S. Mahunka szerk.: Folia Entomologica Hungarica 56. (Budapest, 1995)
sities. After twenty years the density of grasshoppers were much higher on the heavily than on the lightly grazed sites. Miller & Onsager (1991) did not find direct effect of cattle grazing on grasshopper populations. Fielding & Brusven (1993) confirmed that heavy disturbances, livestock grazing, wildfire and some other perturbances caused significant changes in the densities and diversities of grasshopper communities. Gibson et al. (1992) emphasised that different groups of invertebrates respond to grazing in different ways and to different degrees. The intensive grazing could exert effects not only on the community structure and species composition of the different arthropod groups, but on their life-cycle too. Different life-cycles of spiders have been found by Maelfait & De Keer (1990) on an intensively grazed pasture and its border zone. The herbivorous Orthoptera species have an important role in the ecosystem as primary consumers, however, according to the Rodell's (1977) simulation models, the grasshoppers' significance is not always evident in the grassland ecosystems. The model showed that when the plant production is small early in spring or in fall, grasshoppers may constitute an important regulating factor on new plant production, even at low grasshopper densities. But Parmenter et al. (1991) suggested that in the absence of significant grazing of livestock, the omnivorous insects and herbivorous grasshoppers provide an important ecological pathway for energy flow. Because of the high consumption rate of gradating herbivorous grasshoppers they might cause considerable damage in pastures and agricultural crops (Sanchez & Wysiecki 1990). Vertebrate grazing might exert different effects on insect communities. One hypothesis predicts that grazing changes the densities and/or species composition of invertebrate communities, and both of them are decreasing; the other suggests that the microclimate change after grazing is appropriate for many invertebrate species and therefore their densities and/or species number increase. We carried out this study in order to examine the effect of moderate grazing of sheep on grasshopper communities in the Mecsek Mts in Southern Hungary. The first hypothesis is confirmed by our study, but we could not find significant differences in the species composition of the grasshopper communities of the disturbed (grazed) and undisturbed (not grazed) sites. STUDY SITES The study sites are situated in the southern part of Hungary, in the Mecsek Mountains. Our study areas were selected in the western part of the Mecsek, near the village Orfű, (46°10'N, 18°05'E). The total area of the Mecsek Mts is about 1000 km 2 . The basic rock of the mountains is mainly limestone, but volcanic basic rocks are also found there. The climate in this part of the country is sub-Mediterranean with 22-23 °C average temperature in July and 711 mm average annual precipitation parameters. The western part of the Mecsek Mts comprises moderately cool and humid grasslands and therefore there are several wet meadows that highly are appropriate for grazing. Three different study sites were selected: one of them was marked out in an undisturbed steppe-meadow (Festuco rubrae-Cynosoretum; subsequently SM) habitat, and the others were a dry pastureland (Agrostidetum tenuis; PL) and an abandoned alfalfa site (Plantagini-Medicaginetum; AL). Either of the latter sites were grazed by sheep twice a
