Research

Structure of soil animal food webs
Links between the below- and aboveground system
Parthenogenesis vs. sexuality in soil animal species

Focus of the group are belowground communities which are investigated from the soil animal perspective. Our aim is to understand structuring forces in soil animal communities and to uncover the role of belowground animals in soil processes, plant performance and herbivore development. Transcending the ecological time scale, we investigate evolutionary processes in recent and deep in time soil animal communities.
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Structure of soil animal food webs

Understanding the trophic organisation of decomposer systems is the prerequisite to uncover the driving forces for species composition and the causal mechanisms responsible for the spatial and temporal variation of soil animal populations. A wide spectrum of animal groups is investigated, with a focus on earthworms, oribatid mites, springtails and protozoa. Methods include the quantitative measure of density and biomass of soil animal populations and microorganisms, the analysis of natural variations in stable isotope ratios (¹³C, ¹⁵N) and the use of lipids and gene fragments as markers in food chains.
Research topics include:

Food relationships and food web structure
Biodiversity of soil animal communities
Interrelationship between plant and soil animal diversity
Microbial - faunal interrelationships
temperate vs. tropical soil food webs

Links between the below- and aboveground system:

Two links are investigated: (1) interactions mediated by changes in plant growth (decomposer - plant - herbivore pathway) and (2) interactions mediated by generalist predators (decomposer - generalist predator - herbivore pathway). In the first three energy channels are distinguished: primary decomposer, bacterial feeder and fungal feeder channel. Focal groups are earthworms as primary decomposers, protozoa and nematodes as bacterial feeders and collembola and oribatid mites as fungal feeders. Focal groups of the second link are spiders, carabid and staphylinid beetles. Methods include microcosm and perturbation experiments, use of radiotracers (¹⁴C) and stable isotopes (¹⁵N, ¹³C), analyses of microbial communities (respiration, biomass, nutrient status, phospholipid fatty acid patterns, in situ catabolic diversity) and analysis of the chemical and genetic response of plants to rhizosphere interactions. Some further explanations are given here. Topics investigated include:

Relationship between biodiversity and ecosystem functioning (decomposition, mineralization, resilience)
The role of soil animals for ecosystem processes, plant performance and herbivore development
Rhizosphere interactions
Interrelationship between above- and belowground biodiversity
The role of decomposer animals as supplementary food for generalist predators above the ground

Parthenogenesis vs. sexuality in soil animal species:

A large number of soil animal species reproduce by parthenogenesis, including earthworms, enchytraeids and collembola, but is most pronounced in oribatid mites with an estimated 10% of the species being parthenogenetic. Factors responsible for the high incidence of parthenogenesis in soil are largely unknown. Our studies focus on oribatid mites because of their exceptional high rate of parthenogenesis and their amazing life histories. As basis to understand the evolution of parthenogenesis phylogenetic relationships of oribatid mites are investigated. Molecular markers employed include ITS1, COI, COII, 18S rDNA, HSP82 and EF1α. Further, models on the evolution of parthenogenesis vs. sexuality are developed integrating an ecological point of view. Major research topics include:

Genetic variability in parthenogenetic vs sexual soil animal species
Phylogenetic relationship in oribatid mites
General purpose genotype vs frozen niche variation model
Driving factors for sex ratios
Dynamics of transposable elements
Ecological models on the evolution of sex