The correct answer is prey predator relationship.
The given graph possibly shows the prey predator relationship, in which the prey is shown in red and the predator is shown in blue. It is observed that the predator population generally remain less than the prey, in order to get food easily.
The prey predator relationship shows that if the population of the prey start increasing, then the population of the predator would also increase, as the predators have abundant of food. But when the population of the prey start decreasing, the predators start to decline due to the starvation.