Population differentiation in a variable environment is related to the selection pressures that plants experience. Ward et al. compare differences in growth- and defence-related traits in two isolated populations of Acacia raddiana trees from sites at either end of an extreme environmental gradient in the Negev desert. They find no evidence of trade-offs between physical and chemical defences and plant growth parameters; rather, there appears to be positive correlations between plant size and defence parameters. The great variation in several traits in both populations may result in a diverse potential for responding to selection pressures in different environments.
