Invasion and Succession

Invasion and succession are the establishment of one or more species in an area previously uninhabited by those species and the subsequent progression of the ecological community's species composition in that area through time. As ecological terms, invasion and succession are usually discussed independently from each other. Invasion, in an ecological sense, occurs when a species, usually an exotic or nonindigenous species, is introduced to an area and is able to persist in that area, often at the expense of native species. Ecological succession refers to the changes in species composition in an area over time. Succession is typically conceptualized as a progression of species compositions in an area that eventually achieves a climax stage, which remains dominant in an area until a disturbance in that area (e.g., a fire or a strong storm) resets the species composition to an earlier stage of succession. This is an example of secondary succession. Primary succession occurs when ecological communities form in an area that had no previous communities or abiotic habitat development. Ecological community development on land just formed by a volcano or newly uncovered by a landslide is an example of primary succession.

The invasion of an ecological community by an exotic species is typically viewed as a negative process. The invading species can potentially disrupt the interspecies ecological dynamics of the native community. This can result in the loss of native species in an area. The lack of natural predators of the invading species can result in their unchecked population growth. If the invading species are pathogenic to the native species, the natural defenses of the native species may not be able to resist the invading species. These factors can result in catastrophic ecological disruptions to native communities.

Combining the ecological processes of invasion and succession provides an integrative view of the changes that ecological communities experience through time. This has become more important as modern economic globalization continues to expand linkages between different places in the world. These links are often in the form of major physical transportation agents, such as boats, airplanes, and trains, which have transported many species to areas beyond their native ranges. The introduction of these species to new areas provides them with invasion opportunities. Once these invasive species become established in an area, they will compete with native species for niche space within the stages of succession that the area experiences. Successful invasive species eventually find a stable niche within a native community and in time are described as nonnative elements of the community.