1. School of Biological Sciences, University of BristolWoodland Road, Bristol BS8 1UG, UK
2. Department of Mathematics, University of BristolUniversity Walk, Bristol BS8 1TW, UK
3. Behavioural Ecology Research Group, Department of Evolutionary Zoology, University of DebrecenDebrecen 4010, Hungary
4. Department of Animal Science, University of CaliforniaDavis, One Shields Avenue, Davis, CA 95616-8521, USA