Impact of repeated human introductions and the Allee effect on invasive species spread

• A strong Allee effect is beneficial for early control of spreading invasive species.
• Human introductions push invasive populations above the critical threshold.
• We demonstrate the importance of human activity on invasive species populations.

A strong Allee effect, or density dependent growth, has been proposed as a justification for early control of some spreading invasive species. A strong Allee effect implies that if the invader can be caught early in a low density area, then the invasive species will not be able to establish in the new environment and will die off. Yet, economic activity is often responsible for repeated human introductions, and can increase the density of the invader thereby allowing establishment. In this paper, we examine the implications of repeated human introduced invasive species and determine the benefits of policies that reduce introductions. We use the emerald ash borer (EAB) in Ohio as an example and model the relationship between this invasive species with the native environment, as well as economic activity in Ohio. We show that when accounting for a strong Allee effect, the population of the EAB can be managed to remain below endemic levels; we can slow ash tree decline. Understanding the interaction between human activity, repeated introductions, and the Allee effect can assist policymakers in effectively reducing the establishment and spread of invasive species.