, Volume 171, Issue 1, pp 295–307 | Cite as

Evaluating apparent competition in limiting the recovery of an endangered ungulate

  • Heather E. Johnson
  • Mark Hebblewhite
  • Thomas R. Stephenson
  • David W. German
  • Becky M. Pierce
  • Vernon C. Bleich
Conservation ecology - Original research


Predation can disproportionately affect endangered prey populations when generalist predators are numerically linked to more abundant primary prey. Apparent competition, the term for this phenomenon, has been increasingly implicated in the declines of endangered prey populations. We examined the potential for apparent competition to limit the recovery of Sierra Nevada bighorn sheep (Ovis canadensis sierrae), an endangered subspecies under the US Endangered Species Act. Using a combination of location, demographic, and habitat data, we assessed whether cougar (Puma concolor) predation on endangered bighorn sheep was a consequence of their winter range overlap with abundant mule deer (Odocoileus hemionus). Consistent with the apparent competition hypothesis, bighorn sheep populations with higher spatial overlap with deer exhibited higher rates of cougar predation which had additive effects on adult survival. Bighorn sheep killed by cougars were primarily located within deer winter ranges, even though those areas constituted only a portion of the bighorn sheep winter ranges. We suspect that variation in sympatry between bighorn sheep and deer populations was largely driven by differences in habitat selection among bighorn sheep herds. Indeed, bighorn sheep herds that experienced the highest rates of predation and the greatest spatial overlap with deer also exhibited the strongest selection for low elevation habitat. Although predator-mediated apparent competition may limit some populations of bighorn sheep, it is not the primary factor limiting all populations, suggesting that the dynamics of different herds are highly idiosyncratic. Management plans for endangered species should consider the spatial distributions of key competitors and predators to reduce the potential for apparent competition to hijack conservation success.


Conservation Cougar Ovis canadensis sierrae Predation Sierra Nevada bighorn sheep 



We are grateful to all the people who have collected data on bighorn sheep, mule deer, and cougars in the Eastern Sierra including C. Baker, L. Bowermaster, J. Davis, V. Davis, K. Ellis, J. Erlenbach, A. Feinberg, J. Fusaro, L. Greene, D. Jensen, M. Kiner, K. Knox, K. Monteith, R. Noles, J. Ostergard, N. Partridge, P. Partridge, C. Schroeder, D. Spitz, A. Stephenson, J. Wehausen, and others. We thank Landells Aviation and Quicksilver Air for safely conducting bighorn sheep and deer helicopter captures. We are grateful to L.S. Mills, M. Mitchell, D. Pletscher, G. Luikart, and H. Robinson for providing constructive discussion and comments on this manuscript. We also thank J.-M. Gaillard and 2 anonymous reviewers for their suggested revisions. CDFG and the Canon National Parks Scholars Program provided funding for this work.


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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Heather E. Johnson
    • 1
    • 4
  • Mark Hebblewhite
    • 1
  • Thomas R. Stephenson
    • 2
  • David W. German
    • 2
  • Becky M. Pierce
    • 2
  • Vernon C. Bleich
    • 3
  1. 1.College of Forestry and ConservationUniversity of MontanaMissoulaUSA
  2. 2.California Department of Fish and GameSierra Nevada Bighorn Sheep Recovery ProgramBishopUSA
  3. 3.Department of Biological SciencesIdaho State UniversityPocatelloUSA
  4. 4.Colorado Parks and WildlifeDurangoUSA

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