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.

Bemisia tabaci is a complex of closely related genetic types of whiteflies, few of which are invasive. One of these, B biotype, has proven to be particularly adapted to invading new areas, but the underlying reasons as to why it has a well-developed capacity to invade is not known. To develop an understanding of factors that may be contributing to B's invasive capacity, inter-biotype mating interactions and host plant suitability for the exotic B (B. tabaci Mediterranean/Asia Minor/Africa) and the indigenous Australian (AN) biotype (B. tabaci Australia) were examined. The results suggest that when confined to a mutually acceptable host, B cannot establish when the ratio of AN : B exceeds 20 : 1. However, when simultaneously provided with a host that only it prefers, B is able to establish even at 50 : 1 (AN : B). Further, when both biotypes occur together the number of progeny per female increases (relative to the number produced when only one biotype is present). The response is observed for both biotypes, but is considerably greater in the case of B. In addition, B performs better in the presence of the AN biotype B. tabaci Australia while AN perform worse in coexistence with B, but only if the demographics allow B to mate without significant interference. This leads to the prediction that B will invade in circumstances where its unique hosts are of sufficient number to escape the full negative impact of inter-biotype mating interactions and reduced competitiveness in terms of reproductive rate, while exposing the indigenous biotype to the full effects of the interaction.Abbreviation: DNA-polymerase chain reaction; RAPD-PCR -random amplified polymorphic

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Tick populations were observed on zebu (Bos indicus) cattle over a period of 2 years at Entebbe, Uganda where the climate was thought to be highly favourable for the free-living stages of ticks. collections of all instars of ticks were made from the body surfaces of the cattle at intervals of between 1 and 5 weeks. The species recorded in order of decreasing abundance were Rhipicephalus appendiculatus, Amblyomma variegatum, Boophilus decoloratus, Rhipicephalus evertsi evertsi, Rhipicephalus simus, Rhipicephalus compositus and Hyalomma marginatum rufipes. The rankings of the cattle based on burdens of any particular species of tick were always correlated with their rankings for other species; animals that carried more adult stages of a species also carried more of its immature stages. There were more adult males than females of R. appendiculatus, A. variegatum and R. e. evertsi even when the cattle had had all ticks removed 1 week previously; several possible mechanisms are suggested to explain the biased sex ratio. It is concluded that there is promise for improvement in control of 3-host ticks by increasing the resistance of herds of zebu cattle by culling or selective breeding.