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.