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Foliar herbivory pushes plant individuals towards the periphery of a plant-floral visitor interaction network

Rezende, Luiz1; Cosmo, Leandro2; Romero, Gustavo1; Pareja, Martin1

Published Jul 01, 2025 on Dryad. https://doi.org/10.5061/dryad.7h44j106f

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Abstract

Indirect interactions are major forces structuring communities. In terrestrial ecosystems, changes in plant traits caused by herbivory have the potential to mediate cascades of indirect interactions that can profoundly affect community structure. We have begun to understand the mechanisms behind indirect effects mediated by trait changes in plants, but we still know little about how these interaction-level mechanisms affect higher levels of community organization, in particular network structure, and how this is dependent on community context. In this study, we aimed to understand how herbivory affects floral traits, flower visitation and the position of plant individuals in a plant-flower visitor network. To do this, we assessed the natural incidence of leaf and flowerhead herbivory in a tropical shrub and tested how it affects flowerhead density and the interactions between flowers and Lepidoptera, Hymenoptera, and Diptera at the pairwise and network levels. We also tested how the local density of conspecific plants adds context dependency to these interactions by affecting both herbivory and flowerhead visitation in focal plants. Increased leaf herbivory reduced flowerhead density per plant and indirectly reduced flowerhead visitation by Hymenoptera, while for Diptera direct effects of herbivory were important and Lepidoptera were not affected. At the network level, plants with more flowerheads were more connected and central. By reducing flowerhead density, leaf herbivory caused individual plants to lose centrality, becoming less connected and therefore peripheral in the plant-flower visitor network. This dynamic is context dependent since increased plant conspecific local density reduced leaf herbivory in the focal plant and indirectly benefited its flowerhead density, flowerhead visitation and network centrality. Synthesis: We demonstrate how the effects of herbivory on a key plant trait can cascade to shape the interactions between individual plants and their flower visitors and how the indirect effects between herbivores and pollinators can modulate the structure of interaction networks in plant-based ecosystems.