Sheep Grazing Effects on Beetles (Coleoptera) in an Alpine Ecosystem

Norwegian alpine areas have for the past nine decades been subjected to an intensified use in terms of grazing by large domestic herbivores. It is thus essential to know how this affects alpine ecosystems. Grazing studies to date have focused primarily on how plants respond to grazing, while grazing studies on insects are rare. Furthermore, there are indications that grazing effects on insects cannot be deduced from the effects on plants. To advance this field, studies have to be conducted directly on insects. Further, little is known about short- versus long-term effects of grazing, and research on the effects of grazing on invertebrates have shown both positive, negative and even non-linear results. In this study, the responses of beetles to sheep grazing were studied within a fully replicated large-scale experiment with three levels of sheep grazing in an alpine ecosystem in Hol, Norway. Beetles were collected with pitfall traps and classified to a species level. I analysed beetle richness and abundance of five beetle species from two functional groups (Calathus melanocephalus and Patrobus assimilis as carnivores and Otiorhynchus nodosus, Byrrhus fasciatus and Hypnoidus rivularius as herbivores). I predicted long-term (2009) to differ from short-term (2003) effects and that these changes might be driven by changes in plant community. I also predicted beetles responses to be determined by their functional group, and that they would show either a nonlinear, negative or positive response. Beetle richness and occurrence were negatively affected by sheep grazing in 2003, while there generally were neutral or positive responses in 2009. However, different species differed in their responses, and functional groups did not explain the responses adequately. Plant richness or plant composition (DCA-1) were included in all models to see whether sheep grazing through changes in plant community from 2003 to 2009 could explain the changes in beetle richness and the occurrence of beetles, but this was rejected for both richness and all species. In general, it appears that the negative effects of short-term grazing found earlier have been eliminated after an additional 6 years of grazing. This study highlight the importance of long-term studies and that responses of grazing might change over time.