Allee effects in biological invasions

TLDR

The dynamics of small populations, especially in invading species, are crucial because the Allee effect—reduced fitness at low density—can alter spatial ranges, spread, and control efficacy. The authors aim to review Allee effect theory and its empirical support, and to evaluate how detection of the effect informs invasive species management. The study synthesizes theoretical and empirical literature and examines detection methods for Allee effects in invasive species. Allee effects lengthen lag times, slow spread, reduce establishment chances, and alter optimal control decisions, costs, and risk estimates.

Abstract

Abstract Understanding the dynamics of small populations is obviously important for declining or rare species but is also particularly important for invading species. The Allee effect, where fitness is reduced when conspecific density is low, can dramatically affect the dynamics of biological invasions. Here, we summarize the literature of Allee effects in biological invasions, revealing an extensive theory of the consequences of the Allee effect in invading species and some empirical support for the theory. Allee effects cause longer lag times, slower spread and decreased establishment likelihood of invasive species. Expected spatial ranges, distributions and patterns of species may be altered when an Allee effect is present. We examine how the theory can and has been used to detect Allee effects in invasive species and we discuss how the presence of an Allee effect and its successful or unsuccessful detection may affect management of invasives. The Allee effect has been shown to change optimal control decisions, costs of control and the estimation of the risk posed by potentially invasive species. Numerous ways in which the Allee effect can influence the efficacy of biological control are discussed.