Brown Bear Conservation and human interactions and influences

Brown bears have been a “threat” to humans since the 1500s when they were extirpated from North Africa, and eventually over the Middle East, North America, Europe and Asia (McLellan 2008).  However it seems we are the “threat” to brown bear persistence.  They have been under protection from us since the 1973 Endangered Species Act.  Populations have increased in some areas and declined in others.  Charles Schwarts, Mark Haroldson and Gary White in 2013 studied the populations of grizzly bears in The Greater Yellowstone Ecosystem to provide for the first time, a comprehensive assessment of variables possibly affecting survival under current management among the ecosystem..

The grizzly bear (Ursus arctos) of The Greater Yellowstone Ecosystem (GYE) was listed as threatened in 1975, delisted by the United States Fish and Wildlife Service (USFWS) in 2007, and then relisted in 2009 (Schwartz 2010).  Currently, GYE grizzly bears live close to human populations and are considered by Scott et al as “conservation-reliant species” (as cited in Schwartz et al 2010).  These conservation-reliant species are constantly threatened resulting in necessary continuous management to maintain population dynamics.  They are constantly under risk of threat because of humans are their primary factor in the grizzly bear’s mortality.

          The goal of Schwart et al’s study was to focus management activities for grizzlies by inventing a hazard model.  Previous studies used time-series models from 1975 to 1990s to address causes of grizzly bear mortalities.  However they did not provide an ecosystem-wide comprehensive evaluation of factors affecting bears under modern management (Schwartz et al 2010).  To create the comprehensive ecosystem-wide assessment of grizzly bears in the GYE, monthly survival was monitored to determine features of the landscape best describing special variability in grizzly bear survival.  The two other objectives were, illustrating differences in hazards across the GYE and demonstrating the landscape model with female survival to identify source and sink habitats within the GYE.  Schwartz et al hypothesized that human activities would underlie grizzly bear spatial distribution and survival.

          The study area included grizzly bears occupying about 37,000 km² in the GYE concurring with occupied grizzly bear range (Fig. 1) (Schwartz et al 2010).  The results of the study followed the hypothesis that human disturbance best describes grizzly bears hazards and spatial heterogeneity of their mortality (Schwartz et al 2010). Humans were responsible for both determining grizzly bear survival and sources of hazards in the GYW.  This was discovered first through analyzing the effect of food availability on grizzly bear survival.

Features of the landscape that were assumed to relate to bear survival, such as food, proved incorrect.  Schwartz et al monitored grizzly bears movements, plastically shifting among habitats to eat seasonally available food (as cited in Schwartz et al 2010) such as fish-spawning streams, cut worm moths, and whitebark pine seeds. A result showed that bears migrate to lower elevations during poor pine seed years, and this change in elevation does not itself predispose bears to increased mortality (Schwartz et al 2010).  However, humans still were the main variable determining bear persistence in the GYE.   This was because bears that shifted to lower elevations in human modified areas were at much greater risk of mortality, than bears that shifted to non-human modified environments.  In the lower elevations, bears were killed by humans either by vehicle collision, humans hunting for ungulates, humans hunting bears, poaching or malicious killings (Schwartz et al 2010).  These high risk of death areas are called population “sinks”; a map of the sink and source areas for GYE grizzly bears can be seen in Fig. 2.

To conclude, scwartz et al studied grizzly bears of the Greater Yellowstone Ecosystem to create a comprehensive assessment of variables possibly affecting survival under current management among the ecosystem.  Upon natural ecological habitat selection for food, humans’ developments and activities pose threats to bears and play a major role in their spatial distribution.  If we link the grizzly bears population direction with a habitat selection model, then managers may evaluate the state of grizzly bear habitat at various spatial scales (Schwartz et al 2010).  Managers may also measure consequences of prescribed management activities and the effects of changing food resources on the fecundity or habitat selection in conserving grizzly bears (Schwartz et al 2010).  Finally, understanding the movements of grizzlies over the seasons adds a variable to consider when creating successful management plans.