We have growing evidence that ecosystems are lumpy. Along an axis such as body size, for example, we find clusters of similar-sized species separated by intervals of body size in which no species are found. Multiple explanations exist for lumpy patterns, and causes are still debated. Scheffer and van Nes present a simple mathematical explanation for evolution of lumpy patterns in ecosystems. Their article appears in the Early Edition of PNAS on 3 April 2006. The abstract states

Here we show that self-organized clusters of look-a-likes may emerge spontaneously from evolution of competitors. The explanation is that there are two alternative ways to survive together: being sufficiently different or being sufficiently similar. Using a model based on classical competition theory, we demonstrate a tendency for evolutionary emergence of regularly spaced lumps of similar species along a niche axis . . . Our result suggest that these patterns may represent self-constructed niches emerging from competitive interactions.

Later, the authors comment

Finally, it is worth noting a remarkable link to Hotelling’s theory in social sciences suggesting that competition of companies or political parties will often lead to convergence rather than differentiation. In this field of research, the focus is on the problem that such convergence is not in the interest of the public. For instance, having more of the same kind of TV channels is not better. By contrast, the seeming redundancy of similar species in nature may be essential to ensure ecosystem functioning in the face of adverse impacts.

When Scheffer and van Nes’s article is published in the print version of PNAS, it will be accompanied by a commentary written by Craig Allen which places the new findings in the context of research on lumps dating to the original discovery by C.S. Holling in 1992 (Ecological Monographs 62: 447-502).