Article: Insect decline in the Anthropocene — Death by a thousand cuts — PNAS

Click here to read the article from the Proceedings of the National Academy of Sciences of the United States of America (David L. Wagner, Eliza M. Grames, Matthew L. Forister, May R. Berenbaum, and David Stopak):

Nature is under siege. In the last 10,000 y the human population has grown from 1 million to 7.8 billion. Much of Earth’s arable lands are already in agriculture, millions of acres of tropical forest are cleared each year, atmospheric CO2 levels are at their highest concentrations in more than 3 million y, and climates are erratically and steadily changing from pole to pole, triggering unprecedented droughts, fires, and floods across continents. Indeed, most biologists agree that the world has entered its sixth mass extinction event, the first since the end of the Cretaceous Period 66 million y ago, when more than 80% of all species, including the nonavian dinosaurs, perished.

Ongoing losses have been clearly demonstrated for better-studied groups of organisms. Terrestrial vertebrate population sizes and ranges have contracted by one-third, and many mammals have experienced range declines of at least 80% over the last century. A 2019 assessment suggests that half of all amphibians are imperiled (2.5% of which have recently gone extinct) (6). Bird numbers across North America have fallen by 2.9 billion since 1970. Prospects for the world’s coral reefs, beyond the middle of this century, could scarcely be more dire. A 2020 United Nations report estimated that more than a million species are in danger of extinction over the next few decades…

Although a flurry of reports has drawn attention to declines in insect abundance, biomass, species richness, and range sizes, whether the rates of declines for insects are on par with or exceed those for other groups remains unknown. There are still too little data to know how the steep insect declines reported for western Europe and California’s Central Valley—areas of high human density and activity—compare to population trends in sparsely populated regions and wildlands. Long-term species-level demographic data are meager from the tropics, where considerably more than half of the world’s insect species occur. To consider the state of knowledge about the global status of insects, the Entomological Society of America hosted a symposium at their Annual Meeting in St. Louis, Missouri, in November 2019. The Society was motivated to do so by the many inquiries about the validity of claims of rapid insect decline that had been received in the months preceding the annual meeting and by the many discussions taking place among members. The entomological community was in need of a thorough review and the annual meeting provided a timely opportunity for sharing information.

Death by a thousand cuts: Global threats to insect diversity. Stressors from 10 o’clock to 3 o’clock anchor to climate change. Featured insects: Regal fritillary (Speyeria idalia) (Center), rusty patched bumble bee (Bombus affinis) (Center Right), and Puritan tiger beetle (Cicindela puritana) (Bottom). Each is an imperiled insect that represents a larger lineage that includes many International Union for Conservation of Nature “red list” species (i.e., globally extinct, endangered, and threatened species). Illustration: Virginia R. Wagner (artist).

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