MAY 27, 2023 9:28 AM PDT

Nearly Half of All Species Are Declining - Mass Extinction Will Be Worse than Previously Thought

WRITTEN BY: Amelia Rhodeland

Defaunation is the loss or decline of animal species around the world, a phenomenon which is accelerating in recent years and negatively impacts global biodiversity. Termed the “sixth mass extinction,” Anthropocene defaunation is a modern-day, largely human-caused event of mass extinction around the world. 

In a new study, researchers found that the rate of defaunation is accelerating even faster than previously estimated. Looking at population trend data for more than 71,000 species of all five groups of vertebrates (mammals, birds, reptiles, amphibians and fishes) and insects, they discovered that 48% of the species were declining, and only 3% of species had populations that were increasing in number. 

The researchers cite the IUCN Red List, which maintains a database of designated levels of extinction risk for various species around the globe. The list, by the International Union for Conservation of Nature (IUCN), is the traditional way to track levels of extinction risk. But the researchers note that this metric does not account for species that are currently declining, though not yet actively at the risk of extinction — providing an imprecise and incomplete picture of the state of the world’s biodiversity.

After their assessment, the study authors found a startling trend when overlaying their results with the IUCN Red List: 33% of species currently designated as “non-threatened” are actually in decline.

There are patterns geographically, as well, with the species declines largely concentrated around tropical regions, while temperate climates host species that are more likely to be stable or increasing. 

Looking by the species group, amphibians were the most at risk — with 63% of species declining in population, and only 37% of species remaining stable. Among vertebrates, mammals and birds followed, with 56% and 53% of their species declining, respectively. Insects were in a similar state, with 54% of their species experiencing declines in population.

The study was conducted by macro-biologists and life scientists from Queen's University Belfast and Czech University of Life Sciences Prague. 

Sources: Science, Biological Reviews,

About the Author
Master's (MA/MS/Other)
Amelia (she/her) is a writer and editor specializing in earth and the environment at Labroots. She is passionate about helping people connect with nature. She has led outreach for federal land management agencies and previously conducted research at the University of Oregon's Institute for a Sustainable Environment.
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