Bond W J, Midgley J, Vlok J
Saasveld Forest Research Centre, SAFRI, P/Bag X6515, 6530, George, South Africa.
Oecologia. 1988 Dec;77(4):515-521. doi: 10.1007/BF00377267.
According to the equilibrium theory of island biogeography, insularisation will lead to species loss from habitat remnants. Extinctions will continue untill species number equilibrates at a level appropriate for the size and isolation of the island remnants. We tested whether insularisation leads to species loss by comparing plant species numbers on islands of fynbos shrublands surrounded by Afrotemperate evergreen forest with extensive "mainland" tracts of fynbos. Species area curves for islands and subsamples of mainland had significantly different slopes (z =0.43, z =0.16). Small islands had the fewest species (less than one fifth) relative to mainland samples of similar size. The species area curves intersect at 590 ha so that reserve sizes of this order of magnitude are needed to avoid species losses relative to extensive areas of fynbos.We compared traits of species on islands and mainlands to determine processes most affected by insularisation. Island floras did not differ from the mainland in the mix of dispersal types, pollinator syndromes or proportion of dioecious species. Islands did have significantly fewer species of low stature and significantly more species that survive fire only as seed and not by resprouting. We infer that the main cause of species loss is change in disturbance frequency. Islands have fewer fires and lose species dependent on frequent fires. We predict that island effects could be reduced by judicious fire management of small reserves.
根据岛屿生物地理学的平衡理论，岛屿化会导致栖息地残余物种的丧失。物种灭绝将持续，直到物种数量在一个与岛屿残余的大小和隔离程度相适应的水平上达到平衡。我们通过比较被非洲温带常绿森林环绕的开普植物灌木丛林地岛屿上的植物物种数量与大面积“大陆”开普植物区域的物种数量，来测试岛屿化是否会导致物种丧失。岛屿和大陆子样本的物种面积曲线斜率显著不同（z = 0.43，z = 0.16）。相对于类似大小的大陆样本，小岛屿的物种数量最少（不到五分之一）。物种面积曲线在590公顷处相交，因此需要这个数量级的保护区面积，以避免相对于大面积的开普植物区域出现物种丧失。我们比较了岛屿和大陆上物种的特征，以确定受岛屿化影响最大的过程。岛屿植物区系在传播类型、传粉者综合征或雌雄异株物种比例的组合上与大陆没有差异。岛屿上确实显著缺少矮生物种，且显著有更多仅以种子而非通过萌蘖在火灾后存活的物种。我们推断物种丧失的主要原因是干扰频率的变化。岛屿上的火灾较少，依赖频繁火灾的物种会消失。我们预测，通过对小型保护区进行明智的火灾管理，可以减少岛屿效应。
