Ardelean, Gavril (szerk.): Satu Mare. Studii şi comunicări. Seria ştiinţele naturale 6. (2005)

The epigeic spider communities (araneae) of three winter wheat fields in Gherla region (Cluj district)

Satu Mare - Studii şi Comunicări Ştiinţele Naturale — Voi. VI (2005)

The dominancy of the frequent agrobiont species in the different rows of the three sampling sites was calculated (Tab. 2). While Pardosa agrestis seemed to show margin preference, Pardosa prativaga was consequendy more frequent in the middle of the field than in the margin zone. Neither clear margin preference, nor clear field preference was found in the case of Xjsticus kochi, Trochosa ruricola and Oedothorax apicatus. The structure of the three investigated spider community can be characterized by a distorted dominancy structure due to the eudominancy of the agrobiont species Pardosa agrestis.

The adjacent margin seems to be a more dense and rich habitat increasing the diversity and abundance of spiders and other predatory insects (Alderweireldt 1993, Kromp & Steinberg 1992, Luczak 1979, Tóth & Kiss 1999). In our field study the adjacent margin (contact zone between the winter wheat and alfalfa field) can be characterized with a strong dominance of weeds and alfalfa from the neighbouring fields.

The diversity analyses reveal a high diversity of the margin zone (Fig. 2). Iklod 3 sampling site which was the weediest in every sampling row had almost the same three diversity profiles. In the case of Livada

1 we observed a gradually increasing density of the vegetation (winter wheat and weeds) from the middle to the margin of the field due to the herbicid treatment in spring. This gradually increasing vegetation density might be the reason of a greater diversity in spider community. On the sampling site Iklod 2 the diversity profile of the margin row was clearly separated from the diversity profiles of another two rows. In this site the winter wheat field had only the margin row dominated by weeds in combination with alfalfa presumably because of the manual weed management.

Epigeic spider fauna and community structure of these small sized winter wheat fields and their margin zone proved to be very similar to Eastern European agricultural areas. Our results confirm the eudominancy of Pardosa agrestis and other four agrobiont species in Romanian agroecosystems as well i.e. they were dominated by the same agrobiont spider species as in Hungary and Slovakia, which are capable to survive in these periodically disturbed habitats.

Fig. 1. The dominancy structure of the spider communities.

43