S. Mahunka szerk.: Folia Entomologica Hungarica 54. (Budapest, 1993)

may similarly help settling down. For the invertebrates of the urban ecosystems, and for the spiders within that, air pollution and mechanical disturbing are the two most significant troubling factors (Shaefer and Koch 1979). In the case of soil fauna the mechanical effects are obvious, while, the foliage dwellers can only be affected by air pollution and change in the climate of the town, which, similarly, may be responsible for changes in foliage community. Clausen (1986) examined the effect of air pollution on spiders. Sulphur dioxide (SO2) definitely has a negative effect on the species number and density of spiders. Spiders react with varying tolerance to lead burden, so the relative frequency of those less sensitive (e.g. Clubionidae) can increase in more polluted areas (Clausen 1986). Foliage community can indicate environmental changes directly and indirectly, in this way they can indicate: a/ the effect on changes in habitat structure caused by air pollution, which was proved by Gunnarsson's experiments (1988, 1990), b/ the relation of the prey animals abundance and air pollution (with the vegetation in the background as the fitomass may also influence the abundance of its consumers), c/ by their own tolerance, the concentration changes of certain pollutants, such as SO2, Pb, or the climatic conditions of a town. Clausen (1986) assumes that the varying SO2 sensitivity found in different examinations comes from the indication through prey animals. Of spiders as predators besides accumutalion through the food chain, direct accumulation can also be characteristic. They, just like lichen, can accumulate lead, a significant part of the heavy metal gets access to their organism through breathing (Clausen 1986). A relatively small scale lead accumulation of Clubonidae family, shown by Bengtsson and Rundgren (1984) can be explained by their nocturnal activity. The intensive daytime intake of air pollutants, first of all the exhaust gases from traffic, may be of greater volume, while nocturnal species are active and perform more intensive activity in a relatively cleaner environment (prédation, breathing). Among the results, the abundance fluctuation of Theridiidae family along the transects of the town deserves attention. The relative common frequency shows an important growth going towards the town centre (N-S transect). The same tendency is found going from SW to NE. The abundance of the families again grows in the eastern part of the town, where sampling was made in the industrial district (biotope 11), and from trees along the busiest main thoroughfare of the town (biotope 10) (map 1). The xerobiont, -phil character of the family Theridiidae and its certain species is well known (Szinetár 1988, Scheidler 1990). On this basis the above distribution can be well understood (Fig. 3), and can be interpreted as a fact indicating the town's climatic features. All the same, an increased tolerance of the family to air pollutants (e.g. SO2) may also be assumed. With the Salticidae we found a tendency much contrasting to the family Theridiidae (Fig. 2). They are nearly absent from the town centre, and their frequency was extremely low in the industrial district and in the district with heavy traffic. Besides the suburbs, they were only found in larger quantities in biotopes where spruce occupied a relatively spacious, continuous green area (biotope 8, old, closed up cemetery). As regards the Salticidae family, without further examinations die evidence remains insufficient as to the cause of die problem found. Anyway, we may assume that, besides climatic changes, air polution may also cause drop in the specimen number of the Salticidae in the biotopes of the town centre and the district with increased traffic. Nyffeler (1982) examining agricultural plants found that antropogenie causes may result in considerable reductions in the frequencies of some families, such as Salticidae, compared to natural biotopes. In agricultural areas, first of all mechanical effects (cultivation of the soil, mowing) may be involved, while, in our case, in the town biotope we examined, the phenomenon may have relation in most cases only with the quality of the air.