Influence of soil granulometry on average body size in soil ant assemblages: implications for bioindication

Soil granulometric composition can impose constraints on ant species living in ground habitats, being an important factor in defining the habitat templet, which describes how certain animal life histories, including the trait of body size, can be selected. The ant fauna plays a central role in soil formation, and a vast literature describes such influence, but not the converse. Along with termites, worms and other invertebrates, these organisms promote the formation of channels, pores, and aggregates that influence gases and water moving through the soil profile. On the other hand, it is important to understand whether soil traits constrain insect colonization, so we here ask how soil traits can influence niche specificities, which seems to be a neglected ecological issue. A literature search using the key words 'ants or Formicidae' and 'soil structure or pedogenesis' revealed numerous references dealing with the influence of ants on soil, but not conversely. We here present a novel geomorphologic approach to habitat templets for two distinct riparian Neotropical ecosystems, based on the amalgamation of soil/sediment analysis with ecological processes and ant species biology. We found that predominance of fine grains favoured the preponderance of small ant species at a threshold of <5 mm in body length. Based on this, we propose the use of a quantitative, theoretically sound, statistical approach to bioindication.