XVI International Botanical Congess

Species in communities in extreme environmental conditions are shown to be more likely to be drawn from descendant species of one or a few common ancestors, and more related to one another than expected by chance alone. The degree of phylogenetic relatedness of plant communities in Great Britain was calculated over a range of values of temperature and rainfall, and compared to a null model of expected degree of relatedness to account for the possible bias of community size. Greater phylogenetic similarity among species within a community implies greater overall similarity among those species in ecology and physiology, and thus greater similarity of response to perturbation than previously suspected. The findings thus indicate an unexpected source of potential vulnerability for the marginal communities to be found in extreme conditions.