April 20, 2022

expert reaction to study looking at climate, agriculture and insect populations

A study published in Nature looks at agriculture, climate change and insect biodiversity.

Prof Jane Hill, Professor of Ecology, University of York, said:

“There are concerns about losses of insect species richness and abundance given they comprise a huge component of global biodiversity and play key roles in ecosystems. The problem is that there are few data sets across the world that are sufficiently robust to reliably quantify changes, leading to on-going disagreements among researchers about the scale of insect declines and failure to recognise nuances in species responses. The authors analyse short-term ‘snap-shot’ studies, analysing data from ¾ million records of ~18,000 species. There are huge challenges with analysing such heterogeneous data and an urgent need to monitor insect changes using standardised methods from a much wider global network of sites.

“The study shows the detrimental impacts of high-intensity agriculture for insects, and is important in revealing that land-use changes interact with climate warming. Comparing findings from tropical and non-tropical locations reveals the complexity of these land-use/climate interactions, and unlike non-topical locations, the authors show there are likely to be no insect ‘winners’ from climate warming in the tropics.

“I think the finding that retaining natural habitat in the wider landscape can buffer insect declines in low-intensity agriculture is really important, and gives us hope that we can successfully design landscapes to produce food where biodiversity can thrive.”

Prof Tom Oliver, Professor of Applied Ecology, University of Reading, said:

“There has been growing recognition of the importance of interactions between land use and climate change on biodiversity over the last decade. An example is how the recovery of insects like butterflies after an extreme drought event is influenced by the degree of fragmentation of their habitats. This current study by Outhwaite and colleagues is novel in extending analysis of land-use climate interactions to the global level.

“The data are understandably more sparse compared with single-country studies, as the vast majority of locations (99.7% of them) are only sampled for one or two years. This makes understanding the effects of climate change over time more challenging*. For example, higher temperatures tend to be experienced in more recent years, when sites have also had longer to experience the damaging effects of land use intensification. Advanced statistical models can be employed to attempt to untangle the potentially confounding effect between climate and duration of habitat modification. Nonetheless, it highlights the crucial importance of developing our capacity for monitoring insect populations by setting up long term standardised monitoring schemes, especially for less studied parts of the world. One example is butterfly recording across Europe (https://butterfly-monitoring.net/able-results). A standardised methodology is employed with repeat visits to the same sites on multiple occasions every year. The scheme currently operates in 22 countries across Europe (and increasingly beyond), allowing detailed understanding of the effects of extreme weather and long-term climate change on populations. Extending such long-term monitoring schemes to other insect groups would not be a huge outlay in terms of national budgets, and represents a crucial way to monitor the heartbeat of nature, helping us to understand if and how it could falter.

“This Outhwaite study reflects a growing focus on the interactions between multiple drivers in recognition of the need to understand complex risks in our increasingly connected world. Risks may be compounding where one driver increases the vulnerability to another, or risks may cascade along complex chains of causality making them hard to predict. The emergence of animal-borne diseases is a case in point, being influenced by complex environmental factors and well a socio-economic aspects like the connectivity of our global transport system and resilience of our healthcare systems.

“The study is important because insects have a very broad range of roles in ecosystems. Beyond pollination and pest control they are essential for decomposing waste and nutrient cycling. With insects making up a huge proportion of biomass they also have key roles in supporting other species in the pyramid of life, such as providing food for birds, bats and small mammals.

“The paper suggests substantial insect declines in high intensity agriculture in warmer locations or years. This raises concerns about the capacity of insects to support ecosystems in these places. In terms of a potential tipping point where the loss of insects causes whole ecosystems to collapse, the honest answer is we just don’t know when the point of no return is. We know that you can’t just keep losing species without, ultimately, causing a catastrophic outcome. Just like you cannot keep removing rivets from an aeroplane plane without it eventually falling out of the sky, as one famous biologist (Paul Ehrlich) once put it. We just don’t know where that limit is for biodiversity loss. Some marine ecosystems such as coral reefs have been shown to shift rapidly from species rich ecosystems full of colourful fish into a degraded state with very few species and from which recovery is very difficult. With terrestrial systems supported by insects we haven’t widely seen such tipping points yet. In fact, some agricultural systems lose sensitive species quickly but a small subset of hardy, resilient species remain. Whether these remaining insects can continue to support ecosystem functioning, or whether they will eventually be lost themselves is still an open question. Under the precautionary principle, however, it would be best to act now so we don’t ever find out about ecosystem collapse by experiencing it.”

*The authors assessed the effects of the interaction between land use and climate warming on insect abundance and species richness using a spatial analysis of the differences in biodiversity among land-use types. Such space-for-time substitutions are known to sometimes present significant issues due to confounding factors, making inferences about the responses to climate changes over time somewhat uncertain. The authors recognise this caveat stating “This positive relationship with climate change may have occurred at least in part because the most climate-sensitive species have already been lost in non-tropical regions through a long history of land-use change”. One approach would be to include year of study (or even better the duration of time elapsed since habitat conversion) into models explicitly. The global dataset analysed here is hugely impressive reflecting thousands of hours of painstaking observation, but does not preclude the need for expansion to more standardised long-term monitoring schemes to help further improve robustness of our understanding.

‘Agriculture and climate change are reshaping insect biodiversity worldwide States’ by Outhwaite et al. was published in Nature at 16:00 UK time on Wednesday 20^th April.

DOI: 10.1038/s41586-022-04644-x

Declared interests

Prof Jane Hill is a professor of ecology at the University of York, examining how species respond to climate and land-use changes. She receives funding from NERC.

Prof Tom Oliver is currently a recipient of NERC funding on an insect declines consortium project (DRUID), and has recently led a NERC project on complex systemic risk (SysRisk). He is currently seconded to Go-Science working on UK resilience to long term risks up to 2050.