Drivers of functional group changes in arthropod communities living in ant nests

Ant nests harbor a hidden diversity of associated arthropods that thrive in the well-protected and climatically regulated micro-environments. Their nests can be highly variable in terms of size, age, productivity, and connectivity. Here, we wanted to test how the functional groups in a heterogeneous community of arthropods associated with red wood ants respond to these different nest drivers. We monitored in high detail the community of associates in all nests of a red wood ant population (N = 51). The community of red wood ant associates comprises of facultative and obligate associates, and the latter can further be subdivided into detritivores, scavengers and active hunters. More productive and more connected nests supported an overall higher diversity of obligate associates. However, with increasing nest size, we observed a strong proportional increase of scavenging species at the cost of predatory species. Interestingly, obligate myrmecophiles gradually replaced facultative myrmecophiles with increasing nest age, pointing at a succession towards a stable community dominated by obligate symbionts. Overall, these results suggest that functional groups differently respond to the conditions in the host nest. We discuss how the results can be explained by different dispersal capabilities and competitiveness across the different functional groups. The changes in functional groups may have strong implications for the trophic dynamics in these unique microcosms.