Data from: Small mammal herbivores mediate the effects of soil nitrogen and invertebrate herbivores on grassland diversity

1. Simultaneous reductions in herbivore abundance and increases in
nitrogen deposition have led to radical shifts in plant communities
worldwide. While the individual impacts of these human-caused disturbances
are apparent, few studies manipulate both herbivory and N, nor
differentiate among herbivore guilds, to understand contingencies in the
ability of these drivers to affect producer diversity and productivity. As
such, understanding how the main and combined effects of increasing soil N
with declining herbivores may influence plant community structure and
function is critical to better understand the future of grassland
ecosystems under multiple global change drivers. 2. In this study, we
asked: (1) What are the main effects of small mammal herbivores,
invertebrate herbivores, and soil N on plant community structure and
function? and (2) Are the effects of invertebrate herbivores and soil N on
plant community structure and function contingent on small mammal
herbivory? We used a design, with invertebrate and soil N treatments
nested within small mammal manipulations in an existing tall grass
prairie. We quantified plant community structure ( plant richness,
evenness, diversity, and composition). We also recorded total aboveground
biomass to quantify grassland productivity. 3. We found that small mammal
herbivores strongly shaped plant diversity, species composition, and
productivity. Small mammal herbivores also mediated the effects of soil N
and invertebrate herbivores on grassland community structure, but not
composition or productivity. Small mammal reduction lowered plant species
richness while increasing above ground biomass and altering compositional
similarity. Invertebrate herbivores, in the presence of small mammals,
promoted plant dominance by reducing evenness without altering
compositional similarity. Additionally, soil nitrogen addition reduced
plant richness, but only when small mammals were reduced, and no effects
on compositional similarity or productivity. 4. Our findings provide
further evidence that temperate grasslands productivity and diversity are
driven by top and bottom up factors.