Can phenotypic rescue from harvest refuges buffer wild sheep from selective hunting?

Area of Science:

• Evolutionary biology
• Wildlife management
• Conservation science

Background:

• Human harvesting can unintentionally drive evolutionary changes in wild populations, potentially harming natural resource management.
• Harvest refuges are theorized to buffer these effects by providing a source of unselected individuals, but their real-world efficiency is poorly understood.

Purpose of the Study:

• To investigate whether rams migrating from refuges to harvested areas can mitigate the effects of selective trophy harvesting on bighorn sheep horn size.
• To assess the long-term impacts of selective harvesting on bighorn sheep horn morphology and life history traits in Alberta, Canada.

Main Methods:

• Analysis of harvest records for over 7000 bighorn rams (Ovis canadensis) in Alberta, Canada, from 1974 to 2011.
• Comparison of horn size and age at harvest between rams taken near and far from established harvest refuges.
• Examination of temporal trends in horn length and age at harvest across different areas relative to refuges.

Main Results:

• Rams harvested near refuges had slightly larger horns (approx. 3% longer) and were older, suggesting some migration from refuges.
• Despite this migration, rams from areas both near and far from refuges exhibited similar declines in horn length over time.
• These findings indicate that the influx of rams from refuges was insufficient to counteract the selective pressures of trophy harvesting.

Conclusions:

• Harvest refuges alone are not sufficient to mitigate the evolutionary consequences of selective trophy hunting in bighorn sheep populations.
• Selective hunting of highly mobile animals, like rams that move between refuges and harvested areas, may alter population genetic structure.