Long time dynamics of a three-species food chain model with Allee effect in the top predator

TL;DR

This paper analyzes a three-species food chain model with a strong Allee effect on the top predator, demonstrating the existence of a global attractor, decay estimates, overexploitation conditions, and pattern formation influenced by the Allee threshold.

Contribution

It provides the first robustness result for a spatially explicit three-species food chain with an Allee effect and explores the impact of the Allee threshold on dynamics and pattern formation.

Findings

Existence of a global attractor that is upper semicontinuous in the Allee threshold.

Decay rate to the attractor is proportional to m^γ, with explicit γ.

Overexploitation requires the Allee effect and is driven by the middle predator.

Abstract

The Allee effect is an important phenomenon in population biology characterized by positive density dependence, that is a positive correlation between population density and individual fitness. However, the effect is not well studied in multi-level trophic food chains. We consider a ratio dependent spatially explicit three species food chain model, where the top predator is subjected to a strong Allee effect. We show the existence of a global attractor for the the model, that is upper semicontinuous in the Allee threshold parameter $m$. To the best of our knowledge this is the first robustness result, for a spatially explicit three species food chain model with an Allee effect. Next, we numerically investigate the decay rate to a target attractor, that is when $m=0$, in terms of $m$. We find decay estimates that are $\mathcal{O}(m^{\gamma})$, where $\gamma$ is found explicitly. Furthermore, we prove various overexploitation theorems for the food chain model, showing that overexploitation has to be driven by the middle predator. In particular overexploitation is not possible without an Allee effect in place. We also uncover a rich class of Turing patterns in the model which depend significantly on the Allee threshold parameter $m$. Our results have potential applications to trophic cascade control, conservation efforts in food chains, as well as Allee mediated biological control.