Carnivore Re-Colonisation: Reality, Possibility and a Non-Equilibrium Century for Grizzly Bears in the Southern Yellowstone Ecosystem

Most large native carnivores have experienced range contractions due to
conflicts with humans, although neither rates of spatial collapse nor expansion
have been well characterized. In North America, the grizzly bear (Ursus
arctos) once ranged from Mexico northward to Alaska, however its range in the
continental United States has been reduced by 95-98%. Under the U.S.
Endangered Species Act, the Yellowstone grizzly bear population has
re-colonized habitats outside Yellowstone National Park. We analyzed
historical and current records, including data on radio-collared bears, (i) to
evaluate changes in grizzly bear distribution in the southern Greater
Yellowstone Ecosystem over a 100-year period, (ii) to utilise historical rates
of recolonization to project future expansion trends and (iii) 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 (1900-1940) and expansion to the south (1940-2000). 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.

One of the purposes of the dataset is to predict when grizzly bear occupation
of Southern Yellowstone Ecosystem will be total.

We focused on a 24,000 square kilometer mosaic of mostly public land that is
managed by various federal and state agencies. Our analysis of changes in
grizzly bear distribution during 1900-2000 was divided into 20-year periods.
For each, we used various data sources for grizzly bear occurrence to create
digital maps of bear distribution using ArcView GIS 32. (ESRI, Redlands, CA)
We digitized reports, interviews, conflicts, mortalities and observations as
points. We created a polygon for the 1920 source data, a hand-drawn
distribution map by Merriam (1922). More methodology given in Pyare, 2004
paper.