岛屿栖息地鸟类群落的丰富度及其影响因子

The Richness of Island Habitat Avian Communities and Their Influencing Factors

1 997年 1月至 1 997年 1 2月间 ,以杭州市的园林鸟类群落为研究对象 ,对岛屿栖息地鸟类群落的丰富度与面积、人为干扰、内部结构和周围景观结构等多种因素的关系进行了系统的分析和检验。在杭州市各园林中共观察到 82种鸟类。园林单次调查的鸟类物种数 ( S)与园林全年总物种数 ( Sy)与园林面积 ( A)的最佳回归拟合方程分别为 :S =2 .74 32 A0 .3 84 6,Sy=1 0 .6 5 74 A0 .3 669。杭州市园林鸟类群落物种 -面积关系的成因不支持平衡假说、随机取样假说、栖息地多样性假说和干扰假说 ,岛屿栖息地鸟类群落的丰富度是多因素综合作用的结果 ,包括取样面积效应 (排除了取样面积效应之后 ,小园林具有更高的物种密度 )、栖息地结构的多样性 (其中树种多样性是最主要的影响因子 )、干扰因素、物种因素和研究尺度等几个方面。

The species-area relationship of insular faunas has been described and interpreted for over 70 years, but there is little agreement on its cause. Four processes have been proposed to explain this pattern: the equilibrium hypothesis, the passive sampling hypothesis, the habitat diversity hypothesis and the disturbance hypothesis. In this paper, we assessed the four hypotheses and analyzed the richness of island habitat avian communities and their influencing factors. Studies were conducted at 20 urban woodlots in Hangzhou, China during January to December in 1997. These urban woodlots are well separated from one another, forming isolated patches in urban matrix. Each woodlot was visited twice per month during bird migrant seasons in April, May, October and November, once in the other months. So each woodlot was visited 16 times all year. Twenty habitat variables, including woodlot area, shape, the degree of canopy, leave height diversity, horizontal heterogeneity, connectivity, disturbance level, surrounding, etc., were selected to enter multiple stepwise regression to test their influences on the richness of island habitat avian communities. 82 bird species were recorded at 20 urban woodlots all year. The fit equations of species number of one woodlot in one census (S) and species number of one woodlot all year (S y) with woodlot area were: S = 2.7432A 0.3846 and S y = 10.6574A 0.3669. At the basis of species-area relationship above, we discussed the value of z in the equation of S=CA z and its significance, which has drawn much attention and remains questionable. z was traditionally thought to reflect the degree of isolation of an archipelago. We thought that z in the equation was just a constant and had no biological implication. It was affected by many factors besides isolation. To test the effect of sample size, species-area relationship and species density-area relationship of woodlot avian communities were compared. The results showed that species number increased with woodlot area increasing, while species density decreased with woodlot area increasing, which reveals that under the same sample size small woodlots have more species than large one. The best multiple regression models showed that species number of one woodlot in one census (S) was significantly affected by woodlot shape, tree species diversity, number of street tree strips connected to woodlot, leave height diversity, distance to the nearest woodland larger than 2 hm 2 and density of canopy layer. They explained 68.4% the variation in species number, among which tree species diversity was the most important factor influencing species number (58.3%). Species number of one woodlot all year (S y) was significantly affected by woodlot shape and tree species diversity. The results of multiple regression indicate that besides the effect of sample size there are other factors more important influencing species richness. The avian community richness of Hangzhou urban woodlots were the results of synthesized action of multi-factors, including the effects of different sample size, the habitat diversity, disturbance factors, species factors and the effect of different research scales etc. Some of them significantly correlated with woodlot area. This is one of the causes that species number significantly correlate with woodlot area. Though the results of our studies partly supported the habitat diversity hypothesis and the passive sampling hypothesis, no of the four hypotheses alone could explain the species-area relationship of urban woodlot avian communities in Hangzhou. Natural communities are usually complicated. These hypotheses were raised on special communities and focused on some special habitat factors, so they couldn't explain all communities. Most communities are affected by the synthesized actions of multi-factors. If the conclusion is considered as the synthesis hypothesis, the four hypotheses are the special case of the synthesis hypothesis. Models are the simplification of nature, but ecologists should be cautious to simplification. W