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Importance of Genetic Variation to the Viability of Mammalian Populations

Robert C. Lacy
DOI: http://dx.doi.org/10.2307/1382885 320-335 First published online: 21 May 1997


Small populations lose genetic variability because of genetic drift, and inbreeding within populations can further decrease individual variability. Lower variation depresses individual fitness, resistance to disease and parasites, and flexibility in coping with environmental challenges. Lower variation decreases mean fitness of populations (population growth rates), resilience, and long-term adaptability. Genetic drift can threaten viability of populations not just by depleting variation, but also by replacing natural selection as the predominant force driving evolutionary change. Although most genetic studies use laboratory or domesticated populations, evidence is accumulating that the effects of inbreeding are at least as severe on wild animals in natural habitats. Natural selection is expected to reduce the frequency of deleterious alleles in populations that persist through bottlenecks, but as yet there is little evidence for such purging of the genetic load in mammalian populations. No species of mammal has been shown to be unaffected by inbreeding. Genetic problems are contributing to the decline and vulnerability of at least several mammalian taxa. Genetic threats to population viability will be expressed through their effects on and interactions with demographic and ecological processes. Theoretical analyses, experimental tests, field studies, and conservation actions should recognize the fundamental interdependency of genetic and non-genetic processes affecting viability of populations.

Key words
  • conservation
  • extinction
  • genetic drift
  • genetic variation
  • inbreeding depression
  • population viability