Invasive Species

As global travel and trade increase and the global climate changes, the dispersal of species from their [Page 422]natural range into new areas is bound to increase, increasing the likelihood that species will become invasive, often with unexpected consequences. Effective communication with diverse stakeholders is essential for reaching a shared understanding of the perceived costs and benefits of invasive species to the environment, the economy, and society and to inform decisions that prioritize actions and resources to manage the risks posed. This entry considers the traits that make species invasive, the risks invasive species pose, methods for their assessment and management, and the important role of communication throughout the risk management cycle. Stakeholders must work together to address invasive species issues, and understanding risk perception and effective risk communication will be increasingly important components of the management of invasive species.

Invasive alien species are defined by the International Union for the Conservation of Nature (IUCN) as all organisms, animals, or plants that have a negative effect on “the local ecosystem and species” because humans have introduced them to an area that is outside of “their natural range,” and they then establish themselves and become broadly distributed in these areas. It is usually because of their impacts that invasive species are of concern—and sometimes generate controversy. This entry follows the IUCN's ecological emphasis, although impacts on the economy or society may also be of concern.

Historically, species have often shifted their ranges naturally in response to changed environmental conditions. However, documented species invasions have overwhelmingly originated from purposeful or accidental introductions by humans. Growth in international trade and travel is increasing the opportunities for species to invade new areas, both through their accidental transportation and because people deliberately transport exotic species that they value for their use as food, fiber, or medicine; for their beauty; as exotica or as pets; for sport; and for their usefulness in the biological control of other organisms. In Australia, a review led by Malcolm Nairn found that more than 70% of the 290 plant species naturalized during 1971 to 1995 were introduced through human activities. However, not all species that are introduced become pests. One rule of thumb suggests that 10% of species imported are introduced to ecosystems in the receiving area, of which 10% become established, of which 10% become pests.