Transcript Speciation
Speciation The formation of a new species from pre-existing species. What is a species? A population of physically similar organisms that can interbreed and produce fertile offspring fertile= able to produce more offspring Are these spiders the same species? Same Species? + Horse = + Donkey = Mule Mules are sterile – unable to reproduce Conclusion: Horses and Donkeys are different species Limits to Species Definition Impossible to test reproductive compatibility of extinct organisms Some organisms reproduce asexually- they don’t interbreed bacteria-reproduce asexually by binary fission bacteria produced by binary fission are genetically identical to one another How do species form? Speciation requires isolation 2 parts of a population that interbreed are prevented from interbreeding Two Types of Isolation Geographic – A physical barrier separates formerly interbreeding members of a population Example- Desert Pupfish 13 species of small fish in Southwest US. Geographic Isolation Continued Area was once covered in a large lake during the last ice age -ice age ended – lake dried up -small populations of pupfish were isolated in small spring fed lakes- lakes selected different phenotypes – led to new s species Reproductive Isolation Behavioral or physical differences that prevent members of a population from interbreeding Reproductive Isolation Wood Frogs and Leopard frogs very closely related, but different mating calls and mating times prevent interbreeding Reproductive Isolation continued Eastern and Western Meadow Larks-nearly identical,only hybridize at the edge of their range