Wildlife Society Bulletin; DOI: 10.1002/wsb.636 Original Article Range Expansion and Population Growth of Nonnative Mountain Goats in the Greater Yellowstone Area: Challenges for Management ELIZABETH P. FLESCH,1 Fish and Wildlife Ecology and Management Program, Ecology Department, Montana State University, 310 Lewis Hall, Bozeman, MT 59717, USA ROBERT A. GARROTT, Fish and Wildlife Ecology and Management Program, Ecology Department, Montana State University, 310 Lewis Hall, Bozeman, MT 59717, USA P. J. WHITE, National Park Service, Yellowstone National Park, P.O. Box 168, Yellowstone National Park, WY 82190, USA DOUG BRIMEYER, Wyoming Game and Fish Department, 420 N Cache, P.O. Box 67, Jackson, WY 83001, USA ALYSON B. COURTEMANCH, Wyoming Game and Fish Department, 420 N Cache, P.O. Box 67, Jackson, WY 83001, USA JULIE A. CUNNINGHAM, Montana Fish, Wildlife and Parks, 1400 S 19th Avenue, Bozeman, MT 59717, USA SARAH R. DEWEY, National Park Service, Grand Teton National Park, P.O. Box 170, Moose, WY 83012, USA GARY L. FRALICK, Wyoming Game and Fish Department, P.O. Box 1022, Thayne, WY 83127, USA KAREN LOVELESS, Montana Fish, Wildlife and Parks, 1354 Highway 10 W, Livingston, MT 59047, USA DOUG E. MCWHIRTER, Wyoming Game and Fish Department, 2820 State Highway 120, Cody, WY 82414, USA HOLLIE MIYASAKI, Idaho Department of Fish and Game, 4279 Commerce Circle, Idaho Falls, ID 83401, USA ANDREW PILS, United States Forest Service, Shoshone National Forest, 203A Yellowstone Avenue, Cody, WY 82414, USA MICHAEL A. SAWAYA, Fish and Wildlife Ecology and Management Program, Ecology Department, Montana State University, 310 Lewis Hall, Bozeman, MT 59717, USA SHAWN T. STEWART, Montana Fish, Wildlife and Parks, P.O. Box 581, Red Lodge, MT 59068, USA ABSTRACT Population growth and range expansion of nonnative species can potentially disrupt ecosystem function or add conservation value to an area, and evaluation of possible impacts can be a challenge for managers. Nonnative populations of mountain goats (Oreamnos americanus) are present in the Greater Yellowstone Area (GYA) in the U.S. states of Idaho, Montana, and Wyoming because of historical introduction events, but their population trend and range have not been assessed across the area. We used 6,701 location records from 1947 to 2015 to map mountain goat distribution and evaluate, in a descriptive manner, range overlap with native bighorn sheep (Ovis canadensis). We analyzed 136 survey counts using the Exponential Growth State–Space model to estimate population trends and abundance. Mountain goats dispersed 50–85 km from introduction sites to occupy all mountain ranges in the northern GYA and 30–40 km to occupy new areas in the southern GYA. Mountain goat numbers increased in nearly all count units, with the strongest growth rates estimated in areas more recently colonized. Using moderate detection probability (0.70), we estimated approximately 2,355 mountain goats in the GYA. Although not tested in our analysis, the gradual range expansion and population growth rates were consistent with density-dependent processes observed in other introduced large herbivores and demonstrate that mountain goats can successfully disperse over unsuitable locales to colonize new areas. Therefore, we expect mountain goat populations will continue to expand into unoccupied mountain ranges that contain significant numbers of bighorn sheep unless specific management actions are implemented to address their population growth. Ó 2016 The Wildlife Society. KEY WORDS alpine, bighorn sheep, invasive species, mountain goats, Oreamnos americanus, Ovis canadensis, population management, ungulate. The spread of nonnative species is a growing and pervasive biota (Mooney and Hobbs 2000, Lodge et al. 2006). Perhaps conservation challenge world-wide. When nonnative species the best-known example of such a phenomenon in the become invasive they can cause disruptions to ecosystem Greater Yellowstone Area (GYA) in the U.S. states of Idaho, function and may result in local or global extinction of native Montana, and Wyoming, is the introduction and prolifera- tion of lake trout (Salvelinus namaycush) in Yellowstone Lake, which has caused a near collapse of the native Received: 13 July 2015; Accepted: 10 January 2016 Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) population, with subsequent impacts on many other native 1E-mail: elizabeth.fl[email protected] aquatic and terrestrial species (Koel et al. 2005, Gresswell Flesch et al. Mountain Goats in the Greater Yellowstone Area 1 and Tronstad 2013, Middleton et al. 2013). Other nonnative goats may have been part of the fauna in the GYA region species in the GYA causing substantial impacts on ecological during the Pleistocene, reviews of archeological, paleonto- processes or presenting management and policy challenges logical, and historical records suggest that mountain goats for natural resource agencies include the bacteria Brucella were no longer present or were extremely rare in the region abortus that causes the disease brucellosis in wild ungulates 10,000 years prior to European settlement of North America and domestic cattle (Treanor et al. 2013), and the fungal (Laundre 1990, Schullery and Whittlesey 2001). During the pathogen Cronartium ribicola that is contributing to a major 1940s and early 1950s, 158 mountain goats were released at die-off of whitebark pine (Pinus albicaulis) throughout much 7 sites in the mountains of the northern GYA. Twelve of the ecosystem (Olliff et al. 2013). However, not all mountain goats were also introduced into the southern GYA nonnative species disrupt ecological processes and harm at 2 sites in Idaho during the late 1960s and early 1970s. native species (Davis et al. 2011, Vatery et al. 2013); in some These introduced populations of mountain goats expanded situations, nonnative species may augment ecosystem their range, causing concern about potential effects on native services and have conservation value (Schlaepfer et al. species, particularly bighorn sheep (Ovis canadensis; Varley 2011, Strong and Leroux 2014). Thus, natural resource and Varley 1996, Lemke 2004). managers need to carefully evaluate the potential and realized From European settlement until the 1930s, the number impacts of nonnative species before establishing manage- and distribution of bighorn sheep substantially declined ment strategies and initiating control actions that are often because of market hunting, habitat loss, and diseases difficult to execute, expensive, and potentially controversial introduced by domestic animals. Protective regulations, (Davis et al. 2011). habitat conservation, and active restoration efforts over the The mountain goat (Oreamnos americanus) is native to past 75 years have resulted in a modest recovery of the species northwestern North America, with its natural range primarily (Buechner 1960, Krausman and Bowyer 2003). However, in coastal and inland mountains west of the continental periodic catastrophic die-offs and poor recruitment caused by divide. The species’ range at the time of European settlement the effects of domestic animal pathogens continue to be of North America extended from southern Alaska, USA, and prevalent throughout the species’ contemporary distribution along the Pacific Coast of Canada, including the Northwest (Monello et al. 2001, George et al. 2008, Besser et al. 2012, and Yukon Territories, Alberta, and British Columbia, Cassirer et al. 2013). In addition, many populations tend to Canada, and into the northwestern United States, including be small and isolated, increasing their susceptibility to Oregon, Washington, western Montana, and western Idaho stochastic events and extirpation (Berger 1990). Thus, (Cot^ e and Festa-Bianchet 2003, Matthews and Heath 2008). bighorn sheep are considered a species of great conservation During the early to mid-1900s, state wildlife agencies concern. transplanted mountain goats outside their native range to There is potential for both exploitative and interference increase hunting opportunities. These introductions have competition between mountain goats and bighorn sheep, generally been successful, with nonnative populations now because both species occupy alpine and subalpine habitats established in in the states of Wyoming, Colorado, Utah, and have similar diets when evaluated at a coarse scale South Dakota, and Nevada, as well as within new areas in (grasses, forbs, browse; Laundre 1994), with some indication Alaska, Alberta, Washington, Idaho, and Montana (Cot^ eand of less dietary overlap at the plant species level for sympatric Festa-Bianchet 2003). populations (Pallister 1974, Stewart 1975). Although records Although establishment and expansion of nonnative of direct interactions between the 2 species are scarce, mountain goat populations have been embraced by most observations of >100 interactions between nonnative state wildlife agencies, there are some concerns that mountain goats and native bighorn sheep in Colorado nonnative mountain goats may degrade fragile native alpine suggest mountain goats are more likely to displace bighorn, and subalpine plant communities. Most notable have been but that most interactions are benign (Reed 1986). There is the studies conducted in Olympic National Park in also the potential that nonnative mountain goats may pose a Washington that demonstrated high densities of nonnative disease threat to bighorn sheep because many species of mountain goats impacted soils, created dust wallows, and helminths are common to both species