Multi-century dynamics of ant communities following fire in Mediterranean-climate woodlands: Are changes congruent with vegetation succession?

Abstract

As vegetation recovers after disturbances such as fire its composition and structure systematically changes, affecting the availability of resources for fauna and mediating physical conditions. According to the habitat accommodation model, these changes drive a succession of animal species, which enter and leave according to their habitat requirements. While the response of ants to fire has been extensively studied, studies of ant communities in biomes with long fire-return intervals have been overwhelmingly short-term in nature. Here, we explore the response of ant species, functional groups and communities to time since fire using a uniquely long-term (>300years) chronosequence in eucalypt woodlands of south-western Australia. Marked non-monotonic vegetation structural changes occur in non-resprouting Eucalyptussalubris-dominated woodlands following fire, with tree and ground fuel cover peaking at intermediate periods post-fire. Hence, we predicted that changes in the occurrence of Dominant Dolichoderinae, Hot-Climate Specialist and Cold-Climate Specialist functional groups would mirror the non-monotonic changes in habitat complexity, as predicted by the habitat accommodation model. Overall ant species richness and composition did not show clear post-fire successional patterns, with extensive spatial turnover a likely factor. However, richness and abundance of ant functional groups broadly responded as predicted, with Dominant Dolichoderinae and Hot-Climate Specialists more prominent in more-open recently-burnt and long-unburnt habitat, and Cold-Climate Specialists more prominent in less open habitat at an intermediate time since fire. This matching, non-monotonic temporal pattern of changes in ant functional groups and vegetation structure suggests that ant functional group occurrence is mediated through changes in habitat, as posited by the habitat accommodation model, and not simply time since disturbance. Current fire management in E. salubris woodlands aims to minimise wildfire occurrence, which is consistent with the maintenance of ant functional diversity at a regional scale given the long time periods over which changes occur post-fire. The combination of recent large wildfires and predicted fire-facilitating climate changes suggest that future shifts in the relative dominance of ant functional groups are likely if fire management is unsuccessful in limiting wildfires occurring in mature woodlands.