Rare species in a large community are like thin branches on a tree: a random gust can easily snap them. Even if conditions are stable, a small population simply lacks enough individuals to survive a bad season. In a new study, scientists added this factor to an ecosystem model and watched the community clean itself out.
Stochastic fluctuations in population numbers act like a gardener pulling out weak seedlings. Rare species vanish one by one, leaving only a tight cluster of survivors. This core no longer fears random shocks: even if one species loses many individuals, neighbors quickly fill its place.
The authors noticed an unusual pattern: the fraction of surviving species declines following a power law with a heavy tail. This means that after the rapid extinction of rare species, the remaining ones disappear slower and slower. The community gets stuck in a metastable state: it can persist for a long time, though not forever.
This mechanism explains why real ecosystems rarely collapse completely, even when theory predicts chaos. Randomness, usually seen as a nuisance, here acts as a stabilizer.
In a model with a hundred species, almost all rare ones vanish within the first few dozen generations, while the survivors can last for thousands of generations.