Safety in numbers and the spatial scaling of density-dependent mortality in a coral reef fish.
Safety in numbers and the spatial scaling of density-dependent mortality in a coral reef fish.
复制标题
珊瑚礁鱼的数量安全性和密度依赖性死亡率的空间尺度。
DOI：
10.1890/06-1949.1
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发表时间：
2007
期刊：
影响因子：
4.8
通讯作者：
Robert R. Warner
中科院分区：
文献类型：
--
作者：
J. White;Robert R. Warner
在珊瑚礁鱼类中，依赖密度的种群调节通常是通过捕食最近从浮游生物中定居的幼体来调节的。在其他条件相同的情况下，强烈的密度依赖死亡率应该选择不形成高密度聚集，但许多珊瑚鱼的幼鱼聚集。鉴于这一明显的矛盾，我们假设密度依赖的形式和强度随着测量的空间尺度而变化。个体群体在数量上可能是安全的，但捕食者仍然可以在更大的空间尺度上产生密度依赖的死亡率。我们使用最近定居的蓝头鱼幼鱼，一种聚集的小珊瑚鱼，研究了这种可能性。初步的笼养实验表明，蓝头鱼幼鱼遭受高度捕食，空间定居模式表明，蓝头鱼幼鱼优先成群定居，尽管它们也是单独发现的。然后，我们在两个空间尺度上监测了最近定居的幼鱼的死亡率：由单个或一组鱼占据的微小地点，相隔几厘米；以及由大约2400平方米的珊瑚礁面积组成，相隔几公里的地点。在微站点尺度上，我们独立测量了种群规模和有效种群密度，发现人均死亡率随着种群规模的增加而降低，但与密度无关。然而，在更大的空间尺度上，人均死亡率随着定居者密度的增加而增加。这种密度依赖形式随空间尺度的变化可以调和许多珊瑚礁鱼类典型的小规模聚集行为的存在与种群规模密度依赖的存在，这对种群的稳定和持久性至关重要。
In coral reef fishes, density-dependent population regulation is commonly mediated via predation on juveniles that have recently settled from the plankton. All else being equal, strong density-dependent mortality should select against the formation of high-density aggregations, yet the juveniles of many reef fishes aggregate. In light of this apparent contradiction, we hypothesized that the form and intensity of density dependence vary with the spatial scale of measurement. Individual groups might enjoy safety in numbers, but predators could still produce density-dependent mortality at larger spatial scales. We investigated this possibility using recently settled juvenile bluehead wrasse, Thalassoma bifasciatum, a small, aggregating reef fish. An initial caging experiment demonstrated that juvenile bluehead wrasse settlers suffer high predation, and spatial settlement patterns indicated that bluehead wrasse juveniles preferentially settle in groups, although they are also found singly. We then monitored the mortality of recently settled juveniles at two spatial scales: microsites, occupied by individual fish or groups of fish and separated by centimeters, and sites, consisting of approximately 2400-m2 areas of reef and separated by kilometers. At the microsite scale, we measured group size and effective population density independently and found that per capita mortality decreased with group size but was not related to density. At the larger spatial scale, however, per capita mortality increased with settler density. This shift in the form of density dependence with spatial scale could reconcile the existence of small-scale aggregative behavior typical of many reef fishes with the population-scale density dependence that is essential to population stability and persistence.