| Contents |
| Why are large, complex ecosystems stable? Both theory and
simulations of current models predict the onset of instability with
growing size and complexity, so for decades it has been conjectured
that ecosystems must have some unidentified structural property
exempting them from this outcome. We show that {\it trophic
coherence} -- a hitherto ignored feature of food webs which
current structural models fail to reproduce -- is significantly more
correlated with stability than are size or complexity. Furthermore,
we prove that a maximally coherent network will always be stable.
We also propose a simple model which, by correctly capturing the
trophic coherence of food webs, accurately reproduces their
stability and other basic structural features. Most remarkably, our
model shows that stability can increase with size and
complexity. This suggests a key to May's Paradox, and a range of
opportunities and concerns for biodiversity conservation. |
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