Speciation Notes

Speciation-

process by which new species are made Evolution creates (and destroys) new species, but … What is a species?

It’s not as straightforward a question as most believe.

These are members of different species - eastern (left) and western (right) meadowlark.

What is a Species?

There is only one existing human species.

What is a Species?

And these are all members of a single species.

What is a Species

Northern spotted owl (left) and barred owl (right).

What is a Species?

Species-is a group of individuals capable of interbreeding to produce fertile offspring.

This is the biological species concept. Like all attempts to define a species, it has many problems.

Horses and Donkeys can interbreed, but the hybrid (Mule) is not fertile

One Problem in the Biological Species Concept For asexually-reproducing organisms, like these bacteria, what constitutes a species?

How Many Species Are There?

We don’t know. About 2 million species have been described.

Estimates of existing species number range from 4 million to 100 million (with 10-15 million being a more commonly considered estimate).

How Do Species Arise?

The key to speciation is

reproductive isolation

of populations.

Geographic Isolation-physical separation Harris’ antelope squirrel White-tailed antelope squirrel Two species of ground squirrel are postulated to have descended from a common ancestral population that was separated by formation of the Grand Canyon.

Ecological and Temporal Isolation (different habits within an overlapping range)

Courtship rituals, like these, are critical for mating within a species, but ineffective for attracting members of other species.

Behavioral Isolation

Mechanical Isolation

Species Come and Go

Best estimates from the fossil record indicate that greater than 99% of species that have existed are now extinct. A typical “lifetime” for a species is about 1 million years.

Mass Extinctions Are a Fact of Life

The Cretaceous/Tertiary Mass Extinction Gary Larson

Are We Now Causing a Mass Extinction?

Holocene Extinction Event

• Most scientists believe that we are currently in the early stages of a human-caused mass extinction, known as the Holocene extinction event. • In the 20 th every year.

century, it is estimated that 2 million species went extinct.

• It is estimated that up to 140,000 species go extinct • The rate of species extinctions at present is estimated at 100 to 1000 times "background" or average extinction rates in the evolutionary time scale of planet Earth. • Biologist E. O. Wilson estimated that if current rates of human destruction continue, one-half of all species of life on earth will be extinct in 100 years.

Tasmanian Tiger- extinct since 1936 th Irish Elk- extinct 7,700 years ago