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Universität Osnabrück (2018)

Community ecology of African termites (Isoptera)

Schyra, Janine

Titre : Community ecology of African termites (Isoptera)

Auteur : Schyra, Janine

Université de soutenance : Universität Osnabrück

Grade : Doktorgrades der Naturwissenschaften (Dr. rer. nat.) 2018

Résumé
In this study we wanted to investigate the community ecology of African termites and uncover possible mechanisms structuring these species communities. Termites are important ecosystem engineers, crucial for the maintenance of tropical biodiversity and ecosystem functioning, therefore we wanted to show how anthropogenic disturbance influences these termite communities. Using a cross-sectional approach, we studied termite community composition along a disturbance gradient from fields to 12-year-old fallows in a West African savannah. We could show that disturbance was associated with environmental filtering of termites from the regional species pool, maybe via its effect on vegetation type. The most heavily disturbed sites were characterized by a subset of termite species which are well-known pests of crop. This supports a model in which strong anthropogenic disturbance selects for termite pest species. Additionally, we comparatively studied termite communities in the two major West African ecosystems, savannah and forest, both under natural settings and along disturbance gradients. Overall we found 33 species in the forest and 22 in the savannah. However, alpha diversity per site did not differ between both ecosystems with on average around ten species. For both ecosystems, species diversity did not decrease along the studied disturbance gradient but encounter rates did. In general, we found little evidence for strong community structuring mechanisms such as environmental filtering or interspecific competition in the natural habitats. Most local communities did not differ significantly from random assemblages of the regional species pool. Interestingly, only the disturbed sites in the savannah showed some sign of phylogenetic structuring, the teak plantation sites did not. By using stable isotope analysis we could investigate how so many termite species with very similar feeding niches can coexist in an African savannah. We discovered that closely related species either differed in their δ15N and /or δ13C signatures, providing support for our hypothesis that fine-scaled differentiation of the feeding niche exists between termites in the studied area that formerly have been classified as feeding on the same dead plant material. We were able to distinguish feeding groups with stable isotope analysis, as each feeding group had a specific δ15N and δ13C signature, supporting the classification of Donovan et al. (2001). Comparatively, we tested whether southern African termite communities show signs of environmental filtering and / or competition along a rainfall gradient in Namibia. There was a regional species pool of 11 species and we found no evidence for phylogenetic structuring at the local scale. Rather, our results suggest that the assembly of the studied termite communities has as strong random component on the local scale, but that species composition changes along the climatic gradient. Interestingly, species richness and species composition was different to West African termite communities.

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