Trophic interactions of ants, birds and bats affecting crop yield along shade gradients in tropical agroforestry

by Pierre Gras
Doctoral thesis
Date of Examination:2014-12-10
Date of issue:2015-12-09
Advisor:Prof. Dr. Teja Tscharntke
Referee:Prof. Dr. Stefan Vidal
Referee:Dr. Yann Clough
Referee:Dr. Christoph Scherber
Referee:Prof. Dr. Kerstin Wiegand
Referee:PD Dr. Mark Maraun
Persistent Address: http://dx.doi.org/10.53846/goediss-5390

 

 

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Abstract

English

Tropical agroforests are diverse systems where several predator groups shape animal communities and plant-arthropod interactions. Ants, birds and bats in particular can reduce herbivores and thereby increase crop yield. However, the relative importance of these groups, whether they interact, and how this is affected by management and landscape context, is poorly understood. We jointly manipulated access of ants, birds and bats in Indonesian smallholder cacao agroforestry across gradients of shade and distance to natural forest. We quantified arthropod abundance, pest damage and yield. The trophic web within ant communities was investigated by analyzing stable nitrogen and carbon isotopes. Thereby, we examined how trophic positions of ants respond to plant phenology, shade cover and distance to forest margins. Our results suggest: (1) The Impact of ants and birds on cacao yield is economically relevant, and depends on shade-tree management. (2) Intraspecific diets of ants are conditional to plant phenology and help to distinguish species-specific ecosystem services and disservices. (3) Both, trophic plasticity and species turnover are mechanisms defining ecological functions of omnivore communities. (4) Diet shifts are conditional to co-occurring, competing species.
Keywords: ant; bird; bat; shade; forest distance; biological control; Theobroma cacao; trophic interactions; yield; ecosystem service; predation; omnivores; stable isotope; food web
 
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