Explaining and predicting the success of invading species at different stages of invasion

Abstract

The invasion process goes through a series of stages, a cascade, such as import, release or escape, establishing a population, spreading, becoming a problem and others. The probability of each transition is generally not large, the overall probability from import to pest usually rather small. The factors important at each stage can be different, with socio-economic factors being generally important initially, biogeographical, ecological and evolutionary later, but all can affect all stages. Quantification both of the process and of the importance of different factors is still rudimentary. The low probability of success gives a low base rate (or prevalence). The effect of this on explanation and prediction is illustrated with German native plants found alien in Argentina. In this case, explanation and prediction are orthogonal. Climatic matching and range size have been used to explain and predict. The variety of algorithms available, the unsatisfactory tests of fit for observed and predicted ranges, the presence of non-native populations contiguous to native ones and the lack of understanding of the cause of range boundaries all cast doubt on the use of climatic matching. That range sizes offer useful explanations but poor predictions of the behaviour of introduced species is illustrated with birds introduced from Britain to Australia and plants introduced from Europe to Canada. Description (relatively easy) is not explanation (much harder); explanation is not prediction (often extremely difficult).