Modeling black bear population dynamics in a human-dominated stochastic environment

Authors

D. L. Lewis, Colorado State University
S. W. Breck, USDA/APHIS/WS National Wildlife Research CenterFollow
K. R. Wilson, Colorado State UniversityFollow
C. T. Webb, Colorado State UniversityFollow

Document Type

Article

Date of this Version

2014

Citation

Ecological Modelling 294 (2014) 51–58.

Comments

U.S. government work.

Abstract

Many large carnivore populations exist in human-influenced stochastic environments where availabil-ity of natural food sources vary annually and anthropogenic food sources can supplement energeticdemands, but at a potential demographic cost due to human–wildlife conflict and subsequent conflictmanagement. Understanding how these competing factors influence a population is complex and dif-ficult to study, but here we demonstrate the utility of using a stochastic projection matrix model andperturbation analysis to gain insight into this problem. We modeled a black bear population subjectedto stochastic failures of fruiting and masting species, but with access to garbage in urban environments.We parameratized our model with data from a 6-year study on black bears in Aspen, Colorado and datasynthesized from other research studies. Using computer simulation, we investigated the effect that dif-ferent levels of conflict-bear removal can have on a bear population by comparing a “reference” scenariowhere bears did not benefit from human food sources or experience conflict-bear removals with twourban scenarios where bears had varying access to human foods, but conflict bears were removed. Weused perturbation analyses to evaluate consequences for changing population vital rates and to estimatethe impact each vital rate change had on population growth. Simulations were used to identify how muchvariation in each vital rate influenced variation in the population growth rate. We identified the survivalrate of breeding adult females during good natural food years as having the highest elasticity value. Wefound that the benefit of increased cub production from available human food sources during naturalfood failure years was quickly negated if management of conflict bears through removal reduced adultfemale survival. Increasing the frequency of years when natural food production fails resulted in dis-proportionate impacts from available urban food and conflict-bear removals, where population growthrates in a High Removal scenario declined 1.5 times faster than in the reference scenario. Our findingssuggest that for regions where changing climates will increase the frequency of natural food failures, man-agers may need to utilize non-lethal practices in managing conflict bears and municipalities will needto secure human food sources to reduce the need for conflict-bear removals and potential populationdeclines.