Answer:
"The vegetation it eats increases and then decreases repeatedly with changing seasons" would be a reason for species to undergo cyclic population changes.
Step-by-step explanation:
A keystone specie corresponds to an organism species which has disproportionately high environmental effects relative to its abundance or population.Many living organism population typically undergo cyclical shifts in size of population.
Cyclic oscillation leads to regular decline and fall across time in the population size of the living organism concerned.The cyclical population shifts are sometimes triggered by relationships between different organism populations. Disruptions in food availability, for an instance, may bring about cyclical shifts in population.