Experimental evidence for a time-integrated effect of productivity on diversity.

The time-area-productivity hypothesis is a proposed explanation for global biodiversity gradients. It predicts that a bioregion's modern diversity is the product of its area and productivity, integrated over evolutionary time. I performed the first experimental test of the time-area-productivity hypothesis using a model system for adaptive radiation - the bacterium Pseudomonas fluorescens SBW25. I initiated hundreds of independent radiations under culture conditions spanning a variety of productivities, spatial extents and temporal extents. Time-integrated productivity was the single best predictor of extant phenotypic diversity and richness. In contrast, 'snapshots' of modern environmental variables at the time of sampling were less useful predictors of diversity patterns. These results were best explained by marked variation in population growth parameters under different productivity treatments and the long periods over which standing diversity could persist in unproductive habitats. These findings provide the first experimental support for time-integrated productivity as a putative driver of regional biodiversity patterns.