Abiologist studying a desert ecosystem observes that the population of a lizard species increases following particularly hot, dry period that causes a snake population to decline. what could the biologist hypthesize about the roles of these two species?

a) the lizard preys on the snake

b) the lizard is a parasite of the snake

c) the snake and lizard use the same limiting resource

d) the snake is a keystone species in the ecosystem.