Predicting the effect of climate change on aggregation behaviour in four species of terrestrial isopods Mark Hassall 1,3) , David P. Edwards 2,4) , Rachel Carmenta 1,5) , Mia A. Derhé 1) & Anna Moss 1) ( 1 Centre for Ecology, Evolution, and Conservation and School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK; 2 Centre for Ecology, Evolution, and Conservation and School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK) (Accepted: 24 July 2009) Summary Climate warming has changed the spatial distributions and temporal behaviours of several taxa. A key question that remains is how behaviours that alter microclimatic conditions might be used to buffer the effects of climate change. In this study, we focus on the aggregation behaviour of four species of terrestrial isopods, in which groups of individuals clump together to prevent moisture-loss, and use a laboratory protocol to investigate the effects of changes in relative humidity (RH) and temperature on aggregation. We find that three species aggregate more at lower RH and at higher temperatures, and that species that are better adapted to reducing moisture loss aggregate less than do species with fewer such adaptations. These results suggest that behavioural variation can buffer the effects of changes in microclimate. We finish by suggesting that it is critical to determine how such behavioural shifts will affect isopod densities and competitive hierarchies. Keywords: coexistence, coprophagy, global warming, phenotypic plasticity, woodlice. 3) Corresponding author’s e-mail address: m.hassall@uea.ac.uk 4) Present address: Institute of Integrative and Comparative Biology, University of Leeds, Leeds LS2 9JT, UK. 5) Present address: Department of Biological Sciences, Lancaster University, Lancaster LA1 4YQ, UK. © Koninklijke Brill NV, Leiden, 2010 Behaviour 147, 151-164 DOI:10.1163/000579509X12512861455834 Also available online - www.brill.nl/beh