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T a b l e 8. Correlation coefficients (r) (analysis of covariance) between total spider density and environmental factors (Period III). Variable r F P Soil moisture 0.337 67.292
which can determine spider abundance and community composition (DE KEER et al., 1989; RUSHTON, EYRE, 1992; MAELFAIT et al., 1997; MERKENS, 1997). The other important factors influencing spider density are management practice (DUFFEY, 1978; DE KEER et al., 1989; DECLEER, 1990; RUSHTON, EYRE, 1992; MAELFAIT et al., 1997; MERKENS, 1997) and plant complexity (DUFFEY, 1978). Authors have shown that certain species prefer managed or unmanaged patches. In our data, the negative effect of mowing and grazing, on total spider density and species richness is very clear. According to the results of this paper, plant species diversity is less important for the diversity of spiders, than is plant complexity (abundance of microhabitats in an area). This result is in an agreement with UETZ (1979), who showed, experimentally, the relationship between spider density and litter thickness. He considered litter complexity to be the primary factor influencing the structure of spider communities. We observed a similar importance of the moss and litter layer in the range of grasslands analysed in this paper. Properties of dominant species In all the grasslands compared, the family Linyphiidae was of greatest significance. Different members of this family dominated in natural and managed grasslands, and there were only a few common species (Appendix 1). Those dominating in managed grasslands can be characterised according to HÄNGGI et al.(1995), as an eurytopic species. They are abundant in arable fields, urban areas, fens, shrubs, permanent meadows and leys. The species dominant in natural grasslands were categorised by HÄNGGI et al. (1995) as occurring in raised bogs, fens, wet meadows and the shores of inland waters. Among them some endangered species were found. Mobility index 6 5 4 3 2 1 0 0,2 NB3 1 0,3 NA 2 0,52 NB1 3 0,92 MB1 4 1,09 MA1 5 Intensity of management 4,28 MC3 6 3,32 MB2 7 5,29 MC1 8 Fig. 1. Relationship between mobility index (ratio of number of ind. captured per pitfall trap per 10 days to number of ind. per m 2 ) and intensity of grassland management. 1-8 – study sites; symbols A,B,C denote peat origin (explained in table 1), N – natural grasslands, M – managed grasslands. 61
Page 1 and 2: Ekológia (Bratislava) Vol. 19, Sup
Page 3 and 4: collected predominantly at the wate
Page 7 and 8: for use as hay meadows and pastures
Page 9: T a b l e 7. Number of spiders belo
Page 13 and 14: A p p e n d i x 1. Pardosa amentata
Page 17 and 18: Beside biotopes and vegetation, par
Page 19 and 20: The majority of harvestmen recorded
Page 21 and 22: percentage of endangered species 80
Page 23 and 24: Discussion The species spectrum of
Page 25 and 26: T a b l e 4./Cont. Alnus Salix s-me
Page 27: References BUCHAR, J., THALER, K.,
Page 30 and 31: Fig. 1. The study islands in the so
Page 32 and 33: T a b l e 2. The most abundant spid
Page 34 and 35: Worth mentioning are also L. decolo
Page 39 and 40: substrate. Altogether 120 soil samp
Page 41 and 42: istence of many Gamasina species, w
Page 43 and 44: T a b l e 2. Riga Gulf Baltic Sea N
Page 45 and 46: Baltic Sea Coast and Riga Gulf Coas
Page 49 and 50: T a b l e 1. List of species collec
Page 51 and 52: T a b l e 1./3 Cont. Species S-1 S-
Page 53 and 54: References BUCHAR, J., 1992: Koment
Page 57 and 58: some specimens (non-quantitative sa
Page 59 and 60: Web-structure and building behaviou

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