| From July to August 2002 and from July to September 2003, investigations of spiders were made in different habitats in prairies of north Hebei. The spots selected for the study are located in the following counties: Zhangbei County (Anguli Lake, Caibei prairie), Shangyi County (Dayingpan countryside, Badaogou countryside), Kangbao County (Yanyoufang countryside, Sanmianjinag prairie, Xinminbao countryside), Guyuan County (Gaoshanbao countryside, Pingdingbao countryside, River Shandianhe), Fengning County (Datan countryside, Yuershan prairie): Weichang County (Jixie woodland, Yudaokou countryside). During the investigations spiders were were collected at random and quantitatively. Totally 8021 specimens were collected belonging to 125 species, 62 genera and 16 families. Among them the species are Xysticus audaxoides new to science, and three remain to be identified.The community structure and diversity of spiders in the prairie of the north Hebei are studied systematically for the first time. Not only the composition character of populations including the dominant species, the common species, the rare species and the characteristic species(Lie W.L.,1999), but also the density of population was analyzed in the community structure research. The change of parameters and the dominant species were also analyzed. In the study of diversity some important parameters, such as richness index, Shannon-Wiener's diversity index (H'), evenness index (J) and Simpson's dominant index were used (C). Furthermore, the main ecological factors affecting the composition of soil communities were analyzed or discussed. The results show:1. The main dominant families are Lycosidae, Araneidae, Thomisidae and Theridiidae.2. The prairies can be classified into two types: man-made prairie and natural one. Difference between the compositions of different spider communities is very large because of the varied vegetations, the human activities and climatic condition. There are many characteristic species in the communities. The natural prairie in well conditions has more species of the spider than the man-made one.3. Spiders were most sensitive to different niches, the more complicated habitats the more species and the more abundant diversities. The diversity index is higher in the prairie of mixed planting than the prairie of single planting. The diversity index is higher in natural prairie well protected than the prairie over-depastured.4. The diversity index was changing with the growth of grass in man-made prairie. Diversity index was higher in the middle and later growth stages of herbage in the pastureland, and was lower after harvesting. The dominant index is in negative correlation to diversity index.5. The main dominant species are Theridion impressum, Xysticus striatipes, Pardosaastrigera and Neoscona adianta etc. The species and amount of the dominant species were changing with time. The amount of Theridion impressum, a dominant species, in man-made prairie was higher in early July; amount of Xysticus striatipes higher in August; and the species Pardosa astrigera became the richest in number after harvesting.6. Based on the analyse of cluster of the spider commmunities in prairies indicate that the prairies can be classified into four typies: (1) Prairie with Melilotus alba, Astragalus adsurgens and the prairie protected; (2) Prairie between woods and wet prairie; (3) Prairie with Elymus dahuricus and Elymus chincnsis', and (4) degenerating prairie.7. The structure and diversity of communities of spiders appeared to be strongly affected by various factors, such as vegetation type, climatic condition, food, interruption, spatial heterogeneity etc. Among them, food and interruption were two main factors.
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