The ecological and evolutionary legacy of extreme climatic events for food web resilience

There is growing evidence that extreme events such as heatwaves, rather than increases in average temperatures, will have the most immediate and harmful effects on plants and animals as the climate changes. This is particularly true for species-rich tropical ecosystems, where recent heatwaves have already caused severe population crashes for some species.

Most studies investigating the impact of extreme climatic events on biodiversity focus on individual species in isolation. However, natural communities are complex, interacting networks of species, linked by competition, mutualism, predation and parasitism. We therefore need to understand what happens when whole communities of interacting species are subjected to a heatwave or other extreme climatic event, and how these effects change depending on the duration and intensity of the event. How resilient will the surviving populations and species be in the longer term, when faced with further extremes? The answer is likely to depend on both ecological responses (changes in the abundance and interactions of different species depending on their ecological tolerances), and evolutionary processes (the evolution of novel tolerances through natural selection).

To understand fully how and why ecological communities are altered by extreme events, we need to carry out experiments simulating extreme conditions and follow the consequences over multiple generations. In most contexts such experiments would be practically or ethically impossible. However, we can design experiments that do exactly this by focusing on a special study system: food webs of Drosophila fruit flies and the parasitic wasps that consume them. At our study site in the rainforests of tropical Queensland, Australia, these flies and wasps form discrete ecological communities within individual rotting fruits. They have short generation times, allowing us to observe community responses to climate extremes in real time. Australian tropical rainforests are a high-diversity ecosystem that is threatened by climate change, and we expect rainforest insects to be particularly vulnerable because they are already operating close to the upper limits of their thermal tolerances: modest further increases in temperatures could make populations and communities unviable. These characteristics make our study system ideal for understanding the resilience of ecological systems to extreme climatic events.

In our experiments, we will use heating cables in the rainforest to simulate heatwave conditions that are expected to affect Australian rainforests in the coming decades. We will then investigate the ecologically and evolutionary responses of individual species and the food web of interactions among them to further perturbations. By challenging communities that have previously been subjected to heat waves with further heat waves, we will be able to test under what conditions climatic extremes make communities more or less resilient to future shocks and understand the ecological and evolutionary mechanisms that underpin community resilience.