Resilience to fire and climate seasonality drive the temporal dynamics of ant-plant interactions in a fire-prone ecosystem

Abstract

Animal-plant interactions have a major influence on ecosystem structure and functioning. Understanding to what extent the temporal dynamics of interactions is determined by climate and disturbances is thus relevant to predict ecological and evolutionary outcomes in a changing world. Here, we assessed whether the temporal dynamics of ant-plant interactions in a mountainous fire-prone ecosystem is driven by seasonal variation in abiotic conditions, and to what extent fire disturbance alters this dynamic. We also examined the thermal responses of foliage-dwelling ants in order to predict the effects of seasonal oscillations of temperature on ant activity. To do so, we monitored ant-plant associations in 35 sampling plots for one year before an unmanaged fire has occurred. Then, 26 burned and nine unburned plots were monitored for another year after fire. We found that warmer and wetter conditions let to increases in the diversity and frequency of ant-plant interactions, mainly via upturns in plant resource availability and ant foraging activity. Beyond the positive effects of temperature on interaction networks, however, ant species exhibited a low heterogeneity and a huge overlap in thermal niches. Moreover, fire has led to short-term negative effects on the diversity and frequency of interactions in ant-plant networks. In spite of it, these network metrics in burned plots took up to half a year to return to similar levels from unburned plots, highlighting the resilience of ant-plant interactions after fire disturbances. This study shows that wide thermal niches of ant species and fire resilience likely beget ant-plant networks reliability over seasons. The high overlap and broad thermal niches of ant species interacting with plant resources suggest that ant diversity plays a minor role in the tolerance against climatic changes in this fire-adapted community. These findings open a new pathway to explore thermal responses of species and their ecological interactions in broader gradients of environmental conditions and ecosystem disturbances. We advocate that long-term studies comprising assisted burnings are desirable to forecast the impact of fire regimes and how their synergy with climate would affect the functioning of fire-prone ecosystems. Lastly, this study adds evidence that studied interaction networks can be useful to monitor the impacts of environmental changes such as anthropogenic disturbances, being representative of many even more complex species interactions in ecosystems.