Wills C, Condit R
Department of Biology, University of California, San Diego 92093-0116, USA.
Proc Biol Sci. 1999 Jul 22;266(1427):1445-52. doi: 10.1098/rspb.1999.0799.
Quadrat-based analysis of two rainforest plots of area 50 ha, one in Panama (Barro Colorado Island, BCI) and the other in Malaysia (Pasoh), shows that in both plots recruitment is in general negatively correlated with both numbers and biomass of adult trees of the same species in the same quadrat. At BCI, this effect is not significantly influenced by treefall gaps. In both plots, recruitment of individual species is negatively correlated with the numbers of trees of all species in the quadrats, but not with overall biomass. These observations suggest, but do not prove, widespread frequency-dependent effects produced by pathogens and seed-predators that act most effectively in quadrats crowded with trees. Within-species correlations of mortality with numbers or biomass are not found in either plot, indicating that most frequency-dependent mortality takes place before the trees reach 1 cm in diameter. Stochastic effects caused by BCI's more rapid tree turnover may contribute to a larger variance in diversity from quadrat to quadrat at BCI, although they are not sufficient to explain why BCI has fewer than half as many tree species as Pasoh. Finally, in both plots quadrats with low diversity show a significant increase in diversity over time, and this increase is stronger at BCI. This process, like the frequency-dependence, will tend to maintain diversity over time. In general, these non-random forces that should lead to the maintenance of diversity are slightly stronger at BCI, even though the BCI plot is less diverse than the Pasoh plot.
基于样方对两个面积为50公顷的雨林样地进行分析，一个位于巴拿马（巴罗科罗拉多岛，BCI），另一个位于马来西亚（Pasoh），结果表明在这两个样地中，总体而言，幼苗补充与同一样方内同种成年树木的数量和生物量均呈负相关。在BCI，这种效应不受林冠空隙的显著影响。在这两个样地中，单个物种的幼苗补充与样方内所有物种的树木数量呈负相关，但与总生物量无关。这些观察结果表明（但未证明），病原体和种子捕食者产生了广泛的频率依赖效应，这些效应在树木密集的样方中作用最为有效。在这两个样地中均未发现死亡率与数量或生物量的种内相关性，这表明大多数频率依赖的死亡发生在树木直径达到1厘米之前。BCI更快的树木更替所导致的随机效应可能会导致BCI样方之间的多样性差异更大，尽管这些效应不足以解释为什么BCI的树种数量不到Pasoh的一半。最后，在这两个样地中，多样性较低的样方随时间推移多样性显著增加，且这种增加在BCI更为明显。这个过程，与频率依赖性一样，将倾向于随着时间的推移维持多样性。总体而言，这些应能导致维持多样性的非随机力量在BCI稍强一些，尽管BCI样地的多样性低于Pasoh样地。
