Ecological aspects of development of testacean complexes in nests of Formica lugubris and Formica exsecta (Hymenoptera, Formicidae)

Testacean population in the nests of Formica lugubris and F. exsecta was studied in a spruce forest and in a mixed birch forest. Samples of the nest material (spruce litter and grass fragments) were taken from the surface layers, the inner parts of the nests, and from underlying soil. In all, 33 species of testaceans were identified. The highest species diversity and abundance were observed in the Formica lugubris nests, in the upper layer of the F. exsecta nest, and in the spruce litter. In all the samples, 10 widespread aerophilic and edaphic species (Centropyxis aerophila, C. sylvatica, C. orbicularis, Cyclopyxis kahli, Trinema lineare, and others) were the most common, resulting in a uniform species composition in all the habitats studied. In the presence of the relevant substrate, this group is supplemented by species of appropriate ecological groups (bryophilic, acidophilic, and inhabitants of coarse humus). In the inner part of the Formica lugubris nest, the testacean population is characterized by a very high abundance of Plagiopyxis penardi, whereas the surface layer of the F. exsecta nest is characterized by abundant Cyclopyxis eurystoma and very low species diversity in the inner layers. The initial composition and decree of decomposition of plant remains due to ant activity are considered as the main factors responsible for the testacean species diversity, as well as the availability of substrates suitable for the development of different ecological groups of testaceans.