Genetic Variation-In the population of mice there is some mice that are tan and some are brown.
Changes in Gene Pool- All the mice eventually became tan because it was reproduced more often because it survived longer than the dark mice.
Struggle for Existence- Since more birds were reproduced than can survive they will die because there is a limited amount of food for the birds.
Different Survival and Reproduction-In this image the dark bunny struggles to survive because it stands out to it predators but since one fox is gray it struggles to get bunnies to eat. One mice is brown that blends in and the gray mice struggles because it stands out to the hawk.