OIKOS 103: 121–132, 2003 Palatability, decomposition and insect herbivory: patterns in a successional old-field plant community Martin Scha ¨dler, Gertraud Jung, Harald Auge and Roland Brandl Scha ¨dler, M., Jung, G., Auge, H. and Brandl. R. 2003. Palatability, decomposition and insect herbivory: patterns in a successional old-field plant community. – Oikos 103: 121–132. We tested the hypothesis that selective feeding by insect herbivores in an old-field plant community induces a shift of community structure towards less palatable plant species with lower leaf and litter tissue quality and may therefore affect nutrient cycling. Leaf palatability of 20 herbaceous plant species which are common during the early successional stages of an old-field plant community was assayed using the generalist herbivores Deroceras reticulatum (Mollusca: Agriolomacidae) and Acheta domesticus (Ensifera: Gryllidae). Palatability was positively correlated with nitrogen content, specific leaf area and water content of leaves and negatively correlated with leaf carbon content and leaf C/N-ratio. Specific decomposition rates were assessed in a litter bag experiment. Decomposi- tion was positively correlated with nitrogen content of litter, specific leaf area and water content of living leaves and negatively correlated with leaf C/N-ratio. When using phylogentically independent contrasts the correlations between palatability and decomposition versus leaf and litter traits remained significant (except for specific leaf area) and may therefore reflect functional relationships. As palatability and decomposition show similar correlations to leaf and litter traits, the correlation between leaf palatability and litter decomposition rate was also significant, and this held even in a phylogenetically controlled analysis. This correla- tion highlights the possible effects of invertebrate herbivory on resource dynamics. In a two-year experiment we reduced the density of above-ground and below- ground insect herbivores in an early successional old-field community in a two- factorial design by insecticide application. The palatability ranking of plants showed no relationship with the specific change of cover abundance of plants due to the reduction of above- or below-ground herbivory. Thus, changes in the dominance structure as well as potentially associated changes in the resource dynamics are not the result of differences in palatability between plant species. This highlights funda- mental differences between the effects of insect herbivory on ecosystems and pub- lished results from vertebrate-grazing systems. M. Scha ¨dler, G. Jung, H. Auge and R. Brandl, UFZ Centre for Enironmental Research Leipzig -Halle, Dept of Community Ecology, Theodor -Lieser -Str. 4, DE- 06120 Halle, Germany. Present address for MS and RB: Philipps -Uni. Marburg, Faculty of Biology, Dept of Animal Ecology, Karl -on -Frisch -Strasse, DE-35032 Marburg, Germany (schaedler@staff.uni -marburg.de). By changing competition regimes and dominance hier- archies between plant species, invertebrate herbivores may impose strong influences on the structure of terres- trial plant communities (Brown and Gange 1989a, Car- son and Root 1999, Scha ¨dler et al. 2003). These changes are commonly explained by selective feeding of herbivores on particular plant species. Selective feeding by generalist herbivores is supposed to be closely re- lated to functional traits of plants, e.g. growth rates, resource allocation patterns, nutrient uptake and reten- Accepted 9 April 2003 Copyright © OIKOS 2003 ISSN 0030-1299 OIKOS 103:1 (2003) 121