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The architecture of mutualistic networks as an evolutionary spandrel


Mutualistic networks have been shown to involve complex patterns of interactions among animal and plant species, including a widespread presence of nestedness. The nested structure of these webs seems to be positively correlated with higher diversity and resilience. Moreover, these webs exhibit marked measurable structural patterns, including broad distributions of connectivity, strongly asymmetrical interactions and hierarchical organization. Hierarchical organization is an especially interesting property, since it is positively correlated with biodiversity and network resilience, thus suggesting potential selection processes favouring the observed web organization. However, here we show that all these structural quantitative patterns—and nestedness in particular—can be properly explained by means of a very simple dynamical model of speciation and divergence with no selection-driven coevolution of traits. The agreement between observed and modelled networks suggests that the patterns displayed by real mutualistic webs might actually represent evolutionary spandrels.

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The authors thank S. Pimm and the members of the Complex Systems Lab for useful comments and discussions. This work was supported by the Botín Foundation by Banco Santander through its Santander Universities Global Division, the Spanish Ministry of Economy and Competitiveness, grant FIS2016-77447-R MINEICO/AEI/FEDER and European Union (to S.V.). J.M. is supported by the French Laboratory of Excellence TULIP (ANR-10-LABX-41 and ANR-11-IDEX-0002-02), the Region Midi-Pyrenees project (CNRS 121090) and the FRAGCLIM Consolidator Grant, funded by the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 726176). We also thank the Centre for Living Technology and the Santa Fe Institute, where most of this work was done.

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S.V. and R.S. conceived the study, developed the model and prepared the manuscript. B.C.-M. and J.P. developed the theoretical framework; S.V., J.P. and R.S. collected and analysed the data. J.M and L.J. assisted with the study design, conceptual advances and manuscript preparation. All authors wrote the paper, discussed the results and commented on the manuscript.

Correspondence to Sergi Valverde.

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Further reading

Fig. 1: Mutualistic webs and how to model their evolution.
Fig. 2: Connectivity patterns in evolved in silico mutualistic webs.
Fig. 3: Higher-order correlations and network asymmetries.
Fig. 4: Nested evolved networks.