WEAK TROPHIC INTERACTIONS AND THE BALANCE OF NATURE

Ecological models show that complexity usually destabilizes food webs( 1,2), predicting that food webs should not amass the large numbers of interacting species that are in fact found in nature(3-5). Here, using nonlinear models, we study the influence of interaction strength (lik elihood of consumption of one species by another) on food-web dynamics away from equilibrium. Consistent with previous suggestions(1,6), our results show that weak to intermediate strength links are important i n promoting community persistence and stability. Weak links act to dam pen oscillations between consumers and resources. This tends to mainta in population densities further away from zero, decreasing the statist ical chance that a population will become extinct (lower population de nsities are more prone to such chances). Data on interaction strengths in natural food webs(7-11) indicate that food-web interaction strengt hs are indeed characterized by many weak interactions and a few strong interactions.