REID, Adele/M; HOCHULI, Dieter/F; CASSIS, Gerasimos ; University of Sydney; University of Sydney; Australian Museum: Long-term effect of nutrients and grazing on grassland ground-dwelling invertebrates

Sustainable grazing depends on the functioning of ecological processes, but because communities are complex and contain large numbers of species, understanding individual processes are difficult. Community dynamics must be studied holistically and as a functioning unit to determine generalities about disturbances and management. We tested how two levels of stocking intensity and fertilizer application affected the composition, abundance and trophic structure of arthropods over a 24-month period in relation to changes in habitat and vegetation. Our study shows that fertilizer has a significant impact on ground-dwelling arthropod assemblages through a strong bottom up effect from an increase in nutrients. Available phosphorous, plant biomass and cover all increased in the response to nutrient enrichment, whereas plant species richness decreased. Consequently, generalist herbivores, detritivores and scavengers from the orders Acarina, Diptera and Coleoptera showed greatest increases in abundances. Long-term increases in abundances of herbivores and detritivores were not sustained into the second year of the study, despite plant biomass remaining relatively stable. The strength of the bottom-up effect was difficult to determine, as there was a mixed response of general and specific predatory invertebrates. Parasitoid wasps limit the response of several orders of herbivores, s the abundance of parasitoid wasps increased after the first year of fertilizer application. Grazing had minimal effect on ground-dwelling invertebrate communities, but the abundance and composition of foliage inhabiting communities is reduced because of a reduction in vegetation structure.