Integrating a Newcomer: Niche Differentiation and Habitat Use of Eurasian Red Squirrels and Native Species in a Forest Reserve Under Human Disturbance

Understanding the integration of newly recorded species into forest ecosystems is essential for evaluating their ecological impacts on native wildlife diversity. In this study, we examined the spatial and temporal niche dynamics of three sympatric squirrel species within the Labagoumen nature reserve, a temperate forest located in northern China. Particular emphasis was placed on the recently documented Eurasian red squirrel (Sciurus vulgaris) and its potential interactions with two native species: Père David’s rock squirrel (Sciurotamias davidianus) and the Siberian chipmunk (Tamias sibiricus). Using camera trapping data from 91 sites (2019–2024), we examined habitat use, activity rhythms, and niche overlap under contrasting levels of human disturbance. A total of 3419 independent effective photos of squirrels were recorded. S. vulgaris showed a broader spatial distribution and a higher relative abundance index (RAI) in the tourist area, while native species were more abundant in the non-tourist area. All three species showed similar annual activity patterns based on the monthly relative abundance index (MRAI), although native species exhibited an additional activity peak in June–July. Temporal niche overlap (Cih) and the coefficient of overlap (Δ) between S. vulgaris and native species increased during the tourist season, suggesting synchronized activity under high disturbance. In contrast, lower overlap in the non-tourist season indicated stronger temporal partitioning. The daily activity rhythm of S. vulgaris remained stable, while native species displayed more variability, especially in non-tourist areas. S. vulgaris also exhibited a significantly broader spatial niche breadth (Bi), suggesting greater habitat exploitation and adaptability. Non-metric multidimensional scaling (NMDS) revealed no significant spatial segregation among the three species, indicating successful integration of S. vulgaris into the local community. Our findings emphasize the competitive advantage of S. vulgaris and demonstrate how human activities can restructure forest small mammal assemblages by altering spatiotemporal niche partitioning. We recommend long-term ecological monitoring to assess species diversity changes and guide adaptive conservation strategies.