Food web structure in Mediterranean streams: exploring stabilizing forces in these ecosystems R. Sa ´nchez-Carmona • L. Encina • A. Rodrı ´guez-Ruiz • M. V. Rodrı ´guez-Sa ´nchez • C. Granado-Lorencio Received: 18 November 2011 / Accepted: 4 May 2012 / Published online: 29 May 2012 Ó Springer Science+Business Media B.V. 2012 Abstract We constructed the food webs of six Mediterranean streams in order to determine ecolog- ical generalities derived from analysis of their struc- ture and to explore stabilizing forces within these ecosystems. Fish, macroinvertebrates, primary pro- ducers and detritus are the components of the studied food webs. Analysis focused on a suite of food web properties that describe species’ trophic habits, link- age complexity and food chains. A great structural similarity was found in analyzed food webs; we therefore suggest average values for the structural properties of Mediterranean stream food webs. Per- centage of omnivorous species was positively corre- lated with connectance, and there was a predominance of intermediate trophic level species that had estab- lished simple links with detritus. In short, our results suggest that omnivory and the weak interactions of detritivores have a stabilizing role in these food webs. Keywords Food webs Á Mediterranean stream Á Structural properties Á Trophic interactions Introduction Interest in the study and analysis of food web structure has increased considerably over recent decades. Studies show us that food web structure affects ecosystem functioning (May 2006) as well as the response of ecosystems to species loss (Dunne et al. 2002; Srinivasan et al. 2007) and invasion (Torchin et al. 2003). Structural properties have been used in different ecosystems to evaluate changes in hydro- logic regime (Ulanowicz et al. 2003), onset of hypoxic conditions (Baird et al. 2004), impacts of oil spillage (Okey and Pauly 1999), establishment of marine reserves (Watson et al. 2000), consequences of habitat restoration (Ulanowicz and Turttle 1992) and qualifi- cation of ecosystem health (Mageau et al. 1995) and integrity (Ulanowicz 2000). Analysis of food web structure has recently stimulated a revival of ‘descrip- tive’ observation of interactions in the context of natural communities. This provides a view of the ecosystem that incorporates both organization and ecological function, which are not found with com- munity analysis, but are of great importance to the accurate determination of general functioning patterns (Blu ¨thgen 2010). Despite the interesting and valuable information regarding the ecological aspects of an ecosystem that can be provided by analyses of food web structure, studies of this type in Mediterranean streams are scarce. These streams are subject to a characteristic climatic regime, with seasonal droughts (summer to Handling Editor: Piet Spaak. R. Sa ´nchez-Carmona (&) Á L. Encina Á A. Rodrı ´guez-Ruiz Á M. V. Rodrı ´guez-Sa ´nchez Á C. Granado-Lorencio Department of Plant Biology and Ecology, Faculty of Biology, University of Seville, P.O. Box. 1095, 41080 Seville, Spain e-mail: ramoni@us.es 123 Aquat Ecol (2012) 46:311–324 DOI 10.1007/s10452-012-9400-5