Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 83. (Budapest 1991)

Kisbenedek, T.: Habitat preference and seasonality of spider (Araneae) communities in dolomitic grasslands

the cases. During the whole season the majority of both nocturnal and diurnal species are present, but in certain parts of the season the peak of their activity density shows more differentiation. On the basis of the curves 3 species with high activity were identified among the diurnal species (Zodarium, Alopecosa sulzeri, A. accentuata) (Fig. 7). All of them show the maximum activity in the first half of the season (from the middle of spring to midsummer). In the second half of the season (from midsummer to the middle of autumn), they show lower but constant activity. There are two species (Zelotes electus, Zodarium germanicum) which are active only in the first half of the season, but their activity is significantly lower than that of the former species. The changes of activity in the nocturnal species show smaller amplitude but there are 3 species which appear significantly in one or another part of the season: 2 species (Agroeca pullata, Nemesia pannonica) in the early part, and 1 species (Coelotes longispina) at the end of the season (autumn). In the middle of the season (from the end of spring to the end of summer), 1 species has a permanent occurrence (Drassodes lapidosus), while the distribution is steady during the whole season for 2 species (Harpactes rubicundus, Zelotes petrensis) (Fig. 8). Dominance values also characterize the seasonal distribution of species. We can find minimum number of species (2) with high dominance values (D % = 10) per month in July. One of these is a diurnal species (Zodarium sp. D % = 53.22 %), and the other is a nocturnal one (Drassodes lapidosus, D % = 11.67 %). The maximum number appears in April having again 50-50 per cent in the activity guild (Table 5/a, Sib). DISCUSSION The guild of wandering hunters in the dolomite grass studied can be separated into 2 further guilds, namely the guilds of diurnal and nocturnal hunters. There is a strategical difference between the two guilds in habitat preference and seasonal distribution of abundance. The dominant diurnal species prefer the open grass A and B, which provide a more patchy, horizontally heterogenious environment. In these species the peaks of activity show similar distributions. The preferences of nocturnal hunters are lower than that of the diurnals but among the former species there are larger differences in the seasonal distributions. Habitat preference and seasonality also represent significant competition reducing efforts in other insect populations, like in beetle (SCHULTZ 1989), and fly (HANSKI 1987) communities. To study competition well-planned experiments are neccessary where the resources or the sizes of the populations of species has to be manipulated in the field (NAEEM 1990, LOREAU 1990). In absence of such studies for spiders, only indirect evidence can be gained for the competition avoiding strategies (TURNER & POLIS 1979, POST & RIECHERT 1977). Among recent studies primarily those manipulating habitat structure show direct or indirect effects of the structure of vegetation on the structure of spider community (COLEBOURN 1978, GUNNARSSON 1990, NENTWIG 1988, RIECHERT & BISHOP 1990).