Rewiring and indirect effects underpin modularity reshuffling in a marine food web under environmental shifts

• Published in: Ecology and evolution Vol. 9; no. 20; pp. 11631 - 11646
• Main Authors: D'Alelio, Domenico, Hay Mele, Bruno, Libralato, Simone, Ribera d'Alcalà, Maurizio, Jordán, Ferenc
• Format: Journal Article
• Language: English
• Published: Bognor Regis John Wiley & Sons, Inc 01.10.2019; John Wiley and Sons Inc; Wiley
• Subjects: Behavioral plasticity; Cascades; Community ecology; Community structure; Ecological monitoring; ecological networks; Ecologists; Ecosystems; Environmental changes; Environmental impact; Food chains; Food webs; Investigations; Modularity; Modules; Networks; Original Research; Plankton; Reconfiguration; Reproduction (biology); Rewiring; Roles; Species; Trophic levels; Italy
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.5641

Species are characterized by physiological and behavioral plasticity, which is part of their response to environmental shifts. Nonetheless, the collective response of ecological communities to environmental shifts cannot be predicted from the simple sum of individual species responses, since co‐existing species are deeply entangled in interaction networks, such as food webs. For these reasons, the relation between environmental forcing and the structure of food webs is an open problem in ecology. To this respect, one of the main problems in community ecology is defining the role each species plays in shaping community structure, such as by promoting the subdivision of food webs in modules—that is, aggregates composed of species that more frequently interact—which are reported as community stabilizers. In this study, we investigated the relationship between species roles and network modularity under environmental shifts in a highly resolved food web, that is, a “weighted” ecological network reproducing carbon flows among marine planktonic species. Measuring network properties and estimating weighted modularity, we show that species have distinct roles, which differentially affect modularity and mediate structural modifications, such as modules reconfiguration, induced by environmental shifts. Specifically, short‐term environmental changes impact the abundance of planktonic primary producers; this affects their consumers’ behavior and cascades into the overall rearrangement of trophic links. Food web re‐adjustments are both direct, through the rewiring of trophic‐interaction networks, and indirect, with the reconfiguration of trophic cascades. Through such “systemic behavior,” that is, the way the food web acts as a whole, defined by the interactions among its parts, the planktonic food web undergoes a substantial rewiring while keeping almost the same global flow to upper trophic levels, and energetic hierarchy is maintained despite environmental shifts. This behavior suggests the potentially high resilience of plankton networks, such as food webs, to dramatic environmental changes, such as those provoked by global change. We show, for the first time, the fine‐scale dynamics of structural re‐adjustment in a complex food web, under a regime of changing resources. Our observation is novel, since we investigated directed and weighted modularity in an ecological network, which provides a much sounder view of food web architecture, and therefore functioning; our results are exciting, since food web re‐adjustments shown herein are analogous to those “systemic behaviors” described for other complex systems, such as human brain networks, but an analogous behaviour was never shown in ecological studies with such detail; ultimately, our paper is of general interest in ecology, since it demonstrates that food webs compartmentalization overcomes physical barriers, because species can migrate, and is mainly driven by the aggregation of trophic pathways, more than species co‐occurrence.