Omnivory mediates a latitudinal trend in ant size

A key trait in animals that influences their physiology and ecology is body size. Metabolic rates and trophic positions of an animal are heavily predicted by body size as environmental temperature and available resources affect development and growth, especially among ectotherms. As such, global temperature gradients and variation in resource availability can influence body size and play a critical role in the structuring of entire ecological communities. However, in invertebrates, there are few studies that examine the interactive effects that spatial and temporal resource availability have on global trophic assemblages and the size distributions of those assemblages. Here we link functional groups of dietary guilds to global size gradients to explain the more general pattern that ants increase in size with latitude. We assembled a morphometric and spatial global dataset of 11,005 ant species. Using a hypotheses-driven statistical path analysis approach to investigate global assemblages of species occurring in 629,711 km² regions we find; 1) dietary functional roles are largely driven by temperature seasonality and resource variability, 2) size distributions differ among dietary functional roles, and 3) the relative distribution of functional roles in regional assemblages best explain the more general pattern of size increasing with latitude. Largely driving this pattern are omnivorous dietary generalists that tend to be larger and more common in geographic regions that have higher annual temperature seasonality (suggesting resource availability).