The individual “squares” on a turtle’s shell are called

d. Snakes will die out if they do not find an alternative food source.

Explanation:

In the ecosystem, most of the predator species have more than one prey. This ensures availability of food if the population size of one of their prey comes down or becomes extinct.  

Snakes feed in mice. In mice population becomes extinct, snake population size would reduce due to lack of prey population. In the long term, the snakes would have to find some other available prey population to feed on so as to ensure the continuity of their species.