Understanding how complex food webs assemble through time is
fundamental both for ecological theory and for the development of
sustainable strategies of ecosystem conservation and restoration.
The build-up of complexity in communities is theoretically difficult,
because in random-pattern models complexity leads to instability1.
There is growing evidence, however, that nonrandom patterns in
the strengths of the interactions between predators and prey
strongly enhance system stability2–4. Here we show how such patterns
explain stability in naturally assembling communities. We
present two series of below-ground food webs along natural productivity
gradients in vegetation successions5,6. The complexity of
the foodwebs increased along the gradients.The stability of the food
webs was captured by measuring the weight of feedback loops7 of
three interacting ‘species’ locked in omnivory. Low predator–prey
biomass ratios in these omnivorous loops were shown to have a
crucial role in preserving stability as productivity and complexity
increased during succession. Our results show the build-up of foodweb
complexity in natural productivity gradients and pin down the
feedback loops that govern the stability of whole webs. They show
that it is the heaviest three-link feedback loop in a network of predator–
prey effects that limits its stability. Because the weight of these
feedback loops is kept relatively low by the biomass build-up in the
successional process, complexity does not lead to instability
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