Herbivory Modifies the Role of Spatial Processes in a Grassland Plant Metacommunity

Trophic interactions can strongly influence metacommunity dynamics and patterns of biodiversity in spatially heterogeneous environments. Theory predicts that herbivory facilitates plant species coexistence at small scales by reducing extinctions and promoting colonisations but reduces diversity at larger scales by promoting dominance of herbivore-resistant species. We examined how mammalian herbivory interacts with habitat size and connectivity to affect plant diversity in a unique, naturally fragmented grassland metacommunity system located in Southern Finland. We found that herbivory increased plant diversity across scales of measurement. In addition, herbivory reversed the diversity-area relationship such that there was a positive diversity-area relationship in grazed grasslands, but a negative relationship in ungrazed grasslands. Connectivity exhibited a unimodal relationship with diversity but did not interact with herbivory. Our empirical results demonstrate that herbivores can promote plant coexistence across scales and highlight the interplay between habitat area and trophic interactions in facilitating plant biodiversity in grassland metacommunities.