Species-specific dung characteristics and selective grazing jointly affect plant diversity in an experimental grassland community

Mammalian herbivores play a pivotal role in nutrient cycling and plant community composition. Their excreta and grazing activity influence plant diversity, but the relative or interactive effects of these influences are unclear. We manipulated dung quantity, quality (three herbivores with varying dung-N:P), and grazing type (bulk, selective, no) in a 3-year experiment. Neither dung quantity nor bulk grazing influenced plant diversity, despite strongly impacting plant productivity and light. Dung's impact on plant diversity varied among herbivore species but could not be ascribed to nutrients. Effects of selective grazing on plant diversity interacted with dung type (herbivore species), depending on whether it promoted dominance of the consumed plants. Our results highlight that the interactive effects between herbivore species-specific dung characteristics and grazing activities have important indirect effects on plant diversity in terrestrial ecosystems.