Can a Mate-Finding Allee Effect Be Elicited to Help Eradicate Invasive Mammals?

The Allee effect is an important ecological process that has implications for extinction of endangered species and for assisting the management of invasive species. Few instances of Allee effects have been quantified in nature due to the adaptive resilience of species and the difficulty in empirically linking ecological mechanisms to population change. While Allee effects could theoretically assist with invasive species eradications, the mechanism by which a management intervention could achieve both component and demographic Allee effects has not been tested. We developed an individual-based simulation model to explore whether the intentional disruption of animal behaviour could elicit a mate-finding Allee effect to facilitate the eradication of an invasive mammal. We used stoats (Mustela erminea) as a test species and generalised the results by examining the sensitivity of Allee effects to a range of biological attributes and management scenarios. The ecological challenge was to turn the colonising adaptations (high mobility, olfactory communication and delayed placental implantation) into vulnerabilities for Allee effects. Following an initial population reduction through trapping, reproductive pheromone decoys were deployed to disrupt mate finding. When key ecological, management and technological conditions were met during the deployment of decoys, an increase in the probability of eradication demonstrated a demographic Allee effect. The mate-finding Allee threshold occurred only at very low densities, indicating the importance of population control. The Allee effect increased with increasing number of deployed decoys and attractiveness to divert movement direction away from potential mates. Increasing the bias in random walk behaviour towards nearby decoys reduced mate finding, whereas low-biased random walk induced by detection of multiple scents increased reproduction. Increasing survival rates increased longevity and the time for individuals to find mates, which decreased the probability of an Allee effect. The modest increased probability of eradication under optimal biological and management conditions demonstrated the resilience of species to mate-finding Allee effects.