Question

The population size of a predator species is directly controlled by _.

Answer 1

The population size of a predator species is directly controlled by the population size of it's prey. If the predator has no prey the population size will go down because they have no food.

Answer 2

Population size of its prey.

Step-by-step explanation:

Predators are the organisms that derive their nutrition by killing other organisms (prey). Increase in population size of prey increases the food availability for predators and leads to an increase in their population size. On the other hand, reduced prey population reduces the population size of predators due to low food availability.