Population Ecology of Managing Insect Invasions

Abstract

Invasions are characterized by three phases: arrival, establishment and spread. In this chapter we focus on the establishment and spread phases with consideration of how population processes operating during each stage influence the selection of management strategies. Typically, the establishment phase is dominated by the Allee effect in which population growth rates decrease with decreasing abundance. Allee effects can arise from several different mechanisms and are capable of driving low-density populations to extinction. Strategies to eradicate newly established populations should focus on either enhancing Allee effects or suppressing populations below Allee thresholds, such that extinction proceeds without further intervention. Spread of invading populations results from the coupling of population growth with dispersal. The spread of most non-indigenous insects is characterized by “stratified dispersal” in which occasional long-distance dispersal results in the formation of isolated colonies ahead of the continuously infested range boundary. These colonies grow, coalesce and greatly increase spread rates. Allee effects also affect spread, in part, by contributing to the extinction of colonies formed through stratified dispersal. One approach to containing the spread of an invading species focuses on eradicating these isolated colonies. Microbial control is one management tactic that is very appropriate for suppressing populations of invasive species below Allee thresholds and consequently preventing their establishment or limiting their rate of spread.