Abstract
Natural food webs are species-rich, but classical theory suggests that they should be
unstable and extinction-prone. Asynchronous fluctuations in the densities of competing
consumers can stabilize food web dynamics in constant environments. However,
environmental fluctuations often synchronize dynamics in nature. Using the same
⬚diamond-shape⬚ food web model first used to demonstrate the stabilizing effects of
asynchrony in constant environments, we show that weak-to-moderate environmentally
induced fluctuations in consumer mortality rates stabilize food webs while disrupting
asynchrony. Synchrony actually promotes stability because: (i) synchronous declines in
consumer density reduce the maximum abundance of top predators and (ii) resource
competition quickly converts synchronous increases in consumer density into
synchronous declines. These results are robust to details of food web topology and
the implementation of environmental fluctuations. The fluctuation strengths that
enhance stability are within the range experienced naturally by many species, suggesting
that stabilization via environmental fluctuations is a realistic possibility.
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