Exploring variation in diversity of arthropod communities in grasslands of Yellowstone National Park

Abstract

Community ecologists have proposed many hypotheses to explain the mechanisms that drive patterns of diversity in plants and animals. For arthropods, understanding community assembly may have important conservation implications, given that this group provides many vital ecosystem services, yet many arthropods are in decline globally. We investigated drivers of arthropod diversity by testing the habitat complexity hypothesis, productivity hypothesis, and intermediate disturbance hypothesis in grasslands in the northern range of Yellowstone National Park. We collected data on vegetation (vegetation cover, litter cover, vegetation height, remotely sensed biomass, and the normalized difference vegetation index) and bison movement as explanatory variables, and sampled arthropods to help us test our hypotheses. We used generalized linear models and multivariate methods to explore patterns of richness and composition of arthropod communities among our sites. We found limited evidence for the habitat complexity hypothesis; richness of predators increased with heterogeneity in litter cover. In contrast, richness of multiple functional groups decreased with heterogeneity in vegetation cover and we did not detect any relationships with heterogeneity in vegetation height. We found evidence supporting the productivity hypothesis among herbivores; richness of herbivores overall and chewing herbivores were positively related to net primary productivity, whereas richness of omnivorous arthropods decreased with increased biomass. Although the intermediate disturbance hypothesis predicts that species richness will be maximized at moderate levels of disturbance, we found the lowest richness of all arthropods and that of multiple functional groups at moderate levels of disturbance. Overall, we found that herbivorous arthropods were more affected by quality and quantity of vegetation, whereas upper-trophic feeders were more affected by habitat complexity. These findings highlight that different functional groups of arthropods are driven by different mechanisms. By considering diversity metrics beyond taxonomic classification, we can gain important insights about arthropods - a diverse, understudied taxa.