Misapplied management makes matters worse: Spatially explicit control strategies that leverage biotic interactions may more effectively prevent invader spread

Background/Question/Methods

A wide range of approaches have been used to manage the spread of invasive species, yet invaders continue to be challenging to control. Worse yet, in some cases, management actions have no effect on or may even inadvertently benefit the targeted invader. Here, we explore the conditions under which such wasted effort may arise, using the mid-20th century management of the Red Imported Fire Ant, Solenopsis invicta, in the United States as a case study. Introduced around 1940, the fire ant has spread widely and proven to be a problematic pest. Historically, fire ants have been managed with broad-spectrum pesticides; unfortunately, these efforts have been largely unsuccessful. We hypothesize that, by also killing native ants, mass pesticide application reduced competitive burdens on fire ants, and as a result, enabled fire ants to invade more quickly than they would have in the absence of management. We use a mechanistic model, in which we explicitly model competition between native and invasive ants and the location of pesticide applications, to investigate potential ecological mechanisms underlying such invasion patterns and to propose alternative control strategies.

Results/Conclusions

Model results suggest that mass pesticide application could have contributed to the rapid spread of fire ants observed in the southeastern United States. Broad-spectrum pesticides, which kill both native and invasive ants, can significantly change the rate at which an invader spreads. However, the location of the disturbance relative to the invading wave front determines the direction and magnitude of this change. Depending on where it is applied, the same management effort can have a positive, neutral or negative effect on the progress of an invasion. Such impacts are greatest when native ants are stronger competitors, suggesting that existing biotic interactions play an important role in management outcomes. When designing management, the target species is often considered alone; however, this work suggests that explicitly leveraging existing biotic interactions, specifically competition with native species, can significantly increase the efficacy of management. Our model not only highlights the potential unintended consequences of ignoring biotic interactions, but also provides a framework for developing spatially explicit management strategies that take advantage of these biotic interactions to work smarter, not harder.