Effects of habitat quality and access management on the density of a recovering grizzly bear population

Abstract

Abstract1. Human activities have dramatic effects on the distribution and abundance of wildlife. Increased road densities and human presence in wilderness areas have elevated human-caused mortality of grizzly bears and reduced bears' use. Management agencies frequently attempt to reduce human-caused mortality by managing road density and thus human access, but the effectiveness of these actions is rarely assessed.2. We combined systematic, DNA-based mark-recapture techniques with spatially explicit capture-recapture models to estimate population size of a threatened grizzly bear population (Kettle-Granby), following management actions to recover this population. We tested the effects of habitat and road density on grizzly bear population density. We tested both a linear and threshold-based road density metric and investigated the effect of current access management (closing roads to the public).3. We documented an c. 50% increase in bear density since 1997 suggesting increased landscape and species conservation from management agencies played a significant role in that increase. However, bear density was lower where road densities exceeded 0.6 km/km 2 and higher where motorised vehicle access had been restricted. The highest bear densities were in areas with large tracts of few or no roads and high habitat quality. Access management bolstered bear density in small areas by 27%. Synthesis and applications.Our spatially explicit capture-recapture analysis demonstrates that population recovery is possible in a multi-use landscape when management actions target priority areas. We suggest that road density is a useful surrogate for the negative effects of human land use on grizzly bear populations, but spatial configuration of roads must still be considered. Reducing roads will increase grizzly bear density, but restricting vehicle access can also achieve this goal. We demonstrate that a policy target of reducing human access by managing road density below 0.6 km/km 2 , while ensuring areas of high habitat quality have no roads, is a reasonable compromise between the need for road access and population recovery goals. Targeting closures to areas of highest habitat quality would benefit grizzly bear population recovery the most.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Genetic tagging in the Anthropocene: scaling ecology from alleles to ecosystems

“…If increasing this population to 2006 levels is a priority, we provide the evidence required for wildlife managers to implement the reduction of resource road densities and thus human access and bear mortality (Lamb et al. , Proctor et al. ).…”

“…Projects using genetic tagging for these demographic insights have been conducted on every continent, except Antarctica, and have sampled a variety of taxa, using many different sources of DNA, but are biased toward mid-large sized mobile mammals. References to each study are provided on Fig population density to explore density-habitat relationships (but see: Fuller et al 2015, Linden et al 2016, Lamb et al 2018, Sutherland et al 2018. Recently, Sutherland et al (2018) examined the link between contamination (PCB) and the population density of American mink (Neovison vison) using genetic-based SCR.…”

“…Mink, often used as an indicator species for aquatic ecosystems, were found in much lower densities near a contaminated river system compared to those near a more pristine river; underscoring the value of pairing SCR methods with genetic tags to collect individual identities across multiple river systems to reveal cryptic ecological patterns. Similarly, Lamb et al (2018) tested the effects of habitat and road density on the recovery of a threatened grizzly bear population using genetic tags. While grizzly bear density was lower in areas of high road densities, Lamb et al (2018) showed that the creation of protected areas and road closures elevated bear density and mitigated the effects of roads, allowing the population to recover.…”

“…Similarly, Lamb et al. () tested the effects of habitat and road density on the recovery of a threatened grizzly bear population using genetic tags. While grizzly bear density was lower in areas of high road densities, Lamb et al.…”

“…While grizzly bear density was lower in areas of high road densities, Lamb et al. () showed that the creation of protected areas and road closures elevated bear density and mitigated the effects of roads, allowing the population to recover. Results of this work have already been incorporated into regional planning efforts to reduce road densities (Mowat et al.…”