The study of the establishment, spread, and ecological impact of species translocated from one region or continent to another by humans. Biological invasions have gained attention as a tool for basic research, used to study the ecology and evolution of populations and of novel biotic interactions; and as a conservation issue tied to the preservation of biodiversity. The invasion of nonindigenous (also called exotic, alien, or nonnative) species is a serious concern for those charged with managing and protecting natural as well as managed ecosystems. For example, nonindigenous species negativley affect over one-third of the U.S. Endangered Species List.