If You Burn Them, They Will Return: A Case Of Ant-Plant Interactions In A Fire-Prone Brazilian Ecosystem

Climate changes and anthropogenic disturbances are current threats to biodiversity and ecosystem functioning. Ecosystem health depends not only on its biodiversity per se but also on services and functions played by species and their interactions. Ant-plant interactions are an outstanding model to study ecosystem structure and functioning since they each fill distinct ecological roles.

Thus, the understanding of how ant-plant interactions dynamics, or ant-plant interaction networks, are affected by climatic fluctuations and anthropogenic fires is relevant to predict ecological and evolutionary outcomes in a changing world.

Our study looked for whether the temporal dynamics of ant-plant networks is driven by seasonal variation in climatic conditions (i.e., temperature and precipitation), and to what extent fire disturbance alters this dynamic. We also studied the thermal response of ant community in order to understand temperature influence on ant activity, and consequently, ants’ tolerance to climate change. To do so, we carried out this field research in a tropical fire-prone ecosystem, locally known as Campo Rupestre.

Campo Rupestre is a tropical megadiverse mountaintop grassland ecosystem that occurs in Brazil, wherein plant-related rewards located in flowers, fruits, and extrafloral nectaries are used as food by ants. This fire-prone environment has been subjected to recurrent human-made fires and hard climatic filters that shape species distribution and vegetation cycles. Ongoing evidence has shown negative effects of fire on its vegetation structure and on ants that live in the soil. More than that, we already know that climatic conditions strongly change along its mountain range influencing species occurrence.

In this way, we monitored ants foraging on plants and consuming food resources (i.e., plant-derived rewards), quarterly, for two consequent years: one before unmanaged fire events have occurred and the other after the disturbance. We have found that warmer and wetter conditions prompted increases in the diversity and frequency of ant-plant interactions (measured by ecological network metrics). These results are likely due to upsurges in plant resource availability in these periods, and higher ant activity in these abiotic conditions. We also observed that the studied ant community has a low heterogeneity and a huge overlap in its thermal responses, which means a wide thermal niche that leads to higher tolerance to temperature fluctuation. Our study also has shown that, in spite of negative effects of fire on the diversity and frequency of interaction networks, these effects are quick, as interactions recovered up to up to half a year after fire disturbance.

These findings highlight that wide thermal response of ant species and fire resilience to fire shown in ant-plant interactions likely promote ant-plant networks’ reliability over multiple 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 pieces of evidence open a new path to explore thermal responses of species and their ecological interactions in broader gradients of environmental conditions and ecosystem disturbances, such as resource deprivement under deforestation and/or land use.

Long-term studies that consider assisted burnings are desirable to forecast the impact of fire regimes and their synergy with climate on fire-prone ecosystems functioning in our changing world. To end, our findings adds to evidence showing that ecological interaction networks are useful tools to monitor the impacts of environmental changes such as anthropogenic disturbances.