the graph shows the size of two populations of the same species over time.

Option D

Explanation:

As it is clear in the graph that population of species is increasing in both the areas but the rate at which population is growing in area A is much faster as compared to the rate of population growth in area B.  

It is obvious that the factors that favor population growth such as availability of food etc. are in abundance in area A as compared to the area B.  

However, there are some limiting factors in both area A and B as there population is not growing exponentially.

Hence, option D is correct

answer; i believe the answer is hydraulic action;

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.