Rats dying for mice: Modeling the competitor release effect

Authors

Stephane Caut, Ecologie, Systématique & Evolution, UMR CNRS 8079, Bat 362, Univ Paris-Sud, 91405 Orsay Cedex, France
Jorge G. Casanovas, Dynamical Systems Group, Depto. Ecologia. Fac. Biological Sciences, Universidad Complutense de Madrid
Emilio Virgos, Dpto.Matemáticas, Física Aplicada y Ciencias de la Naturaleza, ESCET, Universidad Rey Juan Carlos. C/Tulipán s/n, Móstoles, Spain
Jorge Lozano, Dpto.Matemáticas, Física Aplicada y Ciencias de la Naturaleza, ESCET, Universidad Rey Juan Carlos. C/Tulipán s/n, Móstoles, Spain
Gary W. Witmer, USDA-APHIS-Wildlife ServicesFollow
Franck Courchamp, Ecologie, Systématique & Evolution, UMR CNRS 8079, Bat 362, Univ Paris-Sud, 91405 Orsay Cedex, France

Document Type

Article

Date of this Version

November 2007

Comments

Published in Austral Ecology (2007) 32, 858–868.

Abstract

Introduced vertebrate predators are one of the most important threats to endemic species throughout a range of ecosystems, in particular on islands in biodiversity hot spots. Consequently, the reduction of predator numbers is considered a key conservation action in the management of many native vertebrates vulnerable to predators. It is now established that control attempts may affect non-target species through trophic interactions, but little is known concerning their consequences on competitive relationships. We study a mathematical model mimicking the effects of controlling introduced species in the presence of their competitors. We used two competing rodents to illustrate our study: black rats, Rattus rattus, and mice, Mus musculus. Analyses of the model show that control of only one introduced species logically results in the dramatic increase of the overlooked competitor. We present empirical data that confirm our theoretical predictions. Less intuitively, this process, which we term ‘the competitor release effect’, may also occur when both introduced competitors are simultaneously controlled. In our setting, controlling both predators can promote their coexistence. This occurs as soon as the inferior competitor benefits from the differential effect of the simultaneous control of both competitors, that is, when the indirect positive effect of control (the removal of their competitors) exceeds its direct negative effect (their own removal). Both control levels and target specificity have a direct influence on the extent of this process: counter-intuitively, the stronger and more specific the control, the greater the effect. The theoretical validation of the competitor release effect has important implications in conservation, especially for control management.