The role of climatic mapping in predicting the potential geographical distribution of non-indigenous pests under current and future climates

Climatic mapping, which predicts the potential distribution of organisms in new areas and under future climates based on their responses to climate in their home range, has recently been criticised for ignoring dispersal and interactions between species, such as competition, predation and parasitism . In order to determine whether these criticisms are justified, the differe nt procedures employed in climatic mapping were reviewed, with examples tak en from studies of the Mediterranean fruit fly (Ceratitis capitata), Karnal bunt of wheat (Tilletia indica) and the Colorado potato beetle (Leptinotar sa decemlineata). All these studies stressed the key role played by non-cli matic factors in determining distribution but it was shown that these facto rs, e.g., the availability of food and synchrony with the host plant, toget her with the difficulties of downscaling and upscaling data, were different to those highlighted in the criticisms. The extent to which laboratory stu dies on Drosophila populations, on which the criticisms are based, can be e xtrapolated to general predictions of species distributions was also explor ed. The Drosophila experiments were found to illustrate the importance of c limate but could not accurately determine potential species distributions b ecause only adult and not breeding population densities were estimated. The experimental design overestimated species interactions and ignored other f actors, such as the availability of food. It was concluded that while there are limitations, climatic mapping procedures continue to play a vital role in determining what G.E. Hutchinson defined as the "fundamental niche" in studies of potential distribution. This applies especially for pest species , where natural dispersal is generally less important than transport by man , and species interactions are limited by the impoverished species diversit y in agroecosystems. Due to the lack of data, climatic mapping is often the only approach which can be adopted. Nevertheless, to ensure that non-clima tic factors are not neglected in such studies, a standard framework should be employed. Such frameworks have already been developed for pest risk anal yses and are suitable for general use in studies of potential distribution because, in order to justify the phytosanitary regulation of international trade, they must also consider the potential for pests to invade new areas and the impacts of such invasions. (C) 2000 Elsevier Science B.V. All right s reserved.