Small giants: tributaries rescue spatially structured populations from extirpation in a highly fragmented stream
Small giants: tributaries rescue spatially structured populations from extirpation in a highly fragmented stream
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小巨人：支流在高度分散的河流中拯救了空间结构的种群免遭灭绝
DOI：
10.1111/1365-2664.14200
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发表时间：
2022
影响因子：
5.7
通讯作者：
Kanno Yoichiro
中科院分区：
文献类型：
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作者：
Tsuboi Jun‐ichi;Morita Kentaro;Koseki Yusuke;Endo Shinsuke;Sahashi Genki;Kishi Daisuke;Kikko Takeshi;Ishizaki Daisuke;Nunokawa Masanori;Kanno Yoichiro
栖息地破碎化是对生物多样性的普遍威胁。线性排列的栖息地，如河流网络，特别容易破碎。随着景观日益受到人类的支配，破碎生境斑块的保护价值不容忽视。了解破碎斑块中种群持续或灭绝的人口学机制至关重要。我们研究了两种日本内陆鲑鱼种群的空间结构动态，它们在一个由于主干线低水头水坝而高度破碎的源头流网络中持续了50 - 30年。我们使用9年的标记-再捕获数据对空间矩阵种群模型进行参数化和分析。在生命的某些阶段，支流支持更高的存活率，并且从支流到主干的运动是不对称的。因此，两种物种在支流斑块中的种群增长率均高于主干区，尽管这些支流仅占研究水系网络表面积的12%或18%。这些支流拥有更多的物理和水力复杂的河流栖息地（即更高的木材密度和流动避难所），表明栖息地斑块质量比栖息地斑块大小在决定这些空间结构种群的动态方面更重要。河流网络中的支流位置对这些种群的轨迹很重要。由于包括支流在内的上游鱼类的迁移，上游居住的鱼类持续存在于高度破碎的主河道斑块中（即<500米斑块中有6个无法通行的基础设施）。然而，下游居住的鲑鱼已经逐渐从碎片化的主斑块的最上层灭绝，因为在考虑到移民的损失和碎片化导致的移民阻碍后，它们无法保持正的种群增长率。合成与应用。我们得出结论，小支流拯救了空间结构种群免于灭绝（charr）或至少减缓了灭绝（salmon）。在全球范围内，对水源作为水生栖息地的法律保护薄弱。我们的研究结果表明，低估小支流人口价值的河流管理计划可能无法保护源头居民的种群，从而危及水生生物多样性。我们讨论了本研究对生境连通性和渔业管理的保护意义。
Habitat fragmentation is a pervasive threat to biodiversity. Linearly arranged habitats such as stream networks are particularly vulnerable to fragmentation. As the landscape becomes increasingly human dominated, conservation values of fragmented habitat patches cannot be overlooked. It is critical to understand the demographic mechanisms of population persistence or extirpation in fragmented patches.We studied dynamics of spatially structured populations of two Japanese landlocked salmonids persisting for >30 years in a headwater stream network that is highly fragmented due to low‐head dams in the mainstem. We parameterised and analysed spatial matrix population models using 9‐year mark–recapture data.Tributaries supported higher survival rates in some life stages, and movement was asymmetrical from the tributaries to the mainstem. Accordingly, population growth rates were higher in the tributary patches than the mainstem in both species despite the tributaries occupying only 12% or 18% of the study stream network by surface area. The tributaries harboured more physically and hydraulically complex instream habitats (i.e. higher wood density and flow refugia), indicating that habitat patch quality was more important than habitat patch size in determining the dynamics of these spatially structured populations.Tributary locations in the stream network were important in the trajectory of these populations. The upstream‐dwelling charr persisted in the highly fragmented mainstem patch (i.e. six impassable infrastructures in a <500 m patch) due to immigration of fish from upstream including the tributary. However, the downstream‐dwelling salmon has been gradually extirpated from the uppermost section of the fragmented mainstem patch because they could not maintain a positive population growth rate after loss of emigrants was accounted for and immigration was prevented due to fragmentation.Synthesis and applications. We conclude that small tributaries have rescued the spatially structured populations from extirpation (charr) or at least slowed down extirpation (salmon). Legal protection of headwaters as aquatic habitats is weak globally. Our results suggest that stream management plans underestimating the demographic value of small tributaries will likely fail to conserve populations of headwater inhabitants and therefore endanger aquatic biodiversity. We discuss conservation implications of this study related to habitat connectivity and fisheries management.