Tuesday, April 14, 2009

Corn! and NEPA

While browsing other science blogs I came across a great one about insects and ... well, insects. And one of Bug_girl's reviews was of a recent article predicting impacts of corn for biofuel on ecosystem services - my only thought was "Wow - did congress have to do an EIS before they passed that law?" - they should have! When does a law become a "federal action" that requires compliance with NEPA?

One of the conclusions of that article is that decreasing diversity decreases ecosystem function. I came across another article on the diversity-function debate in last week's Nature. The authors set up > 1000 microbial communities, each with the same suite of 18 taxa of denitrifying bacteria. The key was that the communities varied in "evenness" - the extent to which the community is dominated by one or a few species. They then challenged each micro-community with a dose of nitrite, and then measured how much of the nitrite was removed 20 hours later. Communities with greater evenness performed better - and more importantly, maintained that improved performance to a greater extent when the microcosm was simulataneously challenged with increased salinity.

So, is this resilience sensu Holling and Gunderson? I think not, for a couple of reasons. First, although the functional rate decreases with decreasing evenness, all the microcosms still function to some extent; there is no "flip" to an alternative non-functioning state. The appearance of a non-linear threshold would be the ultimate cool result, but they found only smooth changes. Second, they did not examine the structure of the microbial community AFTER the perturbation. Resilience posits that resilient systems will maintain their structure during and after a perturbation - structure in this case would refer to the relative abundance of the 18 microbial taxa. It is possible that even the control communities that were not challenged would have shifted in relative abundance just because of normal competition between the microbes.

Regardless, it is a really cool experiment!

Full citations:

Douglas A. Landis, Mary M. Gardiner, Wopke van der Werf and Scott M. Swinton. 2008. Increasing corn for biofuel production reduces biocontrol services in agricultural landscapes. PNAS 105(51) 20552-20557

Lieven Wittebolle, Massimo Marzorati, Lieven Clement, Annalisa Balloi, Daniele Daffonchio, Kim Heylen, Paul De Vos, Willy Verstraete & Nico Boon. 2009. Initial community evenness favours functionality under selective stress. Nature 458:623-627. doi:10.1038/nature07840

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