Natural Selection 9 Praha

Blue jays are birds that live in the forest. They can have beaks of different thicknesses. Blue jays use their beaks to get to the seeds they eat. Blue jays with thinner beaks can easily reach and eat the seeds inside pinecones. Blue jays with thicker beaks can easily open and eat seeds with hard shells. The diagrams below show three possible blue jay populations. If their environment changes to have only seeds in pinecones, which of the following blue jay 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 blue jays will change the thickness of their beaks if they need to.

Northern foxes can have different fur colors. The foxes hunt squirrels for food. Foxes that have fur the same color as their environment are better at getting closer to squirrels and catching them. The diagram below shows a population of foxes that live in one area. At time 1, the population had the same number of brown and white foxes. At time 2, after many generations, there were many more brown foxes and fewer white foxes in the population. How did the environment change between time 1 and time 2? How did the population change?

• You cannot tell how the environment changed. With each generation, more foxes passed on the gene for brown fur to their offspring.

• The environment became brown. Brown foxes are more likely to survive, so the white foxes changed to have brown fur.

• The environment became brown. Brown foxes are more likely to survive, so both kinds of foxes passed on the gene for brown fur to their offspring.

• The environment became brown. With each generation, more brown foxes survived long enough to pass on the gene for brown fur to their offspring.

Guppies are small fish that live in South American rivers. They can have differentsized spots on their bodies. The river bottoms are covered in rocks. Guppies with spots that are the same size as the rocks on the bottom are harder for bigger fish to see and catch. The diagrams below show three possible guppy populations. If their environment changes to have only large rocks, which of the following guppy 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 guppies will change the size of their spots if they need to.

•  Populations 1 and 2 will most likely survive.

•  Populations 2 and 3 will most likely survive

Emerald tree boas are snakes that live in rain forest trees. The snakes have scales on their skin that can be different colors. Eagles hunt the snakes in the trees. Snakes with scales that are the same color as the leaves around them are harder for the eagles to see and catch. The diagram below shows a population of snakes that live in a rain forest. At time 1, the population had the same number of yellow and red snakes. At time 2, after many generations, there were many more red snakes and fewer yellow snakes in the population. How did the environment change between time 1 and time 2? How did the population change?

• You cannot tell how the environment changed. With each generation, more snakes passed on the gene for red scales to their offspring.

• There were more trees with red leaves. With each generation, more red snakes survived long enough to pass on the gene for red scales to their offspring.

• There were more trees with red leaves. Red snakes are more likely to survive, so the yellow snakes changed to have red scales.

• There were more trees with red leaves. Red snakes are more likely to survive, so both kinds of snakes passed on the gene for red scales to their offspring.

Barrel cactuses live in the Mexican desert. They are covered in sharp spines. Cactuses can have spines of different lengths. Their sharp spines help protect them from being eaten by bighorn sheep. Cactuses with longer spines are less likely to be eaten by the sheep. The diagrams below show three possible cactus populations.If their environment changes to have many bighorn sheep, which of the following cactus 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 cactuses will change the length of their spines if they need to.

. Brown anoles are lizards that live on islands in the Bahamas. They can have legs of different lengths. Lizards with shorter legs are better at climbing trees than lizards with longer legs. This makes lizards with shorter legs better at escaping from the floods that sometimes cover the islands. The diagram below shows a population of lizards that live on an island. At time 1, the population had the same number of lizards with short legs and lizards with long legs. At time 2, after many generations, many more lizards had short legs and fewer lizards had long legs.How did the environment change between time 1 and time 2? How did the population change?

• You cannot tell how the environment changed. With each generation, more lizards passed on the gene for short legs to their offspring.

• There were more floods. Lizards with short legs are more likely to survive, so the lizards with long legs changed to have short legs.

• There were more floods. Lizards with short legs are more likely to survive, so both kinds of lizards passed on the gene for short legs to their offspring.

• There were more floods. With each generation, more lizards with short legs survived long enough to pass on the gene for short legs to their offspring.

Guppies are small fish that live in South American rivers. They can have large spots, medium spots, or small spots. The river bottoms are covered in rocks. Guppies with spots that are the same size as the rocks on the bottom are harder for bigger fish to see and catch. The population of guppies shown above lives in an environment that has always had large rocks. Could there ever have been guppies with small spots in this population?

•  No guppies could have been born with the small-spot trait because none of the adult guppies had that trait to pass down.

•  No guppies could have been born with the small-spot trait in the past, but some with that trait could be born in the future if the environment changes to have small rocks.

•  A baby guppy could have been born with genes for the mutant small-spot trait and lived for a little while, but it would have died before it had any offspring

• A baby guppy could have been born with genes for the mutant small-spot trait, but its mutant trait would have caused it to die when it was born.

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 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 diagrams below show three possible duck populations.If their environment changes to have very cold water, which of the following duck 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 ducks will change their feather thickness if they need to.

Blue jays are birds that live in the forest. They can have beaks of different thicknesses. Blue jays use their beaks to get to the seeds they eat. Blue jays with thinner beaks can easily reach and eat the seeds inside pinecones. Blue jays with thicker beaks can easily open and eat seeds with hard shells. The diagram below shows a population of blue jays that live in a forest. At time 1, the population had the same number of blue jays with thick beaks and blue jays with thin beaks. At time 2, after many generations, there were many more blue jays with thin beaks and fewer jays with thick beaks in the population. How did the environment change between time 1 and time 2? How did the population change?

• There were more trees that had pinecones with seeds. With each generation, more blue jays with thin beaks survived long enough to pass on the gene for thin beaks to their offspring.

• There were more trees that had pinecones with seeds. Blue jays with thin beaks are more likely to survive, so the blue jays with thick beaks changed to have thin beaks.

• There were more trees that had pinecones with seeds. Blue jays with thin beaks are more likely to survive, so both kinds of blue jays passed on the gene for thin beaks to their offspring.

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

Tree squirrels can have different fur colors. They can be black, brown, or gray. 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 population of squirrels shown above lives in an environment that has always had black trees. Could there ever have been squirrels with gray fur in this population?

• No squirrels could have been born with the gray trait because none of the adult squirrels had that trait to pass down.

• No squirrels could have been born with the gray trait in the past, but some with that trait could be born in the future if the environment changes to have gray trees.

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

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