Forrester Graham E, Steele Mark A, Samhouri Jameal F, Evans Bryn, Vance Richard R
Department of Natural Resources Science, University of Rhode Island, Kingston, Rhode Island 02881 USA.
Department of Biology, California State University-Northridge, 18111 Nordhoff Street, Northridge, California 91330-8303 USA.
Ecology. 2008 Nov;89(11):2980-2985. doi: 10.1890/07-1546.1.
Field experiments provide rigorous tests of ecological hypotheses but are typically of short duration and use small spatial replicates. We assessed empirically whether the results of experiments testing for density dependence applied at larger spatial domains and explained temporal population dynamics. We studied a small coral reef fish, the goldspot goby (Gnatholepis thompsoni), in the Bahamas. We assessed the effects of interactions with conspecifics and with an ecologically similar species, the bridled goby (Coryphopterus glaucofraenum). Two density manipulations on small reef patches revealed that goldspot goby mortality over one month increased as conspecifics became crowded. On five large natural reefs, we correlated the initial year-class density of both species (annual larval settlement) with the subsequent decline of goldspot goby year-classes for five years. Mortality was correlated with conspecific density among reefs for all years, but not among years for all reefs. Thus, spatial density dependence in mortality scaled up qualitatively from small patches to entire reefs but was not associated with temporal density dependence. Our results support the conclusion that field experiments may be extrapolated to larger spatial domains with care, but that using small spatial comparisons to predict temporal responses is difficult without knowing the underlying biological mechanisms.
野外实验为生态假说提供了严格的检验，但通常持续时间较短且使用的空间重复样本较小。我们通过实证评估了在较大空间尺度上进行的密度依赖测试结果是否能解释种群的时间动态变化。我们在巴哈马群岛研究了一种小型珊瑚礁鱼类——金点虾虎鱼（Gnatholepis thompsoni）。我们评估了金点虾虎鱼与同种个体以及与生态位相似的物种——细纹虾虎鱼（Coryphopterus glaucofraenum）之间相互作用的影响。在小珊瑚礁斑块上进行的两次密度操纵实验表明，随着同种个体变得拥挤，金点虾虎鱼在一个月内的死亡率增加。在五个大型天然珊瑚礁上，我们将这两个物种的初始年种群密度（年度幼体定居量）与金点虾虎鱼年种群数量在随后五年中的下降情况进行了关联分析。所有年份中，死亡率在不同珊瑚礁之间与同种个体密度相关，但并非在所有珊瑚礁的年份间都如此。因此，死亡率的空间密度依赖在性质上从小斑块扩大到了整个珊瑚礁，但与时间密度依赖无关。我们的研究结果支持以下结论：野外实验可以谨慎地外推到更大的空间尺度，但在不了解潜在生物学机制的情况下，利用小尺度空间比较来预测时间响应是困难的。
