Food-web complexity, here for islands in the Gulf of California. McCann et al.¹ have shown that complexity in food webs facilitates stability in natural communities, a finding that runs counter to previous theory. This web depicts a subset of interactions on the islands in wet El Niņo years^12,13; marine sources and land plants provide the fuel for an estimated 500-1,000 species. Thick lines represent strong interactions; thin lines, weak interactions

The six food-web configurations studied are: a, a simple food chain, b, a food web with multiple intermediate consumers (exploitative competition), c, a food web with the top predator feeding on two intermediate consumers (apparent competition), d, a food web with consumer 1 feeding on the basal resource and on the second consumer (intraguild predation), e, a food chain including omnivory, and f, a food chain with external inputs. R denotes the basal resource species; C₁ and C₂ denote intermediate consumer species 1 and 2; and P denotes the top predator ( Box 1).

The local minima and maxima for top predator density, P, attained in the attracting solutions for a range of relative interaction strengths. Food-web configurations are given as a function of the relative interaction strengths. Food-web configurations are given as a function of the relative interaction strength. Whenever the configuration lacks an explicit link between a species and the rest of the connected web this implies that the species cannot persist. a, Exploitative competition. b, Apparent competition. c, Intraguild predation. d, The configuration used in b, starting with a limit cycle solution (I_C2R/I_C1R = 0.62).

Figure 1: Prototype two-dimensional image depicting global connectivity among ISPs as viewed from skitter host. Graph layout code provided by W. Cheswick and H. Burch (Lucent/Bell Laboratories).

Figure 2: Interconnection relationships among key Autonomous System networks on December 3, 1998 as viewed from skitter host.