Similarity and dissimilarity

Competition corresponds to how closely to each other the competitors occupy the ecological niche over and in which the competition is takng place. 

Similarity and dissimilarity are a qualitative measure. When we posit extreme similarity what we are positing is the elimination of qualitative values and the reduction of relevant decision-making to quantitative values. 

Quantitative differences allow only substitution and no complementarity. Complementarity presumes qualitative differences. The more dissimilar the competitors, the more likely the behavior will be determined by the particular fit with the ecological niche in question, irrespective of the relative fitness of the ‘competitor.’ The more the alternatives are dissimilar, the more they can function in a complementary fashion. 

The neo-classical model posits agents who relate to the ecological frame as actors who are identical to each other.