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Global change includes climate change and climate variability, land use, water storage and irrigation, human population growth and urbanization, trade and travel, and chemical pollution. Impacts on vector-borne diseases, including malaria, dengue fever, infections by other arboviruses, schistosomiasis, trypanosomiasis, onchocerciasis, and leishmaniasis are reviewed. While climate change is global in nature and poses unknown future risks to humans and natural ecosystems, other local changes are occurring more rapidly on a global scale and are having significant effects on vector-borne diseases. History is invaluable as a pointer to future risks, but direct extrapolation is no longer possible because the climate is changing. Researchers are therefore embracing computer simulation models and global change scenarios to explore the risks. Credible ranking of the extent to which different vector-borne diseases will be affected awaits a rigorous analysis. Adaptation to the changes is threatened by the ongoing loss of drugs and pesticides due to the selection of resistant strains of pathogens and vectors. The vulnerability of communities to the changes in impacts depends on their adaptive capacity, which requires both appropriate technology and responsive public health systems. The availability of resources in turn depends on social stability, economic wealth, and priority allocation of resources to public health

Summary1. Acacia nilotica is a spinescent woody legume that has become highly invasive in several parts of the world, including Australia where it has been declared a weed of national significance. Understanding the likely potential distribution of this notorious plant under current and future climate scenarios will enable policy makers and land managers to prepare appropriate strategies to manage the invasion. 2. CLIMEX was used to synthesize available information from diverse sources to model the invasion potential of A. nilotica and gain insights into the climatic factors limiting its range expansion. The model identified areas at risk of further invasion so that early preventative or ameliorative measures could be undertaken in a timely manner. 3. The potential distribution of A. nilotica in Australia under current climatic conditions is vast, and far greater than the current distribution. 4. Global climate change is likely to increase markedly the potential distribution of A. nilotica in Australia, significantly increasing the area at risk of invasion. The factors of most importance are the expected increases in water-use efficiency of A. nilotica due to increased atmospheric CO 2 concentrations, allowing it to invade more xeric sites further inland, and increased temperatures, allowing it to complete its reproductive life cycle further southward (poleward). Synthesis and applications.Simple paddock quarantine procedures may provide a means of limiting the range of A. nilotica within its potential distribution under current, as well as future, climate scenarios. The projected increased growth potential of A . nilotica throughout its current range suggests that if future management patterns result in seed pods lying unconsumed on the ground, heightened vigilance may be required to identify and eradicate new invasion foci arising from flood dispersal. The increased growth potential may also result in an alteration of the economic balance, in favour of harvesting A. nilotica for agroforestry or local bioenergy projects. A crucial component in containing this invasion will be raising public awareness of the invasion threat posed by A. nilotica , its identification and suitable control techniques.

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A critical comment on M. J. Samways, R. Osborn, H. Hastings & V. Hattingh (1999) Global climate change and accuracy of prediction of species geographical ranges: establishment success of introduced ladybirds (Coccinellidae, Chilocorus spp.) worldwide. Journal of Biogeography, 26,[795][796][797][798][799][800][801][802][803][804][805][806][807][808][809][810][811][812] The use of climate matching to improve the success rate of introductions of biological control agents into new environments is well-established (DeBach, 1964). Similarly, there have been robust examples where the risk of establishment of invasive species has been successfully defined a priori using climatic modelling. These include: Leptinotarsa decemlineata (Say) in Europe , Amblyomma variegatum (Fabricius) and A. hebraeum (Koch) in Zimbabwe (Bruce & Wilson, 1998); Chrysomya bezziana (Villeneuve) in Ethiopia (Hall & Wall, 1995) and Boophilus microplus (Canestrini) in east and southern Africa (Sutherst, 2001). Samways et al. (1999) claim to have tested 'how accurate predictions of range change might be before entertaining global climatic change'. They attempted to do this by using climate matching to predict the success of establishment of fifteen species of ladybirds (Coccinellidae, Chilocorus spp.), which had been the subject of efforts to spread them beyond their native ranges to enhance biological control. The 'percent correct predictions of establishment' was the criterion used to test their hypothesis, expressed also as 'predicting species climatic tolerances'. After achieving an apparently low success rate, they concluded that 'even in the absence of climate change, range cannot always be determined, which means that most predictions of range change with climate change are likely to be wrong'. I discuss here how such a statement demonstrates weak scientific inference.Samways et al. used the CLIMEX model (Sutherst & Maywald, 1985;Sutherst et al., 1995Sutherst et al., , 1999) and its associated 'Match Climates', climate-matching algorithm to make their predictions. The CLIMEX model is a simulation model of moderate complexity for inferring the responses of a species to climate from its geographical distribution. Once response functions have been fitted, the model can be run with meteorological data from other parts of the world to estimate the species response to new climatic environments. The potential range, as determined by climate, can then be estimated. The model parameter values constitute the hypotheses on the climatic factors that determine the species population growth, and survival during adverse seasonal conditions, and so limit the geographical distribution. Alternatively, the meteorological data base can be manipulated to create scenarios of climate change.Samways et al. attempted to explain the success or otherwise of particular introductions of Chilocorus species to new environments based on their estimated potential climatic range. This assumes that both the claims of the predictive success of climate matching, in this case usi...

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Invasive species, biological control and climate change are driving demand for tools to estimate species' potential ranges in new environments. Flawed results from some tools are being used to inform policy and management in these fields. Independent validation of models is urgently needed so we compare the performance of the ubiquitous, logistic regression and the CLIMEX model in predicting recent range extensions of the livestock tick, Rhipicephalus (Boophilus) microplus, in Africa. Both models have been applied to the tick so new, independent data can be used to test their ability to model non-equilibrium distributions. Logistical regression described the spatial data well but failed to predict the range extensions. CLIMEX correctly predicted the extensions without fitting the nonequilibrium data accurately. Our results question the validity of using descriptive, statistical models to predict changes in species ranges with translocation and climate change. More test cases that include independent validation are needed.

Most ecological risk assessments for global change are restricted to the effects of trends in climate or atmospheric carbon dioxide. In order to move beyond investigation of the effects of climate alone, the CLIMEXt model was extended to investigate the effects of species interactions, in the same or different trophic levels, along environmental gradients on a geographical scale. Specific needs that were revealed during the investigations include: better treatment of the effects of temporal and spatial climatic variation; elucidation of the nature of boundaries of species ranges; data to quantify the role of species traits in interspecies interactions; integrated observational, experimental, and modelling studies on mechanisms of species interactions along environmental gradients; and high-resolution global environmental datasets. Greater acknowledgement of the shared limitations of simplified models and experimental studies is also needed. Above all, use of the scientific method to understand representative species ranges is essential. This requires the use of mechanistic approaches capable of progressive enhancement.