Masters Theses

Date of Award

5-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Wildlife and Fisheries Science

Major Professor

Michael R. Pelton

Committee Members

Joe Clark, David Buehler, Dewey Bunting

Abstract

Previous estimates of black bear (Ursus americanus) population density from Great Smoky Mountains National Park (GSMNP or Park) were low to intermediate when compared to other populations throughout the range of the species. These estimates conflicted with other research on GSMNP bears that indicated a high-density population with consistent growth from the early 1970's to the late 1980's. Thus, the focus of my research was to calculate appropriate estimates of population size and density and evaluate them with respect to trapping regime, demographic data, and hard mast production.

I determined effective study area sizes by calculating the average distance between summer centers of activity and capture locations. The average distance for females approximated the average summer home range radius (1.3 km), while the average distance for males was roughly half the average summer home range radius (1.9 km). The mean distance for males was misleading because the distribution was bimodal with one node located near the maximum distance (2.5 km). I used these distances (1.3 and 2.5 km, respectively) as radii for circles circumscribed around each trap site to determine the effective study area sizes. Size of the current study area for males and females is 254.7 km2 and 112.6 km2, respectively.

I used summer capture data of black bears from GSMNP to estimate population size and demographic parameters. Summer trapping between 1972 and 1991 resulted in 887 (501♂; 386♀) captures of 558 (335♂; 223♀) individual bears. For females, average time interval between first and second captures (x- = 2.38 years, SD = 1.85, n = 78) was longer (t' = 3.01, df = 127, P = 0.0031) than the average time interval between subsequent captures (x- = 1.61 years, SD = 1.09, n = 54). Females were older (x- = 6.80, SD = 3.46, n = 211) than males (x- = 4.85, SD = 2.51, n = 321) (t' = 7.04, df = 351, P < 0.001).

Using den records from 1978-1991, I calculated litter size, sex ratio, and cub survival. The average size of 74 litters was 2.24 with a sex ratio of 102♂:100♀. Overall cub survival was 61.3% with females and cubs from intermediate-size litters exhibiting slightly higher survival rates.

I estimated population size using Calendar of captures (or backdating), Lincoln-Petersen, nonparametric, and Jolly-Seber (computer program JOLLY) population estimators. With the exception of the nonparametric estimator, all were highly correlated. JOLLY estimates appear to be most appropriate for long-term studies with low capture probabilities. JOLLY produced an average annual estimate of 185 animals from 1973 to 1990; this equated to a mean density of 1.36 bears/km2. Lincoln-Petersen estimates and trends were surprisingly consistent with those from JOLLY. Backdating provided a reasonable baseline population estimate but the nonparametric estimator was inappropriate for our data set. My data indicated that population estimates generated with <5 years of data may be biased because of long inter-capture intervals for individual bears. This is especially relevant if capture probabilities are low. Using backdating data, the proportion of females in the population was negatively correlated with population size (P = 0.00228).

I estimated population size on groups of trap lines that were consistently sampled over a given time interval because of inconsistencies in trapping from year to year. This partitioning of the data provided an opportunity to examine the effects of study duration and altered trapping regimes on population estimates. Longer time intervals provided more reliable population estimates, but our data indicate inconsistent trapping does not necessarily invalidate the usage of such data to estimate population size. Average population densities for groups of trap lines ranged between 0.81 and 2.47 bears/km2.

Model selection in JOLLY seemed to indicate males and females exhibit different population dynamics. Female models indicated stability with internal recruitment (model A' - death but no immigration) while male models demonstrated more external population forces (model A -death and immigration).

I incorporated estimates of demographic parameters from den work (litter production rate, litter size, and cub survival), computer program JOLLY (adult survival), and backdating (sub-adult survival and beginning population size) into computer program ANURSUS in an attempt to rectify population estimates with demography. ANURSUS simulations predicted severe population declines from 1991-1996 using both stochastic (44% - density independent) and deterministic models (33 % - density independent; 59% - density dependent). Population estimates for 1992 and 1993, however, contradict the simulation results. Estimates of sub-adult and adult survival were suspect and likely caused the predicted declines.

I calculated 4 indices of trap activity to determine whether or not capture success is a reflection of population size. All indices were correlated with population estimates, with the percentage of nights with no activity and the percentage of nights with bear activity exhibiting the strongest relationships. I also calculated 4 indices of female reproductive status to examine potential density-dependant impacts on reproduction. None of the indices were correlated with population estimates.

Using National Park Service (NPS) hard mast index data, I investigated relationships between population size and hard mast production. No distinctive pattern was evident. The most prominent correlations were between population estimates and hard mast production of the same year; this may indicate that both mast production and the bear population respond to the same environmental and climatic conditions.

I constructed models to predict black bear ages from morphological measurements. Because of sexual dimorphism and differential growth rates, I created separate models, by sex, for wild and panhandler Park bears. Total length, height at shoulder, chest circumference, neck circumference, weight, and distance between ears were important (P< 0.0001) predictors of age. However, bears ≥ 5.5 years were indistinguishable with these models. Although models were not applicable beyond the population they were developed for, the method is potentially suitable for most black bear populations. This predictive relationship between morphometrics and age should aid nuisance relocations, telemetry studies, and researchers with bears of unknown age.

Future research on black bear density estimation should utilize home range data to establish trapping grids or routes that effectively cover the desired area. Emphasis should be placed on effectively sampling females because of the primary importance of females to population dynamics and the relative unreliability of male home range estimates. Distance between traps should equal the average female summer home range diameter to provide maximum coverage without gaps in the trapping grid.

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