In a field experiment the impact of phytophagous insects on the structure and dynamic of a highly productive old-field community was examined. Above-ground and soil insects were excluded separately and in combination using insecticides an a full factorial design. The application of both compounds resulted in only small changes of cover abundance and species richness of the plant community in the first two years of succession. The exclusion of soil insects caused a strong shift in the dominance hierarchy of the plant community. Cirsium arvense dominated the experimental plots with reduced root herbivory and the combination treatment, whereas Epilobium adnatum dominated the control plots and the plots treated with foliar insecticide only. Later-successional plant species that established during the second year or at the end of the first year where repressed as a result of root herbivory. It is concluded that below-ground herbivory creates gaps in the established vegetation suitable for the colonization by later-successional plants and prevents inhibitory effects. Accordingly, multivariate analysis showed a decrease in the rate of succession during the first two years with the application of soil insecticide. Preference of generalist herbivores in palatability tests was correlated with ecological and functional leaf and litter traits of plant species. These correlations were still significant after a phylogenetic correction and therefore are predicative of real functional relationships. Therefore, herbivory reduced changes in the dynamics of resources in the plant community may be expected. But the palatability ranking of plants showed no relationship with the species specific change in cover abundance in the insect exclusion experiment. Thus, changes in the dominance hierarchy are not simply the result of the differences in plant palatability. The concentrations of available nutrients and water in soil were changed with the application of soil insecticide. These changes were mediated by herbivory caused changes of vegetation dynamics, so phytophagous insects indirectly influence resource dynamics in plant communities. Using a meta-analytic approach, the relationship between the intensity of invertebrate herbivory and site productivity (Fretwell-Oksanen model) has been examined in a wide range of published studies including the results of this thesis. As yet, the conclusions drawn from the available data do not support the application of this model to invertebrates so far. |