基于MAXENT和最优参数地理探测器的海南长臂猿(Nomascus hainanus)生境适宜度评估

Assessment of habitat suitability for the Hainan gibbon (Nomascus hainanus) based on MAXENT and optimal parameters-based geographical detector

关键词:  MAXENT  生境适宜度评价  地理探测器  海南长臂猿

Key words:  MAXENT  habitat suitability assessment  geographical detector  Hainan gibbon

摘要:

海南长臂猿（Nomascus hainanus）是我国特有的类人猿物种，正处于极度濒危的困境中，对该物种的生境适宜性进行评估具有重要现实意义。文章基于175个海南长臂猿分布点数据，利用MAXENT模型构建了海南长臂猿生境适宜度评估模型，引入Moran’s I指数和最优参数地理探测器进一步解析海南长臂猿生境适宜度分布格局及主导环境变量，并引入景观连通度指数去分析海南长臂猿适宜生境功能连通性。研究结果显示：（1） 海南长臂猿适宜生境分布在保护区中部斧头岭 − 黑岭 − 雅加大岭一带以及保护区东北部的东崩岭区域，适宜生境面积为26.04 km²，生境适宜度呈现显著空间聚集特征；（2）生物气候变量 （总贡献度54.6%，总q值0.7389） 和人类干扰变量 （总贡献度28.0%，总q值0.5035） 对海南长臂猿生境适宜度评估具有重要影响；（3）两两环境变量之间存在相互增强的交互作用，各环境变量对海南长臂猿生境适宜度的影响具有显著差异；（4）海南长臂猿适宜生境功能连通度较低，且适宜生境斑块间距离较远。研究可为濒危野生动物生境评估及栖息地修复提供理论基础和科学依据。

Abstract:

Background, aim, and scope The Hainan gibbon (Nomascus hainanus) is a critically endangered primate species endemic to China. Assessing habitat suitability for this species is critical for conservation initiatives. The maximum entropy (MAXENT) model, although known for its predictive capabilities, lacks ecological interpretability.To address this limitation, we integrate the Geographical Detector (GD) into MAXENT to assess habitat suitability for the Hainan gibbon. From a landscape ecology perspective, this study also explores the habitat connectivity of Hainan gibbons and identifies crucial potential habitat patches. Materials and methods Based on 175 occurrence records of the Hainan gibbon, we constructed a habitat suitability assessment model using the MAXENT model and introduced Moran’s I index and the Optimal Parameters-based Geographical Detector (OPGD) to further analyze the distribution patterns of habitat suitability index and dominant environmental variables. Subsequently, we investigated the ecological quantitative relationships between environmental variables and the habitat suitability of the Hainan gibbon, along with the interactions between the environmental variables. Overall connectivity indices (IIC (integral index of connectivity) and PC (probability of connectivity)) assess functional habitat connectivity, and the patch importance index (dPC) analyzes the importance of each habitat patch. Results The results showed the most suitable habitat covers 26.04 km² (8.69%), concentrated in the Futou Ridge−Heiling Ridge−Yajiada Ridge region and Dongbeng Ridge in the central and northeastern protected areas. Sub-suitable habitat spans 72.11 km² (24.05%), mainly in the central and northern regions. Moran’s I for the Habitat Suitability Index is 0.963, indicating significant spatial clustering. ROC (receiver operating characteristic) curve validation yields an average AUC (area under the curve) of 0.952, indicating high predictive performance. Bioclimatic variables (with a total contribution of 54.6% and an overall q-value of 0.7389) and human disturbance variables (with a total contribution of 28.0% and an overall q-value of 0.5035) exert a substantial influence on the habitat suitability assessment of Hainan gibbons. Interaction detector reveals joint effects, with distance to residential areas and bio12 (annual precipitation) having the highest explanatory power (joint contribution of 0.6809). Ecological detector shows significant differences in environmental variable impacts. Functional connectivity varies under different daily movement distances, reaching maximum potential at dispersal distances exceeding 1500 m. Suitable habitat patches are scattered, with the most important habitat cluster in the Futou Ridge−Heiling Ridge−Yajiada Ridge area (15.85 km² ) and the second in the west of Yajiada Ridge (6.33 km² ). Discussion Hainan gibbons exhibit climate preferences in response to food source requirements, with elevation, precipitation, and temperature crucial in determining vegetation types and food plant abundance. The spatial distribution of suitable food sources and resting plants overlaps with potential suitable habitats. Variables like precipitation in the driest quarter (bio17) correlate with the time of wild foraging by Hainan gibbons. Plant growth conditions are superior near water sources, leading to higher abundance of food plants for Hainan gibbons in areas close to rivers. Human activities impact habitat distribution, with higher elevations experiencing less disturbance. Infrastructure development such as road construction, power lines, and farming activities within Bawangling has fragmented suitable habitats like Futou Ridge, Yajiada Ridge, and Heiling Ridge, creating discontinuous regions and resulting in the “isolation” of populations. The distribution of roads also acts as a barrier hindering the migration and dispersal of Hainan gibbon populations towards suitable habitat patches in the northeast, such as Dongbeng Ridge and the western Yajiada Ridge. Conclusions The most suitable habitat for Hainan gibbons is distributed in the central part of the protected area, specifically in the Futou Ridge−Heiling Ridge−Yajiada Ridge area, and in the northeastern part of Bawangling in the Dongbeng Ridge region. The Sub-suitable habitat is mainly distributed in the central and northern regions of Bawangling. While the habitat suitability for Hainan gibbons exhibits significant spatial clustering, the distribution of suitable habitat patches is relatively scattered, and the functional connectivity among these suitable habitats is poor. Bioclimatic variables and human disturbance variables significantly influence the habitat suitability assessment for Hainan gibbons. Hainan gibbons show a preference for areas with high annual precipitation, moderate temperature differences, higher elevations, steeper slopes, proximity to water bodies, and locations far from human activities. The introduction of OPGD further validates the objectivity of selected environmental variables and the accuracy of MAXENT model results, reducing the subjectivity in discretizing environmental variables and addressing the ecological interpretability gap in MAXENT. Recommendations and perspectives Future research can incorporate additional environmental variables, such as land cover and vegetation types, obtained through remote sensing imagery and field surveys, to further enhance the accuracy of habitat suitability assessments for the Hainan gibbon. Conservation efforts should focus on seven suitable habitat patches within the research area that are larger than 0.1 km² . To enhance connectivity, artificial ecological corridors will be established to link high-suitability habitat patches, especially in regions like Dongbeng Ridge−Futou Ridge, Futou Ridge−Heiling−Yajiada Ridge. When constructing ecological corridors, efforts will be made to choose tree species that align with local phenology and provide stable food resources for Hainan gibbons. Simultaneously, there will be a focus on preserving and restoring potential natural forest corridors. Long-term monitoring and restoration efforts will be implemented in sub-suitable habitat areas, with the aim of transforming them into suitable habitats in the later stages.