection at a fine spatial scale while effectively surveying large, heterogeneous landscapes
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