Maintaining diversity: an experiment

When we talk about biodiversity — including agrobiodiversity — we really mean three things at the same time: diversity among ecosystems, among species, and within species. Scientists usually study these scales separately, but can diversity at one level somehow affect diversity at another? That’s the question tackled by an experiment described last week in Science ((Mutual Feedbacks Maintain Both Genetic and Species Diversity in a Plant Community. Richard A. Lankau and Sharon Y. Strauss (14 September 2007) Science 317 (5844), 1561. DOI: 10.1126/science.1147455.)) and discussed by one of the authors in Scitizen (fortunately, because the full paper is behind a paywall). ((Thanks to Andy for the headsup.))

Richard Lankau and Sharon Strauss grew monocultures of two genetic variants of an annual plant called black mustard, and also a mixture of three species. One of the black mustard varieties produced high levels of a compound called sinigrin, which is toxic to other plants and to beneficial soil micro-organisms, the other produced low levels. The researchers then introduced a “foreign” individual into each of these experimental communities: a low sinigrin plant into the high sinigrin monoculture and the mixture, a high sinigrin plant into the low sinigrin monoculture and the mixture, and a plant of a different species into the monocultures and the mixture. Which would survive?

It turned out that the high sinigrin invader only survived in the mixture, while the low sinigrin variety only survived in the high sinigrin monoculture. No one variety was always best, which meant that each could survive somewhere. Remove any one element, whether variety or species, and the system became dominated by a single thing. Species diversity was necessary to maintain genetic diversity, and vice versa, at least in this experimental microcosm.

I don’t think the authors had agricultural biodiversity particularly in mind, but their conclusion is worth quoting:

Preventing the erosion of genetic diversity within species may require maintaining a diversity of species in a community. At the same time, we may need to focus on protecting high levels of genetic diversity within species in order to maintain diverse communities of species.