Small giants: Tributaries rescue spatially structured populations from extirpation in a highly fragmented stream

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 the 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...生境破碎化（Habitat fragmentation）是对生物多样性的普遍威胁。线性排布的生境（如河网）尤其易受到破碎化的影响。随着景观日益被人类活动所主导，破碎化生境斑块的保护价值不容忽视。阐明破碎化生境斑块中种群存续或局部灭绝的种群动态机制，是至关重要的。 我们以两种日本内陆鲑科鱼类为研究对象，它们的空间结构化种群已在因干流低水头大坝（low-head dams）而高度破碎的源头河网（headwater stream network）中存续超过30年，我们对其动态变化开展了研究。我们利用9年的标记-重捕（mark-recapture）数据，对空间矩阵种群模型（spatial matrix population models）进行了参数化与分析。 部分生活史阶段中，支流生境的存活率更高，且种群迁移呈现从支流到干流的不对称性。据此，尽管支流斑块仅占……，两种鱼类的支流种群增长率均高于干流种群。