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Undesirable evolutionary consequences of trophy hunting


Phenotype-based selective harvests, including trophy hunting, can have important implications for sustainable wildlife management if they target heritable traits1,2,3. Here we show that in an evolutionary response to sport hunting of bighorn trophy rams (Ovis canadensis) body weight and horn size have declined significantly over time. We used quantitative genetic analyses, based on a partly genetically reconstructed pedigree from a 30-year study of a wild population in which trophy hunting targeted rams with rapidly growing horns4, to explore the evolutionary response to hunter selection on ram weight and horn size. Both traits were highly heritable, and trophy-harvested rams were of significantly higher genetic ‘breeding value’ for weight and horn size than rams that were not harvested. Rams of high breeding value were also shot at an early age, and thus did not achieve high reproductive success5. Declines in mean breeding values for weight and horn size therefore occurred in response to unrestricted trophy hunting, resulting in the production of smaller-horned, lighter rams, and fewer trophies.

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Figure 1: Selection against high-breeding-value rams imposed by trophy hunting.
Figure 2: Observed changes in mean weight and horn length and in the population size from 1972 to 2002.
Figure 3: Changes in the mean breeding value of cohorts born between 1967 and 2002.

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We thank the many students, colleagues, volunteers and assistants that contributed to this research over the past 30 years. B. Wishart initiated the Ram Mountain project. Our research was funded by the Alberta Conservation Association, Alberta Fish and Wildlife Division, Alberta Recreation, Sports, Parks and Wildlife Foundation, Eppley Foundation for Research, Foundation for North American Wild Sheep, National Geographic Society, Natural Environment Research Council (UK), Natural Sciences and Engineering Research Council of Canada, Rocky Mountain Elk Foundation (Canada), and the Université de Sherbrooke. We are grateful for the logistical support of the Alberta Forest Service.

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Correspondence to David W. Coltman.

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Coltman, D., O'Donoghue, P., Jorgenson, J. et al. Undesirable evolutionary consequences of trophy hunting. Nature 426, 655–658 (2003).

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