Occupancy, abundance, and population genetics of bobcats in western Maryland, USA
Date
2022
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Monitoring the status and trends of bobcat (Lynx rufus) distribution, abundance, and population genetics are important to wildlife professionals tasked with bobcat conservation and management. In Maryland, USA, bobcats are expanding their distribution east of bobcat range (i.e., Garrett and Allegany counties, Maryland), likely indicating an increase in abundance and prompting interest in bobcats’ status within western Maryland. My objectives were to 1) evaluate the efficacy of non-invasive genetic sampling techniques to detect and individually identify bobcats, 2) evaluate and predict bobcat occupancy, 3) estimate and compare bobcat abundance using 2 methods, and 4) assess bobcat population structure and genetic diversity in western Maryland. I conducted my study on 3 study areas in western Maryland including areas within and surrounding Potomac-Garrett, Savage River, and Green Ridge State Forests. On each study area, I overlaid a 5 × 8 grid network of 40 cells, each cell 5.5 km2 in size, to evenly distribute hair snare and camera locations. During January – March 2019 I conducted hair snaring surveys, scat collection surveys, and snow tracking surveys to compare each non-invasive genetic sampling technique by detections using mitochondrial DNA and individually identified samples using 10 microsatellite loci. During January – March 2019 and 2020, I placed 1 camera in each grid cell and visited cameras weekly to collect photo data and re-bait each location. I used single-season occupancy and Royle-Nichols models to estimate bobcat occupancy and abundance, respectively, over both years and all study areas. I surveyed transects consisting of hiking trails, closed or lightly used roads, and off-highway vehicle trails from May – August 2019 to collect scat samples. I screened scats by species and identified bobcat scats to the individual level for use in spatially explicit capture-recapture (SECR) models. I assessed population structure using the Bayesian clustering method in program STRUCTURE and principal coordinate analysis. In addition, I examined genetic diversity using heterozygosity and number of alleles per locus. ☐ Genetic data collected using non-invasive techniques during January – March 2019 resulted in 5 bobcat detections from hair snares, 9 from scat collection, and 8 via snow tracking. Few individuals were identified: 1 from hair snare samples, 5 from scat samples, and 0 from snow tracking. I organized my camera trapping survey into eight 7-day sampling periods and recorded a detection if ≥ 1 bobcat was detected at a camera location each week. In 2019 and 2020 the camera trapping effort resulted in 105 bobcat detections at 51 of 120 sites and 78 bobcat detection events at 42 of 119 camera locations, respectively. The top occupancy model using AIC included the covariates early successional cover, road density, and stream density which all reduced the probability of occupancy, and terrain ruggedness which increased the probability of occupancy. Occupancy probabilities across the 4 westernmost counties of Maryland ranged from 0.000 – 0.994 with a median of 0.119. The top Royle-Nichols model included the same covariates and relationships as the top occupancy model. I estimated abundance as 162.065 (95% confidence interval = 95.191 – 286.046) bobcats or a density of 6.03 bobcats/100 km2 (95% confidence interval = 3.54 – 10.64 bobcats/100 km2) within Garrett and Allegany counties. I surveyed 488.33 km of transect 5 times, collecting 816 scat samples for species and individual DNA analysis. Species identification yielded 241 bobcat samples from which I identified 23 individuals with ≥ 1 recapture and 12 individuals captured only once. The top SECR model estimated bobcat density as 4.14 bobcats/100 km2 (95% confidence interval = 2.84 – 6.03). I found bobcats in western Maryland to be members of a single population with no clustering of individuals from within study areas. I documented an average of 7.1 alleles per locus and heterozygosity ranging from 0.500 – 0.853 per locus (x̅ = 0.752). My research suggests that bobcats are distributed across western Maryland with density estimates lower than nearby estimates in Virginia and West Virginia, USA reported in the literature. Bobcats in western Maryland are members of a single, genetically diverse population. Managers should consider how land cover types, environmental factors, and human impacts facilitate or inhibit bobcat occurrence, abundance, and gene flow as bobcats expand throughout Maryland. Furthermore, this study illustrates the efficacy of both camera surveys and scat collection for estimating bobcat abundance in this region.
Description
Keywords
Bobcat, Noninvasive genetic sampling, Occupancy modeling, Population genetics, Royle-Nichols model, Spatially explicit capture-recapture modeling