Gillman & Wright (2006): The influence of productivity on the species richness of plants: a critical assessment

Gillman, L. N., and S. D. Wright. 2006. The influence of productivity on the species richness of plants: a critical assessment. Ecology 87:1234-1243.

The relationship between productivity and species richness has been controversial for the last couple of decades and there has been even less consensus about causal processes. Recent meta-analyses have found unimodal relationships predominate, but the authors of these analyses have not scrutinised the member studies for appropriate experimental design. This study presents the results of a survey of 159 productivity-plant species richness relationships following careful assessment of each member study with respect to experimental design and the appropriateness of the surrogates used for productivity. When only robust studies were included, it was found that, in contrast to previous meta-analyses, all relationships at a continental to global extent were positive, regardless of grain, and that almost all were also positive at regional extents. Unimodal relationships were not dominant even in studies of fine grain or small spatial extent. These results have important implications for theory that attempts to explain species richness patterns.