Natural Selection

Natural selection can operate on predator populations as well as on prey. Suppose that over time trees became covered in lichen organisms which are light green and the proportion of light moths increased to nearly 100%. What is the most likely consequence for predator populations?

• Bird populations will decrease, at least for a while.

• Over time, birds with better eyesight will become more common.

• Birds may change hunting strategies or seek other sources of food.

• All three choices are correct.

Which of the following statements best describes what will most likely occur to the moth populations in the image?

• The light moths will be captured by predators more easily than the dark moths, and the population of dark moths will rise.
• The light moths will be captured by predators more easily than the dark moths, and the population of light moths will rise.
• The dark moths will be captured by predators more easily than the light moths, and the dark moths will probably go extinct.
• The light moths will change their wing color to match that of the dark moths.

Which of the following statements best describes what will most likely occur to the moth populations in the image?

• There has been a drought in the area that is affecting all life forms.
• The population of natural predators of the moths has gotten smaller.
• The moths are living in an environment with light trees.
• The moths are living in an environment with dark trees.

The pair of population graphs display the results of two different five-year hunting cycles, one on light trees and one on dark trees. The population of light-colored moths is shown by the light gray dots, and the population of dark moths is shown by the dark gray dots. How do these results demonstrate natural selection?

• The moth populations shown here demonstrate random fluctuations over time that are not explained by tree color.
• On light trees, individual moths tried to become lighter in color to match the tree background. On dark trees, individual moths tried to become darker in color.
• The moths that were the same color as their background were more likely to survive and reproduce. Over time, the populations of these well-adapted moths increased.
• Small particles of tree bark became embedded in the moth's wings, causing the moths to become darker on the dark trees and lighter on the light trees. These acquired traits were then passed down to the next generation of moths, causing the populations to change color over time.

Suppose a certain species of insect lives in the lush green canopy of the rain forest. Some of the insects are bright green in color, and some are bright yellow. Assume there is a natural predator of the insect in the area. What do you expect to happen to the populations of the green and the yellow insects over time?

• The green insect population will increase and the yellow insect population will decrease.
• The green insect population will decrease and the yellow insect population will increase.
• Both insect populations will remain constant over time.
• Both insect populations will increase over time.

Which of the following lions is the "fittest"?

• a lion that has 8 healthy offspring

• the largest and strongest lion

• the lion that was ill but is now healthy

• a lion fathers 3 cubs