Insect herbivory along a gradient of plant species diversity in extensively managed Central European grasslands.
Unsicker, Sybille *,1, Kahmen, Ansgar 2, Wagner, Markus 1, Buchmann, Nina3, Weisser, Wolfgang1, 1 Institute of Ecology, Jena, Germany2 Max Planck Institute for Biogeochemistry, Jena, Germany3 ETH, Zürich, Switzerland
ABSTRACT- Insect herbivores are important agents in plant communities because they can influence the abundance and composition of plant species e.g via biomass consumption. Theory predicts that the effect herbivorous insects have on plant communities should depend on the diversity level of these communities. We studied insect herbivory in 19 semi-natural grasslands covering a gradient of plant species diversity. Such planned comparisons, where sites with different diversities are selected based on a priori decisions about gradients in diversity, have so far rarely been used in biodiversity studies. At all sites, we quantified leaf area loss due to insect grazing in June and September 2003. We sampled (a) plants along a transect, and (b) the five dominant plant species in each community. Additionally, we measured insect herbivory on two phytometer species (Plantago lanceolata and Trifolium pratense) that were reared in the greenhouse and transplanted in each of the grasslands in spring 2003. Plant community biomass and a number of abiotic factors were also measured in each site. We found that insect herbivory decreased significantly with increasing plant species richness for the resident plants in June 2003. Data for the transects in September showed the same trend but were not significant. Interestingly, herbivory in the two phytometer species did not follow this overall pattern but tended to increase with increasing plant species richness or showed no correlation. Above-ground productivity was correlated with plant species richness but generally explained less variability in herbivory than species richness did. The investigated abiotic factors had little influence on insect herbivory.
Key words: Plantago lanceolata, Trifolium pratense
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