Presentation on theme: "Speciation Notes. What is a species? It’s not as straightforward a question as most believe. Speciation-process by which new species are made Evolution."— Presentation transcript:
What is a species? It’s not as straightforward a question as most believe. Speciation-process by which new species are made Evolution creates (and destroys) new species, but … 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 million being a more commonly considered estimate).
How Do Species Arise? The key to speciation is reproductive isolation of populations.
Geographic Isolation-physical separation Two species of ground squirrel are postulated to have descended from a common ancestral population that was separated by formation of the Grand Canyon. Harris’ antelope squirrel White-tailed antelope squirrel
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
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
Gary Larson The Cretaceous/Tertiary Mass Extinction
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 century, it is estimated that 2 million species went extinct. It is estimated that up to 140,000 species go extinct every year. 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.
Irish Elk- extinct 7,700 years agoWholly Mammoth- extinct 3,700 years agoCave Lion- extinct 2,000 years ago Dodo Bird- extinct since 17 th Century Stellar’s Sea Cow: Defenseless Beast - extinct since 1768 The last living Tasmanian tiger is seen in this picture, dated Tasmanian Tiger- extinct since 1936