Effects of multiple herbivore guilds on population dynamics are subadditive in a model forb species

Abstract

We have a good understanding of how individual herbivore guilds affect herbaceous communities. Invertebrate herbivores reduce grassland biomass and change species composition dramatically. Bison reduce grass biomass and increase forb cover. Small mammals have weak effects. Few studies quantify how multiple co-occurring herbivore guilds jointly impact populations and communities. Potential for super- or subadditive effects. Many ecosystems house multiple herbivores. Critical to predicting impacts of herbivore declines, extirpations, or reintroductions. Here, we use Kuhnia eupatorioides at Konza LTER to ask whether effects of herbivores tend to be additive, super-, or subadditive. We measure individual vital rates (survival, growth, recruitment) to dissect mechanisms driving sub- or super-additivity