Microhabitat features influencing habitat use by Florida black bears

Understanding fine-scale habitat needs of species and the factors influencing heterogeneous use of habitat within home range would help identify limiting resources and inform habitat management practices. This information is especially important for large mammals living in fragmented habitats where resources may be scarcer and more patchily distributed than in contiguous habitats. Using bihourly Global Position System (GPS) location data collected from 10 individuals during 2011–2014, we investigated microhabitat features of areas within home ranges that received high vs. low intensity of use by Florida black bears (Ursus americanus floridanus) in north-central, Florida. We identified areas receiving high and low levels of use by bears based on their utilization distributions estimated with the dynamic Brownian bridge movement model, and performed vegetation sampling at bear locations within high- and low-use areas. Using univariate analyses and generalized linear mixed models, we found that (1) canopy cover, visual obstruction, and hardwood density were important in defining high-use sites; (2) the probability of high use was positively associated with principal components that represented habitat closer to creeks and with high canopy and shrub cover and higher hardwood densities, likely characteristic of forested wetlands; and (3) the probability of high use was, to a lesser extent, associated with principal components that represented habitat with high canopy cover, high pine density, and low visual obstruction and hardwood density; likely representing sand pine and pine plantations. Our results indicate that the high bear-use sites were in forested wetlands, where cover and food resources for bears are likely to occur in higher abundance. Habitat management plans whereby bears are a focal species should aim to increase the availability and quality of forested wetlands. Keywords: Habitat selection, Heterogeneous habitat use, Forest management, Microhabitat, Principal components analysis, Compositional features of microhabitat, Structural features of microhabitat, Ursus americanus, Vegetation samplin

Determining the potential mitigation effects of wildlife passageways on black bears

North Carolina’s U.S. Highway 64 is currently being expanded from a two-lane road to a four-lane divided highway from Raleigh to the Outer Banks. Concerns exist that collisions with vehicles may affect the demographics of wildlife populations and that potential disturbances and fragmentation associated with the highway may affect the ecological integrity of the landscape, particularly with regard to large carnivores. In response to these concerns, the North Carolina Department of Transportation (NCDOT) included three wildlife underpasses into the design of a 19.3- km section of the new U.S. Highway 64 in Washington County. The locations of the wildlife underpasses were determined based on a study by the North Carolina Wildlife Resources Commission during 1999. Areas that received frequent wildlife use were identified based on surveys of track counts, ditch crossings, and infrared cameras. The resulting data were used in combination with a geographic information system (GIS) to identify travel corridors for wildlife. Once the locations of the wildlife underpasses were established, the University of Tennessee initiated research in 2000 to determine whether wildlife passageways can mitigate impacts from highways. We chose a wideranging carnivore, the American black bear (Ursus americanus), as the focus species of our study because of its dependence on regional landscapes. We developed an experimental study design that will allow for collection of data before and after highway construction on a treatment and a control area. During the pre-construction phase of the study, we have collected over 6,000 locations on a total of 35 bears to document home-range sizes, activity patterns, movements, and habitat use. We are also analyzing 337 DNA samples from hair collected at 140 barbed-wire hair traps to estimate population density and to determine genetic relatedness within and among the two populations. Finally, we are using 243 photographs of wildlife from infrared cameras to measure use of the areas where the highway underpasses will be constructed. Field data collection during the pre-construction period was completed in June 2001; post-construction data will be gathered and compared after the anticipated completion of the highway in 2004

Determining the potential mitigation effects of wildlife passageways on black bears

North Carolina’s U.S. Highway 64 is currently being expanded from a two-lane road to a four-lane divided highway from Raleigh to the Outer Banks. Concerns exist that collisions with vehicles may affect the demographics of wildlife populations and that potential disturbances and fragmentation associated with the highway may affect the ecological integrity of the landscape, particularly with regard to large carnivores. In response to these concerns, the North Carolina Department of Transportation (NCDOT) included three wildlife underpasses into the design of a 19.3- km section of the new U.S. Highway 64 in Washington County. The locations of the wildlife underpasses were determined based on a study by the North Carolina Wildlife Resources Commission during 1999. Areas that received frequent wildlife use were identified based on surveys of track counts, ditch crossings, and infrared cameras. The resulting data were used in combination with a geographic information system (GIS) to identify travel corridors for wildlife. Once the locations of the wildlife underpasses were established, the University of Tennessee initiated research in 2000 to determine whether wildlife passageways can mitigate impacts from highways. We chose a wideranging carnivore, the American black bear (Ursus americanus), as the focus species of our study because of its dependence on regional landscapes. We developed an experimental study design that will allow for collection of data before and after highway construction on a treatment and a control area. During the pre-construction phase of the study, we have collected over 6,000 locations on a total of 35 bears to document home-range sizes, activity patterns, movements, and habitat use. We are also analyzing 337 DNA samples from hair collected at 140 barbed-wire hair traps to estimate population density and to determine genetic relatedness within and among the two populations. Finally, we are using 243 photographs of wildlife from infrared cameras to measure use of the areas where the highway underpasses will be constructed. Field data collection during the pre-construction period was completed in June 2001; post-construction data will be gathered and compared after the anticipated completion of the highway in 2004

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

<div><p>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 (<i>Ursus americanus floridanus</i>) 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 (<i>A</i>_R = 3.57; <i>H</i>_E = 0.49) and effective population size was small (<i>N</i>_E = 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.</p></div

Spatial capture-recapture models for estimating density of female and male Florida black bears in the Highlands-Glades subpopulation of south-central Florida, USA (2010–2012).

<p>We modeled percent natural cover (Pnat) as a habitat covariate on density (<i>D</i>), allowed <i>D</i> to vary among sessions (Y), or fixed (~1) <i>D</i>. We modeled a trap-specific behavioral response (bk) and 2-class finite mixtures (h2) on the probability of detection at the activity center of an individual (<i>g</i>_<i>0</i>), and fixed the spatial scale of the detection function (σ). Model selection was based on ≤ 2 ΔAIC_<i>c</i>, which is the relative difference between AIC_<i>c</i> (Akaike’s Information Criterion corrected for small sample size) of the model and the highest ranked model. Weight (w_i) and log-likelihood (logLik) are presented for each model.</p

Locations of 46 sampling cells in south-central Florida, USA, in which a single, baited barbed-wire hair trap was placed in each cell to collect black bear hair for estimating density and population genetics of the Highlands-Glades subpopulation of Florida black bears (2010–2012).

<p>Locations of 46 sampling cells in south-central Florida, USA, in which a single, baited barbed-wire hair trap was placed in each cell to collect black bear hair for estimating density and population genetics of the Highlands-Glades subpopulation of Florida black bears (2010–2012).</p

Habitat fragmentation metrics estimated for natural habitats supporting the Highlands-Glades and Ocala-St. Johns subpopulations of Florida black bears.

<p>We estimated percent land area that was natural habitat (% HLA), patch density (PD; patches/km²), mean patch size (MPS; km²), and contagion (Contag; %) for lands occupied by the HGS, and compared to values produced by Hostetler et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181849#pone.0181849.ref089" target="_blank">89</a>] for lands occupied by the comparatively larger Ocala-St. Johns subpopulation.</p

Spatial capture-recapture model coefficient estimates (β) from the top spatially inhomogeneous density model for male and female Florida black bears in the Highlands-Glades subpopulation of south-central Florida, USA (2010–2012).

<p>Model structure included density (<i>D</i>) varying with percent natural cover (Pnat), a trap-specific behavioral response (bk) on the probability of detection at the activity center of an individual (<i>g</i>_<i>0</i>), and fixed spatial scale of the detection function (σ). Estimate standard errors (SE) and lower (LCL) and upper (UCL) 95% confidence limits are presented.</p

Sex-specific posterior modes of activity centers estimated by spatially inhomogeneous and homogenous density spatial capture-recapture models relative to percent natural cover for Florida black bears in the Highlands-Glades subpopulation of south-central Florida, USA (2010–2012).

<p>Posterior modes from inhomogeneous (varies by percent natural cover) and homogenous density models are indicated by red and black circles, respectively. Locational shifts for each posterior mode between models are denoted by solid black lines, and crosses (<b>×</b>) represent the 46 hair traps that were established. Locations where only a red circle is visible without a solid black connector line indicates a black circle is at the same location. Percent natural cover within the state space is the background color gradient from white (low %) to dark green (high %).</p