稻田蜘蛛生态位变化及杀虫剂对捕食功能的影响

Influence of Seasonal and Daily Changes of Spatial Niche of Spiders in Paddy Field and Two Insecticides to Spatial Niche and Predatory Function

通过对稻田各蜘蛛和害虫空间生态位的研究发现 ,空间生态位宽度随季节而变化 ,狼蛛的生态位宽度值逐渐变大 ;肖蛸两头高中间低 ;微蛛在 7月下旬最大 ;球腹蛛在 8月下旬 9月上旬最大。各类群的数量是影响该类群空间生态位的重要因素。空间生态位具有明显的日节律 ,狼蛛在 7～ 8月份以中午最宽 ,微蛛变化不大 ;肖蛸在 7～ 8月份下午的生态位宽度值大于上午 ,9月份则上午大于下午 ;球腹蛛 7～ 8月份以上午为最大 ;跳蛛下午大于上午。不同种类农药在一天中不同时间施用对各类蜘蛛存活率及捕食功能的影响不同 ,杀虫双上午用药对蜘蛛集团的捕食功能减退率影响较小 。

The experiment was conducted in the experimental farm of Yangzhou Agricultural School. Rice was transplanted on 21, June 1999. A plot (0\^1333hm\+2) was selected for spatial niche observation, and another four plots, 0\^01667hm\+2 for each plot, were used for comparing the effect of spraying of two insecticides, bisultap and methamidophos, at common dosage at different time on niche breadths of spiders and planthopper and predation function of spiders. Rice plants were distinguished into three resource grades, upper leaf layer, stem and base. Number of spiders and planthoppers was recorded on schedule. Number of various species in leaf, stem and base was observed in morning (6∶00), at noon (12∶00) and in afternoon (18∶00) at three selected stages of rice, 21 July, 22 August and 10 September (representatives of early\|, middle\| and late\|stage of rice, respectively). The niche breadth ( Bn ) was measured using the equation index, Bn=1∑si=1P\+2\-i(s), where Bn is the niche breadth of observed species, P i is the proportion occupied by the species in total resource series, and s is total resource series number. Measurements of similarity were calculated using Schoener index of proportional similarity of niche, C\-\{ij\}=1-12∑sh=1|P\-\{ih\}-P\-\{jh\}| , where C ij is the measurements of similarity of niche, P ih is the proportion occupied by species i in resource series h, P jh is the proportion occupied by species j in some resource series h . Function decrease rate was also used to evaluate the effect of spraying two insecticides on predation function of spiders, FD t=D t+(1-D t)(F ck -F t)/F ck , where FD t is the function decrease rate of natural enemies at time t, D t is the mortality rate of natural enemies at time t, F t is the predation function of surviving natural enemies at time t after insecticide application, F ck is the one of control (CK), meanwhile, the spiders were considered as a predator guild, thus the function decrease rate of the guild after insecticide application ( FD ) can be obtained by the following equation, FD=∑si=1a\-i×FD\-t , where a i is the predation share of species i in the whole predation number of the guild, calculating by the following equation, a\-i=N\-\{a\-i\}×B\-i∑ni=1N\-\{a\-i\} , where N a\-i is the mean predation number of the spider i in the field, which was the predation number in disc equation of function response when N is 10, B i is the relative abundance of the species i in the guild. The results were as follows: The spatial niche breadth of spiders and planthopper varied with season, but different species had different regularity. The trend of the spatial niche breadth of Micryphantidae and planthopper was consistent before 22 august, but opposite after that. That of Lycosidae increases gradually as rice development, but that of Tetragnathidae was just opposite; that of Tetragnathidae decreased continually before 22 august, but there was a peak on September 1, and declined quickly. That of Theridiidae reached the maximum during late august to early September. Change of spatial niche in a day varied with species. The spatial niches of planthopper and Theridiidae were broadest in morning, narrowest in afternoon; that of Saltidae was narrowest in morning, but broadest in afternoon; Tetragnathidae was similar with Saltidae during July to August, but inversely during September. However, that of wolf spiders was narrowest in morning and broadest at noon during July to August, but narrowest at noon during September; that of Micryphantidae and Araneidae was changeable, without obvious regularity. Proportional similarity index ( C ij ) was an important index reflecting the species similarity for resource utilization. The bigger the value is, the bigger the similarity extent of the distribution in resource series between species was. The index of wolf spiders was smaller than other species, but other species had bigger ones w