Answer: Microevolution occurs on small time scales within species. Migration takes places when a population moves from one area to another. These processes can affect an ecosystem's form and functionality. Migration can negatively impact an ecosystem if the migration is permanent and leads to the loss of native species. Temporary migration, such as in the case of birds flying south in the winter, can maintain the biodiversity of an ecosystem. As microevolution occurs, the genetic composition of a species alters. The changes make species more adapted to their environment, so that way they'll survive long enough to reproduce.