Study unearths cliques in the food web

November 19, 2003

EAST LANSING, MI -- A study published this week in the journal Nature has revealed that even the food chain has cliques.

Research by a team at Michigan State University, University of Maryland and National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory examined what ecologists have previously theorized: that plants and animals in a complex network of interconnecting food chains - called a food web -- interact more frequently with each other than with species outside of their group.

It's a dynamic that's crucial to understanding the food web - the interaction of multiple food chains. This understanding will help natural resource managers make better management decisions that affect food webs.

"This fascinating breakthrough will help us better understand food system dynamics," said William Taylor, chair of MSU's Department of Fisheries and Wildlife and a member of the research team. "Having a structured way to look at complex food webs could give natural resource professionals a clearer vision of how to manage ecosystems for sustainability."

This research contributes to a more sophisticated understanding of food web dynamics by illustrating how species interact and, thus, how they impact each other.

Strong interactions exist among species within their group - also called compartments -- and weaker interactions exist between individual compartments.

The research applies principles for describing social systems to food webs-an exciting new way to view food web structures and to identify compartments in food-webs. The scientists employed a recently developed social network method that identifies cliques.

The research also applies principles for describing social systems to food webs -- an exciting new way to view food web structures and to identify compartments in food webs. The scientists employed a recently developed social network method.

"This appears also to be the case for food web compartments in ecology, and this method identifies compartments in which interactions are concentrated." said Ken Frank, associate professor of fisheries and wildlife and education said. "This study highlights the importance and necessity of interdisciplinary science and problem solving."

"With humans, we often find evidence of cliques. This appears also to be the case for food web compartments in ecology, and this method identifies compartments in which interactions are concentrated," said research team member Ken Frank, an MSU associate professor jointly appointed in counseling, educational psychology and special education and fisheries and wildlife. "This study highlights the importance and necessity of interdisciplinary science and problem solving."

Predators are likely to have more than one prey and prey are likely to have more than one predator, thereby creating a web of interactions, not a chain. A common approach of understanding how species interact in food webs is to categorize them into hierarchical levels, where groups of species with similar food resources and predators are associated with each other.

The one-level concept alone, however, provides an incomplete understanding of food webs, because it only provides one view of the picture; it looks at which species are competitors, but not at the other associations that species make in the food web.

For example, in economics, people's purchasing decisions are not solely influenced by the decisions made by their neighbors, who are likely in the same economic bracket. Rather, people also are influenced by their friends, who may be in another economic bracket, but in a same clique or compartment.

"The compartment method of measuring species interactions in an ecosystem has its benefits," said Ann Krause, an MSU doctoral student, and the paper's first author. "This method is more systematic and rigorous, as it assigns species to certain compartments based on observed research-not based on a researcher's hypothesis-and tests the results for statistical significance. Moreover, if compartments can be found to enhance stability in nature like they were found to do in theoretical research, we now have another tool with which to better understand stability in ecosystems.

"Stability is important for maintaining ecosystem health, and compartments may strengthen delicate food webs."

"This study will provide a mechanism for others to study and measure the stability of food webs," added Doran Mason of the NOAA Great Lakes Environmental Research Laboratory, a member of the research team. "Understanding food web stability significantly enhances our understanding of ecosystems which, of course, helps biologists and managers in their efforts to protect and improve the system.

"With future applications based on this research, we may find that managers should also focus on maintaining compartments in food webs, which are whole groups of species, not just maintaining the population of a single species, to maintain ecosystem health and integrity."
-end-
This research was funded by the Great Lakes Fishery Commission, the National Institute of Child Health and Human Development, and the National Science Foundation.

Michigan State University

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