Oecologia

, Volume 144, Issue 2, pp 257–267

The role of predation in the decline and extirpation of woodland caribou

  • Heiko U. Wittmer
  • Anthony R. E. Sinclair
  • Bruce N. McLellan
Population Ecology

DOI: 10.1007/s00442-005-0055-y

Cite this article as:
Wittmer, H.U., Sinclair, A.R.E. & McLellan, B.N. Oecologia (2005) 144: 257. doi:10.1007/s00442-005-0055-y

Abstract

To select appropriate recovery strategies for endangered populations, we must understand the dynamics of small populations and distinguish between the possible causes that drive such populations to low numbers. It has been suggested that the pattern of population decline may be inversely density-dependent with population growth rates decreasing as populations become very small; however, empirical evidence of such accelerated declines at low densities is rare. Here we analyzed the pattern of decline of a threatened population of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada. Using information on the instantaneous rate of increase relative to caribou density in suitable winter foraging habitat, as well as on pregnancy rates and on causes and temporal distribution of mortalities from a sample of 349 radiocollared animals from 15 subpopulations, we tested 3 hypothesized causes of decline: (a) food regulation caused by loss of suitable winter foraging habitat, (b) predation-sensitive foraging caused by loss of suitable winter foraging habitat and (c) predation with caribou being secondary prey. Population sizes of caribou subpopulations ranged from <5 to >500 individuals. Our results showed that the rates of increase of these subpopulations varied from −0.1871 to 0.0496 with smaller subpopulations declining faster than larger subpopulations. Rates of increase were positively related to the density of caribou in suitable winter foraging habitat. Pregnancy rates averaged 92.4% ±2.24 and did not differ among subpopulations. In addition, we found predation to be the primary cause of mortality in 11 of 13 subpopulations with known causes of mortality and predation predominantly occurred during summer. These results are consistent with predictions that caribou subpopulations are declining as a consequence of increased predation. Recovery of these woodland caribou will thus require a multispecies perspective and an appreciation for the influence of inverse density dependence on population trajectories.

Keywords

Allee effect Apparent competition Inverse density dependence Rangifer tarandus caribou Population dynamics 

Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Heiko U. Wittmer
    • 1
    • 4
  • Anthony R. E. Sinclair
    • 2
  • Bruce N. McLellan
    • 3
  1. 1.Agroecology, Faculty of Agricultural SciencesUniversity of British ColumbiaVancouverCanada
  2. 2.Centre for Biodiversity ResearchUniversity of British ColumbiaVancouverCanada
  3. 3.Ministry of Forests, Research BranchRevelstokeCanada
  4. 4.Department of Environmental Science, Policy and ManagementUniversity of CaliforniaBerkeleyUSA

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