Evidence that reciprocal interactions between productivity and richness operate in natural grasslands

Background/Question/Methods

The mechanisms that connect community productivity with species richness remain a major interest in ecology. After decades of emphasis on ways that productivity might act to limit richness, the past two decades have produced a large body of work demonstrating the ability of richness to promote productivity. Thus, experimental studies have shown evidence that suggest reciprocal effects, but most modeling and analyses continue to emphasize one set of mechanisms or the other. In this investigation, we utilize data from the Nutrient Network grassland study to evaluate structural equation models in which reciprocal effects are hypothesized to connect community productivity with plant species richness.

Results/Conclusions

The simple relationship between productivity and richness in the Nutrient Network dataset has been debated, though our analyses again show that any bivariate relationship, either for the mean or the upper boundary, to be weak at best. In contrast, multivariate analyses using structural equations find support for strong and clear reciprocal effects at both the across-site and within-site levels of organization. These results suggest that models of the productivity-richness relationship that do not involve manipulations of either of the components need to consider analysis methods that allow for the isolation of reciprocal interactions.