GEOGRAPHIC ISOLATION AND SPECIATION

What is a species?

group of individual organisms that are capable of interbreeding to produce fertile offspring in nature.

Male (Purple) and female purple martin (Progne subis )

Speciation

Basically, this is the evolution of a new species from an existing species. May occur from selective pressures as

we spoke of before Although there are several means in

which speciation occurs, we will look at geographical isolation

Speciation and Geographical Isolation~Geographical isolation is just what the name implies. A species of organisms becomes separated by a physical barrier such as a stream that develops into a river, mountain formation, lava flow, after deforestation, even when cities are built (urbanization)!

~~ Since they are divided into difference environments, natural selection occurs within each of the two populations forming two distinct species. If they can no longer interbreed and produce fertile offspring, we can say that speciation has occurred.

Geographic Isolation

Over time, different populations of distinct species are formed but physical or behavioral changes MUST have occurred!!

Leads to reproductive isolation Interbreeding organisms can no longer mate and produce fertile offspring

Another Example of Geographical Isolation

and Speciation

Geographic Isolation After Deforestation

*We’ll use this population of tree frogs as an example. As of now, they live in a subtropical area.

Geographic Isolation After Deforestation

• After deforestation, erosion occurs and a stream is formed. This causes the frog population to become divided. Remember that there is already genetic variation in the frog population!

Geographic Isolation After Deforestation

• Notice the difference in phenotypes between the two frog populations. Those that were caught on the side that had trees cut down are now in a new ecological environment….remember natural selection??? These could be two different species of frogs that can no longer interbreed.