A new theory about what triggered the loss of a number of large carnivores around two million years ago in East Africa has been launched recently at a symposium on human evolution and climate change.
On 19th April, Lars Werdelin of the Swedish Museum of Natural History in Stockholm presented his hypothesis at the symposium which was hosted by Columbia University’s Lamont-Doherty Earth Observatory.
In short it comes down to our ancestors who started to use stone tools and developed an omnivorous diet that included significantly more meat than their predecessors consumed. So they became competitors for the 18 large carnivores present about two millions years ago. Because they were more flexible in their diet — as omnivores they could survive in times when prey was scarce, unlike the large predators which relied on meat — and able to drive away the large predator from its prey with their stone tools. And so our ancestors drove about 12 large carnivore species to extinction in East Africa. This triggered cascades of ecosystem disruption, because when top predators disappear the population size of their prey will increase followed by several other consequences.
Werdelin developed this theory because he discovered that two million years ago the number of small carnivore species that went extinct was significantly less than the number of large carnivore species that disappeared. Likewise, the pattern of loss in the fossil records that Werdelin studied bore no resemblance to the pattern of climate change related losses that modern carnivores have been experiencing. This led to Werdelin’s conclusion that climate change was not the cause of the decline in large predators. Yet climate change probably caused environmental changes between two to three million years ago, forcing our earliest ancestors to leave the trees and onto the open savanna where they had to face the large carnivores.
Although Werdelin impressed his peers at the symposium, several questions were raised, especially about the timing. When exactly did our ancestors start to use stone tools, and when did the decline of large predator species set in, as well as how did this coincide or not with the climate change events? Furthermore, quite a few assumptions in Werdelin’s theory can be challenged. Some work has to be done before this theory can be proven as being valid. Some more fossil data has to be studied. Until then it is work in progress.
(Source: Scientific American, 25.04.2012; Wikipedia)