Ecological and evolutionary effects of climate change on rainforest food webs

Ecological communities are complex, interacting networks of species, linked by competition, mutualism, predation and parasitism. In the 'Origin of Species', Charles Darwin famously wrote of 'an entangled bank', comprising a bewildering richness of species and an even more complex web of connections among them. Fundamentally, ecologists and evolutionary biologists seek to unravel this complexity, by establishing why species occur where they do, why they replace each other under certain conditions, and how the species interactions that make up ecosystems will change as environments change.

As the climate warms and extreme events become more frequent, existing connections between species are changing in strength, or being severed completely; and new connections are forming as species change in abundance and shift their distributions (e.g. colonising cooler habitats, while becoming locally extinct in warmer habitats). Biologists use information about the range of temperatures where species currently occur to predict where species will occur in a future, warmer world. However, better predictions about the consequences of climate change will be possible if we can also take into account changing interactions between species, as well as the potential for species to evolve to cope with new conditions.

We urgently need to test how whole food webs of interacting species are structured by biological processes (e.g. competition and predation) and by temperature, and how these ecological networks will respond to climate change. It is also important to test the extent to which current adaptive divergence across species' geographical ranges will increase their resilience to future climate change. To achieve this, our project will exploit a unique model system (Drosophila fruit-flies and parasitic wasps that are associated with them, called parasitoids) in a high-diversity ecosystem threatened by climate change (Australian tropical rainforests). With this system we will use field observations, field transplant experiments and mathematical models to test: (i) what determines species' local distributions and food web structure; (ii) the responses of natural and simulated networks of interacting species to simulated climate change; and (iii) the underlying mechanisms driving these changes, including the effects of genetic variation among populations within species and the potential for rapid evolutionary adaptation to warmer temperatures. The outcome will be a better and more predictive understanding of how climate change will affect the biotic interactions that characterise biodiversity and underpin the functions and services of natural ecosystems.

We have identified three categories of beneficiary:

(1) The General Public:
The UK public has an enormous interest in wildlife, and a particular fascination with rainforests. People are concerned about how biodiversity is responding to climate change, and the future consequences of biodiversity loss for human economies, climate stability, and our health and happiness.

(2) Policy-makers and conservation organisations:
The ability to predict species' responses to climate change is critical for conservation, agriculture and medicine, but the mechanisms governing these responses remain poorly understood. An important knowledge gap concerns the direct influence of climate on species distributions versus its effects via interacting species and habitats. Our work will thus be of interest to policy-makers, landscape-planners and stakeholders in agriculture and medicine who are concerned by how climate change may alter interactions among invertebrates, with relevance for species acting as disease vectors, agricultural pests or invasive alien species in natural and managed landscapes.

(3) Wider society:
By examining the mechanisms driving observed changes to species distributions resulting from climate change, our research will contribute to UK leadership in predicting the regional and local impacts of environmental change. Of particular importance at the moment is defining a safe "operating limit" for key environmental pressures. Of these pressures, there is greatest uncertainty about biodiversity loss, and how it will reduce planetary resilience in the face of anthropogenic climate change. Our research will contribute new data to the evidence base that will empower society to respond to global climate change. It will do this by refining forecasts of how species and ecological communities respond to the interacting effects of climate change and interacting species. In particular, our data will address these issues in tropical rainforests which are the planet's most species-rich ecosystems, and also amongst the most sensitive to climate change.