Latitudinal patterns in European ant assemblages: variation in species richness and body size

Abstract

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 number of ant species decreased significantly with increasing latitude. For Ireland and Great Britain, species richness also increased significantly with region area. Second, although rarely demonstrated for ectotherms, the body size of ant species, as measured by worker length, increased significantly with increasing latitude. We found that this body-size pattern existed in the subfamily Formicinae and, to a lesser extent, in the Myrmicinae, which together comprised 95% of the ant species in our study area. There was a trend for formicines to increase in size with latitude faster than myrmicines. We also show that the pattern of increasing body size was due primarily to the ranges of ant species 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. We conclude by discussing five potential mechanisms for generating the observed body-size patterns: the heat-conservation hypothesis, two hypotheses concerning phylogenetic history, the migration-ability hypothesis, and the starvation-resistance hypothesis.

Dung beetle communities: a neotropical-north temperate comparison

“…Most of the dung beetles in our study fall into the former category as they generally produce more than one generation per year. Second, modern body sizes may be "phylogenetic ghosts" (Cushman et al 1993). During the Pleistocene, the temperate forests in our study, although not glaciated, would have been much colder than they are today.…”

“…Tropical forests were also cooler in the past, but not to the extent of the Southern USA. The larger size of modern beetles in North America may be an adaptation to the prolonged glaciations of the past (Cushman et al 1993). Last, large body sizes may be an adaptation to resist starvation in seasonal or unpredictable environments (Cushman et al 1993).…”

“…The larger size of modern beetles in North America may be an adaptation to the prolonged glaciations of the past (Cushman et al 1993). Last, large body sizes may be an adaptation to resist starvation in seasonal or unpredictable environments (Cushman et al 1993). Both tropical and temperate regions experience seasonality (rainfall and temperature, respectively) and mammals respond by decreasing their activity levels when resources are scarce, but the response in temperate mammals is probably more extreme, especially given that the tropical forests studied here are relatively aseasonal.…”

“…In temperate climates, many species of dung beetles enter into diapause, a dormancy phase, during the cold months of the year . Larger body sizes allow for extra reserve storage and decrease the probability of starvation during times when food is scarce or unavailable (Cushman et al 1993).…”

“…Second, we expect greater community similarity, measured as rank-abundance distributions, rank-volume distributions and beta-diversity within tropical forests and within temperate forests than between temperate and tropical forests. Third, as Bergmann's rule predicts larger body sizes at higher versus lower latitudes (Cushman et al 1993), we compare mean body size with the expectation of larger dung beetles in temperate forests than in tropical forests. Finally, in addition to abundance, we add biomass to our community comparisons within and across latitudes, as biomass is generally a better indicator of the functionality within a community (Saint-Germain et al 2007).…”