5a Natural Selection Using Data

The graphs below show the changes in crab color at one beach.

Which of the following is most likely to have caused the change in the distribution?

• A new predator arrived that preferred dark-tan crabs.

• A new predator arrived that preferred light-tan crabs.

• A change in beach color made medium-tan crabs the least visible to predators.

• A change in beach color made medium-tan crabs the most visible to predators.

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The figure shows how natural selection of a single-trait gene affects lizard survival.

Which of the following most likely causes the changes in allele distribution?

• The allele for light gray coloration disappears from the population. This may be because light gray lizards are more visible to predators and therefore they might be less likely to survive and reproduce.

• The allele for black coloration decreases fitness and becomes less common. This may be because black coloration keeps the lizards cool during hot summer temperatures.

• Medium gray coloration in lizards appears to be a neutral mutant allele that allows the lizards to hide better from predators. This leads to increases in phenotype and allele frequency of gray coloration.

• Because black and medium gray lizards are less visible to predators, these alleles are neutral to natural selection and therefore will not disappear from the population of lizards.

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What is the most likely explanation of the data shown below?

• 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.

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The pair of population graphs below 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.

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What is the correct explanation for what is happening in this graph?

• There are a lot of average-sized beaks
• There are no beaks
• There are a lot of small beaks only
• There are a lot of small and large beaks, but not average-sized ones

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Hummingbirds can have different beak lengths.

They use their beaks to reach to the nectar (their food) at the bottom of flowers. Hummingbirds with longer beaks can get food from long flowers. Hummingbirds with shorter beaks cannot reach the nectar in long flowers. If a hummingbird can’t easily reach its food, it will die.

The diagrams below show three possible hummingbird populations.

If their environment changes to have only long flowers, which of the following hummingbird populations will most likely survive?

• Only population 2 will survive because it is the only population with variation.

• All the populations will survive because the hummingbirds will change the length of their beaks if they need to.

• Populations 1 and 2 will survive.

• Populations 2 and 3 will survive.

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Eider ducks live in the ocean and have a layer of warm feathers underneath their regular feathers. They can have feathers of different thicknesses.

These feathers helps the ducks stay warm in cold water. Ducks with thicker feathers are more likely to stay warm and survive in cold water. But, in warm water, thicker feathers can make the ducks overheat and die.

The diagram below shows a population of ducks that live in an area of an ocean. At time 1, the population had the same number of ducks with thin and thick feather layers. At time 2, after many generations, there were many more ducks with a thin feather layer and fewer ducks in the population with a thick feather layer.

How did the environment change between time 1 and time 2? How did the population change?

• The water became warm. As a result, ducks with thin feathers were more likely to survive, so the ducks with thick feathers changed to have thin feathers.

• The water became warm. As a result, ducks with thin feathers were more likely to survive, so both kinds of ducks passed on the gene for thin feathers to their offspring.

• The water became warm. With each generation, more ducks with thin feathers survived long enough to pass on the gene for thin feathers to their offspring.

• You cannot tell how the environment changed. With each generation, more ducks passed on the gene for thin feathers to their offspring.

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There is a kind of snake that can be born with red, yellow, or green skin. Eagles hunt these snakes, but snakes that are the same color as their environment are harder for the eagles to see and catch.

A population of snakes once lived in an environment where there was sand and dirt, but no grass. The image above shows what the population looked like then. The environment changed so that green grasses and plants now grow there.

The diagrams below show two predictions for what the population could look like after many generations.

Which prediction best shows what the population could look like after many generations? What caused it to change?

• Prediction 1 is best. Two yellow or red snakes had a baby with a mutation in its genes for the green-skin trait. Because green snakes are more likely to survive, that baby survived long enough to pass on its mutation, so the green trait became more common over generations.

• Prediction 1 is best. Green snakes are more likely to survive, so yellow and red snakes began to have offspring with mutations in their genes for the green- skin trait so that their offspring would have a better chance of surviving.

• Prediction 2 is best. A snake could have been born with a mutation in its genes for the green-skin trait and lived for a little while. Because green snakes are more likely to die, it would have been more likely to die before it had offspring, so the final population will only have yellow and red snakes.

• Prediction 2 is best. A snake could have been born with a mutation in its genes for the green-skin trait, but having a mutation in its genes would have caused it to die when it was born, so the final population will only have yellow and red snakes.

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Scientists measured the height of the giraffes in two different populations. Which population has the largest number of tall giraffes?

• The population in Niger has the largest number of tall giraffes.

• The population in Somalia has the largest number of tall giraffes.

• Both populations have the same number of tall giraffes.

• These bar graphs do not show which population has more tall giraffes.

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Harbor seals live in northern oceans and a have layer of blubber (fat) that keeps them warm. Seals can have blubber of different thicknesses.

Seals with thicker blubber are more likely to stay warm and survive in cold ocean waters. But, in warm ocean waters, thicker blubber can make the seals overheat and die.

The diagrams below show three possible seal populations.

If their environment changes to have warm water, which of the following seal populations will most likely survive?

• Populations 1 and 2 will most likely survive.

• Populations 2 and 3 will most likely survive.

• Only Population 2 will survive because it is the only population with variation.

• All the populations will survive because the seals will change the thickness of their blubber if they need to.

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