A new analysis of 500 years of extinction data reveals that species losses peaked about a century ago and have since declined, contradicting assumptions of a rapidly worsening crisis. Researchers from the University of Arizona found that past extinctions were mainly driven by invasive species on islands, while current threats center on habitat destruction on continents. The study emphasizes the need for accurate assessments to inform conservation efforts.
For years, scientists have warned of a mass extinction event driven by accelerating species losses. However, a comprehensive study published in the Proceedings of the Royal Society B challenges this view. Led by Kristen Saban and John Wiens from the University of Arizona's Department of Ecology and Evolutionary Biology, the research analyzed data from nearly 2 million species and detailed 912 extinctions over the past five centuries.
The findings show that extinction rates among plants, arthropods, and land vertebrates reached their highest point around the early 1900s and have been decreasing since. 'We show that extinction rates are not getting faster towards the present, as many people claim, but instead peaked many decades ago,' Wiens said.
Historically, invasive species like rats, pigs, and goats caused most island extinctions, particularly in places like the Hawaiian Islands. Mollusks and vertebrates suffered the most losses, often in isolated habitats. On continents, extinctions were concentrated in freshwater environments. Today, habitat destruction poses the greatest risk to mainland species, with no evidence from the past two centuries linking climate change directly to increased extinctions.
'We discovered that the causes of those recent extinctions were very different from the threats species are currently facing,' Wiens noted. 'This makes it problematic to extrapolate these past extinction patterns into the future.' Saban added, 'To our surprise, past extinctions are weak and unreliable predictors of the current risk that any given group of animals or plants is facing.'
The authors reviewed threat assessments for 163,000 species from the International Union for Conservation of Nature, finding that most threatened species today face habitat loss on the mainland, unlike past patterns. While emphasizing ongoing biodiversity risks, they highlight conservation successes: 'Investing money in conservation actually works,' Wiens said. Saban stressed the importance of rigorous science: 'Biodiversity loss is a huge problem right now... But it's important that we talk about it with accuracy.'