Natural Selection Pre Assessment

Tree squirrels can have different fur colors. Squirrels live in forests where foxes also live. Foxes hunt squirrels for food. Squirrels that have fur the same color as the trees are harder for the foxes to see and catch. The diagram above shows a population of squirrels that lived in a forest. Scientists had previously only seen brown and gray squirrels in this forest; they had never seen squirrels of any other color. The diagram below shows how the population changed after many generations. How did the color of the trees in the squirrels’ environment change? Explain what happened to the squirrels over many generations.

• The squirrel's environment will did not change, the trees stayed the same color. New Squirrels were born, with the black fur on squirrels reproducing's more rapidly.

• The squirrels’ environment changed to have lots of black trees. At some point, a brown or a gray squirrel had a baby with a mutation for the black-fur trait. It was easier for that baby to survive, so it lived a long time and reproduced. It passed down its mutant black-fur trait to some of its offspring. Over many generations, these black squirrels had more offspring with black fur, so black fur became the most common trait. Most brown and gray squirrels died before they could have offspring, so, over time, fewer brown and gray squirrels were born, and those traits became less common.

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Harbor seals live in northern oceans and have a 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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Scientists measured the spine size of a population of cactuses found in an area in 1970. They measured the spine size of the cactus population again in 2015. Which of the statements below best describes the difference in the cactuses at the two time points?

• The cactuses in 1970 had smaller spines than the cactuses in 2015.

• The cactuses in 1970 had larger spines than the cactuses in 2015.

• There were more cactuses in 1970 than there were in 2015.

• There was more variation in spine size in 1970 than there was in 2015.

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Scientists measured the spot size of all the guppies (small fish) that lived in a river 40 years ago. They measured the spot size of the guppy population again last year. When was there more variation in the spot size of guppies in the river?

• These bar graphs do not show the amount of variation in the population.

• There was the same amount of variation in spot size 40 years ago and last year.

• There was more variation 40 years ago.

• There was more variation last year.

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Eider ducks live in the ocean and have a layer of warm feathers underneath their regular feathers. They can have thin feathers, medium feathers, or thick feathers. These feathers help 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 population of ducks shown above lives in an environment that has always had very cold water. Could there ever have been ducks with thin feathers in this population?

• No ducks could have been born with the thin-feather trait because none of the adult ducks had that trait to pass down.

• No ducks could have been born with the thin-feather trait in the past, but some with that trait could be born in the future if the environment changes to be warmer.

• A duck could have been born with a mutation in its genes for the thin-feather trait and lived for a little while, but it would have been more likely to die before it had offspring.

• A duck could have been born with a mutation in its genes for the thin-feather trait, but having a mutation in its genes would have caused it to die when it was born.

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Scientists measured the beak length of a population of birds in a lake in 1960. They measured the beak length of the bird population again in 2010. What do the graphs show you about the variation in the beak lengths of the birds by the lake?

• There was the same amount of variation in 1960 and in 2010.

• These bar graphs do not show the amount of variation in the population.

• There was more variation in 2010.

• There was more variation in 1960.

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How would you describe the histogram above?

• Most of the ostrilopes have no fur

• Most of the ostrilopes have medium length fur

• There is only one type of fur in this population

• Most of the ostrilopes have thick fur

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How would you describe the variation in this histogram?

• There is high variation

• There is no variation

• There is low variation

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How would you describe the population shown in the histogram?

• The ostrilopes have thick fur

• The ostrilopes don't have a lot of fur

• the population has a lot of variation

• the population has no variation

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Which of the following is an adaptive trait?

• yellow ostrilopes in a green environment with predators present

• yellow ostrilopes in a yellow environment with predators present

• multiple colors of ostrilopes in a yellow environment with predators present

• all of the ostrilopes dying off

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