Carnivore re‐colonisation: reality, possibility and a non‐equilibrium century for grizzly bears in the southern Yellowstone ecosystem

Abstract

Most large native carnivores have experienced range contractions due to conflicts with humans, although neither rates of spatial collapse nor expansion have been well characterised. In North America, the grizzly bear (Ursus arctos) once ranged from Mexico northward to Alaska, however its range in the continental USA has been reduced by 95-98%. Under the U. S. Endangered Species Act, the Yellowstone grizzly bear population has re-colonised habitats outside Yellowstone National Park. We analysed historical and current records, including data on radio-collared bears, (1) to evaluate changes in grizzly bear distribution in the southern Greater Yellowstone Ecosystem (GYE) over a 100-year period, (2) to utilise historical rates of re-colonisation to project future expansion trends and (3) to evaluate the reality of future expansion based on human limitations and land use. Analysis of distribution in 20-year increments reflects range reduction from south to north and expansion to the south . Expansion was exponential and the area occupied by grizzly bears doubled approximately every 20 years. A complementary analysis of bear occurrence in Grand Teton National Park also suggests an unprecedented period of rapid expansion during the last 20-30 years. The grizzly bear population currently has re-occupied about 50% of the southern GYE. Based on assumptions of continued protection and ecological stasis, our model suggests total occupancy in 25 years. Alternatively, extrapolation of linear expansion rates from the period prior to protection suggests total occupancy could take > 100 years. Analyses of historical trends can be useful as a restoration tool because they enable a framework and timeline to be constructed to pre-emptively address the social challenges affecting future carnivore recovery.

Temporal, Spatial, and Environmental Influences on the Demographics of Grizzly Bears in the Greater Yellowstone Ecosystem

“…Since the grizzly bear population's nadir in the mid-1980s, evidence from a variety of sources indicates that grizzly bear numbers in the GYE have increased through the 1990s. Counts of unique females with cubs-of-year (i.e., unduplicated females as per Knight et al [1995], ) have increased, and geographic distribution of grizzly bears has expanded (Basile 1982, Blanchard et al 1992, Pyare et al 2004. Consistent with these trends, estimates of k derived from radio-monitored bears indicated a positive population trend (Eberhardt et al 1994, Boyce et al 2001, due in large part to reduced female mortality.…”

Contrasting Activity Patterns of Sympatric and Allopatric Black and Grizzly Bears

“…If differences in activity patterns between black and grizzly bears were a product of evolutionary pressures to reduce competition, we hypothesized that sympatric and allopatric black bear populations would behave similarly. Historically, black bears were sympatric with grizzly bears throughout the Greater Yellowstone Ecosystem, and it was not until the 1940s that grizzly bears were extirpated from Teton Park (Pyare et al 2004). According to reported sightings, grizzly bears began to recolonize Teton Park in the 1970s, but rapid expansion did not occur until the late 1980s through the 1990s (Pyare et al 2004).…”

“…During the 1980s and 1990s, grizzly bears expanded southward into Grand Teton National Park, Wyoming, USA (hereafter, Teton Park [Basile 1982;Blanchard et al 1992;Schwartz et al 2002Schwartz et al , 2006). Over the last decade, the northern half of Teton Park has been consistently occupied by grizzly bears, where they are now considered common (Pyare et al 2004); as of 2006 grizzly bears had yet to recolonize the southern half of Teton Park. American black bears (U. americanus) historically and currently occur throughout the Greater Yellowstone Ecosystem.…”

Life-history characteristics of mule deer: Effects of nutrition in a variable environment

“…The relative influence of nutrition (bottom‐up) and predation (top‐down) on the regulation of populations remains a common theme in ecological studies (Hairston et al , Skogland , Estes et al , Pierce et al ). Indeed, the reintroduction and expanding populations of large carnivores have fueled, and likely will continue to promote, the controversy behind the ecological consequences of their presence (Bangs et al , Pyare et al , Carroll et al , Kauffman et al , Smith et al ). In systems where ungulates co‐occur with large carnivores, predation is commonly the leading proximal cause of mortality among young ungulates (Linnell et al , Singer et al , Bowyer et al , Ballard et al ), but simply identifying cause of death is of little value without characterizing the implications or underlying basis of those mortalities (Bleich and Taylor , Ballard et al , Bowyer et al ).…”