The correct answer is C. Competitive exclusion
Step-by-step explanation:
In ecology, competitive exclusion principle or competitive exclusion occurs when organism of different species compete for a specific resource (food, space, water, etc) and one of the species has an advantage over other, which leads to the second one to experience a decrease in population and disappear over time, except if adaptation occurs. This principle is based on the idea that competitors cannot coexist especially if one is in the advantage of others. This principle occurs in the example presented because as elephants have an advantage over deers to feed on certain plants, deers are excluded and began to disappear, which would lead to extinction.