Testing the size‐grain hypothesis in a generalist predator: The case of an ant species in the Brazilian savannah

Abstract According to the size‐grain hypothesis (SGH), there is a positive allometric relationship between body length and leg length in ants, considering the ease of navigating complex environments while foraging for food. The aim of this study was to evaluate morphological changes in populations of Ectatomma permagnum in response to environmental alterations, by (i) assessing whether there is a proportion of leg size relative to body size according to the size‐grain theory, (ii) comparing morphometric measurements of the legs and the body to verify if the proportion is influenced by environmental variables, and (iii) checking if environmental heterogeneity influences the size of morphological traits used for foraging and predation. Eight hundred forty‐four individuals of E. permagnum from four urban fragments with different types of Cerrado vegetation were measured, where 11 morphological measurements were used to describe morphometry, as well as seven environmental variables to characterize the environment. For data analysis, we used (i) Weber's length and leg length to verify the allometric relationship, (ii) non‐metric multidimensional scaling and multivariate analysis of variance to differentiate areas considering morphometric characteristics, (iii) principal component analysis to analyze characteristics among fragments, and (iv) canonical correspondence analysis to verify the influence of environmental variables on morphological characteristics. The total length of the leg in relation to Weber's length corroborated with the SGH, and there was a significant difference in this measurement between fragments when compared with all morphometric variables. We did not find evidence that area heterogeneity influences the sizes of the measured traits in the study. We conclude that individuals of E. permagnum corroborate with the size‐grain hypothesis, thus confirming a positive allometry for the species. Our morphometric measurements did not show a significant influence of environmental variables, suggesting that other internal and external factors may also be important for selecting individual traits.