On Prevention and Control of an Uncertain Biological Invasion

This paper examines how optimal prevention and control policies depend on the economic and biological characteristics of a randomly introduced biological invasion where the objective is to minimize the expected social costs from prevention, control, and invasion damages. The results characterize how optimal prevention and control policies vary with the initial invasion size, the invasion growth rate, and the probability distribution of introductions. The paper also examines the conditions under which the optimal policy relies solely on either prevention or control, the conditions under which it is optimal to completely prevent new introductions, and the conditions under which eradication of established invasions is optimal All rights reserved. Readers may make verbatim copies of this document for non-commercial purposes by any means, provided that this copyright notice appears on all such copies. The invasion of ecological systems by non-indigenous species is a significant component of global environmental change (Vitousek et. al.) that imposes substantial economic and ecological damages. In the United States alone, the number of harmful invasive species is in the thousands, approximately one-fourth of the value of the countryNs agricultural output is lost to non-indigenous plant pests or the costs of controlling them (Simberloff), and the total costs of non-indigenous species have been estimated to be as high as $137 billion per year (Pimentel, et. al.). Prevention and control are the two basic ways the costs of an invasive species can be reduced. Approximately half of U.S. federal expenditures for invasive species are for prevention activities (National Invasive Species Council). Control of an invasive species after it becomes established may involve significant control costs and pest damages. For example, $5 billion are spent annually on herbicides (Keily, et.al.) while the value of annual crop losses to weeds has been estimated at $20 billion (in 1991 dollars) (AHPIS PPD) with roughly 50-75% of these costs attributed to nonindigenous weed species (OTA). Prevention policy reduces the invasive species damages and the need for control, but prevention is costly, imperfect, and may restrict the flow of beneficial goods and services. Given that prevention and control have different costs and that they target the damages from invasive species in different ways, a fundamental issue in invasive species management is the appropriate balance between prevention and control policy. 1 2 The purpose of this paper is to examine how optimal prevention and control policies depend on the economic and biological characteristics of a randomly …