A) The Competitive Exclusion Principle states that if two competing species coexist in a stable environment, then they do so as a result of differentiation of their realized niches.
B) The Competitive Exclusion Principle states that all species within a community coexist in an unstable environment, and that they are structured by competition that leads to realized niches.
C) The Competitive Exclusion Principle states that if a guild of competing species coexist in an stable environment, they do so as a result of differentiation of their fundamental niche.
D) None of the above

A) Removal study
B) Reciprocal transplant study
C) Laboratory observation study or a "glass bottle study"
D) Ecological survey study

A) Because you cannot directly observe evolution that has already occurred.
B) Because you cannot directly test interspecific competition.
C) Because you cannot control experiments for competition.
D) All of the above.