Data from: Gene flow of a forest-dependent bird across a fragmented landscape

Habitat loss and fragmentation can affect the persistence of populations by reducing connectivity and restricting the ability of individuals to disperse across landscapes. Dispersal corridors promote population connectivity and therefore play important roles in maintaining gene flow in natural populations inhabiting fragmented landscapes. In the prairies, forests are restricted to riparian areas along river systems which act as important dispersal corridors for forest dependent species across large expanses of unsuitable grassland habitat. However, natural and anthropogenic barriers within riparian systems have fragmented these forested habitats. In this study, we used microsatellite markers to assess the fine-scale genetic structure of a forest-dependent species, the black-capped chickadee (Poecile atricapillus), along 10 different river systems in Southern Alberta. Using a landscape genetic approach, landscape features (e.g., land cover) were found to have a significant effect on patterns of genetic differentiation. Populations are genetically structured as a result of natural breaks in continuous habitat at small spatial scales, but the artificial barriers we tested do not appear to restrict gene flow. Dispersal between rivers is impeded by grasslands, evident from isolation of nearby populations (~ 50 km apart), but also within river systems by large treeless canyons (>100 km). Significant population genetic differentiation within some rivers corresponded with zones of different cottonwood (riparian poplar) tree species and their hybrids. This study illustrates the importance of considering the impacts of habitat fragmentation at small spatial scales as well as other ecological processes to gain a better understanding of how organisms respond to their environmental connectivity. Here, even in a common and widespread songbird with high dispersal potential, small breaks in continuous habitats strongly influenced the spatial patterns of genetic variation.

栖息地丧失与破碎化可通过降低连通性、限制个体跨景观扩散的能力，对种群存续造成不利影响。扩散廊道能够提升种群连通性，因此在栖息于破碎化景观中的自然种群内，对维持基因流发挥着关键作用。在草原生态系统中，森林仅局限于河流沿线的河岸带，而这些河岸带正是依赖森林的物种在大片不适宜的草原生境间进行扩散的重要廊道。然而，河岸系统内的自然与人为屏障，已导致这些森林生境发生破碎化。本研究采用微卫星标记（microsatellite markers），对阿尔伯塔省南部10条不同河流沿岸的依赖森林物种——黑头山雀（Poecile atricapillus）的精细尺度遗传结构进行了评估。借助景观遗传学研究方法，研究发现景观特征（如土地覆盖）对遗传分化模式具有显著影响。在小空间尺度下，连续生境的自然断裂带导致种群形成了遗传结构分化，但本研究测试的人工屏障似乎并未对基因流形成限制。河流间的扩散活动受到草原的阻隔——这一点可从相距仅约50公里的邻近种群间的隔离现象得到印证；而在河流系统内部，跨度超过100公里的大型无树峡谷同样阻碍了个体扩散。部分河流内出现的显著种群遗传分化，与不同棉白杨（河岸杨树）物种及其杂交种的分布区域高度对应。本研究证实，若要更全面地理解生物如何响应其所处环境的连通性，需同时考量小尺度栖息地破碎化的影响以及其他生态过程。即便对于这类常见且分布广泛、具备高扩散潜力的鸣禽而言，连续生境中的微小断裂也会对遗传变异的空间格局产生强烈影响。