Behaviour moderates the impacts of food‐web structure on species coexistence

How species coexistence (mathematical ‘feasibility’) in food webs emerges from species' trophic interactions remains a long-standing open question. Here we investigate how structure (network topology and body-size structure) and behaviour (foraging strategy and spatial dimensionality of interactions) interactively affect feasibility in food webs. Metabolically-constrained modelling of food-web dynamics based on whole-organism consumption revealed that feasibility is promoted in systems dominated by large-eat-small foraging (consumers eating smaller resources) whenever (1) many top consumers are present, (2) grazing or sit-and-wait foraging strategies are common, and (3) species engage in two-dimensional interactions. Congruently, the first two conditions were associated with dominance of large-eat-small foraging in 74 well-resolved (primarily aquatic) real-world food webs. Our findings provide a new, mechanistic understanding of how behavioural properties can modulate the effects of structural properties on species coexistence in food webs, and suggest that ‘being feasible’ constrains the spectra of behavioural and structural properties seen in natural food webs.

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Fig 3. Feasibility of synthetic food webs of all topology x body-size arrangement x foraging strategy x dimensionality combinations. (a) The feasibility index (i.e. the peaking number of feasible species at equilibrium for each web, across magnitudes of interference strength). It appears that food webs with many top consumers (i.e. Nested and Modular-1 webs) and a strong body-size structure (i.e. with the Original arrangement) have high feasibility. (b) The difference in feasibility between the Original and Across-Guild-Shuffled arrangements (i.e. Ori - AGS), which reflects the importance of being body-size structured for maximising feasibility. Such importance is higher in webs with many top consumers but fewer Top-eat-Basal links (i.e. Modular-1), and with 2D, non-active-capture foraging. The error bars indicate the standard error. (Abbreviations Ori, WGS and AGS stand for the Original, Within-Guild-Shuffled, and Across-Guild-Shuffled body-size arrangements, respectively.).

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Published in Ecology Letters, 2021

Authors: Hsi‐Cheng Ho, Jason M Tylianakis, Samraat Pawar

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