Data from: Landscape genetic analyses reveal fine-scale effects of forest fragmentation in an insular tropical bird

Within the framework of landscape genetics, resistance surface modelling is particularly relevant to explicitly test competing hypotheses about landscape effects on gene flow. To investigate how fragmentation of tropical forest affects population connectivity in a forest specialist bird species, we optimized resistance surfaces without a priori specification, using least-cost (LCP) or resistance (IBR) distances. We implemented a two-step procedure in order (i) to objectively define the landscape thematic resolution (level of detail in classification scheme to describe landscape variables) and spatial extent (area within the landscape boundaries) and then (ii) to test the relative role of several landscape features (elevation, roads, land cover) in genetic differentiation in the Plumbeous Warbler (Setophaga plumbea). We detected a small-scale reduction of gene flow mainly driven by land cover, with a negative impact of the nonforest matrix on landscape functional connectivity. However, matrix components did not equally constrain gene flow, as their conductivity increased with increasing structural similarity with forest habitat: urban areas and meadows had the highest resistance values whereas agricultural areas had intermediate resistance values. Our results revealed a higher performance of IBR compared to LCP in explaining gene flow, reflecting suboptimal movements across this human-modified landscape, challenging the common use of LCP to design habitat corridors and advocating for a broader use of circuit theory modelling. Finally, our results emphasize the need for an objective definition of landscape scales (landscape extent and thematic resolution) and highlight potential pitfalls associated with parameterization of resistance surfaces.

在景观遗传学（landscape genetics）框架下，抗性表面建模（resistance surface modelling）尤为适用于明确检验关于景观对基因流影响的各类竞争性假说。为探究热带森林片段化如何影响林栖专化鸟类的种群连通性，我们未预先设定参数，采用最小成本路径（least-cost path, LCP）或抗性距离（resistance distance, IBR）对抗性表面进行优化。我们采用两步研究流程：其一，客观界定景观的主题分辨率（即描述景观变量的分类方案细节等级）与空间范围（景观边界覆盖的区域）；其二，检验海拔、道路、土地覆被等多种景观要素在铅色林莺（Setophaga plumbea）遗传分化中的相对作用。我们检测到小规模的基因流降低现象，其主要由土地覆被驱动，非森林基质对景观功能连通性造成负面影响。然而，不同基质组分对基因流的约束程度并不均等：其传导性随与森林生境的结构相似度提升而增强——城市区域与草甸的抗性值最高，而农业区域的抗性值处于中等水平。研究结果显示，相较于LCP，IBR在解释基因流方面表现更优，这反映出该受人类活动改造的景观中存在次优移动行为，挑战了学界普遍采用LCP设计生境廊道的惯例，并呼吁更广泛地应用电路理论建模。最后，本研究结果强调了客观界定景观尺度（包括景观范围与主题分辨率）的必要性，并揭示了抗性表面参数化过程中潜在的误区。