Department of Integrative Biology, Oregon State University, Corvallis, Oregon, 97331-2914, USA.
Department of Biological Sciences, California State University, Long Beach, California, 90840, USA.
Ecology. 2018 Jun;99(6):1419-1429. doi: 10.1002/ecy.2343.
Many ocean species exist within what are called marine metapopulations: networks of otherwise isolated local populations connected by the exchange of larval offspring. In order to manage these species as effectively as possible (e.g., by designing and implementing effective networks of marine protected areas), we must know how many offspring are produced within each local population (i.e., local demography), and where those offspring disperse (i.e., larval connectivity). Although there is much interest in estimating connectivity in the relatively simple sense of identifying the locations of spawning parents and their settling offspring, true measures of demographic connectivity that account for among-site variation in offspring production have been lacking. We combined detailed studies of local reproductive output and larval dispersal of a coral reef fish to quantify demographic connectivity within a regional metapopulation that included four widely spaced islands in the Bahamas. We present a new method for estimating demographic connectivity when the levels of dispersal among populations are inferred by the collection of genetically "tagged" offspring. We estimated that 13.3% of recruits returned to natal islands, on average (95% CI = 1.1-50.3%), that local retention was high on one of the islands (41%, 95% CI = 6.0-97.0%), and that larval connectivity was appreciable, even between islands 129 km apart (mean = 1.6%, 95% CI = 0.20-8.8%). Our results emphasize the importance of properly integrating measurements of production with measurements of connectivity. Had we not accounted for among-site variation in offspring production, our estimates of connectivity would have been inaccurate by a factor as much as 6.5. At a generational timescale, lifetime offspring production varied substantially (a fivefold difference among islands) and the importance of each island to long-term metapopulation growth was dictated by both larval production and connectivity. At the scale of our study (local populations inhabiting 5-ha reefs), the regional metapopulation could not grow without external input. However, an exploratory analysis simulating a network of four marine protected areas suggested that reserves of >65 ha each would ensure persistence of this network. Thus, integrating studies of larval connectivity and local demography hold promise for both managing and conserving marine metapopulations effectively.
这些网络由原本相互隔离的局部种群组成，通过幼体后代的交换而连接。为了尽可能有效地管理这些物种（例如，通过设计和实施有效的海洋保护区网络），我们必须知道每个局部种群内产生多少后代（即局部种群动态），以及这些后代在哪里扩散（即幼体连通性）。尽管人们对识别产卵亲鱼及其定居后代的位置等相对简单的连通性估计方法很感兴趣，但缺乏真正考虑到后代产生的地点间变异的种群动态连通性的度量方法。我们结合了珊瑚礁鱼类的局部繁殖输出和幼体扩散的详细研究，以量化包括巴哈马群岛四个相距甚远的岛屿在内的区域复合种群内的种群动态连通性。我们提出了一种新方法，用于在通过收集遗传“标记”后代来推断种群间扩散水平的情况下估计种群动态连通性。我们估计，平均而言，有 13.3%的补充个体返回出生地岛屿（95%置信区间为 1.1-50.3%），其中一个岛屿的本地保留率很高（41%，95%置信区间为 6.0-97.0%），即使在相隔 129 公里的岛屿之间，幼体连通性也相当可观（平均值为 1.6%，95%置信区间为 0.20-8.8%）。我们的研究结果强调了正确整合繁殖测量与连通性测量的重要性。如果我们没有考虑到后代产生的地点间变异，我们的连通性估计值将不准确，误差高达 6.5 倍。在世代时间尺度上，终生后代的产生量变化很大（岛屿之间相差五倍），每个岛屿对长期复合种群增长的重要性取决于幼体的产生和连通性。在我们的研究规模（栖息在 5 公顷珊瑚礁上的局部种群）上，没有外部输入，区域复合种群就无法增长。然而，一项模拟四个海洋保护区网络的探索性分析表明，每个保护区面积超过 65 公顷将确保该网络的持续存在。因此，整合幼体连通性和局部种群动态的研究有望有效管理和保护海洋复合种群。
