Tropical forests have the highest productivity and biodiversity of any terrestrial system. Insects make up a large proportion of that diversity and carry out essential ecological processes such as pollination and nutrient cycling. In our work at the Biodiversity and Environmental Change lab at the University of Hong Kong, we have applied a range of tools including experimental manipulations, stable isotope analysis and long-term resampling efforts to better understand the functional roles of tropical rainforest insects, as well as how they are responding to a range of compounding anthropogenic stressors, including deforestation and climate change.

Tropical soil fauna, such as termites and earthworms are essential for soil function, shaping nutrient availably and productivity through their decomposition and soil bioturbation processes, however a temperate bias in our understanding means they are often seen as only facilitators of microbial decomposition. We developed novel mesocosm methods to quantify decomposition carried out by soil fauna and microbes and the consequences for plant nutrient uptake. We found that in the presence of soil fauna, plant 15N uptake is 60% higher, with major differences in nutrient pathways for disturbed, primary, tropical and temperate forests. These results highlight the essential roles of insects in ecosystem function and resilience, however, the ways in which insects and their processes are shifting in response to global change remain poorly understood.

Reports of insect declines have been widely reported, with most evidence from heavily modified temperate landscapes. Some reports are emerging that tropical insects are also in decline, even in habitats that are not undergoing habitat transformation. However, due to a lack of long-term monitoring data of insects in tropical regions, we have a very poor understanding of how insects are changing through time. We have been locating and assessing pan-tropical data sets while continuing to re-sample insect diversity across pristine tropical Asian and Australian rainforests to disentangle the effects of climate change from other drivers. Analysis of existing data show that five major invertebrate groups – spiders, termites and cockroaches, beetles, true bugs, moths and butterflies, appear to be in long-term El Niño-associated declines, with correlated changes to herbivory and decomposition processes. Our own resampling efforts across an elevational gradient show moths, ants, dung beetles and plants are contracting towards mid-elevations, shaped by increasingly extreme microclimates. These results indicate that even in primary tropical forests, insects are in trouble, with wide-scale implications for the future of functioning of tropical ecosystems.