Abundance and density of Louisiana black bears on the Tensas River National Wildlife Refuge

Author

Mark Ryan Boersen

Date of Award

5-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Wildlife and Fisheries Science

Major Professor

Joseph D. Clark

Committee Members

Michael Pelton, Frank van Manen, Mary Sue Younger

Abstract

Extensive habitat loss throughout the historic range of the Louisiana black bear (Ursus americanus luteolus) has resulted in small remaining isolated populations existing primarily on publicly owned lands. The U.S. Fish and Wildlife Service provided federal protection to the Louisiana bear by granting it "threatened" status on the Endangered Species List in 1992. Accordingly, the Louisiana Black Bear Recovery Plan mandated research efforts to determine the current status of the remaining bear populations within the historic range.

I sampled the bear population at the Tensas River National Wildlife Refuge, the adjacent Big Lake State Game Management Area, and adjoining privately owned forested lands (these areas together are hereafter referred to as the Tensas River Tract) to estimate population size from 1998-99. Because the Tensas River Tract is entirely surrounded by agricultural lands, it represents an "island" situation permitting use of models that assume geographic population closure. The study area for the Tensas complex encompassed nearly all-available black bear habitat.

Two approaches were used to sample the bear population at Tensas. Livetrapping resulted in 50 captures of 42 bears during 2 years of study. However, the live-trapping sample seemed to be affected by unequal capture probabilities among bears. Therefore, a non-invasive sampling technique was employed to provide population estimates. This method was based on microsatellite DNA analysis of hair samples collected from hair-trapping stations to allow use of mark-resight population models. Hair traps were constructed throughout the study area to simultaneously sample the population. During 14 weeks of hairtrapping, project personnel collected 1,939 hair samples. A subsample of 116 hair samples was randomly chosen for analysis. All samples were analyzed at 8 microsatellite loci to individually identify bears. Matching samples were reanalyzed at 4 additional loci to improve identification power. Complete multilocus genotypes from 58 bears were obtained from 114 hair samples. Model Chao M_th produced an estimate for the Tensas bear population size of 115 (95% CI = 85-182), averaging 0.35 bears/km². My study provided the first estimate of population size for the Tensas bear population based on rigorous statistical sampling. The bear population at Tensas appears to have increased based on former guesses of population size by the U.S. Fish and Wildlife Service.

This study represents the first black bear population estimate in the Southeast based on non-invasive sampling techniques. The hair-trapping approach provided several advantages over livetrapping including increased sample sizes, low bias, and improved precision. Additionally, the genetic data can be used to assess genetic variability within and between populations. Inbreeding and genetic drift may have already impacted the isolated Tensas population. Tensas bears were found to have 1-2 fewer alleles per locus than populations in northwest Arkansas and east-central Louisiana.

Recommended Citation

Boersen, Mark Ryan, "Abundance and density of Louisiana black bears on the Tensas River National Wildlife Refuge. " Master's Thesis, University of Tennessee, 2001.
https://trace.tennessee.edu/utk_gradthes/6527