The Impact of Roads on the Demography of Grizzly Bears in Alberta

<div><p>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 have 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. We 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 we explored factors which caused biological and spatial variation in population trend. We found that sex and age class survival was 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 dependant offspring resulted in lower road density thresholds to ensure stable bear populations. Our 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.</p></div

Model selection for multi-state reproductive model analysis of grizzly bears in Alberta, Canada.

<p>Model selection for multi-state reproductive model analysis of grizzly bears in Alberta, Canada.</p

Road density for watershed units as subdivided by core and secondary areas for grizzly bear range in Alberta[17].

<p>Mountainous areas (to the west of core secondary areas) were primarily protected parklands with low (<0.6 km roads/km²) road densities.</p

The effect of road density (km roads/km²) population trend (λ) assuming reproductive state specific survival (left, <b>Fig. 2</b>) and pooled adult female survival rates (right, <b>Fig. 2</b>) of grizzly bears in Alberta, Canada.

<p>Grey lines indicate 95% confidence intervals for predictions. The horizontal dashed line indicates population stability (λ = 1). The dashed vertical lines indicate threshold road densities where lambda = 1.</p

Summary of sample sizes of events (<i>n</i>) and transition probabilities (<i>p</i>) from multi-state model reproductive analysis of grizzly bears in Alberta, Canada.

<p>Summary of sample sizes of events (<i>n</i>) and transition probabilities (<i>p</i>) from multi-state model reproductive analysis of grizzly bears in Alberta, Canada.</p

Estimates of survival of females as a function of road density and reproductive status (Model 1, <b>Table 3</b>) from the multi-state model analysis of grizzly bears in Alberta, Canada.

<p>Data points are given as grey circles with mortalities filled red. For the Females with 2 year olds or no cubs, there are 2 overlapping mortality points at a road density of 1.4. Grey lines indicate 95% confidence intervals for predictions.</p

Known fate survival analysis model selection results of grizzly bears in Alberta, Canada.

<p>Known fate survival analysis model selection results of grizzly bears in Alberta, Canada.</p

The focal study area for the Foothills Research Institute grizzly bear project in Alberta, Canada.

<p>The Grande Cache (north of Hinton) and Yellowhead (south of Hinton, AB) are displayed. The majority of collared bears in the analysis were within these 2 management units.</p

Estimated coefficients (<i>β_i</i>), robust standard errors [SE] and 95% confidence intervals [CI] for top models describing the probability of occurrence for grizzly bear resting sites by land designation in west-central Alberta, Canada as assessed by Δ<i>_i</i> and <i>w_i</i>.

<p>[CI] did not overlap zero are given in bold. Missing estimates for habitat features refer to variables not present in the respective model. Estimates for which the </p><p>∧ Coefficient reported at 10³ times its actual value.</p

Estimated coefficients (<i>β_i</i>), robust standard errors [SE] and 95% confidence intervals [CI] for top models describing log selection ratios for vertical (V) and horizontal (H) cover at grizzly bear resting sites in west-central Alberta, Canada as assessed by Δ<i>_i</i> and <i>w_i</i>.

<p>Missing estimates refer to variables not present in the respective model. Estimates for which the confidence intervals do not overlap 0 are given in bold.</p><p>The following strata within variables were withheld as reference category:</p><p>Reclaimed mine (Land designation); Spring (Season); Diurnal (Time of day).</p