title: Trophic groups and modules: two levels of group detection in food webs.
abstract: Within food webs, species can be partitioned into groups according to various criteria. Two notions have received particular attention: trophic groups (TGs), which have been used for decades in the ecological literature, and more recently, modules. The relationship between these two group concepts remains unknown in empirical food webs. While recent developments in network theory have led to efficient methods for detecting modules in food webs, the determination of TGs (groups of species that are functionally similar) is largely based on subjective expert knowledge. We develop a novel algorithm for TG detection. We apply this method to empirical food webs and show that aggregation into TGs allows for the simplification of food webs while preserving their information content. Furthermore, we reveal a two-level hierarchical structure where modules partition food webs into large bottom-top trophic pathways, whereas TGs further partition these pathways into groups of species with similar trophic connections. This provides new perspectives for the study of dynamical and functional consequences of food-web structure, bridging topological and dynamical analysis. TGs have a clear ecological meaning and are found to provide a trade-off between network complexity and information loss.
authors: UMR 7618-iEES Paris (CNRS, UPMC, UPEC, Paris Diderot, IRD, INRA), Université Pierre et Marie Curie, Bâtiment A, 7 quai St Bernard, 75252 Paris cedex 05, France UMR 6553 Ecobio, Université de Rennes 1, Avenue du Général Leclerc, Campus de Beaulieu, 35042 RENNES Cedex, France benoit.gauzens@univ-rennes1.fr.
authors: Benoit
authors: B
authors: Gauzens
authors: UMR 7618-iEES Paris (CNRS, UPMC, UPEC, Paris Diderot, IRD, INRA), Université Pierre et Marie Curie, Bâtiment A, 7 quai St Bernard, 75252 Paris cedex 05, France.
authors: Elisa
authors: E
authors: Thébault
authors: UMR 7618-iEES Paris (CNRS, UPMC, UPEC, Paris Diderot, IRD, INRA), Université Pierre et Marie Curie, Bâtiment A, 7 quai St Bernard, 75252 Paris cedex 05, France UMS 3194 (CNRS, ENS), CEREEP - Ecotron Ile De France, Ecole Normale Supérieure, 78 rue du Château, 77140 St-Pierre-lès-Nemours, France.
authors: Gérard
authors: G
authors: Lacroix
authors: UMR 8197 IBENS (CNRS, ENS), École Normale Supérieure, 46, rue d'Ulm, 75230 Paris cedex 05, France.
authors: Stéphane
authors: S
authors: Legendre
mesh_terms: D000465:Algorithms; D000818:Animals; D003198:Computer Simulation; D017753:Ecosystem; D020387:Food Chain; D006801:Humans; D015233:Models, Statistical; D010363:Pattern Recognition, Automated / Q000379:methods*; D011235:Predatory Behavior / Q000145:classification*
keywords: clustering method; community detection; food webs; key species; trophic groups