Optimal Control Strategies for Invasive Exotics in South Florida

Science Center Objects

The establishment and proliferation of exotic plants and animals can interfere with native ecological processes and can cause severe stress to sensitive ecosystems.

Researchers capture a Burmese python in the Everglades

Researchers capture a Burmese python in the Everglades

The Science Issue and Relevance: The establishment and proliferation of exotic plants and animals can interfere with native ecological processes and can cause severe stress to sensitive ecosystems. Perhaps nowhere in the contiguous U.S. is this more evident than in South Florida, where millions of dollars are spent annually to monitor and control the spread of exotics such as Brazilian pepper, melaleuca, the Mexican bromeliad weevil, and Burmese python, just to name a few. With the number of established exotic species now numbering well into the hundreds in South Florida, the potential impact of invasives has emerged as a high-priority issue in planning the restoration and conservation of the Greater Everglades. However, agencies with responsibility for protecting native ecosystems in South Florida have limited resources with which to control the spread of invasive exotics. Therefore, there is a pressing need to develop cost-effective monitoring programs, new control methods, and decision-support tools.

Methodology for Addressing the Issue: Within the constraints of their budgets, responsible agencies must routinely make tradeoffs inherent in controlling the spread of invasives; e.g., monitoring abundance in well-established areas vs. monitoring potential sites for colonization, eradicating large infestations vs. eradicating newly colonized sites, and monitoring populations vs. implementing control measures. There are also temporal tradeoffs that must be considered because decisions made now produce a legacy for the future (e.g., how long to wait before implementing controls). These tradeoffs can be investigated formally within the context of a decision-theoretic framework, which can identify optimal actions based on management goals and constraints, available budgets, and the demography of the invasive population. Key advantage of a decision-theoretic framework is the ability to make optimal decisions in the face of various sources and degrees of uncertainty, such as the rate at which an invasive will colonize new areas or the variable effectiveness of control measures. The product of this approach is a state-dependent management strategy that prescribes an optimal action for each time period for each possible state of the system. In this case, the state of the system would be characterized by extant knowledge of the spatial distribution and abundance of the target invasive. The state-dependent strategy can also be adaptive, as predicted and observed system responses are compared over time.

Future Steps: Current focus is on the control of Burmese pythons and Argentine black and white tegu lizards. Manuscripts describing assessment and control methods are being prepared.

Publications:

Bonneau, M., F. A. Johnson, and C. M. Romagosa. 2016. Spatially explicit control of an invasive species using a reaction-diffusion model.  Ecological Modeling: In press.