In the not so distant past, before there was a “collective fixation on global warming as the mother of all environmental problems,” as Jon Foley lamented in 2009, biodiversity was the poster child for environmental crises. It was an issue that captivated journalists, scientists and greens alike–much as climate change does today. Indeed, concern over the loss of biodiversity and how that impacted the overall health of the planet was once a frequent topic of discussion in leading scientific journals. For example, here is the summary overview of a review article for Nature in 2000 by a group of biologists:
Human alteration of the global environment has triggered the sixth major extinction event in the history of life and caused widespread changes in the global distribution of organisms. These changes in biodiversity alter ecosystem processes and change the resilience of ecosystems to environmental change. This has profound consequences for services that humans derive from ecosystems. The large ecological and societal consequences of changing biodiversity should be minimized to preserve options for future solutions to global environmental problems.
At this time, there was a lively debate within the field of ecology as to what extent species richness (i.e., diversity) contributed to productive (and resilient) ecosystem function. (This debate pivoted off a 1972 paper by Robert May, published in Nature, that suggested ecosystems with higher diversity actually tended to be less stable; the mathematical formula that May used–which upended a long-held assumption in ecology– was revisited last year.) In 2010, Michel Loreau published an excellent essay on the state of this debate, tracing its history, underlying tensions, and connection to global environmental policy. He noted:
The relationship between biodiversity and ecosystem functioning has emerged as a central issue in ecological and environmental sciences during the past 15 years. The idea that greater plant diversity allows greater plant biomass production dates back to Darwin (McNaughton 1993; Hector & Hooper 2002), but it was only in the 1990s that the interest in the effects of biodiversity on ecosystem functioning penetrated experimental and theoretical ecology. This interest spread very rapidly, leading to an entire new research field at the interface between community ecology and ecosystem ecology (Schulze & Mooney 1993; Tilman 1999; Chapin et al. 2000; Loreau 2000; Kinzig et al. 2001; Loreau et al. 2001; Loreau et al. 2002b; Hooper et al. 2005; Balvaneraet al. 2006; Cardinale et al. 2006; Cardinale et al. 2007).
Loreau goes on to discuss the experimental field and laboratory research that “has now clearly established that biodiversity does indeed affect ecosystem processes.” But the final verdict was not exactly ironclad, as he sort of admits here:
Although rigorous empirical support for the new diversity”“stability theory is scantier than for the effects of diversity on biomass and production, a few experiments that have manipulated species diversity have provided clear evidence for its stabilizing effect on ecosystem properties in both plant communities (Tilman et al. 2006) and aquatic food webs (Steiner et al. 2005).
In any case, the biodiversity = robust ecosystems train had already left the station, as Loreau explains:
Because its initial impetus was provided by the societal relevance of the issues it was addressing, biodiversity and ecosystem functioning research also impacted on social sciences and environmental management. The results of this research supported the work of the Millennium Ecosystem Assessment (2005) on the links between biodiversity, ecosystem services and sustainable development. The value of biodiversity as insurance against the uncertain provision of ecosystem services is being incorporated formally in ecological economics (Armsworth & Roughgarden 2003; BaumgÃ¤rtner 2007).
Meanwhile, in a 2009 historical overview of ecological paradigms, Matt Chew observed that “different concepts of stability, diversity, and complexity” have, over time, shaped the studies that have sought to identify the most essential properties of ecosystem function.
There is mounting evidence that biodiversity increases the stability of ecosystem functions through time.
Diverse communities are more productive because they contain key species that have a large influence on productivity, and differences in functional traits among organisms increase total resource capture.
Coincidentally, and just before I saw the latest Nature paper, I had inquired on twitter about the status of the biodiversity/ecosystem function debate. “Which side came out on top,” I asked? One scientist responded, “Neither.. it was a theoretical vs. non-theoretical ecologists debate.” Another said, “It’s a subjective question, b/c it asks what we value about ecosystems.”
Precisely. The debates we’re now having over planetary boundaries and tradeoffs between development and conservation are based, in large part, on subjective notions, so asking what we value (and why) seems like something that should be a big part of the discussion.