Which of the following is not a possible reason for migration?
a. climate changes
b. diminished food supply
c. reproduction patterns
d. increased biodiversity
d?

The answer is d. increased biodiversity.

Migration is an adaptation that helps animals to survive. There are many reasons for migration. For example, if climate changes or food supply reduces, some animals will move to the area with adequate climate or enough food, respectively. Some animals, on the other hand, move to reproduce, such as the Atlantic Salmon.
But, an increased biodiversity is not the reason for migration. The increased biodiversity will positively affect the food chain. It will also increase a diversity of abiotic factors. These will help animals to survive in their living areas, not urging them to migrate.