Putting the Lake Back Together: Reintegrating Benthic Pathways into Lake Food Web Models: Lake Ecologists Tend to Focus Their Research on Pelagic Energy Pathways, but, From Algae to Fish, Benthic Organisms Form an Integral Part of Lake Food Webs

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Lakes are often used as model ecosystems because they have clearly defined boundaries and identifiable connections with adjacent ecosystems. Furthermore, small lakes are tractable units for construction of ecosystem energy budgets and whole-ecosystem experiments. Thus, limnology has contributed substantially to the understanding of basic ecological principles. However, limnologists themselves are inconsistent in their treatment of the very boundaries that make lakes such valuable conceptual models for ecosystem ecology. The body of limnological research in recent decades has had an overwhelmingly pelagic focus, with the benthic habitat often viewed as merely a source or sink of pelagic nutrients or energy. Two seminal papers in ecology, “The Trophic Dynamic Aspect of Ecology” (Lindeman 1942) and “The Lake as a Microcosm” (Forbes [1887] 1925), fully integrated benthic processes into their description of lake dynamics. Even though these works are still frequently cited, benthic and pelagic habitats have often been treated as discrete food webs with parallel but separate compartments of bacteria, primary producers, and consumers. Thus, most limnologists study either the benthic or, more often, the pelagic habitat, although research on the role of macrophytes in shallow lakes is one important exception (Sand-Jensen and Borum 1991, Scheffer et al. 1993, Jeppesen et al. 1998). We examined the role of benthic primary and secondary production in lake food webs to demonstrate that division of lakes into benthic or pelagic habitats, to be studied in isolation by different researchers, skews the perception of lake food webs. This is particularly true for most of the world's lakes, which are small and have high ratios of littoral surface area to pelagic volume (Wetzel 1990). We chose to use the word reintegrating in our title because we are appealing for a return to the roots of limnological research, in which benthic pathways are viewed as fundamental to a thorough understanding of lake ecosystem function.