Which of the following distinguishes why deer populations have increased? The amount of predator animals has decreased.
Fewer hunters are culling the population of deer.
The amount of other grazing animals has decreased.
Fewer cattle are allowed to graze on open grasslands.

The most correct option is the first option

Explanation:

A deer is an herbivorous animal that is usually preyed upon by many wild carnivorous animals like lions, tigers and leopards. Hence, when the population of these wild predatory carnivorous animals reduce, the population of the deer would increase because fewer of them would them would be killed by predators despite them (the deers) reproducing.

Note that a predator is an animal that feeds upon another animal (referred to as prey) of lower "strength".