Biodiversity–ecosystem functioning (BEF) theory has largely focused on species richness, although studies have demonstrated that evenness may have stronger effects. While theory and numerous small-scale studies support positive BEF relationships, regional studies have documented negative effects of evenness on ecosystem functioning. We analysed a lake dataset spanning the continental US to evaluate whether strong evenness effects are common at broad spatial scales and if BEF relationships are similar across diverse regions and trophic levels. At the continental scale, phytoplankton evenness explained more variance in phytoplankton and zooplankton resource use efficiency (RUE; ratio of biomass to resources) than richness. For individual regions, slopes of phytoplankton evenness–RUE relationships were consistently negative and positive for phytoplankton and zooplankton RUE, respectively, and most slopes did not significantly differ among regions. Findings suggest that negative evenness effects may be more common than previously documented and are not exceptions restricted to highly disturbed systems.
Bibliographical noteFunding Information:
This project was completed with funding from the US National Science Foundation Macrosystems Biology program to PA Soranno (NSF #1638679), which supported KBSK and IMM. CTF thanks JA Downing for salary support used to complete this work. We thank Claire Boudreau (Michigan State University) for help with preliminary analyses, as well as the entire Continental Limnology research team for helpful advice during project development. We thank three anonymous referees for insightful critiques of an earlier manuscript draft. NLA 2012 data were a result of the collective efforts of dedicated field crews, laboratory staff, data management and quality control staff, analysts, and many others from EPA, states, tribes, federal agencies, universities and other organisations.
© 2019 John Wiley & Sons Ltd/CNRS
- National Lakes Assessment
- ecosystem functioning