Ants are abundant and functionally important arthropods in tropical and subtropical forests. The vast majority of vegetation-foraging ants were thought to be predacious or omnivorous, until studies of stable isotopes showed that those ants are essentially feeding as herbivores, mostly by visiting extrafloral nectaries and by tending Hemiptera for honeydew. Additionally, there are anecdotal records of wound feeding, i.e. the consumption of plant sap from wounds created by sucking or chewing herbivorous insects. However, to our surprise, no study has investigated and quantified wound feeding at the level of entire ant communities. We conducted over several years an exhaustive survey for wound-feeding ants in the experimental tree plantations of the BEF-China experiment, located in subtropical South-East China. In total, we observed wound-feeding ants on 23 out of 40 planted tree species. There was a strong bias towards Fagaceae species; 90% of all observations occurred on eleven species of Fagaceae, albeit Fagaceae species accounted for less than 50% of all surveyed tree individuals. Almost all trophobiotic ant species known from the study area were also found at wounds. Our data indicate that wound feeding is an unspecific, opportunistic, and facultative behavior. Albeit less common by an order of magnitude when compared to trophobioses, feeding on wound sap might be an important but underestimated food source that contributes to fuel the diversity and abundance of vegetation foraging ants, for example in cases when herbivorous insects are abundant or trophobiotic Hemiptera are scarce. Interestingly, increasing tree diversity decreased the specialization while increasing the complementarity of plant-ant networks. Both effects were independent of network size and sampling effort, and support recent theoretical and experimental studies, which demonstrated a structuring and stabilizing effect of tree diversity on species interaction networks.

Data were collected by visually scanning 20 leaves per tree individual for all trees in the extended core areas of all plots (plots with conifers, free succession, and plots with shrubs were not sampled). Site A was assessed once in 2011 and twice in 2014, site B once in 2013 and twice in 2014.

BEF China Main Experiment, near Xingangshan, Jiangxi

Mai 2011 - October 2014

Ants foraging for wound sap

The data unit of all data is the occurrence of an ant-wound interaction, i.e. every interaction between an ant and a plant wound observed on an individual tree was only counted once, regardless of the number of ant individuals involved. Hence data are 'occurrences', i.e. whenever an ant interacted with a wound it was counted as a '1'. Raw abundance data (which are not very meaningful) are available from Michael Staab (michael.staab@nature.uni-freiburg.de).