Introduction: Population Biology, Evolution, and Control of Invasive Species

Invasion by nonindigenous species has been recognized as second only to loss of habitat and landscape fragmentation as a threat to global biodiversity (Walker & Steffen 1997). The economic impact of these species is a major concern throughout the world. For example, an estimated 50,000 nonindigenous species established in the United States cause major environmental damage and economic losses that total over an estimated U.S.$125 billion per year (Pimentel et al. 2000). Management and control of nonindigenous species is perhaps the biggest challenge that conservation biologists will face in the next few decades. The six papers in this special section and these introductory remarks consider the role that population biology can play in understanding invasive species through life-history studies, demographic models, genetic considerations, and knowledge of the ecology and evolution of both invasive and native species in a community context. Studies of genetic diversity and the potential for rapid evolution of invasive species may provide useful insights into what causes species to become invasive. Life-history studies may also lead to predictions of which species are likely to become serious pests or identify critical life-history stages during which control will be most successful. Population biology might be useful in identifying the point where containment rather than eradication efforts would be more practical. Demographic models may be useful for examining the spread of invasive species and methods of control. More information about the genetics and evolution of invasive species or native species in invaded communities, as well as their interactions, may lead to predictions of the relative susceptibility of ecosystems to invasion, identification of key alien species, and predictions of the subsequent effects of removal. Two major themes emerge from the papers in this special section. First, invasive species provide an exceptional opportunity for basic research in the population biology and short-term evolution of species. Many unresolved central issues in the application of genetics to conservation—such as the inbreeding effects of small populations and the importance of local adaptation—can be much better experimentally addressed with introduced species. Second, the management and control of invasive species is a controversial and incredibly complex problem. There may be much to be gained from the study of introduced species, but it is unclear how much this increased understanding of the biology of invasive species will be helpful in their management and control. In addition, the use of biological controls introduces a completely new set of dangers.