Biological Control in Support of Nature Conservation

Natural ecosystems, biological reserves, and other undeveloped land and water of conservation importance are regularly invaded by nonindigenous plant and animal species. Such invasions reflect, in part, the level of human activity in the region, with the consequent human-assisted movement of adventive species by commerce (Fig. 1.1). Some adventive species threaten the continued existence of native flora or fauna, by competition or direct attack. Other adventive species alter basic properties of the ecosystems they invade, rendering them less suitable for the continued existence of broad sets of native species. Efforts to combat such adventive species by chemical or mechanical means are often unsatisfactory, the former because of the risk of chemical pollution, damage to nontarget species, and cost, and the latter because of cost and the difficulty of applying mechanical remedies to any large region. Biological control, through the introduction of natural enemies specialized to attack the undesired adventive species, offers a method to solve this problem in many cases. This chapter discusses the principles behind the use of biological control for conservation of natural areas, the past achievements of such efforts, and future prospects for additional applications. Means to ensure that biological control agents themselves do not become environmental pests are discussed in the safety sections in Chapters 8, 9, 10, and 11.