Data and code from: The Great Dividing Range as a driver of genetic divergence in a low-dispersing dragonfly

Across complex landscapes, genetic structure can arise through a combination of geographic, ecological, and historical processes. In mountain systems, isolation by distance (IBD), environment (IBE), and resistance (IBR) represent three such mechanisms, but are often difficult to distinguish. The Great Dividing Range (GDR) of eastern Australia provides an ideal system for evaluating their relative contributions because of its varying elevation and climatic gradients. Here, we investigate the drivers of genetic structure in the Swamp Tigertail (Synthemis eustalacta) using an integrative framework combining population genomics, demographic analysis, morphology, and ecological data. Results showed overall low genetic differentiation and no evidence for discrete population structure. Linear mixed‐effect models provided no support for IBD but instead showed IBE and IBR, in which any observed genetic differentiation was correlated with environmental gradients, particularly precipitation and temperature extremes, vegetative cover, and landscape resistance. Morphological analyses revealed minimal variation among sampled sites, but several traits were sexually dimorphic, suggesting potential sex‐biased dispersal. Demographic reconstructions and paleo‐niche models suggest long‐term population stability, with shifts in suitable habitat following during past climatic oscillations. Together, these results highlight ecological and topographic isolation as key mechanisms shaping genetic variation in S. eustalacta and that montane dragonfly populations may maintain gene flow through climate cycles by tracking suitable conditions across elevation rather than persisting in long-isolated refugia.