Groundbreaking Research: Habitat Productivity Does Not Predict Diversity of Plant Species
Sept. 22, 2011 (Embargo lifts at 2 p.m., Sept. 22, Eastern Standard Time)
This is the research site at the Sagehen Creek Field Station managed by ecologists Louie Yang of UC Davis and Dan Gruner of the University of Maryland.
DAVIS--An international team of 58 ecologists, including Louie Yang of the Department of Entomology, University of California, Davis, announced today that habitat productivity does not predict the diversity of plant species, as previously assumed for several decades.
The groundbreaking research, to be published Sept. 23 in the journal Science, shows “no clear relationship between productivity and the number of plant species in small study plots,” said Utah State University plant ecologist Peter Adler, lead author of the paper.
“We challenged a prevailing model developed in the early 1970s by British ecologist J. Philip Grime,” Adler said in a National Science Foundation/Utah State University news release. “He proposed that the number of species rises then declines with increasing productivity.”
Not generally so, they said. The ecologists sampled 48 diverse grassland sites on five continents in an innovative, unprecedented project partially supported by the National Science Foundation (NSF).
Louie Yang Dan Gruner
The paper in Science is one of the first to emerge from the research, launched five years ago when the ecologists formed the Nutrient Network or “NutNet,” a cooperative research initiative dedicated to investigating biodiversity and ecosystem processes in global grasslands.
University of Minnesota researchers Elizabeth Borer and Eric Seabloom received funding from NSF to coordinate the network research. NSF also funds an annual meeting workshop in Minneapolis, where the researchers gather to analyze data.
“It’s a really innovative approach to ecology,” said Yang, an assistant professor at UC Davis. “We conducted a coordinated study in diverse grasslands at the 48 sites and we pooled our data together to address some persistent issues in the field. In this paper, we show that plant diversity is not predicted by productivity in any general or simple way; instead, it looks like patterns of plant diversity result from more complex processes which are variable at local, regional and global scales.”
Yang’s research contributions to the network came from a field site at the Sagehen Creek Field Station, located near Truckee in Nevada County. He and Dan Gruner, a faculty member at the University of Maryland, have managed a montane or highland meadows site (elevation 6500 feet) since 2007 for their research. Some of Yang’s graduate students and undergraduates also participate.
“I think this paper shows the value of this kind of large-scale research,” Yang said. “We expect to continue working on this project for several years. It’s been a great experience working with this group.”
The idea originated in Adler’s classroom. His graduate students challenged what had been “standard textbook knowledge” for nearly four decades, Adler said. “Why do ecologists spend so much time on this model when the evidence to support it is so weak?” they asked him.
“That,” Adler said in the news release, “was the kick in the pants I needed to pursue this question.”
Said Borer: “Our work not only sheds light on this classic question, it also demonstrates the power of our network approach. “NutNet data are poised to inform many pressing ecological questions. Similar global, grassroots collaborations would help settle other longstanding debates.”
Other research may target factors regulating biodiversity, such as evolutionary history, disturbance and resource supply, the researchers said.
How Do You Measure Productivity?
The researchers used a standard measure, ecologist Louie Yang explained. "We estimated 'aboveground net primary production (ANPP)' as peak growing season live biomass; in other words, we carefully clipped small sections of our plots and dried and massed the resulting plant biomass. This method is considered an an effective measure of ANPP in herbaceous vegetation, especially when consumption by herbivores is low. This is considered a very direct measure of productivity (as opposed to measuring plant height, or even using rainfall and temperature, or other variables), and all the sites used the same measure (as opposed to previous meta-analyses which try to combine the results of various different studies), which is very good."
"Our main hope," Yang said, "is that people can get over the idea that there is a hump-shaped relationship when the evidence for it is actually pretty weak. The conclusions of this study don't mean that there are no patterns, or that we shouldn't try to explain patterns of diversity, but they suggest that the real world is too complex to assume that there is a consistent, general productivity-richness relationship. Instead, we hope that future research will be directed toward trying to develop some more mechanistic explanations for variation in diversity, instead of trying to support or refute a pattern that doesn't seem to be very general."
Science Journal Abstract
Perspective on Biodiversity and Productivity (Michael Willig, Center for Environmental Sciences and Engineering, and Department of Ecology and Evolutionary Biology, University of Connecticut)
Louie Yang Research Lab
News story about Elizabeth Borer and Eric Seabloom
--Kathy Keatley Garvey
UC Davis Department of Entomology