S. Mahunka szerk.: Folia Entomologica Hungarica 52. (Budapest, 1992)

Discussion Odúm (1969) summarized the changes in the ecosystems during an ecological succession. According to structure parameters of communities, such as species diversity, number of layers and spatial heterogeneity, values are higher in the mature stages than in the developmental stages. Number of studies have pointed out that vegetation succession has strongly affected the structure of insect communities. The organization of early colonizing plant and insect communities has been debated by Simberloff (1976), and expected interactions in mature communities have been tested by Lavvton and Strong (1981). Southwood et al. (1979) concluded, that in early succession, insect diversity was strongly associated with plant diversity, but in the later stages structural attributes of the vegetation (with both spatial and architectural components) became increasingly important. Hendrix et al. (1988) found that the earliest stages of succession display the dominance of phytophagous insects. In the present study the majority of Orthoptera species were phytophagous, mostly belonging to the family of Acrididae. There were detected significant differences between the pairs of the three dolomitic plant associations according to the structure parameters of grasshoppers communities. Based on the results I stated the following: (1) The neighbouing sites showed higher similarity to each other than to the isolated sites. (2) Although the vegetation structure of the north-facing closed grassland is much more similar to the well developed steppe meadow, the structure of its Orthoptera community is rather similar to that of the open site. (3) The grasshopper communities of the open grasslands (open grassland, and steppe meadow) showed a high correlation to the structure of vegetation. This result agrees with the findings of Southwood et al. (1979). They reported that species richness, diversity, abundance, and life-history strategies of Heteroptera and Coleoptera taxa changed in a systematic way during the development of habitat. In cases of the south-facing plant associations, the open grassland gradually develops to the steppe meadow. According to Odum's model of succession (Odum 1969), in these plant associations the Orthoptera communities also show developmental differences: in the steppe meadow the structure of the Orthoptera community is more complicated (higher in species number and diversity values) than that in the open grassland. Brown and Hyman (1986) revealed a similar close relationship between plants and phytophagous beetles throughout the ecological succession on sandy soil, from the bare ground through permanent pastureland to birch woodland. In the present study the north-facing closed grassland has a different microclimate from the southern open grasslands and this is reflected in the structure of the Orthoptera community. Acknowledgment - I thank Cs. Moskát for his advice during the study, and A Báldi and Z Waliczky for their assistance with data collection. I thank Z Varga for helpful comments on the manuscript. This study was made within the framework of the "Succession project", an OKKFT programme of the Hungarian Natural History Museum supported by the Hungarian Academy of Sciences. Appendix List of grasshopper species collected on dolomitic grasslands in the Buda Hills, in 1989.