Full curl bighorn sheep (L Simmons; Travel Alberta)
Recreational hunting is a popular sport in Western Canada, generating considerable revenues for local communities and funding for conservation programs. Wildlife managers aim to balance hunting opportunities with the maintenance of healthy populations; however, sustained harvests can lead to changes in animal behaviour, population demographics (e.g., age structure), and even physical traits.
Sport hunting regulations for male sheep, or rams, typically set a minimum horn curl for an individual to be legally harvested (for example, the tip of the horn extending beyond the eye or making a complete 360 degree turn). Minimum size regulations limit the harvest of males and protect younger animals; however, they may also create artificial selection for smaller horns as individuals with full curls are more likely to be taken as trophies. This hunting pressure conflicts with natural selection processes, which favour larger horns for competing with other rams over mating rights.
Bighorn sheep fighting at Jasper National Park (T Elniski; Government of Alberta)
To determine whether selective trophy hunting causes evolutionary changes in bighorn sheep populations, researchers from the Université de Sherbrooke and University of Alberta examined 39 years of data on the horn sizes and genetic structure of sheep from Ram Mountain, Alberta. The Ram Mountain bighorn population was subject to 23 years of sustained hunting pressure before harvests were reduced, and eventually stopped. The researchers found that trophy hunting diminished the genetic value of horn length, creating an artificial selection for shorter horns. They also found that recovery by natural selection occurred at a much slower rate than the hunting-induced changes. This study shows the potential evolutionary consequences of trophy hunts targeting specific physical traits. Further, post-hunt population monitoring revealed that genetic changes persist long after harvests stop, creating additional challenges for the conservation of game species.
This is a summary article authored by Charlie Loewen. For further information, please see the original published research:
Gabriel Pigeon, Marco Fest-Bianchet, David W. Coltman and Fanie Pelletier (2016) Intense selective hunting leads to artificial evolution in horn size. Evolutionary Appliations, 9:521–530 (doi:10.1111/eva.12358).