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GLIN==> New study reveals existence of "compartments" in natural food webs


Marc Gaden, Great Lakes Fishery Commission, 734-662-3209 x. 14
Patricia Stewart, Michigan State University, 517-355-1821
Jana Goldman, Nat. Oceanic and Atmos. Admin., 301-713-2483


Innovative research published this week in the journal Nature

ANN ARBOR, MI-A new study, published this week in the journal Nature, has
revealed the existence of what in human interactions would be referred to as
"cliques" in natural food webs.  This research examined what ecologists have
previously theorized:  that plants and animals organize themselves into
cliques, just as humans do.  These cliques, also known as compartments, are
groups of species in a food-web that interact more frequently with each
other than with species outside of that compartment.  Strong interactions
exist among species within compartments and weaker interactions exist
between individual compartments.  This research contributes to a more
sophisticated understanding of food web dynamics by illustrating how species
interact and, thus, how they impact each other.  This better understanding
of food webs will help natural resource managers make better management
decisions that affect food webs.

Food webs are multiple interconnecting food chains.  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
trophic-or hierarchical-levels, where groups of species with similar food
resources and predators are associated with each other.  The trophic 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 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 (or same hierarchical level).  Rather, people are also influenced by
their friends, who may be in another economic bracket, but in a same clique
or compartment.

The discovery of compartments within food webs provides a more advanced
understanding of species interactions with each other in the environment.
The research, published this week in Nature, 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.  "It has been proposed
that social systems are more efficient and durable when composed of
subgroups in which interactions are concentrated," said Dr. Ken Frank of
Michigan State University and member of the research team. "This appears
also to be the case for food-web compartments in ecology, and this method
identifies compartments in which interactions are concentrated." Dr. William
Taylor of Michigan State University and a member of the research team added:
"This study highlights the importance and necessity of interdisciplinary
science and problem solving."

A simple illustration of the trophic and compartment concepts is to consider
state governments.  The trophic level model would put the US governors in a
category, the state representatives in another category, and the people in a
third category.  The compartment model, however, groups people by state, so
a state would be one compartment, with a governor, the representatives, and
people having strong interactions with each other, and weaker interactions
with other compartments, the other states.

            "The compartment method of measuring species interactions in an
ecosystem has its benefits," said Ann Krause of Michigan State University, a
member of the research team.  "This method is more systematic and rigorous,
as it assigns species to certain compartments based on observed research-not
based on a researcher's guess-and tests the results for 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."

"This study will provide a mechanism for others to study and measure the
stability of food-webs," added Dr. Doran Mason of the 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."

This research is a collaborative among scientists Ann E. Krause, Kenneth A.
Frank, and William W. Taylor from Michigan State University's Department of
Fisheries & Wildlife; Robert E. Ulanowicz from the University of Maryland;
and Doran M. Mason of the National Oceanic and Atmospheric Administration's
Great Lakes Environmental Research Laboratory.  This research was funded by
the Great Lakes Fishery Commission, the National Institute of Child Health
and Human Development, and the National Science Foundation.  Contact
information for members of the research team is as follows:

Krause: (734) 662-3209 x.21 (krausean@msu.edu)

Frank:  (512) 475-8642 (kenfrank@msu.edu)

Taylor:  (517) 353-3048 (taylorw@msu.edu)

Ulanowicz: (410) 326-7266 (ulan@cbl.umces.edu)

Mason:  (734) 741-2148 (doran.mason@noaa.gov)


The complete citation for the research is Krause, A.E., K.A. Frank, D.M.
Mason, R.E. Ulanowicz, and W.W. Taylor.  2003.  Compartments revealed in
food-web structure. Nature 426:282-285

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