Topic 7.4 - Types of Natural Selection

Label the three types of natural selection illustrated below:

• Directional

• 
• Stabilizing

• 
• Disruptive

• 

Starlings produce an average of five eggs in each clutch. If there are more than five, the parents cannot adequately feed the young. If there are fewer than five, predators may destroy the entire clutch. This is an example of:

• disruptive selection.

• stabilizing selection.

• directional selection.

• none of the above.

The occurrence of large or small beak sizes among seed crackers in the absence of medium sized beaks is an example of:

• directional selection.

• stabilizing selection.

• disruptive selection.

• none of the above.

A scientist measures the circumference of acorns in a population of oak trees and discovers that the most common circumference is 2 cm. What would you expect the most common circumference(s) to be after 10 generations of stabilizing selection?

• 2 cm

• greater than 2 cm or less than 2 cm

• greater than 2 cm and less than 2 cm

• can't tell from the information given

A scientist measures the circumference of acorns in a population of oak trees and discovers that the most common circumference is 2 cm. What would you expect the most common circumference(s) to be after 10 generations of disruptive selection?

• 2 cm

• greater than 2 cm or less than 2 cm

• greater than 2 cm and less than 2 cm

• can't tell from the information given

A scientist measures the circumference of acorns in a population of oak trees and discovers that the most common circumference is 2 cm. What would you expect the most common circumference(s) to be after 10 generations of directional selection?

• 2 cm

• greater than 2 cm or less than 2 cm

• greater than 2 cm and less than 2 cm

• can't tell from the information given

Spotted brown-and-white butterflies blend into lichen-covered tree bark, making it difficult for predators to see them, while solid brown and solid white butterflies are easier to see and get eaten.

• stabilizing selection

• disruptive selection

• directional selection

Panthers with teeth that are too short have difficulty capturing prey, while panthers with teeth that are too long have difficulty chewing their food.

• directional selection

• stabilizing selection

• disruptive selection

In a lake in South Africa, guppies are eaten by the pike fish, and the larger the guppy, the more difficulty it has escaping its pike fish predator.

• disruptive selection

• stabilizing selection

• directional selection

The rocks at the bottom of a stream are either black or white. Snails that live on these rocks are a range of color from solid black to gray to solid white. A local freshwater fish loves to munch on these snails, but it cannot see the solid black or solid white snails when the snails are on matching rocks. Grey does not blend into either rock color and is much easier to see.

• Stabilizing

• Disruptive

• Directional