The following graph depicts changes in two populations (A and B) of herbivores in a grassy field. A possible reason for these changes is that:

Explanation

Both the populations are herbivorous, thus they cannot affect each other. If the food sources for these populations A and B have decreased, then both the populations A and B would have declined. If population A has produced more offspring, then the graph of A should have increased. Based on the graph, population B is more successful in competing with population A, that is why the number of organisms in population B increased while that in population A decreased, as they get access to limited resources.