Food preferences and mode of reproduction of oribatid mites along a land use gradient

Soil samples were taken in forests along a land use gradient. The thickness of the litter layer differs between forests and will be used as a measurement for resources. Sex and species identity of sampled oribatid mites were determined. Subsequently the sex ratios were correlated with the amount of resources and oribatid mite density. Stable isotope ratios of 15N and 13C of single species were measured to classify their trophic position. In cooperation with the projects ‘LitterLinks‘ and ‘ModelWeb‘, the data will be merged for characterizing and modeling a soil food web. For investigations about the influence of resources on oribatid mite communities and their mode of reproduction on bark, fertilization with carbon and nitrogen will be applied. The species communities were sampled after different time spans of continuous fertilization.Erdmann et al. (2007) highlighted the difference of species identities on bark and in soil habitats. Oribatid mites on bark are associated with the growth cover and therefore with the food resource. This implies the hypothesis that oribatid mites in soil and on bark live in the respective habitat and use their specific food. To test this hypothesis, feeding experiments will be conducted in the laboratory. The Project ‘SoilAlgae‘ provides algal cell cultures. Typical oribatid mite species from bark and soil will be fed with typical algae each from soil and above ground habitats. We hypothesize that mites feed specific and prefer the algal species from their corresponding habitat.To test food preferences in the field, oribatid mites were collected (in cooperation with Steffen Boch, project Botanik) on bark and lichens. We want to proof if abundances of oribatid mites correlate with secondary compounds produced by lichens which potentially act as repellents.It is assumed that the interaction between resources and oribatid mites is an important factor which drives evolution. Especially the evolution of arboricolous and lichenivorous oribatid mites could be pushed by ecological factors.We constructed a phylogenetic tree for soil living and arboricolous mite species. The colonization of bark habitat occurred multiple times and convergently in the evolutionary younger taxa. These taxa consist mainly of strong sclerotized species which reproduce sexually. The data support the thesis that ecological factors were most important for the multiple colonization of bark by oribatid mites (Maraun et al. 2009).