Abstract

Biological invasions occur when species or distinct populations breach biogeographical barriers and extend their ranges to areas where they were not historically present. Invasion biology concerns the causes and consequences of these new species, which are also referred to as invasive, introduced, alien, exotic, nonnative, or nonindigenous species. Biological invasions occur in five steps: arrival, establishment, population growth, population spread, and impact. Only a small proportion of species that arrive actually reach the first step; thus, each step acts as a filter for the invasion process. No widely accepted method currently exists for identifying the characteristics that promote invasion a priori.