Using water-filled container analogues of natural treeholes placed in a subtropical rainforest, the source of energy in both experimental and natural systems was detrital leaves. Ten-fold and hundred-fold reductions in energy input reduced food chain lengths by an extra link. The principal predator was less prevalent in less productive habitat units. Food webs with fewer trophic links and fewer species were found in habitat units that were less productive. Numbers of species, trophic links and abundance of the most common prey species increased during food web assembly. A natural perturbation created by low rainfall caused numbers of species, trophic links and food chain length to be temporarily reduced at 36 wk. The effect on food chain length was most marked in the most productive system. While relatively long food chains were possibly only in the most productive systems, these systems were especially vulnerable to external perturbations. -from Authors