Mechanisms of Biological Invasions

Abstract

This paper considers two alternative hypotheses for explaining biological invasions. One hypothesis currently prevalent in ecology, is based on the assumption that a `balance of nature' exists and that biologically functional interactions dominate all other factors. An alternative hypothesis assumes that species are independent and respond individualistically to all factors, their individualism depending on species-specific responses relative to particular factors. The first hypothesis views community composition and external environmental factors as stable; invasions occur either when community resistance (`inertia') is overcomer, or when species change genetically so that they can colonize new climatic or biotic environments. The second hypothesis views community composition as flexible and external factors as dynamic. The first is often described using deterministic models, wherea the second emphasizes stochastic ones. After briefly surveying theories concerning the `balance of nature', I describe a stochastic model of range structure and extend it to invasions. This is illustrated by the invasion of the collared dove, Streptopelia decaocto (Friev.), into Europe.