The importance of quantifying inbreeding costs relative to population dynamics to effectively manage endangered populations

Translating Effects of Inbreeding Depression on Component Vital Rates to Overall Population Growth in Endangered Bighorn Sheep

HEATHER E. JOHNSON,L. SCOTT MILLS,JOHN D. WEHAUSEN,THOMAS R. STEPHENSON,GORDON LUIKART

Conservation Biology

Volume 25, Issue 6, pages 1240–1249, December 2011

Here is a paper that would be of great interest to those engaged in the conservation efforts of wild goats and sheep.

Evidence of inbreeding depression can be detected from the fitness traits of animals, but, its effects on population growth rates of endangered species ha not been properly assessed. Here the researchers examined whether inbreeding depression was affecting Sierra Nevada bighorn sheep (Ovis canadensis sierrae), a subspecies listed as endangered under the U.S. Endangered Species Act. 

The objectives were

1)     To characterize genetic variation in this subspecies

2)     Test whether inbreeding depression affects bighorn sheep vital rates (adult survival and female fecundity)

3)      Evaluate whether inbreeding depression may limit subspecies recovery;

4)      Examine the potential for genetic management to increase population growth rates. 

 Matrix-based projection models demonstrated that inbreeding depression would not substantially inhibit the recovery of Sierra Nevada bighorn sheep populations in the next approximately 8 bighorn sheep generations (48 years).  Simulations of genetic rescue within the subspecies did not suggest that such activities would appreciably increase population sizes or growth rates during the period the researchers modeled (10 bighorn sheep generations, 60 years).

 Only simulations that augmented the Mono Basin population with genetic variation from other subspecies, predicted any significant increases in population size.  

The researchers say although they recommend that recovery activities should minimize future losses of genetic variation, genetic effects within these endangered populations—either negative (inbreeding depression) or positive (within subspecies genetic rescue)—appear unlikely to dramatically compromise or stimulate short-term conservation efforts.

 The researchers conclude that distinction between detecting the effects of inbreeding depression on a component vital rate (e.g., fecundity) and the effects of inbreeding depression on population growth underscores the importance of quantifying inbreeding costs relative to population dynamics to effectively manage endangered populations.