Bottom-up forces affecting arthropod community diversity through space and time

Few studies have quantified how a diverse community of arthropods representing multiple trophic levels responds to similar spatial and temporal gradients of stress. This link is important because it enables us to make predictions regarding community responses to global change through time based on spatial differences at one point in time. We utilized a 3,000,000 year old volcanic chronosequence which represents gradients in soil age, nutrient content, and environmental stress, to determine how bottom-up forces such as nutrient and water availability influence canopy arthropod diversity and community structure on a foundation tree species (pinyon pine – Pinus edulis) in a semi-arid ecosystem. Four major patterns emerged. 1. Arthropod richness, abundance, and biomass track soil organic C and total soil N, and total soil P across a gradient of soil age. 2. In a community of 380 species, arthropod abundance was 4X greater and richness was 2X greater at the lowest stress site where neither N nor P was severely limited. 3. The ratio of predators to herbivores was highest where stress was lowest. 4. Older stands show greater arthropod diversity. Together these results argue that arboreal arthropod communities are sensitive to belowground nutrient regimes and changes in availability of these nutrients have effects both in space and time. We contrast our studies of arthropods with other studies of mycorrhizal fungi and with other studies of spatial and temporal stress gradients. These comparisons are important as they show similarities and differences between very different taxonomic groups. They also may allow us to determine how effectively studies of spatial gradients of environmental stress can be used to predict temporal changes along similar gradients, which are important for determining the impacts of climate change on community diversity.