捆绑SM社区

An international team of scientists, with labs at 捆绑SM社区 and Oxford Universities, has published three crucial experiments in Nature which between them consolidate several decades of ecological research on biodiversity. Biologists Graham Bell (捆绑SM社区) and Paul Rainey (Oxford) have shown how understanding the impact of three fundamental patterns - heterogeneity, productivity, and disturbance- is key to what Dr. Bell calls "one of the most important scientific issues of modern times." Rees Kassen (from the Bell lab) and Angus Buckling (from the Rainey lab) are also on the international scientific team. The latest article in the series is to be published in the Dec. 21 issue of Nature.

Dr. Bell, who is director of 捆绑SM社区聮s Redpath Museum, explains, "we have two main research programs. The first is conducted in the laboratory, where we use cultures of microbes [a bacterium called Pseudomonas fluroescens, notable for the range of ecological types that arise by mutation in laboratory culture] in simple, highly-defined systems to investigate the ecological mechanisms responsible for the gain or loss of diversity. The second takes us into the field, where we study patterns of diversity in natural communities at the 捆绑SM社区 research stations around Quebec. In this way, we hope to build a solid theory of biodiversity that will enable us to protect it more effectively."

The first experiment: heterogeneous environments
The original experiment (Nature vol 394, pp 69-72, 1998) confirmed the crucial role of environmental heterogeneity in the maintenance of diversity. Bell explains, "聮Heterogeneity聮 here means the number of different habitats that are available in a given environment - thus, a landscape with pools, marshes, woodland and open clearings would be more heterogeneous than a uniform forest or prairie." The scientists have been able to show that a homogeneous environment with few competitors for the habitat leads to a loss of diversity.

The second experiment: diversity and productivity
The second experiment was concerned with productivity (Nature vol. 406, pp 508-512, August 2000). Says Bell, "It is easy to appreciate that diversity will often be greater in more productive environments. After all, at low productivity there are few individuals and there must therefore be few species. A familiar example might be a pristine northern lake that becomes steadily more polluted. It would originally support a sparse community comprising only a few species of fish, crustaceans and plants. As it becomes enriched by nutrients such as phosphate or nitrate, its productivity will increase, and with it the diversity of the community. If too much nutrient is added, however, the result is a polluted, highly productive lake dominated by a few species.

By varying the concentration of nutrients in the culture medium, Bell and Rainey聮s team were able to show that diversity does indeed peak at intermediate levels of productivity - but only in heterogeneous environments. "The key concept is that a type which is specialized to live in a particular habitat will be able to persist in the community only if the habitat is sufficiently extensive," states Professor Bell.

The third experiment: diversity and disturbance
A similar theory was constructed to explain the effects of disturbance, the subject of the third experiment (Nature, December ?, 2000). According to Bell, "Mowing a lawn provides a familiar example of disturbance. If a lawn is mown only at long intervals, it will become dominated by a few species of grass able to crowd out and overshadow their neighbours. At the other extreme, of course, very frequent mowing will remove all species except those capable of tolerating the frequent loss of tissue, or able to grow without competitors at high light levels. Thus, maximal diversity should be associated with intermediate frequencies of mowing - the high diversity of plants in semi-natural grasslands grazed by sheep would be a good example of this."

"Our experiment confirmed that diversity is maximal at intermediate rates of disturbance - but, again, only in heterogeneous environments. The principle is directly analogous to that governing the effect of productivity: if one habitat is much more productive than another, the type that is best adapted to that habitat will swamp the community and cause the elimination of the type specialized to the less productive habitat. The only difference is that in this case the 聮habitats聮 are represented by the state of the culture medium at different times.

Conclusion

Bell describes the laboratory systems as unimpressive to look at -"small glass tubes filled with a cloudy liquid." In creating such simple microcosms, validating them in the laboratory and then comparing them with nature observed in the field, the Bell-Rainey team is, however, building a solid foundation for understanding the much larger and richer canvas of biodiversity in natural communities.