Risk and Nonindigenous Species Management ∗

S nonindigenous species threaten people by contributing to biodiversity loss and environmental damage (Elton; Kareiva). Managing such threats cost-effectively requires a consistent framework that captures the biological and economic circumstances that jointly determine the level of risk and the optimal mix of prevention and control strategies. The economic theory of endogenous risk provides such a framework (see Ehrlich and Becker; Shogren and Crocker). Endogenous risk refers to the notion that people and managers influence the risk they face through their behavior. They choose the level of risk they want to avoid through their effort and investments, while accounting explicitly for the costly tradeoffs involved in these decisions. This is in contrast to the traditional “damage function” perspective which tends to separate risk assessment from risk management (Freeman). When merged with applied population ecology, endogenous risk captures the risk–benefit tradeoffs created by ecosystem conditions, invasive species characteristics, economic circumstances, and the feedbacks between the systems (Crocker and Tschirhart). Our choices, driven in part by economic circumstances, affect the ability of a biological system to absorb these changes. Analyses that explicitly account for these economic