Three evolutionary hypotheses for the hump-shaped productivity-diversity curve

We consider the problem of the hump-shaped relationship between productivit y and diversity from an evolutionary perspective, based on the assumption t hat productivity is positively correlated with population size. Although pr oductivity has little evolutionary meaning, population size is evolutionari ly meaningful, leading to three hypotheses: (1) Diversity is higher at inte rmediate productivities because the maximum difference between speciation r ates and extinction rates occurs in such habitats. (2) Diversity is higher at intermediate productivities because, in those areas, most species evolve at the maximal rate. (3) Diversity is higher at intermediate productivitie s because, in those environments, there are more types of successful adapta tions. We recommend tests of the hypotheses based on differing predictions of the origin of evolutionary novelties and the response to mass extinction events.