Floater mortality within settlement areas can explain the Allee effect in breeding populations

The Allee effect (the positive relationship between population growth rate and population size) is a constraint of some animal populations at low numbers, which increases their likelihood of extinction because of a decrease in reproduction and/or survival. We were able to demonstrate that the Allee effect can be the result of a mortality increase affecting floaters (i.e. dispersing individuals able to enter as breeders in the reproductive population when a breeding territory or a potential mate - owner of a suitable breeding territory - becomes available). Previously, potential mechanisms underlying Allee effects were always related to the breeding portion of a population only. In contrast, our understanding of or solutions to population declines due to the Allee effects can reside elsewhere, away from breeding territories. (C) 2007 Elsevier B.V. All rights reserved.