Consequences of severe habitat fragmentation on density, genetics, and spatial capture-recapture analysis of a small bear population

Abstract

Loss and fragmentation of natural habitats caused by human land uses have subdivided several formerly contiguous large carnivore populations into multiple small and often isolated subpopulations, which can reduce genetic variation and lead to precipitous population declines. Substantial habitat loss and fragmentation from urban development and agriculture expansion relegated the Highlands-Glades subpopulation (HGS) of Florida, USA, black bears (Ursus americanus floridanus) to prolonged isolation; increasing human land development is projected to cause ≥ 50% loss of remaining natural habitats occupied by the HGS in coming decades. We conducted a noninvasive genetic spatial capture-recapture study to quantitatively describe the degree of contemporary habitat fragmentation and investigate the consequences of habitat fragmentation on population density and genetics of the HGS. Remaining natural habitats sustaining the HGS were significantly more fragmented and patchier than those supporting Florida’s largest black bear subpopulation. Genetic diversity was low (AR = 3.57; HE = 0.49) and effective population size was small (NE = 25 bears), both of which remained unchanged over a period spanning one bear generation despite evidence of some immigration. Subpopulation density (0.054 bear/km2) was among the lowest reported for black bears, was significantly female-biased, and corresponded to a subpopulation size of 98 bears in available habitat. Conserving remaining natural habitats in the area occupied by the small, genetically depauperate HGS, possibly through conservation easements and government land acquisition, is likely the most important immediate step to ensuring continued persistence of bears in this area. Our study also provides evidence that preferentially placing detectors (e.g., hair traps or cameras) primarily in quality habitat across fragmented landscapes poses a challenge to estimating density-habitat covariate relationships using spatial capture-recapture models. Because habitat fragmentation and loss are likely to increase in severity globally, further investigation of the influence of habitat fragmentation and detector placement on estimation of this relationship is warranted.

Factors associated with black bear density and implications for management

“…Capture probability was low for hair traps throughout the project but within the range of similar studies (Murphy et al , Sun et al , Gould et al ), and multiple years of data maintained high precision in density estimates. The low number of spatial recaptures within years in our study suggests that detectors may have been too widely distributed given the size of bear movements in the study areas.…”

Integrating multiple genetic detection methods to estimate population density of social and territorial carnivores

“…In the presence of individual heterogeneity in k 0 , spatial capture-recapture models will generally estimate an averaged but positively biased k 0 (Royle et al 2014). This pushes the activity centers of the lower k 0i individuals further away from the detector array or into holes in the array where no detectors exist and those individuals are less likely to be detected, thereby accommodating their lower than expected observed detection rate (sensu Murphy et al 2017). If individual heterogeneity…”

Identifying core habitats and corridors of a near threatened carnivore, striped hyaena (Hyaena hyaena) in southwestern Iran

“…Human activities have threatened large carnivores through habitat loss, fragmentation and isolation at multiple scales 1 – 3 . With increasing loss and fragmentation of habitats, there is a crucial need to identify the most important areas for conservation actions 4 .…”