# Mathematical Digest

### Short Summaries of Articles about Mathematics

in the Popular Press

"Stability is woven by complex webs", by Gary A. Polis. *Nature,* 22October 1998, page 744.

The earth is full of complex ecosystems. One species of rodent may feed on many varieties of plants and insects, and in turn become food for several species of snakes and birds. The survival of each of these organisms is linked to each of the others. Until recently, mathematical models of ecosystems could not explain this complexity. According to the models, an ecological system with a complex web of species was not stable -- over time, many species would die out, and the system would lose its complexity. This article explains that a new mathematical model introduced by McCann and colleagues shows complex relationships actually stabilizing an ecological model. The new model supports the intuition of empirical ecologists.

*--- Elizabeth Moisan*