McConkey Kim R, Drake Donald R
School of Biological Sciences, Victoria University, Wellington, New Zealand.
Ecology. 2006 Feb;87(2):271-6. doi: 10.1890/05-0386.
Rare species play limited ecological roles, but particular behavioral traits may predispose species to become functionally extinct before becoming rare. Flying foxes (Pteropodid fruit bats) are important dispersers of large seeds, but their effectiveness is hypothesized to depend on high population density that induces aggressive interactions. In a Pacific archipelago, we quantified the proportion of seeds that flying foxes dispersed beyond the fruiting canopy, across a range of sites that differed in flying fox abundance. We found the relationship between ecological function (seed dispersal) and flying fox abundance was nonlinear and consistent with the hypothesis. For most trees in sites below a threshold abundance of flying foxes, flying foxes dispersed < 1% of the seeds they handled. Above the threshold, dispersal away from trees increased to 58% as animal abundance approximately doubled. Hence, flying foxes may cease to be effective seed dispersers long before becoming rare. As many species' populations decline worldwide, identifying those with threshold relationships is an important precursor to preservation of ecologically effective densities.
珍稀物种发挥的生态作用有限，但特定的行为特征可能使物种在变得珍稀之前就倾向于功能性灭绝。狐蝠（果蝠科）是大型种子的重要传播者，但据推测它们的传播效率取决于能引发攻击性互动的高种群密度。在一个太平洋群岛，我们在一系列狐蝠数量不同的地点，量化了狐蝠传播到结果树冠层之外的种子比例。我们发现生态功能（种子传播）与狐蝠数量之间的关系是非线性的，且与该假设一致。对于狐蝠数量低于阈值的地点的大多数树木，狐蝠传播的它们处理过的种子不到1%。高于阈值时，随着动物数量大约翻倍，从树木处传播出去的种子比例增加到58%。因此，狐蝠在变得珍稀之前很久可能就不再是有效的种子传播者了。由于全球许多物种的种群数量在下降，识别出具有阈值关系的物种是维持生态有效密度的重要前提。
