Density-dependent mortality and the latitudinal gradient in species diversity
Density-dependent mortality and the latitudinal gradient in species diversity
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DOI：
10.1038/nature00809
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发表时间：
2002-06-13
期刊：
影响因子：
64.8
通讯作者：
Beckage, B
中科院分区：
文献类型：
--
作者：
HilleRisLambers, J;Clark, JS;Beckage, B
生态学家长期以来一直认为，密度依赖的死亡率维持了热带地区高度的树木多样性（1-6）。如果物种丰富时死亡率更高，那么更多的稀有物种可以持续存在（1,2,7-9）。密度依赖性致死因子（如宿主特异性捕食者和病原体）可能在热带森林中更为普遍或具有更强的影响，因为它们不受气候因素的限制（1-5）。如果是这样，随着纬度的增加，密度依赖性死亡率的降低可以部分解释树木多样性的纬度梯度（4-6）。这一假设从未得到纬度数据的检验。在这里，我们发现一些温带树种在种子传播和幼苗建立之间经历了密度依赖的死亡率。受影响的物种比例与热带森林相当（6,10-16），无法支持这种机制在热带纬度地区更为普遍的假设。我们进一步表明，在以前的研究中，密度依赖性死亡率被误解了。我们的结果和其他研究的证据表明，在许多森林中，密度依赖的死亡率很重要。因此，除非密度依赖性死亡率的强度随纬度变化，否则这种机制不太可能解释热带森林的高度多样性。
Ecologists have long postulated that density-dependent mortality maintains high tree diversity in the tropics(1-6). If species experience greater mortality when abundant, then more rare species can persist(1,2,7-9). Agents of density-dependent mortality (such as host-specific predators, and pathogens) may be more prevalent or have stronger effects in tropical forests, because they are not limited by climatic factors(1-5). If so, decreasing density-dependent mortality with increasing latitude could partially explain the observed latitudinal gradient in tree diversity(4-6). This hypothesis has never been tested with latitudinal data. Here we show that several temperate tree species experience density-dependent mortality between seed dispersal and seedling establishment. The proportion of species affected is equivalent to that in tropical forests(6,10-16), failing to support the hypothesis that this mechanism is more prevalent at tropical latitudes. We further show that density-dependent mortality is misinterpreted in previous studies. Our results and evidence from other studies suggest that density-dependent mortality is important in many forests. Thus, unless the strength of density-dependent mortality varies with latitude, this mechanism is not likely to explain the high diversity of tropical forests.