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Abstract

Changes in the diversity of plant communities may undermine the economically and environmentally
important consumer species they support. The structure of trophic interactions
determines the sensitivity of food webs to perturbations, but rigorous assessments of plant
diversity effects on network topology are lacking. Here, we use highly resolved networks from
a grassland biodiversity experiment to test how plant diversity affects the prevalence of
different food web motifs, the smaller recurrent sub-networks that form the building blocks of
complex networks. We find that the representation of tri-trophic chain, apparent competition
and exploitative competition motifs increases with plant species richness, while the representation
of omnivory motifs decreases. Moreover, plant species richness is associated with
altered patterns of local interactions among arthropod consumers in which plants are not
directly involved. These findings reveal novel structuring forces that plant diversity exerts on
food webs with potential implications for the persistence and functioning of multitrophic
communities.