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Keywords:

  • Ursus;
  • Chao estimator;
  • count data;
  • PVA;
  • Yellowstone;
  • senescence;
  • grizzly bear

Abstract

Sampling effort and demographic assumptions may powerfully shape conclusions about the status of endangered species. We re-examined data sets that suggest recent increases, and hence relative safety from future extinction, of the grizzly bear population inhabiting the Greater Yellowstone Ecosystem (GYE), one of the best studied large carnivore populations in the world. We find that inadequate attention to increasing observation effort and also to the life history characteristics of bears is likely to have substantially influenced past analyses of the population's trajectory. We conclude that the GYE grizzly has probably increased far less than generally believed, but also that past analyses have been too inaccurate to allow any firm conclusions about the dynamics or status of this population. The problems we illustrate here apply to many other threatened species and suggest the need for more careful consideration of observation processes that can shape our perceptions of species’ history and status.