GRASSY FIELD MARGINS AND ARTHROPOD DIVERSITY - A CASE-STUDY ON GROUND BEETLES AND SPIDERS IN EASTERN AUSTRIA (COLEOPTERA, CARABIDAE, ARACHNIDA, ARANEI, OPILIONES)

In 1983, the species composition and diversity of carabids, spiders and harvestmen was investigated by pitfall traps in a grassy field margin and in an adjacent, biologically farmed wheat field at Obere Lobau, Vienna, Austria. The carabid fauna of both habitats was diverse; it showed a high degree of similarity, the abundant species in both habitats being represented by typical field species. Only Metophonus spp. predominantly lived in the margin. Numerous species of different habitat origin occurred in the margin at low abundances indicating transitional stay rather than permanent populations. In contrast, the spider fauna showed a low degree of similarity, with few agrobiotic species strongly dominating the field fauna. In the field margin, a rich spider fauna containing rare elements indicates the general importance of grassy margins for nature conservation. The apparently low faunal exchange of spiders between the two habitat types is discussed. Harvestmen occurred mainly in the field margin; only two thermophilic species invaded the field. Seasonal fluctuations in the trapping numbers of Bembidion lampros, Platynus dorsalis and Brachinus explodens are interpreted as indicating migrations between field margin and field. Poecilus cupreus and certain other field species, however, apparently spend their entire life cycle in the field. The possible function of field margins for restoration of carabid losses due to impacts of intensive cultivation is discussed. It is concluded that both grassy field margins and sustainable farming methods, in particular biological farming, are necessary to maintain a diverse predatory arthropod fauna in agroecosystems.