Land use and climate change interact to drive steep insect declines

Tim Newbold, Charlie Outhwaite, Peter McCann and Jessica Williams, Centre for Biodiversity and Environment Research, University College London, United Kingdom, Peter Soroye and Jeremy Kerr, Biology, University of Ottawa, Ottawa, ON, Canada

Background/Question/Methods
Land use and climate change are widely recognised as the predominant pressures on terrestrial biodiversity. Recently, there has been an increasing interest in the potential for interactions between pressures to modify changes in biodiversity. At the same time, there has been a growing awareness of declines in insect populations and occupancy, using data from study sites around the world. We asked whether interactions between climate and land-use change can help to explain observed changes in insect occupancy and abundance. We use global data on insect responses to land use from the PREDICTS (Projecting Responses of Ecological Diversity in Changing Terrestrial Systems) Database, and data on temporal changes in bumblebee occupancy across Europe and North America. We compare models that capture key interaction mechanisms between pressures (impedance of dispersal by habitat fragmentation and local climatic changes caused by human land use), with simpler models of the effects of land use or climate alone.
Results/Conclusions
Global patterns of insect occupancy and abundance across land uses, and also continental temporal changes in bumblebee occupancy were much better explained by models that captured interactions between climate change and land use than by simpler models. Interactive models explained around half of variation in bumblebee occupancy trends and around 10% of global insect abundance patterns (a substantial improvement over other models of typically highly dynamic insect abundances). Interactive models predicted very large future declines of bumblebees and other insects under all scenarios. Insects play a vital role in the functioning of ecosystems, and support key ecosystem services of tremendous value to human societies. Animal pollination (to which bumblebees are important contributors) alone is estimated to be worth $230-410 billion annually. Better understanding the factors driving insect declines will allow us to anticipate and hopefully mitigate further declines. More broadly, our results, which identify a synergistic combination of key pressures on biodiversity, suggest that previous projections of biodiversity changes may have substantially under-estimated likely future changes, with very important implications for the future of life on Earth.