Scientists Examine Historical Loss of Diversification of Species Leading to Extinction

The death of individual species is a problem, but so is a lack of new, emerging species, reports a study by researchers at the University of California, Berkeley.

"Virtually no biologist thinks about the failure to originate as being a major factor in the long term causes of extinction," Charles Marshall, professor of integrative biology and co-author of the report, said in a press release. "But we found that a decrease in the origin of new species is just as important as increased extinction rate in driving mammals to extinction."

The effects of such a decrease are hard to see through human eyes, given that they play out on scales of millions of years, versus hundreds or thousands. However, the findings should help biologists better understand the pressure today's flora and fauna are under and what drove evolution and extinction in the past, Marshall argues.

Published in the journal Science Express, the study is based on a look at 19 groups of mammals that are all either extinct or in decline in terms of diversity, as in the case of horses, elephants and rhinos. The researchers selected the animals under examination because they boasted a substantial fossil record and had their origins in the last 66 million years, during the Cenozoic Era.

In particular, researchers wanted to test a popular evolutionary theory called the Red Queen hypothesis, named after Lewis Carroll's character who, in the book "Through the Looking Glass," said her country was a place where "it takes all the running you can do, to keep in the same place."

In terms of biology, this translates into the theory that animals and plants don't simply disappear out of bad luck in a static and unchanging environment, but instead face a constant change, be it a deteriorating environment or better equipped predators, that requires them to continually adapt and evolve new species simply to survive.

Based on their findings, the researchers concluded that, while the specific cause of declining originations and rising extinctions for the animals they studied was unclear, they did conclude that their deaths were not simply the result of a bad night at the slot machines of life.

"Each group has either lost, or is losing, to an increasingly difficult environment," Marshall said. "These groups' demise was at least in part due to loss to the Red Queen - that is, a failure to keep pace with a deteriorating environment."

Specifically, they found that the animal groups were initially driven to higher diversity until they reached the carrying capacity of their environment, meaning the maximum number their environment could tolerate. Once this happened, their environment suffered to the point that the diversity could not be sustained, eventually leading to extinction.

"In fact," Marshall explained, "our data suggest that biological systems may never be in equilibrium at all, with groups expanding and contracting under persistent and rather, geologically speaking, rapid change,"