Why Can Varied Species Live Together in Particular Ecosystems?

Question

Consider the following question:

The Piney Woods of Eastern Texas is home to a wide variety of organisms ranging from the grass Longleaf Oats to coyotes. Which of the following best explains why these varied specifies can live together in this particular ecosystem? A.) Each species lives in a slightly different habitat B.) Each spices occupies a different niche C.) Each species functions at a different trophic level D.) A and B E.) A, B, and C

I chose answer choice E with the reasoning that: Oats and Coyotes do not share the same habitat; they occupy a different niche -- Coyotes eat organisms, oats use photosynthesis; coyotes are at a completely different trophic level when compared to oats -- oats being primary producers. The answer choice E however is incorrect and I'd like to know why and what the correct answer should be. Is there a flaw in my logic?

Answer 1

The answer should be B "Each spices occupies a different niche" because this is the only answer that reflects a model of species coexistence. Niche theory proposes a mechanism that allows multiple species to occupy the same space and time any yet avoid competition for limited resources. Briefly, the model says that a species niche is the total suite of resources that it requires to survice and reproduce and that coexisting species will limit their niche overlap to avoid competition (and its requisite reduction in fitness). Species can limit niche overlap by preferentially using a subset of resources that are not shared with potentially competing species (this is called the realized niche) or by evolving a new niche that does not overlap with the competitor (this is called character displacement).

Note that your reasoning is incomplete because the question does not specify that the organisms listed are the complete set of organisms in the community. For example if the community contained another species of grass, then choice "C" would be false. Most importantly though, habitat or trophic variation are not mechanisms of coexistence, so they should not be used as general hypotheses explaining coexistence.