Perspective: Allee Effects in Theory and Reality.

The Allee effect is an important biological concept with a long history and broad interdisciplinary reach into mathematics and related fields. In this brief Perspective, we examine the pronounced mismatch between the limited evidence for Allee effects in the real world and the intense attention they receive in the theoretical literature. Our examination suggests that this theoretical enthusiasm is often driven less by biological facts than by the mathematical appeal of the dynamical complexity that Allee-type mechanisms introduce into models. The challenges inherent in empirical studies-including limited observation windows and the difficulty of isolating low-density effects within transient dynamics-have constrained empiricists' attention to Allee effects in connection with spatial processes, whereas this same interface is well studied in the theoretical literature. To help bridge this gap between theoretical studies and field observations, we advocate greater use of stochastic spatial models that can link processes such as local extinction, spatial spread, and pattern formation to the kinds of biological data available from real systems. Tighter connections are needed between theoretical models and the biological processes that inspire them, and mathematical research identifying spatial signatures of Allee effects would help clarify the importance of those effects in nature.