Answer: With no natural predators to regulate the population, the deer population continued to grow.
Step-by-step explanation:
In 1906 a preserve was created for the deer. In creating this they drove both the cows as well as the deer's natural predators away. This meant that the deer population was no longer regulated by the predators hunting and eating them which led to an explosion in deer population.
The land which had been overgrazed at some point could not support this population and so the deer started starving because there simple wasn't enough food to support their population.