Climate or agriculture: which contributes more to insect mortality? – Knowledge

It remains unclear how large regional differences are in the global decline of insects and which groups are most affected by this decline. The data on this matter can be described as superficial at best. But where there is data, it appears in the vast majority of cases that the insect kingdom is shrinking, both in terms of species diversity and biomass. It’s also pretty certain that insects are experiencing many stresses at the same time: habitat loss, pesticides, environmental pollution, and climate change.

But what is the role of each of these factors, and what are the interactions? This has not been definitively clarified for a long time. In a recent study in the journal Science temper nature Researchers led by Charlotte Otwate of University College London are trying to read the answer from a large number of data. In total, they studied studies from 6,000 sites and nearly 18,000 insect species, including beetles, flies, bees, butterflies and grasshoppers. They focused on agriculture and climate change, which are generally considered major stresses in the biodiversity crisis. The result: when intensive agriculture is practiced and global warming begins to exceed the range of natural fluctuations, average insect biomass decreases by about half and species diversity by about a quarter compared to nearby landscapes without warming.

However, it is known that it is difficult to make such statements because there are few long-term studies on insect diversity. One of the rare exceptions is 2017 in PLUS ONE A study was published in Krefeld, which documented a reduction in flying insect biomass of about 80 percent in several German protected areas since 1989. However, such data is available from very few places, certainly not from outside Europe.

In the semi-natural landscape, the diversity of insects has remained fairly intact

The researchers tried to get around this problem by combining data from different locations: although most of the studies used lasted a maximum of two years, they covered the period from 1992 to 2012. On the other hand, Outhwaite’s team was able to compare relatively pristine regions with landscapes. Natural agricultural heavily used. On the other hand, surveys conducted in one place in the early 1990s, when global warming was barely noticeable, can be compared with those conducted in other places two decades later, when warming was already noticeable. By combining a large amount of data, it is hoped that the relative impacts of land use and warming will be determined.

This approach has weaknesses. Of course, the diversity of insects in tropical rainforests is different from that in the steppes. The forms of agriculture in Asia, Africa, or the United States are hardly comparable. “Such meta-studies are academically interesting, but it is difficult to draw practical conclusions from them,” says Joseph Seitel of the Helmholtz Center for Environmental Research in Hull, co-chair of the latest Global Biodiversity Report. “Even classification is difficult, what counts as intensive cultivation, and what landscaping?”

Despite this, the researchers were able to identify some plausible trends. It has been shown, for example, that intensive cultivation always has significant negative effects, while the diversity of insects in nearby landscapes has been somewhat preserved despite the warming. However, it is questionable whether this will remain the case for long, especially since only data up to 2012 were considered – since then the warming has already progressed significantly. “Until now, agriculture has actually been more important as a factor in biodiversity decline,” says Seitel. “But as global warming increases, climate change is going to catch up, you can really see that trend today.”

Landscaping near fields can act as a buffer zone

In some cases, insect abundance appears to increase with increasing temperature, at least in semi-natural areas outside of the tropics. However, the researchers caution against interpreting this as too obvious: many species that are particularly sensitive to warming have long since disappeared there. Additionally, while climate change is allowing some species to invade more northern regions, this cannot compensate for losses in other regions as it has become too hot for them.

What is also clear is that the landscape around the fields can act as a buffer to compensate for other stresses. At least in places where farming is not monoculture and does not use significant pesticides, Othwaite and colleagues find that leafy retreats with natural vegetation can fully offset the global warming effect. In areas with 75 percent of semi-natural areas, warming has caused a slight decrease in insects. On the other hand, if there were only 25 percent of the natural area in the area, the biomass of insects would have collapsed by more than 60 percent with the increase in temperature.

For him, this buffering effect is the most exciting thing about the study, says Settel. “This goes well with the other findings: If you have a structurally rich landscape with semi-natural areas, this can greatly increase the species’ chances of survival.”

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