Different burning intensities affect cavity utilization patterns by arboreal ants in a tropical savanna canopy

Fire is a natural disturbance in many ecosystems worldwide, including tropical savannas, where it drives the assembly of animal and plant communities. The effect of fire is often indirect, impacting the availability of essential resources like food and shelter. The Brazilian Cerrado is the largest tropical savanna in the world, and ants comprise a very high proportion of its animal biomass. About one-third of the Cerrado ant fauna actively forages in the canopy. These ants use trees not just in search of food but also as their main shelter resource, as most arboreal ants nest mainly in cavities produced by wood-boring beetles. While it seems clear that fire can have important direct and indirect effects on arboreal ants, the number of studies using an experimental approach focusing on such impacts is relatively few. Here, we aimed to understand the impacts of fire on arboreal ants usage of shelter resources. Moreover, we also evaluated the potential influence of different fire intensities on these resources usage. For this, we assessed the colonization rates of experimental cavities under four different burning intensities: control, low-intensity, intermediate-intensity, and high-intensity. We hypothesized that fire would have a detrimental effect on cavity occupation. This effect would be stronger in higher intensity burns, once they can dramatically decrease the availability of natural cavities and, thus, the abundance and richness of arboreal ants. We also predicted that some ant species would be indicative of different fire intensities, due to differences in heat tolerance and colony size. Our data showed that fire had a major positive effect on experimental cavity use by arboreal ants, with more ant species, more colonized trees, and higher cavity occupation under fire treatments. This effect was higher with the increase of fire intensity. Some ant species were found more commonly on distinct fire treatments, which was mainly due to their different nesting site requirements and colony sizes. Jointly, these results show that fire affects arboreal ant cavity colonization patterns, and that fire intensity is extremely critical in shaping these patterns. Altogether, our work offers important insights for a better understanding of the effects of ecological disturbances on resource use patterns of a highly abundant and diverse organism.