Ecology and Management of Invasive Alien Species: Management

Biological invasions by non-native species constitute one of the leading threats to natural ecosystems and biodiversity, and they also impose an enormous cost on agriculture, forestry, fisheries, and other human enterprises, as well as on human health. The ways in which non-native species affect native species and ecosystems are numerous and usually irreversible. The impacts are sometimes massive but often subtle. Natural barriers such as oceans, mountains, rivers, and deserts that allowed the intricate co-evolution of species and the development of unique ecosystems have been breached over the past five centuries, and especially during the twentieth century, by rapidly accelerating human trade and travel. Planes, ships, and other forms of modern transport have allowed both deliberate and inadvertent movement of species between different parts of the globe, often resulting in unexpected and sometimes disastrous consequences.

Introduced species often consume or prey on native ones, overgrow them, infect or vector diseases to them, compete with them, attack them, or hybridise with them. Invaders can change whole ecosystems by altering hydrology, fire regimes, nutrient cycling, and other ecosystem processes. Often the same species that threaten biodiversity also cause grave damage to various natural resource industries. The zebra mussel (Dreissena polymorpha), Lantana camara, kudzu (Pueraria lobata), Brazilian pepper (Schinus terebinthifolius), and rats (Rattus spp.) are all economic as well as ecological catastrophes. Invasive non-native species are taxonomically diverse, though certain groups (e.g., mammals, plants, and insects) have produced particularly large numbers of damaging invaders. Thousands of species have been extinguished or are at risk from invasive aliens, especially on islands but also on continents. Many native ecosystems have been irretrievably lost to invasion. Weeds cause agricultural production losses of at least 25% and also degrade catchment areas, near-shore marine systems, and freshwater ecosystems. Chemicals used to manage weeds can further degrade ecosystems. Ballast water carries invasives that clog water pipes, foul propellers, and damage fisheries. Imported pests of livestock and forests reduce yields drastically. Further, environmental destruction, including habitat fragmentation, and global climate change are extending the range of many invaders.

Not all non-native species are harmful. In many areas, the great majority of crop plants are introduced, as are many animals used for food. Some productive forest industries and fisheries are based on introduced species. And introductions for biological control of invasive pests have often resulted in huge savings in pesticide use and crop loss. However, many of the worst introduced pests were deliberately introduced. Horticultural varieties and zoological novelties have become invasive and destructive; fishes introduced for human consumption have extirpated many native species, and even biological control introductions have occasionally gone awry. The rapid development of the science of invasion biology, as well as growing technologies for detecting unintentionally introduced invaders and managing established invasive species, can provide major advances in the war against invasive exotic species, so long as the public and policymakers are aware of them.