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. Herbivory is predicted to facilitate plant species coexistence on small scales by reducing extinctions and promoting colonisations, but could lead to a reduction in the size of the regional species pool and homogenization at larger scales. We examined how mammalian herbivory interacts with habitat size and connectivity to affect plant diversity in a natural grassland metacommunity. 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 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.