16-3 The Process of Speciation

I. Isolating Mechanisms

Speciation- the formation of a new species Species- A group of organisms that breed with one another and produce fertile offspring Speciation- the formation of a new species Horse + Donkey = Mule which is sterile and therefore not a species

Discuss w/ Partner: What factors are involved in the formation of new species?

Answer: What factors are involved in the formation of new species? The gene pools of two populations must become separated for them to become new species.

As new species evolve, populations become reproductively separated from each other. Reproductive Isolation- When the members of two populations can’t interbreed & produce fertile offspring Reproductive Isolation results in separate gene pools.

The 3 causes of reproductive isolation: Behavioral Isolation Geographic Isolation Temporal Isolation

Behavioral Isolation- when two populations are able to interbreed but different courtship rituals or other reproductive strategies that involve behavior. Different species of bowerbird construct elaborate bowers & decorate them with different colors in order to woo females. The Satin bowerbird (left) builds a channel b/w upright sticks, and decorates with bright blue objects, while the MacGregor’s Bowerbird (right) builds a tall tower of sticks and decorates with bits of charcoal. Evolutionary changes in mating rituals, such as bower construction, can contribute to speciation.

Geographic Isolation - when two populations are separated by geographic barriers such as rivers or mountains.

Temporal Isolation-when two or more species reproduce at different times

Discuss w/ Partner: Pg. 406 Figure 16-13 The woodpecker finch uses its beak to hold a cactus spine, which pokes into holes in tress in order to spear insects. What tool does its beak resemble? If another species of fruit-eating finch was discovered, what type of beak do you think it would have?

Answers: What tool does its beak resemble? Pliers or needle-nosed pliers. If another species of fruit-eating finch was discovered, what type of beak do you think it would have? It would have a beak like the vegetation tree finch which also eats fruit.

Discuss w/ Partner: Figure 16-15 page. 407 How would the graph be different if birds with medium-sized beaks were more likely to survive?

Answer: How would the graph be different if birds with medium-sized beaks were more likely to survive? It would resemble a normal curve (bell shaped curve)

II. Speciation in Darwin’s Finches

Speciation in the Galápagos finches occurred by: founding of a new population geographic isolation changes in new population's gene pool reproductive isolation ecological competition

Founders Arrive- A few finches—species A—travel from South America to one of the Galápagos Islands. There, they survive and reproduce

Geographic Isolation- Some birds from species A cross to a second island. The two populations no longer share a gene pool.

Changes in the Gene Pool- Seed sizes on the second island favor birds with large beaks. The population on the second island evolves into population B, with larger beaks.

Reproductive Isolation- If population B birds cross back to the first island, they will not mate with birds from population A. Populations A and B are separate species.

Continued Evolution- This process of isolation, genetic change, and reproductive isolation probably repeated itself often across the entire Galápagos island chain.