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Summary: Ecological subsystems via graph theory: the role of strongly connected
components
Stefano Allesina, Antonio Bodini and Cristina Bondavalli
Allesina, S., Bodini, A. and Bondavalli, C. 2005. Ecological subsystems via graph
theory: the role of strongly connected components. Á/ Oikos 110: 164Á/176.
In this paper we investigate ecological flow networks via graph theory in search of
the real sequential chains through which energy passes from producers to consumers
in complex food webs. We obtain such fundamental pathways by identifying
strongly connected components (SCCs), subsystems that groups species that take
part in cycling, and performing topological sorting on the acyclic graphs that
are obtained. Topological sorting identifies preferential directions for energy to flow
from sources to sinks, while recycling remains confined within each SCC. Resolving
food web networks for SCC highlights the possibility that compartments can be
found in ecosystems, but this does not seem a general rule. The four aquatic food webs
described in detail show a rather clear subdivision between benthic and pelagic
subcommunities, a result that is discussed in the light of other studies. Should further
research confirm these results, new insight into the way ecosystems use energy will
be provided, with implications on cycling, reciprocal dependency of variables and
indirect effects.
S. Allesina, A. Bodini, and C. Bondavalli, Dept of Environmental Sciences, Univ. of
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