Crustacean Zooplankton Food Web Structure in Lakes of Varying Acidity

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Abstract
Crustacean zooplankton food web models were constructed for 25 softwater United States lakes of varying pH (4.7–7.2). Eight lakes on the North Mountain Plateau of Pennsylvania were sampled in 1987, and data from 17 Adirondack Mountain, NY, and White Mountain, NH, lakes were taken from Confer et al. (1983. Can. J. Fish. Aquat. Sci. 40: 36–42). In the most acidic lakes, the zooplankton food webs were simplified, with only two or three crustacean species; the highest pH lakes contained 6–10 species. Positive relationships were found between lake water pH and species richness, total number of predator–prey interactions, average number of interactions per species, and average generalization of predators. Inverse relationships were found between pH and both the degree of omnivory and cannibalism in the webs, perhaps reflecting the adaptiveness of those feeding strategies under circumstances where energy flow from adjacent trophic levels is reduced. Reduced energy flow may limit the number of trophic levels in the most acidic lakes. Lakes of pH < 5 had only two or three modal trophic levels, while lakes of pH > 5 had three, four, or five levels.