Population Processes During Establishment and Spread of Invading Species: Implications for Survey and Detection Programs

Three important population processes occur during any biological invasion: arrival, establishment, and spread. Arrival is the process by which individual(s) of the invading organism are transported to their new habitat. Estab-lishment can be considered the opposite of extinction and represents the growth of a newly arrived population sufficient such that extinction is impossible. Spread is the process by which the species expands its range into the new habitat. Because most biological invasions are caused by human activities, these activities are important to understanding the arrival process and the design of detection programs. Establishment is a highly stochastic process and Allee dynamics may be of considerable importance depending upon the life history of the invading species. These characteristics should be'lncorporated into the timing of responses to positive detection. Popula-tion spread is an area of considerable research currently. Early attempts to understand population spread were based upon a simple theory of reaction-diffusion. However, more recent studies indicate that spread often involves two or more forms of stratified dispersal whereby isolated colonies are founded ahead of the expanding population front; these colonies expand and coalesce with the expanding population front. Efforts to monitor spread should incorporate these characteristics