Patterns in community composition, abundance, and diversity at higher trophic levels (e.g. herbivores, predators) are hypothesized to be regulated by two forces: 1) bottom-up effects, i.e. nutrient availability and structure of lower trophic levels (plants) and/or 2) top-down effects of predation and/or parasitism. These forces can further interact with environmental disturbances to shape consumer community structure, either by subjecting organisms to lethal conditions (e.g. fire) or changes in habitat structure (e.g. alterations of plant community structure). To address the relative contributions of bottom-up forces and recurrent disturbances on consumer community structure, I conducted arthropod surveys a long-term grassland management experiment in northeastern Kansas. Over the past ten years, this tract has undergone a factorial manipulation of annual nitrogen fertilization, haying, and native plant species sowing, resulting in the divergence of six distinct plant communities differing in plant productivity, composition, and diversity. To investigate potential bottom-up effects of nitrogen availability (a bottom-up force) and haying (a cyclic disturbance) on the arthropod community and, more specifically, among arthropod guilds (i.e. ground-dwelling, grass-dwelling, and aerial), I analyzed arthropod community structure in response to fertilization and haying treatments.
Arthropod community composition differed between fertilization treatments, but fertilization did not affect arthropod diversity, evenness, or abundance. Fertilization interacted with arthropod guild to cause a divergence in grass-dwelling arthropod composition between treatments but not in ground-dwelling and aerial arthropod guilds. Arthropod guild communities differed in their degree of similarity/beta diversity across experimental plots (e.g. low similarity across replicates would reflect high beta diversity); both aerial and grass-dwelling guilds had significantly higher beta diversity than ground-dwelling arthropods. Haying increased arthropod richness and abundance, but decreased community evenness. Arthropod community composition differed between haying treatments. Haying significantly interacted with fertilization treatment; non-fertilized communities differed between haying treatments, whereas fertilized communities did not. This study finds strong evidence for effects of bottom-up forces, recurrent disturbance, and interactions between the two on arthropod community structure.