Formation of Species Section 3

The Concept of Species Speciation – species formation. Existing species are changed versions of older species.

Morphological Concept of Species Morphology – internal and external structure and appearance of an organism. CONCEPT: Species is defined according to their morphology. PROBLEM: -phenotype differences among species.

Biological Species Concept Proposed by Ernst Mayer 1904 A species is a population of organisms that can interbreed and produce healthy offspring. They cannot breed with other species.

Isolating Mechanisms Speciation begins with isolation.

Geographic Isolation Physical separation of members of a population Ex. Deep canyon, river, crying climate in a valley When the subpopulations become isolated, gene flow between them stops. Natural selection and genetic drift cause the two subpopulations to diverge, eventually making them incompatible for mating. (2 new species)

Example Pupfish Death valley has many ponds. Each pond has a different species of fish that lives only in that pond. Why did this happen? The valley was covered by a lake during the last ice age. The ponds formed when the ice age ended. Fish species became isolated and the environments of each pond differed enough that the separate populations of fish diverged.

Reproductive Isolation Results from barriers to successful breeding between population groups in the same area. Two types of Reproductive Isolation: Prezygotic isolation- occurs before fertilization Postzygotic isolation- occurs after fertilization.

Prezygotic Isolation Mating calls that are not recognized by the mate. Difference in mating seasons. Mechanical Isolation – difference in anatomy not allowing them to mate. Ex. Wood frog and leopard frog, mating calls and mating times differ so they do not mate in the wild. They do mate in captivity.

Postzygotic Isolation Offspring our not healthy (sterile). Zygote dies after fertilization. Offspring die quickly.

Rates of Speciation Speciation sometimes requires millions of years but some can form more rapidly. Punctuated equilibrium – sudden shift or change; species arise quickly or die quickly.

Homework Pg. 312 1-6