Johnson Darren W
Department of Ecology and Evolutionary Biology, University of California, Santa Cruz 95060, USA.
Ecology. 2006 Feb;87(2):319-25. doi: 10.1890/04-1665.
Experimental manipulation of population density has frequently been used to demonstrate demographic density dependence. However, such studies are usually small scale and typically provide evidence of spatial (within-generation) density dependence. It is often unclear whether small-scale, experimental tests of spatial density dependence will accurately describe temporal (between-generation) density dependence required for population regulation. Understanding the mechanisms generating density dependence may provide a link between spatial experiments and temporal regulation of populations. In this study, I manipulated the density of recently settled kelp rockfish (Sebastes atrovirens) in both the presence and absence of predators to test for density-dependent mortality and whether predation was the mechanism responsible. I also examined mortality of rockfish cohorts within kelp beds throughout central California to evaluate temporal (between-generation) density dependence in mortality. Experiments suggested that short-term behavioral responses of predators and/or a shortage of prey refuges caused spatial density dependence. Temporal density dependence in mortality was also detected at larger spatial scales for several species of rockfish. It is likely that short-term responses of predators generated both spatial and temporal density dependence in mortality. Spatial experiments that describe the causal mechanisms generating density dependence may therefore be valuable in describing temporal density dependence and population regulation.
对种群密度进行实验性操控常常被用于证明种群密度依赖。然而，此类研究通常规模较小，且一般仅提供空间（同代内）密度依赖的证据。空间密度依赖的小规模实验测试能否准确描述种群调节所需的时间（代际间）密度依赖，这一点往往并不明确。了解产生密度依赖的机制或许能在空间实验与种群的时间调节之间建立起联系。在本研究中，我在有捕食者和无捕食者的两种情况下，对新定居的海带石斑鱼（Sebastes atrovirens）的密度进行了操控，以测试密度依赖的死亡率，以及捕食是否为其背后的机制。我还研究了加利福尼亚中部海带床内石斑鱼群组的死亡率，以评估死亡率的时间（代际间）密度依赖情况。实验表明，捕食者的短期行为反应和/或猎物避难所的短缺导致了空间密度依赖。在更大的空间尺度上，也检测到了几种石斑鱼在死亡率方面的时间密度依赖。捕食者的短期反应很可能在死亡率方面同时产生了空间和时间密度依赖。因此，描述产生密度依赖的因果机制的空间实验，对于描述时间密度依赖和种群调节可能具有重要价值。
