Jennifer Dunne, Neo Martinez, Richard Williams

Paper #: 03-04-024

Previous studies suggest that food-web theory has yet to account for major differences between marine food webs and the trophic structure of other ecosystems. We examined this issue by analyzing the structure of food webs for Benguela (South Africa), a Caribbean reef, and the Northeast U.S. shelf with 29, 50, and 81 taxa, respectively. Marine webs tend to have somewhat higher connectance (links/species2), link density (links/species), mean chain length, and fractions of intermediate, omnivorous, and cannibalistic taxa than food webs from other ecosystems. Given that most food-web properties are scale dependent on network diversity and complexity, we used the empirically well corroborated "niche model" that accounts for such dependence to compare the structure of marine and other food webs. Our results show that the niche model accurately predicts 15 properties of the marine food webs 81% of the time, similar to the 79% success rate previously reported for other food webs. This suggests that common mechanisms underlie emergent network structure across ecosystems and that the uniqueness of marine food-web structure has been exaggerated. The structural robustness of marine food webs to species loss, in terms of potential secondary extinctions, was also consistent with trends from other food webs. Marine webs appear relatively robust to loss of the most connected taxa as well as random taxa, as expected given their relatively high connectance. However, the short average path length between marine taxa (1.6 links) also suggests that effects from perturbations such as overfishing can be transmitted more widely throughout marine ecosystems than has previously been appreciated.