A Structured Decision-Making Framework for Controlling, Monitoring, and Containment of Invasive Species through Trapping: An Application to the Argentine Black and White Tegu

Science Center Objects

USGS is applying decision analysis to identify cost-effective methods for controlling invasive species like the Argentine black and white tegu.

Invasive black and white tegu lizards (Salvator merianae).

Invasive black and white tegu lizards (Salvator merianae). 

(Public domain.)

The Science Issue and Relevance: The Argentine black and white tegu and other newly invasive reptiles brought to the U.S. through the pet trade pose a threat to native species in the Everglades including Federally protected species. The population size of invasive species is often unknown until the population has grown large enough to cause noticeable damage and is difficult to control. Trapping is a common method of removal for invasive animals, and it also can serve as a method of monitoring a population. Uncertainty in population size leads to costly trapping policies, as more traps are needed to hedge bets against uncertainty. We propose to apply decision analysis to identify cost-effective methods for controlling tegus. Our findings should be applicable to other invasive animal species in South Florida and elsewhere.

 

Methodology for Addressing the Issue: Until recently, there was no method to estimate abundance while considering imperfect detection of animals from the recovery of unmarked animals. We are proposing to apply a newly developed method that allows for the estimation of abundance based on the known number of traps deployed and removals. We would then incorporate this method in an optimal trapping framework (using stochastic dynamic programming) to inform how many traps should be deployed to best meet eradication and monitoring objectives of tegus for the least cost possible. Trapping may be paired with other forms of monitoring (e.g., camera trapping) in this framework to help inform monitoring and trapping efforts to improve early detection rapid response. 

Trapping may also be used as a form of containment, for example, in keeping tegus out of Everglades National Park. We propose extending this trapping framework to inform trapping policies in different spatial zones and in connecting corridors. We will apply this framework to the problem of monitoring, eradication, and control of tegus in the Greater Everglades ecosystem, to further the efforts of an already ongoing collaboration between state and federal management agencies.

 

Future Steps: This framework would inform how many traps to set in each location and corridor in order to achieve specified management goals of eradication and containment. Given target levels for the long-run average population size in each spatial zone, a least-cost control policy can be determined. Such a framework has the added benefit of informing policy makers on how much it will cost to control an invasion to a specified level. This would provide an analytical framework for the first formal implementation of adaptive management for the control of invasive species in the Everglades.