A Test for Shelter Limitation of Reef Fish Populations at Large Spatial Scales: An Integrated Empirical and Theoretical Approach

该项目旨在了解两种珊瑚鱼在中尺度（范围超过数十公里）上种群动态的原因。大多数礁鱼和其他底栖海洋物种都有一个复杂的生命周期，包括一个附着在某个地点的成鱼阶段和一个幼虫阶段，在这个阶段，个体可能会在开阔的海洋中分散很远的距离。许多争论集中在底栖动物种群动态是由上层幼虫的涌入（幼虫定居）还是由底栖动物栖息地中幼体和成体之间的密度依赖相互作用控制。过去的争论基于密度依赖性与强烈的幼虫输入信号不相容的概念，在认识到定居前和定居后的过程都会影响大多数种群的动态之后，已经解决了这一争议。一个广泛适用的假说（吸收-成虫假说）预测，控制幼虫流入的海洋学过程在中尺度上造成了种群之间可预测的差异：高定居点的资源长期有限，而低定居点的资源很少达到其承载能力，成虫密度随幼虫流入而变化。底栖动物栖息地的承载能力及其内部的定居后相互作用在中尺度站点之间是一致的。然而，所有关于沉降后相互作用性质的实验证据都是基于小空间尺度（范围为几个m）的研究。然而，在其他环境中的研究表明，种群动态可能随空间尺度而变化，现在的一个主要挑战是测试海洋系统中的小规模结果是否可以推断到更大的空间领域。这些研究人员过去对两种珊瑚鱼进行的小规模实验表明，为躲避捕食者而争夺庇护地点是这两种鱼类小规模密度依赖的原因。然而，密度依赖的强度取决于当地庇护所的可用性，并且在提供充足庇护所的生境斑块中被消除。他们假设，除了海洋过程导致不同的定居之外，底栖生物栖息地的承载能力也将在中尺度上发生变化，并导致种群之间密度依赖性死亡率的强度差异。研究人员认为，在这个系统中，承载能力是庇护所数量的函数。他们将对中尺度的遮蔽限制进行实验测试。为了补充野外工作，将建立一个数学尺度模型来明确地将局部和中尺度种群联系起来。该模型将包括对地方尺度上住房限制的功能描述，并将用于检验地方和中观尺度上人口动态一致性（或不一致性）的具体假设。测试扩展版的招募-成人假设将为在大空间尺度上形成种群动态的因果相互作用提供罕见的实验测试。对中尺度种群的研究很少，但对其动态的深入了解具有实际意义，因为正是在这个尺度上，海洋保护区被指定，大多数珊瑚礁渔业也在这个尺度上进行管理。对中尺度承载能力取决于珊瑚礁提供的庇护这一假设的支持，也将对珊瑚礁生境持续退化对鱼类的影响产生重要影响。

The project is aimed at understanding the causes of population dynamics in two species of reef fish at the meso-scale (over areas tens of km in extent). Most reef fishes, and other benthic marine species, have a complex life cycle that includes a site-attached adult phase and a larval stage during which individuals may disperse long distances across open ocean. Much debate has centered on whether benthic population dynamics are controlled by the influx of pelagic larvae (larval settlement) or by density-dependent interactions among juveniles and adults in the benthic habitat. Past controversy, based on the notion that density-dependence is not compatible with a strong larval-input signal, has been resolved following recognition that both pre- and post-settlement processes influence the dynamics of most populations. One broadly applicable hypothesis (the recruit-adult hypothesis) predicts that oceanographic processes controlling the influx of larvae create predictable differences among populations at the meso-scale: sites with high settlement are chronically resource limited, whereas sites with low settlement rarely reach their carrying capacity and adult densities track larval influx. The carrying capacity of the benthic habitat, and the post-settlement interactions within it, are assumed to be consistent among meso-scale sites. All experimental evidence on the nature of post-settlement interactions is, however, based on study at small spatial scales (a few m's in extent). Studies in other environments indicate that population dynamics can potentially vary with spatial scale, however, and a major challenge now is to test whether small-scale results in marine systems will extrapolate to larger spatial domains. Past small-scale experiments by these investigators on two reef fishes indicate that competition for shelter sites used as refuges from predation is the cause of small-scale density dependence in both species. The strength of density dependence, however, depends on the local availability of shelter, and is eliminated in habitat patches that provide abundant shelter. They hypothesize that, in addition to oceanographic processes causing differential settlement, the carrying capacity of the benthic habitat will also vary at the meso-scale and cause differences among populations in the strength of density-dependent mortality. In this system, the investigators suggest that carrying capacity is a function of shelter abundance. They will test experimentally for shelter limitation at the meso-scale. To complement the field work, a mathematical scaling model will be constructed to explicitly link local- and meso-scale populations. This model will include a functional description of shelter limitation at local scales and will be used to test specific hypotheses for the congruence (or lack of it) in population dynamics at local and meso-scales. Testing the expanded version of the recruit-adult hypothesis will provide a rare experimental test of the causal interactions shaping population dynamics at large spatial scales. Meso-scale populations are little studied, but a deeper understanding of their dynamics is of practical importance because it at this scale that marine reserves are designated and at which most reef fisheries are managed. Support for the hypothesis that meso-scale carrying capacity depends on shelter provided by the reef would also have important implications for the effects on fishes of the ongoing habitat degradation on coral reefs.