Nieuws - 14 februari 2008

Chaos is only natural

Animals and plants always make sure that the balance between them is restored after a disturbance in the ecosystem. At least, that was the general wisdom, but now there is evidence that ecological equilibrium is not necessarily a matter of course. Researchers from the Aquatic Ecology group and the University of Amsterdam publish proof in Nature this week that populations continue to fluctuate even under stable conditions.

Nearly ten years ago, the now-retired German biologist Reinhard Heerkloss took plankton out of the Baltic Sea and put it in an aquarium. Keeping light and temperature constant, he counted the numbers of each type of plankton in the water twice a wekk. He was surprised to discover that the ecosystem never stabilised. The numbers continued to vary, despite the constant environmental factors. Impossible, according to the notion of ecological equilibrium.

Elisa Benincà, who did her PhD research at the Aquatic Ecology group and the Institute for Biodiversity and Ecosystem Dynamics at the University of Amsterdam, examined this unusual state of affairs and concluded that it really is one of chaos. Benincà discovered that, through predation and competition for food, the species themselves ensured that no one particular kind of plankton gained a permanent upper hand.

‘It’s a real breakthrough,’ says Professor Marten Scheffer, chair of Aquatic Ecology. Scheffer and Professor Jef Huisman of the University of Amsterdam had already discovered that unpredictable chaos is possible in ecosystems. They did this by constructing mathematical models, but without experimental evidence, their hypothesis of random fluctuations made little headway.

Benincà’s research shows that nature is far less predictable than previously thought. Scientists always assumed that they could estimate changes in populations if they knew what factors were exerting an influence on the system. Now that this does not seem to be the case, the projections made for plant and animal populations are probably inaccurate. ‘Detailed predictions concerning numbers of different species in ecosystems are impossible in the long run. At best we can indicate the boundaries within which species will fluctuate,’ says Benincà.