How are diversity and productivity related?

The number of species within a region usually varies unimodally with the rate of ecosystem energy flow. This hump-shaped pattern shows up in many biogeographical provinces. Plant and animal taxa, including vertebrates and invertebrates, follow it. We find it in marine and in terrestrial biomes. Most ecologists agree that the increase in diversity that occurs over low productivities comes about because the total abundance of all species together increases over that range of productivities. The authors describe and evaluate nine hypotheses to explain the decrease phase of the pattern, ie why diversity declines as productivity grows past a certain point. They discuss the relationship of the regional pattern to global patterns such as the latitudinal gradient. The effect of productivity on diversity is best studied at the regional level. -from Authors