Biodiversity and ecosystem function

The ‘biodiversity and ecosystem function (BDEF) debate’ that has raged in ecology for several decades specifically addresses the question: Given the current unprecedented rate of extinction on Earth, to what extent does the loss of species affect how stable ecosystems are and what functions and services they provide? For instance, what is the effect of decline in plant species richness from a grassland ecosystem on properties such as nutrient cycling, decomposition rates, water capture and carbon sequestration? Numerous studies have shown that biodiversity influences ecosystem processes (and vice versa). In recent reviews, such as Naeem et al. (2012), which we discussed this week, it appears ecologists are trying to synthesise this large volume of work (showing that biodiversity does indeed have an effect on ecosystem function) and move the field on to the next stage of maturity – what have we learned over the last 20 years, how can we use this information and what should we be researching now? We felt that the Naeem et al. paper has some useful points in it, such as a box explaining seven ‘dimensions’ of biodiversity that provide six different ways of examining the effects of diversity on ecosystem function besides (the probably overused measure) species richness. The authors offer some well-stated challenges for future researchers including demonstrating effects in larger-scale, natural systems, accounting for these multiple forms of diversity as well as multiple ecosystem functions in their projects, using small amounts of information on species’ traits to predict trait states across greater numbers of species within ecosystems, and to start making the most of advanced technology such as pyrosequencing and newer statistical methods. The authors also remark on the importance of considering cultural values of biodiversity as another ecosystem service because although it is a non-utilitarian aspect of conservation, it is also important in terms of maintaining biodiversity.

Our discussion of this paper started us thinking about how useful the BDEF relationship is to ecology, conservation, and restoration ecology. We concluded first that the demonstration that biodiversity loss can impact ecosystem function justified what many of us do (try to understand spatio-temporal patterns in biodiversity in its various forms). Second, we discussed the notion that given that much of conservation applies to rare species conservation and the removal of rare species (e.g., the flightless New Zealand takahē (Porphyrio hochstetteri), decline in tussock grasslands of the South Island), doesn’t appear to affect the functioning of their native ecosystem, is it something that conservationists need to know or worry about? We concluded that the BDEF research was most relevant to restoration ecology where practitioners should want to know about the ecosystem-level effects of their efforts. We talked about integrating different measures of diversity and multiple ecosystem functions into our monitoring of restoration success.

We then moved on to a discussion of differences between ecosystem functions and ecosystem services and how these things might be measured in a restoration context. We talked about the effect of scale on evaluating restoration success, what restoration success was in general and what questions we needed answers to in order to make ‘recommendations’ to land managers who wanted advice on restoring a given area of land. We also debated the constraints on our ability to feed everyone on Earth now and into the future.

Questions:

·       We started to talk about how we would measure things in a real system, such as a restoration experiment, but it would be worthwhile to think more about this. How can ecosystem functions be measured? How can ecosystem services be measured?

·       Several other recent review papers were suggested to be relevant to our debate including Cardinale et al. (2012), Ehrlich et al (2012), and Hooper et al. (2012). How are these differ from the Naeem et al. paper?

References cited

Cardinale, et al. 2012. Biodiversity loss and its impact on humanity. Nature 486: 59-67.

Ehrlich et al. 2012. Securing natural capital and expanding equity to rescale civilization. Nature 486: 68-73.

Hooper et al. 2012. A global synthesis reveals biodiversity loss as a major driver of ecosystem change. Nature 486: 105-109.

Naeem et al. 2012. The functions of biological diversity in an age of extinction. Science 336: 1401-1406.