Colonisation or colonization is the process in biology by which a species spreads to new areas. Colonisation often refers to successful immigration where a population becomes integrated into a community, having resisted initial local extinction. One classic model in biogeography posits that species must continue to colonize new areas through its life cycle (called a taxon cycle) in order to achieve longevity. Accordingly, colonisation and extinction are key components of island biogeography, a theory that has many applications in ecology, such as metapopulations.