S. Mahunka szerk.: Folia Entomologica Hungarica 53. (Budapest, 1992)

FOLIA ENTOMOLOGICA HUNGARICA ROVARTANI KÖZLEMÉNYEK LUI 1992 139-153 Drosophilid assemblages in mountain creek \alle>s in Hungary (Diptera: Drosophilidae) I.* By L. PAPP (Received April 17, 1992) Drosophilid assemblages in mountain creek valleys in Hungary (Diptera: Drosophilidae) I. - In 1988-90 apple-bait collections of Drosophilidae were made in four sites of low mountain creek valleys in N and NE Hungary (yielding more than 9,000 ex.). Representatives of 40 species were caught (31, 31, 36 spp./year), some of them are new to Hungary [1988 (n= 12): 6 to 18 spp./sample, 1989(n= 13): 7 to 16 spp./sample, 1990(n= 10): 5 to 21 spp./sample]; 8, 8, and 9 spp. were caught only once, 6, 5, and 7 spp. were represented by a single specimen. The population frequencies in the assemblages changed profoundly from one year to another as a natural process. The population size ratio of the rare and the dominant species is supposed to be 1 to 10

3-10

4 or even higher. The S.-W. diversity index values are not high, evenness is highly variable (from medium to low). The differences in the assemblages of the collecting sites were analysed by some quantitative methods (Berger-Parker index, similarity indices: Czekanowski, Renkonen indices, dendrograms of the similarity indices). It was found that a good part of the drosophilid species is so rare that only an indefinite part of the extant rare species is to be detected at all in a given area. However, ratios of the populations of the dominant-subdominant, constant-subconstant species are hypothesized, with which more non-detected species are to be expected than behind population frequencies deformed by human activity. INTRODUCTION This study was made in order to test a well-known and very simple principle: any disturbance in an ecosystem is likely to be indicated earlier and more efficiently by changes in the structure of a commumty/communities rather than by abundance changes or presence/absence relations of individual species. We selected two test-groups of flies: the so-called synanthropic flies (collections made with Gregor-Povolny's traps baited with human feces, results published elsewhere) and the drosophilids. Drosophilids were chosen because the Hungarian fauna is rather well known (see Papp and Pecsenye 1988) and the quantitative methods for population analysis are comparatively well elaborated (Bächli 1979). The extensive literature on the studies on the Palaearctic drosophilids is summarized by Bächli and Rocha Pité (1982). Originally we intended to assess the deformation of the community structure of *Supported by the Ministry of Environment and Water Management (No. 146/AK (177/88.)).