Evaluating population expansion of black bears using spatial capture‐recapture

Abstract

The population of American black bears (Ursus americanus) in southern New York, USA has been growing and expanding in range since the 1990s. This has motivated a need to anticipate future patterns of range expansion. We conducted a non-invasive, genetic, spatial capture-recapture (SCR) study to estimate black bear density and identify spatial patterns of population density that are potentially associated with range expansion. We collected hair samples in a 2,519-km 2 study area in southern New York with barbed-wire hair snares and identified individuals and measured genetic diversity using 7 microsatellite loci and 1 sex-linked marker. We estimated a mean density of black bears in the region of 13.7 bears/100 km 2 , and detected a slight latitudinal gradient in density consistent with the documented range expansion. However, elevation and the amounts of forest, crop, and developed landcover types did not influence density, suggesting that bears are using a diversity of resources in this heterogeneous landscape outside their previously described distribution. These results provide the first robust baseline estimates for population density and distribution associated with different landcover types in the expanded bear range. Further, genetic diversity was comparable to that of non-expanding black bear populations in the eastern United States, and in combination with the latitudinal density gradient, suggest that the study area is not at the colonizing front of the range expansion. In addition, the diversity of landcover types used by bears in the study area implies a possible lack of constraints for further northern expansion of the black bear range. Our non-invasive, genetic, spatial capturerecapture approach has utility for studying populations of other species that may be expanding in range because SCR allows for the testing of explicit, spatial ecological hypotheses. Ó 2017 The Wildlife Society.

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.…”

Incorporating citizen science data in spatially explicit integrated population models

“…We set the scale parameter σ to 5 km, approximating the extent of movement of individual American black bears ( Ursus americanus) in a region of New York State (Sun et al. ).…”

“…We initialized the scaling parameter σ = 5 km and set the data augmentation parameters to M = 4,500 and ψ = 0.6 based on expectations of bear density in a geographically proximate region (Sun et al. ). We initialized SCR and PA detection probabilities to p SCR = 0.05 and p PA = 0.05.…”

Unifying population and landscape ecology with spatial capture–recapture

“…the spatial recaptures), and so in many situations, the spatial analysis is actually the more appropriate. For example, a black bear data set analyzed by Sun et al (2017) involved 457 unique 'individual by week by trap' encounter events over a 10 week study but 408 'individual by week' encounter events that would be used by ordinary CR models. Given the time and expense to collect such a data set, making use of the additional spatial recapture information is desirable.…”