Human activities are rapidly transforming the planet, causing dramatic changes in wildlife habitats and posing severe threats to many animal populations (Kalbitzer and Chapman 2018). Habitat destruction, fragmentation, and degradation, including deforestation, agricultural expansion, and urban development are the primary drivers of the declines in wildlife populations (Laurance et al. 2014; Estrada et al. 2017). These changes reduce the availability of food and water and increase the predation risk and human disturbance, severely affecting the survival and reproduction of many species (Arroyo-Rodríguez and Mandujano 2006). Additionally, changes in habitat diminish biodiversity and disrupt crucial ecosystem functions and services vital for human well-being (Sodhi et al. 2010). Understanding the ecological factors that maintain habitat quality is essential for effective conservation and restoration strategies.
The spatial distribution of food resources is crucial for promoting habitat quality and wildlife conservation. Food resource availability directly affects the distribution of animals, prompting them to congregate in areas rich in food and expand their home ranges during periods of scarcity to secure adequate resources (Fan et al. 2013; Mourthé 2014; Camaratta et al. 2017). For example, food scarcity often leads to larger home ranges and increased competition in primate species (Guan et al. 2018), while abundant food resources promote higher population densities and improve reproductive success (Chapman et al. 1995). However, some studies suggest that simply increasing food availability is insufficient for conservation; the spatial distribution and quality of these resources are equally important (Marshall and Wrangham 2007). Therefore, understanding the spatial distribution patterns of food plants is essential for improving habitat quality and supporting population growth (Deng and Zhou 2018).
The distribution of food plants is affected by a variety of ecological factors, including altitude, temperature, soil nutrients, light availability, water-use efficiency, and the soil microbial community, which significantly affect plant growth and distribution (Körner 2007; Crimmins et al. 2011; Baribault et al. 2012; Zelnik and Čarni 2013). The higher temperatures, abundant rainfall, and rich soil nutrients in low-altitude regions promote greater plant diversity and abundance (Kitayama 1992). In contrast, the lower temperatures, reduced rainfall, and poor soil nutrients in high-altitude areas create harsher growing conditions, leading to lower species richness and abundance (Bruijnzeel et al. 2010). These high-altitude plant communities are more affected by cold tolerance and water retention capabilities (Ashton 2003; Wright et al. 2018). For example, the temperature-energy hypothesis suggests that higher temperatures and available energy increase plant growth rates and reproductive success, thus supporting greater species diversity and abundance at lower altitudes (Currie et al. 2004). Although studies have documented the diversity of food plants in the gibbon habitat, research on the spatial distribution and factors driving the distribution of these plants remains limited. This gap highlights the need for a comprehensive exploration to develop effective conservation and restoration strategies (Zhang et al. 2022).
The Hainan gibbon (Nomascus hainanus (Thomas, 1892) is a critically endangered species (Fan 2017) that has only 42 individuals remaining in a 15 km² area of Bawangling, Hainan, China (Turvey et al. 2017; Zhang et al. 2020). These gibbons primarily consume fleshy and juicy berries, which constitute more than 80% of their diet, and mainly occupy altitudes between 400 and 1,200 m (Deng and Zhou 2018). Previous studies indicate a decline in the quantity and quality of food plants with increasing elevation (Lin et al. 2006). Du et al. (2022) predicted the distribution of six key food tree species using the MaxEnt model and reported that they were predominantly located around specific mountainous areas. These findings underscore the critical importance of food plant distribution for the survival and reproduction of the Hainan gibbon. However, most of the research has focused on specific regions or individual groups, lacking a systematic analysis of the factors affecting the spatial distribution of food plants across different altitudes within the various Hainan gibbon family groups. Additionally, the unique historical impact of slash-and-burn agriculture on the Hainan gibbon’s habitat has resulted in lower habitat quality at lower altitudes (Chan et al. 2020), suggesting that the factors driving food plant distribution may differ from those in other regions (Chen et al. 2009). This highlights the need for a comprehensive study of the influence of these ecological factors on food plant distribution across different altitudes to develop effective conservation and restoration strategies.
This study aims to address these gaps by systematically analyzing the spatial distribution of food plants and their driving factors in the habitats of different Hainan gibbon family groups across various altitudes. We seek to provide insight into how habitat quality can be improved and inform conservation and restoration strategies tailored to the unique conditions of the Hainan gibbon’s environment. Specifically, we hypothesized that (1) ecological factors and food plant richness vary significantly at different altitudes, (2) soil nutrients, temperature, and precipitation are the main factors affecting the spatial distribution of food plants, and (3) the key driving factors affecting food plant distribution differ across various altitudes. These hypotheses will be tested using comprehensive field surveys and advanced modeling techniques, contributing to the scientific understanding necessary for the effective conservation of this critically endangered species.