Application of Threshold Concepts in Natural Resource Decision Making

pp 67-86


Application of Threshold Concepts to Ecological Management Problems: Occupancy of Golden Eagles in Denali National Park, Alaska

  • Mitchell J. EatonAffiliated withPatuxent Wildlife Research Center, U.S. Geological SurveySoutheast Climate Science Center, U.S. Geological Survey Email author 
  • , Julien MartinAffiliated withPatuxent Wildlife Research Center, U.S. Geological SurveyFlorida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute
  • , James D. NicholsAffiliated withPatuxent Wildlife Research Center, U.S. Geological Survey
  • , Carol McIntyreAffiliated withNational Park Service
  • , Maggie C. McCluskieAffiliated withNational Park Service
  • , Joel A. SchmutzAffiliated withAlaska Science Center, U.S. Geological Survey
  • , Bruce L. LubowAffiliated withNatural Resource Ecology Laboratory, Colorado State University
  • , Michael C. RungeAffiliated withPatuxent Wildlife Research Center, U.S. Geological Survey

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In this chapter, we demonstrate the application of the various classes of thresholds, detailed in earlier chapters and elsewhere, via an actual but simplified natural resource management case study. We intend our example to provide the reader with the ability to recognize and apply the theoretical concepts of utility, ecological and decision thresholds to management problems through a formalized decision-analytic process. Our case study concerns the management of human recreational activities in Alaska’s Denali National Park, USA, and the possible impacts of such activities on nesting Golden Eagles, Aquila chrysaetos. Managers desire to allow visitors the greatest amount of access to park lands, provided that eagle nesting-site occupancy is maintained at a level determined to be acceptable by the managers themselves. As these two management objectives are potentially at odds, we treat minimum desired occupancy level as a utility threshold which, then, serves to guide the selection of annual management alternatives in the decision process. As human disturbance is not the only factor influencing eagle occupancy, we model nesting-site dynamics as a function of both disturbance and prey availability. We incorporate uncertainty in these dynamics by considering several hypotheses, including a hypothesis that site occupancy is affected only at a threshold level of prey abundance (i.e., an ecological threshold effect). By considering competing management objectives and accounting for two forms of thresholds in the decision process, we are able to determine the optimal number of annual nesting-site restrictions that will produce the greatest long-term benefits for both eagles and humans. Setting a utility threshold of 75 occupied sites, out of a total of 90 potential nesting sites, the optimization specified a decision threshold at approximately 80 occupied sites. At the point that current occupancy falls below 80 sites, the recommended decision is to begin restricting access to humans; above this level, it is recommended that all eagle territories be opened to human recreation. We evaluated the sensitivity of the decision threshold to uncertainty in system dynamics and to management objectives (i.e., to the utility threshold).


Golden Eagles Aquila chrysaetos Utility threshold Ecological threshold Decision threshold Occupancy modeling Structured decision-making Adaptive management Uncertainty Wildlife disturbance