Population viability reveals hidden extinction risk within stable habitat in fragmenting mountain landscapes: A case study from the skywalker gibbon

Stable habitat patches are areas that remain suitable across decades of landscape change. They can guide conservation in fragmenting landscapes, but their capacity to sustain viable populations remains poorly quantified. Using records from the 1980s to the 2020s, we reconstructed habitat trajectories for the endangered skywalker gibbon (Hoolock tianxing) in Mt. Gaoligong, southwest China. We combined ensemble ecological niche models with population viability analysis under continuous-habitat and road-isolation scenarios. Suitable habitat declined by 26%, with losses concentrated below 2 000 m, especially at 1 600–2 000 m (34%). Habitat below 1 600 m partially recovered after 2000 but remained below the 1980s baseline. Four stable patches were identified; three support the known Chinese population. Carrying capacities reached 28 times current population sizes, suggesting patch size alone does not limit recovery. Population viability analysis showed that road isolation, slow life history, and human pressures create hidden extinction risks within stable patches. Longer breeding intervals increased risk to 12%; high hunting pressure raised it to 66%. With road isolation, risk reached 100% under high hunting pressure. We recommend zero-poaching enforcement, low-elevation restoration, canopy bridges, translocation, and protected-area expansion. Our workflow offers a transferable conservation prioritization framework in mountain fragmenting landscapes.