基于群落与种群水平的沙地柠条灌丛“虫岛效应”随林龄的变化

Changes of "arthropod island" along with the age of Caragana shrub in desertified land

以宁夏盐池沙地不同年龄柠条灌丛为研究对象,利用响应比率(Response ratio,RR)和相对互相作用强度指数(Relative interaction intensity,RII),在群落与种群2个水平上分析沙地灌丛"虫岛效应"的变化规律.结果显示:在群落水平上,RR与RII在表征基于节肢动物个体数和丰富度的不同年龄灌丛"虫岛效应"间差异性时完全相同,但在表征节肢动物Shannon指数和均匀度指数时存在较大差异性.在种群水平上表征柠条灌丛"虫岛效应"时RII值反映的类群数超过RR值的17%以上,在24年生灌丛林地达到38%以上,更好地反映了灌丛与节肢动物类群间的作用关系.利用RR值分析群落水平灌丛"虫岛效应",在6年生林地只有节肢动物个体数表现出灌丛"虫岛效应",在15年生林地基于Shannon指数与均匀度指数的灌丛"虫岛效应"显著增强(P<0.05),而基于节肢动物个体数的灌丛"虫岛效应"减弱,但在之后的24年和36年林地基于Shannon指数与均匀度指数的灌丛"虫岛效应"急剧减弱,而基于节肢动物个体数的灌丛"虫岛效应"又逐渐增强(P<0.05).利用RII值分析种群水平灌丛"虫岛效应",不同年龄林地均有超过50%的动物类群受到灌丛影响而呈现出"虫岛"现象,反映了灌丛对节肢动物的聚集作用.本研究表明,响应比率RR在分析节肢动物群落指数效果较好,而相对互相作用强度指数RII可以完整地表征节肢动物种群在灌丛内外的空间分布;随着灌丛年龄增加,灌丛"虫岛"对灌丛间节肢动物多样性分布具有辐射作用,灌丛"虫岛效应"有利于沙化草地生态系统结构与功能的有效恢复.

＂Arthropod island＂ contributed by Caragana shrub was found to play the key role in the structure and function recovery process of desertifided ecosystems. Taking the Caragana shrubs of different ages in desertified land of Yanchi, Ningxia as study models, the response ratio （RR） and relative interaction intensity （RII） were used to discuss the changes of ＂arthropod island＂ along with the age of the shrub at the community and population levels. The results showed that at the community level, when the ＂arthropod island＂ was compared between shrubs of different ages, the RR and RII based on total abundance and richness were the same but the RR and RII on Shannon index and evenness index were completely different. At the population level, RII was found to indicate 17% more arthropod richness than RR. In particular, for the shrubland of 24 years, 38% more arthropod richness was indicated by RII in comparison to RR. It was suggested that RII was a good indicator of interactions between shrub canopy and taxonomical distribution. Based on RR value, only the total abundance indicated an ＂arthropod island＂ in 6-year-old shrubland; in a 15-year-old shrubland, the Shannon index and evenness index indicated a marked （P 〈 0.05） increase of ＂arthropod island＂, while the total abundance showed no differences between shrub-canopy and intershrub values. However, in 24- and 36-year-old shrubland the RR values based on the Shannon index and evenness index declined strongly while that based on total abundance increased markedly （P 〈0.05）. Based on RII value, 50% more arthropod taxa indicated an ＂arthropod island＂, which was characterized by assemblage effect contributed by shrub canopy. In conclusion, RR and RII can be used to quantify ＂arthropod island＂ for community level and population level, respectively. Along with the shrub ages, the ＂arthropod island＂ contributed by the shrub canopy can facilitate the recovery of arthropod diversity outside shrub canopy, thus beneficial for the recovery process of desertified grassland ecosystems.