Diploma

Aspects of coloniality in the sociable weaver (Philetairus socius)

The spatial organization of individuals, or groups of individuals, within a population can provide valuable information about social organization and population dynamics. In my Diploma thesis I analysed the spatial distribution of nests of the sociable weaver ( Philetairus socius ) on two farms in the Kalahari. Sociable weavers build large communal nests on big savannah trees, forming a pattern of trees with and without nests.

I used two spatial statistics, Ripley's K and the pair correlation function, to describe characteristics of the point patterns over a range of distances. (i) At distances of 200 and 300 m, communal nests were clustered. (ii) At distances greater than 1000 m, communal nests were regularly distributed. These findings are independent of the spatial distribution of trees. Furthermore, I used Moran's I to analyse spatial autocorrelation of nest sizes. I expected negative autocorrelation because of competition between nests. But on both farms there was no significant autocorrelation of nest sizes for any distance class. The regular distribution observed at larger distances may indicate competition and/or territoriality among different nests, but the lack of spatial autocorrelation between nest sizes suggests that these interactions may happen between nest clusters rather than between single nests. This was confirmed by significant clustering of nests on small scales. Thus, I suggest that colonies of P. socius consist of several nests on adjacent trees forming a cluster of subcolonies. The question why sociable weavers establish subcolonies instead of adding more chambers to the natal nest, could not simply be answered by limitation of nesting space. I suggest a strategy to avoid costs due to increasing colony size.

PhD

Biodiversity and ecosystem functioning in the Atlantic Rainforest, Brazil

The loss of species diversity because of human activities is one of the most threatening ecological problems in our time. We just begin to realize the value of biodiversity for humankind as it provides valuable resources or ecosystem services. One of the major issues of the loss of biodiversity is its possible influence on ecosystem functioning. Thus, the extinction of species could lead to changes in ecosystem processes with unpredictable consequences for the whole ecosystem. In particular, tropical rainforests are likely to suffer a great loss of species due to human activity. Knowledge of ecosystem processes in tropical rainforests is still scanty, thus its difficult to predict the effects of biodiversity loss.

1) Litter decomposition dynamics in a highly diverse ecosystem

One essential process in terrestrial ecosystems is the decomposition of organic material and thereby the recycling of carbon and nutrients. Especially in the tropics, fast decomposition rates are crucial to provide nutrients to plants, because of the low nutrient storage capacity of tropical soils. Despite the great importance of decomposition in tropical ecosystems, studies investigating litter mixing effects on decomposition in the tropics are still underrepresented.

As a part of my PhD theses I investigate the influence of litter diversity and invertebrate activity on decomposition in the highly species-diverse Atlantic Rainforest in Brazil. I investigate if there are 1) non-additive effects of litter mixing on decomposition rates, 2) interactions between mixture effects and presence/absence of invertebrates 3) relationships between decomposition rates and initial C and N ratios as a measure of litter quality.

Fungi are of great ecological and economical value. However, the knowledge about fungal diversity, especially in the tropics, is still scanty.

Due to the proceeding destruction of old growth tropical rainforests and the associated loss of plant hosts and capable habitat, a loss of fungal diversity is expected. Old growth forests are often replaced by secondary forests. The successional dynamics of fungal diversity in these secondary habitats is unknown and therefore even the magnitude of the expected loss in fungal diversity can not be evaluated. As a first step, a rapid assessment of fungal diversity in secondary forest sites of different successional age is necessary to direct the conservation and restoration of fungal biodiversity.

My study is part of the SOLOBIOMA project, a German-Brazilian co-operation with its focus on the Atlantic rainforest in the Brazilian state of Paraná. This rainforest is known to be a biodiversity hotspot and also one of the most endangered rainforests in the world. The aim of the study is an assessment of fungal diversity in forest sites of different successional age.

I use ARISA, a genetic fingerprinting method, which is appropriate for a quick assessment of fungal diversity with a high resolution and reproducibility. On the basis of length variability of a given, non-coding DNA region (ITS) operational taxonomic units are defined, which are used for further diversity analyses.

Publications

U.C. Giesselmann, T. Wiegand, J. Meyer, M. Vogel, R. Brandl (2008): Spatial distribution of communal nests in a colonial breeding bird: benefits without costs ?, Austral Ecology 33: 607 - 613

U.C. Giesselmann, K. Geronazzo Martins, M. Brändle, R. Brandl: Litter decomposition dynamics in a highly diverse ecosystem (in preparation)

U.C. Giesselmann (2008): Rapid assessment of fungal diversity using genetic fingerprints, Poster at the Conference Biodiversity Research - Safeguarding the Future 2008 in Bonn

Links

http://www.solobioma.ufpr.br/