Ecological Entomology (2013), 38, 364–373 DOI: 10.1111/een.12027 Functional diversity decreases with temperature in high elevation ant fauna ALAIN REYMOND, 1 JESSICAPURCELL, 1 DANIEL CHERIX, 1 ANTOINE GUISAN 1 and L O ¨ IC PELLISSIER 2 1 Department of Ecology and Evolution, University of Lausanne, Bˆ atiment Biophore, Lausanne, Switzerland and 2 Department of Bioscience, The Arctic Research Centre, Aarhus University, Aarhus, Denmark Abstract. 1. Severe environmental conditions filter community species compositions, forming clines of functional diversity along environmental gradients. Here, the changes in functional diversity in ant assemblages with severe environmental conditions in the Swiss Alps were investigated. 2. Eight sites were sampled along an elevation gradient (1800–2550 m). The variation in functional diversity was analysed along an elevation gradient considering four traits: social structure (monogynous vs. polygynous), worker size, pupal development, and nest structure. 3. Ant species richness and functional diversity decreased with decreasing temperature. Species found in colder habitats tended to live in subterranean nests rather than in mounds and exhibit a polymorphism in queen number, either within or across populations. The phylogenetic diversity did not decrease at colder temperature: Formicinae and Myrmicinae occupied the full range of elevations investigated. 4. An insulation experiment indicated that mounds are more thermally insulated against the cold compared with soil. The absence of a mound-building ant from high elevations probably results from a reduction in the amount of vegetal materials provided by coniferous trees. 5. More severe abiotic conditions at higher elevations act as a filter on ant assemblages, directly through physiological tolerances to the abiotic conditions and indirectly as the vegetation necessary for nest building shifts with elevation. Key words. Community, environmental filtering, gradient, hymenoptera, phylo- genetic diversity. Introduction Tolerances to environmental conditions vary across species as illustrated by the large differences in species distributions across the globe. Environmental niche discrepancies among species are mediated by species-specific physiological and behavioural adaptations (Pellissier et al ., 2011, 2012). While in milder and more productive environmental conditions, species display different strategies to reduce competition for the more diverse resources (Pianka, 1970); as environment severity increases, the number of successful strategies available can be greatly reduced (Weiher & Keddy, 1999). As a Correspondence: Loïc Pellissier, The Arctic Research Centre, Department of Bioscience, Aarhus University, Aarhus, Denmark. E-mail: loip@dmu.dk consequence, in harsh environments, species often display convergent evolution towards a few successful strategies, a mechanism called environmental filtering (Violle et al ., 2007; Pellissier et al ., 2010). Hence, understanding species distributions and gradients of biodiversity requires prior information regarding the functional traits mediating species’ survival under particular environmental conditions (Pellissier et al ., 2011; in press). Many environments exhibit forms of severity that could potentially cause environmental filtering. In particular, ele- vation gradients from lowlands to mountain summits exhibit highly contrasting environmental condition over short geo- graphical distances (K¨ orner, 2007). In alpine habitats, species experience a stressful abiotic environment (Brinck, 1974; Hod- kinson, 2005) as, for instance, air temperature declines with increasing elevation (K¨ orner, 2007). In general, insect species 364  2013 The Royal Entomological Society