According to a new study, dominant species with a population spread around the globe are just as vulnerable in a mass extinction as more fragile species confined to a single locale. In the Earth’s history there has been five mass extinction events, including climate change caused by volcanoes and an asteroid hit 66 million years ago that wiped out the dinosaurs.
Generally, geographically widespread animals are less likely to become extinct than animals with smaller geographic ranges, giving them a hedge against regional environmental catastrophes. But a study by UK scientists has found this insurance is made useless during global mass extinction events, and that widely distributed animals are just as likely to suffer extinction as those that are less widespread.
Dr Alex Dunhill, from the School of Earth and Environment at the University of Leeds, and Professor Matthew Wills from the University of Bath’s Milner Centre for Evolution, investigated the fossil record of land-living vertebrates, which includes dinosaurs, from the Triassic and Jurassic periods (252-145 million years ago).
They found that although large geographic ranges do offer insurance against extinction, this insurance disappeared across a mass extinction event that occurred around 200 million years ago, at the Triassic-Jurassic boundary, associated with massive volcanic eruptions and rapid climate change which caused the demise of around 80 per cent of species on the planet.
Not good news for humans.
This is the first ever study analyzing the relationship between geographic range and extinction in the terrestrial fossil record. The results are similar to those obtained from the marine invertebrate fossil record.
Dr Dunhill said:
“The fact that the insurance against extinction given by a wide geographic distribution disappears at a known mass extinction event is an important result. Many groups of crocodile-like animals become extinct after the mass extinction event extinct at the end of the Triassic era, despite being really diverse and widespread beforehand.
In contrast, the dinosaurs which were comparatively rare and not as widespread pass through the extinction event and go on to dominate terrestrial ecosystems for the next 150 million years.
These results shed light on the likely outcome of the current biodiversity crisis caused by human activity. It appears a human-driven sixth mass extinction will affect all organisms, not just currently endangered and geographically restricted species.”
Alexander M. Dunhill & Matthew A. Wills
Geographic range did not confer resilience to extinction in terrestrial vertebrates at the end-Triassic crisis
Nature Communications 6, Article number: 7980 doi:10.1038/ncomms8980
Illustration: “Thalassiodracon BW” by Nobu Tamura CC BY 2.5