Data from: How disturbance and dispersal influence intraspecific structure

1. Recent studies have suggested that spatial patterns of intraspecific diversity can be influenced by density-dependent processes, which can inhibit effective migration of new lineages to established populations. How mechanisms such as dispersal and disturbance influence these processes is, however, still poorly understood. 2. We hypothesised that i) species with leptokurtic dispersal (frequent on small scales but rare on larger scales) would show no spatial structure on small scales and strong structure on large scales, and ii) disturbance would influence the chance of genetic turnover in a population. 3. We tested these hypotheses using empirical genetic (mtDNA) data from field observations of a model taxon (the buoyant, forest-forming kelp Durvillaea, which exhibits leptokurtic dispersal distribution), and by conducting simulation analyses. 4. Our data supported the first hypothesis, with no spatial structure detected on fine (metres) scales despite evidence of strong structure on larger (10s to 100s kms) scales. The second hypothesis was also supported, with simulations showing that disturbance increased the rate at which structure developed, and reduced the time to fixation (monopolisation by a single lineage). The chance of any lineage reaching fixation was directly related to its initial proportion in the population, and this relationship was unaffected by changes in disturbance size or dispersal capacity. We conclude that, in the absence of selection, extirpation is typically a prerequisite for population-genetic ‘turnover’, with remnant (refugial) individuals otherwise outnumbering immigrants. 5. Synthesis: Disturbance plays a critical role in releasing density-dependent blocks to colonisation, and thus enables lineage turnover within species. Our results indicate that although both disturbance size and dispersal capacity play important roles in the formation of spatial structure within species, unless a population is totally extirpated, establishment of genetic lineages from elsewhere (turnover) is unlikely even for species that can disperse well.1. 已有研究表明，种内多样性的空间格局可受密度依赖过程调控，该类过程会抑制新谱系向已建立种群的有效迁移。然而，诸如扩散与干扰这类机制如何影响上述过程，目前仍未得到充分阐明。 2. 我们提出两项假说：其一，具有狭峰扩散特征（小尺度下扩散频繁，大尺度下扩散稀少）的物种，其种群在小尺度上不会呈现空间结构，而在大尺度上则表现出显著空间结构；其二，干扰会影响种群内遗传周转的发生概率。 3. 我们通过两种途径验证上述假说：一是利用模式类群——具备狭峰扩散分布特征的浮性、形成藻林的褐藻Durvillaea——的野外观测实证遗传数据（线粒体DNA（mtDNA））；二是开展模拟分析。 4. 本研究数据支持第一项假说：尽管在大尺度（数十至数百公里）下存在显著空间结构，但细尺度（米级）下未检测到任何空间结构。第二项假说同样得到验证，模拟结果显示，干扰可加快空间结构的形成速率，并缩短遗传固定所需的时间——遗传固定指单一谱系完全垄断种群。任一谱系达到遗传固定的概率与其在种群中的初始占比直接相关，且该关系不受干扰规模或扩散能力变化的影响。我们的结论为：在无选择作用的前提下，局部灭绝通常是种群遗传‘周转’的前提条件，否则避难所残留个体的数量将超过迁入个体。 5. 综合结论：干扰在解除殖民过程的密度依赖阻滞中发挥关键作用，进而可推动物种内的谱系周转。本研究结果表明，尽管干扰规模与扩散能力均对物种内空间结构的形成具有重要作用，但除非种群被完全局部灭绝，否则即便对于扩散能力较强的物种，外来遗传谱系的建立（即谱系周转）仍难以实现。