The insect assemblage in water filled tree-holes in a European temperate deciduous forest: community composition reflects structural,trophic and physicochemical factors

(1) A study of the metazoan community occurring in water-filled tree-holes in southern Germany has been performed to determine the relationships among the key species of arthropods found within the community and a range of structural, physical and chemical factors, using multivariate techniques. (2) Four animal species were sufficiently common to allow identification of the preferred environments for their larvae. The aedine mosquito, Aedes geniculatus, prefers shallow open tree-holes with relatively little leaf litter even though these may represent less permanent water-bodies. The scirtid beetle, Prionocyhon serricornis, occurs in larger, deeper holes with greater amounts of leaf litter and a more predictable aquatic environment, although open water is not a requisite. Larvae of the orthocladiine chironomid, Metriocnemus cavicola, favours shallow more open tree-holes with higher litter content but with sufficient open water to ensure an adequate oxygen supply. The eristaline syrphid, Myatropa florea, favours shallow, open tree-holes with low litter content. (3) There is no evidence that interspecific interactions affect the distribution or abundance of any of these species. (4) The autecological results are discussed in light of those available for phytotelm dwellers elsewhere. The food-web overall may be interpreted as so simple that it is driven by ‘bottom-up’ environmental factors with no part played by those community-level ‘top-down’ processes that may be adduced for more complex, multi-trophic level webs occurring elsewhere. No “processing chain commensalism” could be found in the arthropod community of the temperate German deciduous tree-hole dwellers. Handling editor: K. Martens