Controlled Habitat and Natural Selection

There are 12 white mice, 12 brown mice, and 12 black mice in a population in the forest. Some of the mice have long tails, some have medium sized tails, and others have really short tails. There are 36 mice in total. Four each of the white, brown, and black mice have long tails; four each of the white, brown, and black tails have medium sized tails, and four each of the white, brown, and black mice have really short tails. They will be put in a scenario and the possible outcomes will be noted. This will show the frequency of each phenotype will change within the populations. Also, this is an example of natural selection within a population.

33% of the population is white. 33% of the population is brown. 33% of the population is black. Also; 33% of the population has a long tail. 33% of the population has a medium tail. 33% of the population has a short tail.

The mice population is put into a large forest environment for 9 weeks. The only predators in this island are snakes. The environment has some very light habitats that are easy for the white population to blend in with. What can be predicted from this?

The snakes get hungry and begin their search for food. They are able to find the black mice the easiest, and these 12 black mice and one brown mouse are all gone within the first four weeks of nine weeks. During the next week, the brown and white mice mate together making the new mice have a phenotype of very light brown colored fur, allowing them to camouflage as well. Within the next weeks, the dark brown mice are targeted, removing them from the island population. At the end of the 9 weeks, the snakes are removed and the mice population is observed on the phenotype of fur color. Results show that the light brown and white fur mix fur coat was the most fit for the environment on the island. Even though the white mice were much hidden within the environment, the snakes could find them easier than the light brown ones. The black population died out because they did not reproduce offspring with more “fit” qualities such as white OR brown fur. The white population ended with 13 white mice. The brown mice ended with 0 mice with this phenotype, and the brown and white fur population was 7 at the end of the 9 week period. The white population grew by one member, making the white mice have 65 percent of the new overall island mice population. The brown and white grew to be 45% of the overall population, and grew from 0 to 7, having a 100% increase. The black mice were 0% of the overall population, and the brown population was 0% of the overall population. This shows how natural selection can affect the frequency of each phenotype within a population.