Services and disservices  driven by ant communities in tropical agroforests

Wielgoss, Arno Christian

dc.contributor.advisor	Tscharntke, Teja Prof. Dr.	de
dc.contributor.author	Wielgoss, Arno Christian	de
dc.date.accessioned	2013-05-30T08:23:39Z	de
dc.date.available	2013-05-30T08:23:39Z	de
dc.date.issued	2013-05-30	de
dc.identifier.uri	http://hdl.handle.net/11858/00-1735-0000-001D-AF1A-7	de
dc.identifier.uri	http://dx.doi.org/10.53846/goediss-3869
dc.language.iso	eng	de
dc.rights.uri	http://creativecommons.org/licenses/by-nc-nd/3.0/
dc.subject.ddc	570	de
dc.title	Services and disservices driven by ant communities in tropical agroforests	de
dc.type	doctoralThesis	de
dc.contributor.referee	Tscharntke, Teja Prof. Dr.	de
dc.date.examination	2013-05-15	de
dc.description.abstracteng	Agricultural 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 models.	de
dc.contributor.coReferee	Schaefer, Matthias Prof. Dr.	de
dc.contributor.thirdReferee	Clough, Yann Dr.	de
dc.contributor.thirdReferee	Hövemeyer, Klaus Prof. Dr.	de
dc.contributor.thirdReferee	Wiegand, Kerstin Prof. Dr.	de
dc.contributor.thirdReferee	Brose, Ulrich Prof. Dr.	de
dc.subject.eng	yield	de
dc.subject.eng	predation	de
dc.subject.eng	indirect interactions	de
dc.subject.eng	Theobroma cacao	de
dc.subject.eng	ant fauna manipulation	de
dc.subject.eng	ant exclusion	de
dc.subject.eng	Indonesia	de
dc.subject.eng	Sulawesi	de
dc.subject.eng	agroforestry	de
dc.subject.eng	Conopomorpha cramerella	de
dc.subject.eng	Helopeltis sulawesi	de
dc.subject.eng	herbivory	de
dc.subject.eng	interference competition	de
dc.subject.eng	oviposition choice	de
dc.subject.eng	pest management	de
dc.subject.eng	predation	de
dc.subject.eng	food preference	de
dc.subject.eng	Philidris cordata	de
dc.subject.eng	Dolichoderus thoracicus	de
dc.identifier.urn	urn:nbn:de:gbv:7-11858/00-1735-0000-001D-AF1A-7-4	de
dc.affiliation.institute	Biologische Fakultät für Biologie und Psychologie	de
dc.subject.gokfull	Biologie (PPN619462639)	de
dc.identifier.ppn	747316570	de

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