Predator-driven component Allee effects may exacerbate the risk of extinction of small populations

Predator-driven component Allee effects in a wild ungulate

Aurélie Bourbeau-Lemieux, Marco Festa-Bianchet,Jean-Michel Gaillard,Fanie Pelletier

Article first published online: 15 FEB 2011
Ecology Letters

DOI: 10.1111/j.1461-0248.2011.01595.x

Here is a good paper on exacerbating effects of Allee effects (positive density dependence) on small populations. Negative density dependence of course is an important driver of population dynamics of large vertebrates. 

Allee effects can be generated by predation. Recent research has come up with potentially important indirect effects of predation on population dynamics. The researchers monitored for 27 years a bighorn sheep (Ovis canadensis) population that declined dramatically as cougar (Puma concolor) predation depressed survival. The researchers say predation led to a positive relationship between lamb survival and population size below a threshold, and to an overall positive relationship between yearling and adult ewe survival and population size. 

During years of high predation, lambs also suffer mortality through reduced growth. This contributed to a third of the total impact of predation on lamb survival. 

The researchers sign off saying “Our results support the contention that predator-driven component Allee effects may exacerbate the effects of other environmental drivers and increase the risk of extinction of small populations”.