Multi-trophic interactions of Butterflies Along a gradienT of MANagement intensity in grasslands and forest (BATMAN)

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The impact of management intensity on ecosystem processes like predation and parasitism of herbivores is poorly studied in changing environments. Field exclosure experiments are a good method to quantify effects of bottom up and top down control of herbivores. In this project we aim to quantify the relative importance of different predator groups and endophytic fungi in food plants on butterfly larvae along a management intensity gradient. We further detect the species diversity of butterflies and their parasitoids and of the endophyte infection rate of one grass species along the management intensity gradient. The surveys will be conducted on all 300 intensive study plots (forest and grasslands) in the three exploratories. The exclosure experiments will be conducted in half of these plots and partly in the very intensive research plots. In a first experiment on the very intensive plots exclosures on each site will differ in their access for different predator groups. We hypothesize that predators do control herbivores more successfully in less intensively managed study sites. In a second experiment we also manipulate the food plant quality by using endophyte infected food plants, which produce insect toxic alkaloids, and compare it with endophyte free plants. With predator exclosures and full access of insect predators to a fixed number of reared butterfly larvae on the standardized food plants we will quantify the relative importance of bottom up and top down control along a management gradient. We hypothesize that bottom up control becomes more important and top down control less important on plots with higher management intensity. We will further quantify endophyte infection rates with the fungi Neotyphodium sp. of a grass species and will test the effects of endophyte presence on the life history of butterfly larvae in laboratory experiments. Finally we will quantify the diversity of butterflies with transect counts and their parasitoid diversity in reared butterfly larvae. We hypothesize that the parasitoid diversity is more negatively affected by increasing management intensity than the lower trophic level of butterflies and much lower than vascular plants.