Community Ecology

Free Response

Describe the competitive exclusion principle and its effects on competing species.


The competitive exclusion principle states that no two species competing for the same resources at the same time and place can coexist over time. Thus, one of the competing species will eventually dominate. On the other hand, if the species evolve such that they use resources from different parts of the habitat or at different times of day, the two species can exist together indefinitely.

Jaguars are a keystone species in the Amazon. Describe how they can be so essential to the ecosystem despite being significantly less abundant than many other species.


Jaguars are an apex predator in the Amazon, eating a variety of prey animals and not serving as prey to any other predators. Through predation, they control the population sizes of the smaller herbivores and omnivores. If jaguars were to disappear from the ecosystem, the smaller herbivore populations would dramatically increase, and could overconsume the plant populations.