Global changes in insect populations reflect both decline and growth

April 23, 2020

The widely reported "insect apocalypse" is far more nuanced than previous studies have suggested, according to a new study, which reports the findings of a meta-analysis featuring data from 166 long-term surveys across 1,676 sites worldwide. The results demonstrate that global insect population trends are highly spatially variable and reflect both decline and growth. Insects are among the most abundant and diverse animals on the planet and serve a critical role for ecosystem services and in the food web. Several recent case studies have reported drastic declines in insect abundance and species richness - with some global regions estimating biomass losses as high as 25% per decade. When extrapolated globally, such findings paint an apocalyptic picture for Earth's insects, a suggestion that has sparked serious concern among policymakers, scientists and the public. However, despite the alarm, insects are critically understudied and it remains uncertain just how widespread these patterns of decline are. To address this, Roel van Klink and colleagues evaluated a comprehensive dataset of long-term insect surveys from sites across the globe - what Maria Dornelas and Gergana Daskalova call "the largest and most complete assessment to date," in a related Perspective. The analysis by van Klink and colleagues revealed considerable variation in insect population trends, even among adjacent sites. Although highly variable, van Klink et al. report an average decline in terrestrial insect abundance of roughly 9% per decade, which, while lower than other published rates, confirms the general trend. On the other hand, their data also revealed an increase in the abundance of freshwater insects at a rate of nearly 11% per decade, perhaps partly due to successful clean water efforts. "As we continue to tackle challenges in disentangling different insect biodiversity trends, we will be better poised to predict their consequences for ecosystem function and services, such as pollination, decomposition and pest control," write Dornelas and Daskalova.
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American Association for the Advancement of Science

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