Human-Induced Invasion of Species

An invasion of a species is defined as the introduction, establishment, and subsequent spread of that species in a geographic area different from its original or native geographical range. Once a species has been introduced into a new habitat, it can be naturalized; that is, it can adapt to the new environment and expand its population, usually producing negative effects on native species and on the whole ecosystem structure. Not all human-induced introductions of species are successful, and invasive populations can become extinct shortly or even after a long time. There are two aspects to consider in the ecological study of invasions: (1) the susceptibility of a territory to an alien invasion (i.e., the suitability of a territory to the ecological requirements of an invasive species and its proclivity to be invaded) and (2) the invasiveness of the species (i.e., its capacity to become an invader), which depends on its ethological, physiological, and morphological characteristics, as well as on the number and frequency of invasions on the same habitat over time. This entry [Page 1471]discusses how an invasion occurs, the effects of invasive species on ecosystems, the history of invasions on islands and elsewhere, and future efforts to control invasive species.

Water hyacinth filling a canal in the Mississippi Delta. Water hyacinth stops boat traffic and interferes with the circulation of water.

Source: Dr. Terry McTigue, National Oceanic and Atmospheric Administration/Department of Commerce.

The invasive capacity of plant species will be determined primarily by its capacity for dispersal and spread, rapid growth, great height (increasing its access to light), high leaf area, high use efficiency of the available resources, and great tolerance to environmental stress. Invasive animal species tend to have more flexibility in behavior (including partnership with humans), more aggressiveness, higher reproductive rates, and broader ecological niches (more generalist species).

With regard to habitats, disturbed and highly isolated ecosystems are prone to be invaded. They support communities structured in simplified networks. New invasive species modify the ecological relationships in the networks, even affecting the whole ecosystem when aliens are recruited among top predators or herbivores.