LATITUDINAL PATTERNS IN EUROPEAN ANT ASSEMBLAGES - VARIATION IN SPECIES RICHNESS AND BODY-SIZE

Using published distributions of 65 species from the British Isles and northern Europe, we show that ant assemblages change with latitude in two ways. First, as commonly found for many types of organisms, the n umber of ant species decreased significantly with increasing latitude. For Ireland and Great Britain, species richness also increased signif icantly with region area. Second, although rarely demonstrated for ect otherms, the body size of ant species, as measured by worker length, i ncreased significantly with increasing latitude. We found that this bo dy-size pattern existed in the subfamily Formicinae and, to a lesser e xtent, in the Myrmicinae, which together comprised 95% of the ant spec ies in our study area. There was a trend for formicines to increase in size with latitude faster than myrmicines. We also show that the patt ern of increasing body size was due primarily to the ranges of ant spe cies shifting to higher latitudes as their body sizes increased, with larger formicines becoming less represented at southerly latitudes and larger myrmicines becoming more represented at northerly latitudes. W e conclude by discussing five potential mechanisms for generating the observed body-size patterns: the heat-conservation hypothesis, two hyp otheses concerning phylogenetic history, the migration-ability hypothe sis, and the starvation-resistance hypothesis.