Interactions across trophic levels influence plant diversity effects on ecosystem functions, but the complexity of these interactions remains poorly explored. For example, the interplay between different interactions (e.g. mutualism, predation) might be an important moderator of biodiversity-ecosystem function relationships. We tested for effects of trophobioses (facultative ant-hemipteran mutualism) on leaf chewer herbivory in a subtropical forest biodiversity experiment. We analysed trophobiosis and herbivory data of more than 10,000 trees along a tree species richness gradient.

Both the herbivory and trophobiosis assessments were conducted at the end of the main growing season in September to quantify standing levels of leaf damage. In monocultures and two species-mixtures, all trees in the enlarged core area of 6 x 6 individuals (= 36 trees) were measured. In species-mixtures with 4 species, the core area to be measured comprised 9 x 9 individuals (= 81 trees) and in 8, 16 and 24 species-mixtures, the core area was 12 x 12 individuals (= 144 trees). On each large 4-mu plot, measurements were conducted in the core area of only one of the four 1-mu subplots (i.e. in the VIP subplots without additional shrubs planted). The degree of foliar damage by insects, defined as the combined removal of photosynthetic tissue by leaf-chewing, mining and galling (and, if visible, sucking) insects, was estimated using percentage classes of herbivore damage. On each tree, seven leaves on three randomly selected branches from different parts of the canopy (= 21 leaves per tree) were visually inspected. Herbivory was quantified as the overall leaf damage caused by chewing, mining, galling and (if visible) sucking insects per leaf. We used predefined percentage classes (estimated as 0%, <5%, <25%, <50%, <75%, >75%). Values provided here are the means of each category (i.e. 0%, 2.5%, 15%, 37.5%, 62.5%, 87.5%). The same trees checked for herbivory were inspected for trophobioses in a separate sampling campaign, but at the same time of the year (September to beginning of October) in 2014. On each tree, a total of 20 young leaves and the attached branch sections of three randomly selected branches were visually inspected for the occurrence and the number of sap-sucking Hemiptera and honeydew-collecting ants. Common and conspicuous ants and Hemiptera were identified in the field. Of other trophobioses, voucher specimens were collected (stored in 99% ethanol). Vouchers were subsequently grouped into morphospecies and identified to the lowest possible taxonomic level.

Main Experiment

2014-2015