Academic Minute
5:00 am
Thu March 13, 2014

Dr. Charles Marshall, University of California Berkeley - Biodiversity Loss and Extinction

The extinction of a specific species is a sad reality in the animal kingdom.

In today’s Academic Minute, Dr. Charles Marshall, professor at the University of California’s Berkeley campus discusses the mitigating factors that can contribute to the eventual dying out of a particular species of animal.

Dr. Charles Marshall is a professor of integrated biology at the University of California Berkeley. His research specializes in how paleontological studies can inform our knowledge of life today. He earned a PhD in evolutionary biology at the University of Chicago in 1989

About Dr. Marshall

The Marshall Lab Website

Dr. Charles Marshall - Biodiversity Loss and Extinction

While the 5 big mass extinctions attract great attention, for example the end-Cretaceous event that wiped all the dinosaurs (except the birds), more species went extinct between the mass extinctions, during times of background extinction.  To better understand background extinction we analyzed mammalian groups that are now fully extinct or that appear to be on their way to extinction, including rhinos, horses, and elephants. 

We targeted groups with exceptionally rich fossil records, selecting 19 in all.  What did we find?  First, we established that their species loss was not just bad luck, but was in fact due a failure to keep pace with a deteriorating environment. We call this losing to the Red Queen, taking inspiration for Lewis Carroll’s Red Queen who tells Alice the she must run as fast as she can just to stay where she is.  The fact that the groups’ demise is more than just bad luck is not too surprising.  But what did surprise us was that their species loss was driven as much by depressed origination rates (the onset of an evolutionary sterility), as by elevated extinction rates.

This is striking given that most biologists don’t think about a decrease in origination when they think about groups going extinct.  We don’t know what causes evolutionary sterility (although we have some ideas)! We also made a second discovery. Theory suggests that as a group becomes more species rich increased competition should reduce its origination rate and increase its extinction rate.  Eventually the origination and extinction rates become equal, and the group is said to have reached its equilibrium species richness.

Surprisingly we found that the processes that drove groups into decline happen so fast that the species richness of each clade never settled on its equilibrium species richness.  So, how then do mammals lose the Red Queen?  Through evolutionary sterility as well as elevated extinction, and via processes that act sufficiently fast that the groups never settled into their natural equilibrium species richnesses.

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