title: How habitat-modifying organisms structure the food web of two coastal ecosystems.
abstract: The diversity and structure of ecosystems has been found to depend both on trophic interactions in food webs and on other species interactions such as habitat modification and mutualism that form non-trophic interaction networks. However, quantification of the dependencies between these two main interaction networks has remained elusive. In this study, we assessed how habitat-modifying organisms affect basic food web properties by conducting in-depth empirical investigations of two ecosystems: North American temperate fringing marshes and West African tropical seagrass meadows. Results reveal that habitat-modifying species, through non-trophic facilitation rather than their trophic role, enhance species richness across multiple trophic levels, increase the number of interactions per species (link density), but decrease the realized fraction of all possible links within the food web (connectance). Compared to the trophic role of the most highly connected species, we found this non-trophic effects to be more important for species richness and of more or similar importance for link density and connectance. Our findings demonstrate that food webs can be fundamentally shaped by interactions outside the trophic network, yet intrinsic to the species participating in it. Better integration of non-trophic interactions in food web analyses may therefore strongly contribute to their explanatory and predictive capacity.
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands Department of Marine Ecology, NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands Altenburg and Wymenga Ecological Consultants, Suderwei 2, 9269 TZ Veenwouden, The Netherlands.
authors.forename: Els M
authors.initials: EM
authors.lastname: van der Zee
authors.affiliation: Department of Environmental Engineering Sciences, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Angelini
authors.affiliation: Aquatic Ecology and Environmental Biology Group, Institute for Wetland and Water Research, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
authors.forename: Laura L
authors.initials: LL
authors.lastname: Govers
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands.
authors.forename: Marjolijn J A
authors.initials: MJ
authors.lastname: Christianen
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Altieri
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands Institute for Marine Resources and Ecosystems, Haringkade 1, 1976 CP IJmuiden, The Netherlands.
authors.forename: Karin J
authors.initials: KJ
authors.lastname: van der Reijden
authors.affiliation: Division of Marine Science and Conservation, Duke University, Beaufort, NC 28516, USA.
authors.forename: Brian R
authors.initials: BR
authors.lastname: Silliman
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands Centre for Estuarine and Marine Ecology, NIOZ Royal Netherlands Institute for Sea Research, PO Box 140, 4400 AC Yerseke, The Netherlands.
authors.forename: Johan
authors.initials: J
authors.lastname: van de Koppel
authors.affiliation: Department of Marine Ecology, NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands.
authors.forename: Matthijs
authors.initials: M
authors.lastname: van der Geest
authors.affiliation: Department of Marine Ecology, NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands.
authors.forename: Jan A
authors.initials: JA
authors.lastname: van Gils
authors.affiliation: Department of Marine Ecology, NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands.
authors.forename: Henk W
authors.initials: HW
authors.lastname: van der Veer
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands Department of Marine Ecology, NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands.
authors.forename: Theunis
authors.initials: T
authors.lastname: Piersma
authors.affiliation: Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, PO Box 94248, 1090 GE Amsterdam, The Netherlands.
authors.forename: Peter C
authors.initials: PC
authors.lastname: de Ruiter
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands h.olff@rug.nl.
authors.forename: Han
authors.initials: H
authors.lastname: Olff
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands Aquatic Ecology and Environmental Biology Group, Institute for Wetland and Water Research, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
authors.forename: Tjisse
authors.initials: T
authors.lastname: van der Heide
mesh_terms: D059001:Aquatic Organisms / Q000502:physiology*; D044822:Biodiversity; D020387:Food Chain; D008435:Mauritania; D009511:New England; D013559:Symbiosis; D053833:Wetlands
keywords: consumer–resource interactions; ecological networks; ecosystem engineering; facilitation; foundation species; non-trophic interactions