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Back to the future: using palaeolimnology to infer long-term changes in shallow lake food webs

By Ruth Rawcliffe, Carl D. Sayer, Guy Woodward, Jonathan Grey, Thomas A. Davidson and J. Iwan Jones

Abstract

1. Shallow lakes are often cited as classic examples of systems that exhibit trophic cascades but, whilst they provide good model systems with which to test general ecological theory and to assess long-term community change, their food web linkages have rarely been resolved. \ud 2. We sought to redress this, and to demonstrate the potential benefits of integrating palaeolimnological and contemporary data, by constructing highly resolved food webs for the extant communities of two shallow U.K. lakes from different positions along a gradient of eutrophication. The surface sediment cladoceran and submerged macrophyte assemblages in the less enriched site, Selbrigg Pond, matched the palaeolimnological assemblages of the more enriched site, Felbrigg Hall Lake, in the 1920s. Thus, Selbrigg was a temporal analogue for Felbrigg, from which the consequences of long-term eutrophication on food web structure could be inferred. These data represent the first steps towards reconstructing not just past assemblages (i.e. nodes within a food web), but also past interactions (i.e. links within a food web): a significant departure from much of the previous research in palaeolimnology. \ud 3. We found that, in line with theoretical predictions, the structure of the food web changed in the latter stages of eutrophication. Not only were species lost, but so were the interconnections between them, so that the network collapsed into a simpler, less reticulate state. This structural change, which was associated with a greater channelling of energy through a smaller number of nodes as alternative feeding pathways disappear, could lead to reduced dynamic stability, pushing the network towards further simplification. Our data suggested that these changes were linked to reductions in the spatial extent of submerged vegetation and a shift from a benthic towards a more pelagic-dominated system, as the plant-associated subweb eroded over time.\ud 4. Although these data are among the first of their kind, the palaeo-analogue approach used here demonstrates the huge potential for applying food web theory to understand how and why these ecological networks undergo dramatic changes during eutrophication. Furthermore, because of the rich biological record preserved in their sediments, shallow lakes represent potentially important models for examining long-term intergenerational dynamics, thereby providing a means by which models and data can be integrated on meaningful timescales – a goal that has long proved elusive in food web ecology.\u

Topics: Ecology and Environment
Year: 2010
DOI identifier: 10.1111/j.1365-2427.2009.02280.x
OAI identifier: oai:nora.nerc.ac.uk:5562
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