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Services and disservices driven by ant communities in tropical agroforests

dc.contributor.advisorTscharntke, Teja Prof.
dc.contributor.authorWielgoss, Arno Christiande
dc.titleServices and disservices driven by ant communities in tropical agroforestsde
dc.contributor.refereeTscharntke, Teja Prof.
dc.description.abstractengAgricultural productivity and human well-being are built upon ecosystem services and disservices. Ants in tropical agroecosystems drive a complex network of direct and indirect interactions between crops and their mutualists and antagonists. Until now most studies of ecosystem services of ants only focus on single interactions. But little is known about the dynamics between multiple interactions, their relative importance, how they are affected by ant community properties and how they add up to final yield quantity and quality. We tested the hypothesis that ecosystem services of ant communities differ depending on their community structure, species richness and evenness, and on the presence and identity of dominant ants. We experimentally manipulated ant communities in 15 smallholder cacao agroecosystems with four treatments each: (i) Unmanipulated ant communities with relatively high species richness and evenness; (ii) Dominance by the native Dolichoderus cf. thoracicus, which is considered as possible biocontrol agent and maintains a similar species richness and evenness; (iii) Dominance by the invasive Philidris cf. cordata, which reduces ant species richness and evenness; (iv) Exclusion of all ants as zero-control. For 16 months we monitored the ant fauna, cacao fruit development, pests and disease incidents and yield. Ants provided ecosystem services, including reduced leaf herbivory, reduced cacao fruit pest damage and enhanced fruit set, but also disservices, including increased density of mealybugs (their mutualistic trophobionts) and higher fruit loss due to pathogen dissemination. We discovered a negative plant trait mediated indirect effect of a minor pest, the mirid bug Helopeltis sulawesi, on the major pest of cacao in Southeast Asia, the pod-boring moth Conopomorpha cramerella, leading to yield maxima with moderate fruit damage rates by Helopeltis. Therefore top down control of Helopeltis by ants can be detrimental for cocoa production and be considered as indirect ecosystem disservice. Marketable yields were highest with species-rich, even and unmanipulated communities. The effects of single species dominance strongly depended on the traits of the dominant species. With the invasive ant Philidris, ecosystem disservices outweighed the benefits leading to yield losses of 34% compared to the control, while dominance of the native Dolichoderus resulted in high yields as in the control. Ant exclusion decreased yield by 27%. Using the example of top down control of leaf herbivores by ants we give an example that correcting abundance data for physiological and behavioural traits like body size and food preferences can improve the accuracy of ecological
dc.contributor.coRefereeSchaefer, Matthias Prof.
dc.contributor.thirdRefereeClough, Yann
dc.contributor.thirdRefereeHövemeyer, Klaus Prof.
dc.contributor.thirdRefereeWiegand, Kerstin Prof.
dc.contributor.thirdRefereeBrose, Ulrich Prof.
dc.subject.engindirect interactionsde
dc.subject.engTheobroma cacaode
dc.subject.engant fauna manipulationde
dc.subject.engant exclusionde
dc.subject.engConopomorpha cramerellade
dc.subject.engHelopeltis sulaweside
dc.subject.enginterference competitionde
dc.subject.engoviposition choicede
dc.subject.engpest managementde
dc.subject.engfood preferencede
dc.subject.engPhilidris cordatade
dc.subject.engDolichoderus thoracicusde
dc.affiliation.instituteBiologische Fakultät für Biologie und Psychologiede
dc.subject.gokfullBiologie (PPN619462639)de

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