Small Population Biology
The National Bison Range research site from space. The Range is an island refuge in an agricultural landscape.
Rocky Mountain bighorn ewe "Catfish" and her newborn lamb "Marmot" at the National Bison Range research site.
Many animal populations that were once numerous and widely distributed have been subdivided and reduced in number by a rapidly growing human population. Small, isolated populations pose special problems for conservation. Among these is the potential for loss of individual and population fitness from “inbreeding”. Despite concern about inbreeding, surprisingly little is known about the timescale over which inbreeding effects may develop in natural populations or the number and kinds of traits likely to be affected.
Our objective in this long-term study is to answer these two questions for a population of bighorn sheep isolated at small size for 65 years. Our conclusions to date were recently published in the Proceedings of the Royal Society B (Genetic rescue of an insular population of large mammals) and highlighted in research commentaries by the journals Science and Nature. In this paper, we report that significant inbreeding effects accumulated in less than 10 bighorn generations and that adverse affects were detectable in almost every trait we were able to measure. Affected traits included male and female longevity, male and female reproductive success, birthing date and birth weight.
MOCSI research biologist Jack Hogg records birth weight for a bighorn lamb.
The take home message from this study is that significant inbreeding effects – effects sufficient to jeopardize population persistence – can accumulate in ecological time. Connecting isolated populations by encouraging migration is the obvious remedy. However, this is easier said than done. The problem of restoring and maintaining connectivity is the subject of a companion study of bighorn migration in the Canadian Rockies of southwestern Alberta.
Collaborators/cooperators:
- Steve Forbes
- Brian Steele
- Gordon Luikart
- Dave Coltman
- Jocelyn Poissant
- US Fish and Wildlife Service