The impact of roads on the demography of grizzly bears in Alberta

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One of the principal factors that have reduced grizzly bear populations has been the creation of human access into grizzly bear habitat by roads built for resource extraction. Past studies have documented mortality and distributional changes of bears relative to roads but none has attempted to estimate the direct demographic impact of roads in terms of both survival rates, reproductive rates, and the interaction of reproductive state of female bears with survival rate. The authors applied a combination of survival and reproductive models to estimate demographic parameters for threatened grizzly bear populations in Alberta. Instead of attempting to estimate mean trend the authors explored factors which caused biological and spatial variation in population trend. Sex and age class survival were found to be related to road density with subadult bears being most vulnerable to road-based mortality. A multi-state reproduction model found that females accompanied by cubs of the year and/or yearling cubs had lower survival rates compared to females with two year olds or no cubs. A demographic model found strong spatial gradients in population trend based upon road density. Threshold road densities needed to ensure population stability were estimated to further refine targets for population recovery of grizzly bears in Alberta. Models that considered lowered survival of females with dependent offspring resulted in lower road density thresholds to ensure stable bear populations. The results demonstrate likely spatial variation in population trend and provide an example how demographic analysis can be used to refine and direct conservation measures for threatened species.

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ELECTRONIC FILE - Zoology

SWAP (2/19/2016) citation:
Boulanger J, Stenhouse GB. 2014. The impact of roads on the demography of grizzly bears in Alberta. [accessed 2015 Jun 1]; PLoS ONE. 9(12):e115535. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0115535