Effects of Ecological Factors on the Spatial Distribution of Food Plants in Hainan Gibbon (Nomascus hainanus) Habitat: Conservation and Habitat Restoration Insights

doi:10.21203/rs.3.rs-5027780/v1

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Effects of Ecological Factors on the Spatial Distribution of Food Plants in Hainan Gibbon (Nomascus hainanus) Habitat: Conservation and Habitat Restoration Insights

https://doi.org/10.21203/rs.3.rs-5027780/v1

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Food resources are crucial for conserving endangered species. Quantifying the distribution of food plants and their driving factors in Hainan gibbon habitats helps to understand food supply characteristics and guide targeted habitat restoration. This study was based on a survey of 122 grid plots (20 × 20 m), categorized as food plants by size (large: diameter at breast height [DBH] ≥ 15 cm; small: 1 cm ≤ DBH < 15 cm) and seasonality (dry season and preferred food plants). The results showed: 1) Significant differences in the ecological factors between high-altitude and low-altitude habitats (t = − 9.04–11.03, P < 0.05). 2) Significantly higher species richness (t = 2.08–5.02, P < 0.05) in high-altitude habitats than low-altitude ones, with a long dry season, and preferred food plants were more abundant in the A and C family groups. 3) Key factors affecting the spatial distribution of food plants included elevation, the soil carbon-to-nitrogen ratio, average temperature, and annual precipitation, with effects varying by food plant type and elevation. These findings indicate that successional low-altitude secondary forests are potential habitats for Hainan gibbons (e.g., family group E) but require further restoration for population growth and spatial expansion. In contrast, high-altitude areas remain ideal. This research underscores the importance of tailored restoration strategies for different food plant groups. Practices, such as thinning, are recommended to enhance food plant diversity and ensure a stable food supply. Future research should focus on human disturbances and plant interactions to fully understand the food plant distribution patterns.

Nomascus hainanus

food plants

spatial distribution

ecological characteristics

habitat restoration

Understanding the factors affecting food resource distribution patterns is crucial to regulating the Hainan gibbon population and improving habitat quality.
Hainan gibbons thrive and reproduce in low-altitude secondary forests, albeit in a significantly lower habitat quality compared to higher-altitude habitats.
Elevation, C/N, mean annual temperature, and annual precipitation were the main factors affecting the spatial distribution pattern of the food plants.
Future habitat restoration efforts should consider the differential effects of ecological factors across various elevations.

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.

2.1. Study site

We conducted our study in Bawangling within the Hainan Tropical Rainforest National Park (HTRNP; 19°05'00''–19°12'00''N, 109°11'00''–109°16'00''E), which is one of the 34 global biodiversity hotspots. This area spans an elevation range of 100–1,654 m and covers 4,269 km². It experiences distinct wet and dry seasons, with rainfall from May to October and a dry period from November to April. As elevation increases, the vegetation transitions from tropical lowland rainforest to tropical montane rainforest and then to tropical cloud rainforest. Correspondingly, the soil type varies from brick red loam and montane red loam to montane yellow loam and montane meadow soil (Long et al. 2011). Tropical lowland rainforests, found at elevations less than 800 m, are dominated by species, such as Terminalia hainanensis, Lannea coromandelica, Bombax ceiba, Albizzia procera, and Albizia odoratissima. The tropical montane rainforests, located at intermediate elevations (800–1,200 m), are primarily composed of Dacrydium pierrei and Podocarpus imbricatus. The tropical cloud forests above 1,200 m are dominated by Distylium racemosum, Syzygium buxifolium, and Rhododendron moulmainense (Jiang 2015).

2.2. Delineation of the home range

We monitored five Hainan gibbon groups (A, B, C, D, and E) year-round from March 2023 to March 2024, observing each group for 5 to 15 days per month and collected more than 20,000 location data points. Using ArcGIS 10.8 and the Home Range Tool (HRT) 2.0, we delineated the home range boundaries of these groups by combining Kernel Density Estimation with digital topographic maps. Due to the limited observational periods for groups A, B, and D, we also incorporated historical home range data spanning nearly 20 years, provided by the Bawangling division of HTRNP, along with satellite imagery (Fig. 1, Zhang et al. 2022). Based on Bryant et al. (2017), the average home range of Hainan gibbons is approximately 1.49 km² and varies seasonally. We defined home ranges with a buffer zone to better reflect actual space use patterns and potential boundary effects. Groups A, B, C, and D primarily inhabited tropical montane rainforests at elevations of 800–1,200 m around Futou Mountain, while group E was observed migrating from high-altitude areas to low-altitude secondary lowland rainforests at elevations of 500–750 m on Dongbeng Mountain in 2020. Following Zhang et al. (2022), we defined the habitats of groups A, B, C, and D as high-altitude habitats and the distribution area of group E as a low-altitude habitat.

2.3. Grid-plot layout and investigation

Using a Leica total station (Leica TPS1200+, Leica Geosystems, Heerbrugg, Switzerland), we established 122 plots, each 20 × 20 m, spaced 0.5 km apart, within the delineated home ranges. No monitoring plots were set up in rubber forests within the buffer zones around groups C and E. We considered overlapping habitats as part of the home range of each group for statistical analysis. There were 37 plots for group A, 35 for group B, 19 for group C, 39 for group D, and 30 for group E (Fig. 1).

Based on long-term observations of the Hainan gibbon food habits by the Bawangling division of HTRNP Administration, we identified 49 families, 92 genera, and 135 species as Hainan gibbon food plants (Zhang et al. 2022). Each 20 × 20 m plot was divided into sixteen 5 × 5 m subplots. We mapped, marked, and identified food trees with a diameter at breast height (DBH; 1.3 m) ≥ 1 cm, and recorded tree measurement factors, such as DBH, tree height, and crown width. We also recorded ecological factors for each subplot, including the slope aspect, elevation, and soil nutrients. We taxonomically identified the specimens following the Flora Reipublicae Popularis Sinicae (Editorial Committee of Flora of China, 2004).

2.4. Classification of food plants

Gibbons typically inhabit the large food tree canopy (Zhang et al. 2022). Classifying food trees by diameter helps understand the composition of potential food sources for gibbons. McConkey (2009) reported that the median DBH of food trees for Bornean gibbons is approximately 18 cm. Based on consultations with experienced local gibbon monitors and research on gibbon food preferences (Zhong et al. 2023), we used a DBH of 15 cm as the threshold preference for gibbons. We classified food source plants into small (1 cm ≤ DBH < 15 cm) and large (DBH ≥ 15 cm) categories. Studies show that Hainan gibbons prefer certain food plants during the rainy season when fruit availability is high but have a more diverse diet during the dry season when fruit availability is low (Du et al. 2020). We identified 33 major preferred food source plants (Appendix 2) and 40 major dry season food source plants (Appendix 3) based on long-term monitoring and literature studies (Liu and Tan 1990; Liu 2015; Tang and Jin 2021).

2.5. Ecological factor data

We obtained meteorological data from the WorldClim website (https://www.worldclim.org), which provides global data for 19 meteorological factors from 1970 to 2000 at a 1 km resolution. We extracted climate factor data for each plot based on the coordinates. Topographic data were sourced from the Geospatial Data Cloud (http://www.gscloud.cn) and further analyzed by stitching and cropping to obtain slope, slope orientation, and elevation data for the Hainan gibbon habitats. We measured slope direction, gradient, and elevation at each plot using a handheld GPS (Jisibao G130BD), a clinometer (Suunto PM-5/360 PC), and a geological compass (Brunton Geo Pocket Transit). This combination ensured accurate measurements of topographic variables in each plot. Soil data were collected from the surface layer (0–20 cm) in each plot using a five-point sampling method, involving samples from the four corners and the center of each plot. Samples were processed in the lab for soil physicochemical properties (Lu 2000). We extracted and analyzed all ecological data using ArcGIS 10.2 software (Li 2013).

2.6. Data analysis

2.6.1. Calculation of food plant diversity

We measured species richness and relative abundance to determine alpha species diversity. Relative abundance was calculated as the number of food plant species in each plot divided by the total number of individuals. Food plant richness was the number of species in each plot (Ma 1994).

2.6.2. Distribution patterns of the food plants

We used ordinary kriging with the Geo-statistical Analyst tool in ArcGIS 10.2 software (Li 2013) to aggregate and interpolate the richness and relative abundance of food plant species in each plot, creating a food plant distribution map. We analyzed differences between the high and low-altitude habitats using t-tests, where the t-value represented the test statistic, df denoted degrees of freedom, and the P-value indicated the probability (Student 1908).

2.6.3. Abiotic factors influencing the food plant distribution

To avoid spatial autocorrelation among habitat ecological factors affecting the regression results, we excluded variables with correlation coefficients > 0.8. We performed Pearson’s correlation analysis using the cor function (Oksanen 2011) and plotted a correlation heatmap with the corrplot package (Appendix 1). We constructed Random Forest models using the rfPermute function in the rfPermute package to explore the main factors influencing food plants (Li 2013), with each 20 × 20 m plot serving as a sampling unit. Predictor variables included climate, topographic, and soil factors, while response variables were food plant richness and abundance. Climatic factors included annual mean temperature, daily temperature difference, annual precipitation, precipitation seasonality, and warmest seasonal precipitation. We included all topographic and soil factors in the analysis. We further analyzed key driving factors using general linear models (Nelder and Wedderburn 1972) to quantify their differential effects on food plant distribution across various elevations. All analyses were conducted using ArcGIS 10.2 and R 3.6.2.

3.1. Spatial distribution of ecological factors

The habitat ecological factors of the Hainan gibbons revealed significant differences between the high and low-altitude groups. Groups A, B, C, and D were located on steeper slopes, while group E was on a gentler slope.

The high-altitude habitats had higher soil organic matter (t = 2.16, P = 0.03; mainly in groups B and D), total nitrogen (t = 2.74, P < 0.01; mainly in groups B and D), and nitrogen-to-phosphorus ratio (t = 5.18, P < 0.01). In contrast, the low-altitude habitats had higher fast-acting phosphorus (t = − 2.48, P = 0.01; mainly in group E). Soil organic matter and total nitrogen were lower in the eastern parts of groups A and C, while fast-acting phosphorus was lower in the eastern part of group A, the northern part of group C, and the central part of group D.

The high-altitude habitats (groups A, B, C, and D) exhibited lower annual mean temperatures (t = − 9.03, P < 0.01) and greater daily temperature differences (t = − 9.00, P < 0.01), along with higher annual precipitation (t = 8.07, P < 0.01), precipitation seasonality (t = − 6.13, P < 0.01), and warmest season precipitation (t = 4.98, P < 0.01). In contrast, low-altitude habitats (group E) had higher annual mean temperatures and daily temperature differences but lower precipitation levels (Fig. 2; Fig. 3).

3.2. Spatial distribution patterns of the food plants

3.2.1. Distributions of the different diameter classes of food plants

The high-altitude habitats had significantly higher species richness of food plants compared to the low-altitude habitats (t = 5.02, P < 0.01; Fig. 4-d). The higher richness areas were in the A, western C, northern B, and southern D groups, while lower richness was mainly in the E group. Relative abundance was similar across altitudes except for the southern B and eastern D groups. (Fig. 4-a). The small-diameter food plants had a higher richness in high-altitude habitats (t = 4.23, P < 0.01; Fig. 4-d). Higher relative abundance was noted in the eastern A, northern C, and eastern E groups, with lower values observed in the southern B and eastern D groups (Fig. 4-a). Large-diameter food plants had higher richness (t = 4.83, P < 0.01) and relative abundance (t = 3.80, P < 0.01) in the high-altitude habitats (Fig. 4-d). The higher abundance areas were in the southern A family group and southern D family group, and lower abundance was found in the E family group, particularly in the north (Fig. 4-a).

3.2.2. Distribution of preferred food plants

The preferred food plants had higher richness (t = 2.82, P < 0.01) and abundance (t = 2.76, P < 0.01) in the high-altitude habitats (Fig. 4-d). The higher richness areas were in the A, B, western C, and southern D groups. Lower richness was found in the E group. Higher abundance was detected in the A and C groups, while lower abundance was observed in the northern D, western B, and northern E groups. (Fig. 4-b). Additionally, family group E had a limited distribution of large-diameter preferred food plants.

3.2.3. Distribution of dry-season food plants

Dry-season food plants had higher species richness in the high-altitude habitats (t = 3.74, P < 0.01; Fig. 4-d). The higher richness areas were in the southern A and D groups, whereas lower richness was observed in the E group. Relative abundance was not significantly different by altitude, with higher values in the eastern A, C, and E groups, and lower values in the B group. Small-diameter dry-season food plants had a higher richness in the high-altitude habitats, with similar abundance across altitudes. Large-diameter dry-season food plants had higher richness and abundance in the high-altitude habitats (Fig. 4-c).

3.3. Factors affecting the spatial distribution pattern of the food plants

The Random Forest model identified elevation as a critical driver for all food plant distributions (P < 0.05). Key factors included the soil C/N ratio, mean annual temperature, and annual precipitation. Slope gradient, slope aspect, and total P had less influence. Elevation, mean annual temperature, and the soil C/N ratio were positively correlated with food plant abundance (P < 0.01). Preferred food plant species richness correlated with elevation and the soil C/N ratio (P < 0.01). Dry season food plant richness was correlated with elevation, the soil C/N ratio, and the soil N/P ratio (P < 0.01) (Fig. 5). Significant factors differed by diameter classes: fast-acting N, total P, and precipitation seasonality affected small-diameter plants (P < 0.05), while annual precipitation, daily temperature difference, soil organic matter, and slope influenced large-diameter plants (Fig. 5).

General linear models showed varying effects of the main factors across altitudes. Bio1 reduced the food plant distribution at high altitudes (β = −1.61, P < 0.05) but not at low altitudes (β = 0.11, P = 0.92). TP decreased the food plant abundance at high altitudes (β = −38.39, P < 0.01) and increased it at low altitudes. Other factors, such as TN, C/N, N/P, and Bio15, did not reveal any significant altitude-dependent differences in their effects on the food plant distribution (Fig. 6).

Based on a survey of 122 grid plots within the Hainan gibbon habitats, we identified significant differences in species richness and distribution of food plants between high- and low-altitude areas, as well as varying effects of key driving factors across different plant types and elevations. Our main findings include 1) significant differences in ecological factors and food plant distribution between high and low altitudes, with higher species richness at higher altitudes; 2) key drivers of food plant distribution, such as elevation, the C/N ratio, mean annual temperature, and annual precipitation; and 3) differential effects of these factors across altitudes and food plant types. These findings highlight the need for tailored conservation and restoration efforts that consider specific ecological factors and their varying effects under different scenarios, emphasizing the potential of low-altitude secondary forests to support the critically endangered Hainan gibbon by expanding their habitat and enhancing population growth.

4.1. Spatial distribution of food plants varies among altitudes and family groups

Our study identified significant differences in the spatial distribution of the food plants between high and low elevations in the Hainan gibbon habitats, validating our first hypothesis. High-altitude habitats (family groups A, B, C, and D) exhibited higher species richness due to the presence of the tropical montane old-growth forests around Futou Mountain, which have significantly greater plant species richness compared to lowland secondary forests (Zhou 2008; Fibich et al. 2016). Additionally, high-altitude habitats had a higher relative abundance of preferred food plants, particularly in family groups A and C, supporting larger gibbon populations. In contrast, low-altitude areas had significantly fewer large food plants, particularly large preferred food plants, indicating substantial differences in community supply. Liu and Tan (1990) reported that gibbons primarily move and feed in tall trees, and a lack of large food plants could negatively affect their survival and reproduction (Hamard et al. 2010). These results support the hypothesis that high-altitude habitats provide superior resources for gibbons, consistent with previous research on higher biodiversity in tropical montane forests (Zhou 2008).

Despite these deficiencies, our study showed that low-altitude secondary forests (family group E) had a sufficient number of small food plants (Fig. 4-d), indicating potential as future habitat for Hainan gibbons. The presence of family group E in these low-altitude areas suggested that these habitats could become viable for gibbons with appropriate restoration. This finding aligns with historical data showing that gibbons primarily inhabit elevations of 400–1,000 m (Liu and Tan 1990). Reforestation efforts have been successful in Hainan since 1994, leading to the gradual recovery of the secondary forests. Enhancing low-altitude forest management through thinning and other practices could accelerate succession, transforming secondary forests into mature lowland rainforests (Zhang and Zang 2018). These measures would increase food plant richness, ensuring a stable food supply during the dry season. Our study differed from previous research by focusing on the successional potential of secondary forests, highlighting the importance of restoring low-altitude forests to provide substantial habitat for gibbons. This underscores the necessity for continued conservation and restoration efforts to ensure the long-term survival and habitat expansion of the critically endangered Hainan gibbon.

4.2. Factors affecting the food plant distribution

Our study identified elevation, the C/N ratio, annual mean temperature, and annual precipitation as the primary factors affecting food plant distribution in the Hainan gibbon habitats (Fig. 5), consistent with Hypothesis 2. Previous research has shown that elevation significantly affects plant species distribution, with species richness peaking at mid-elevations (Liu et al. 2007; Arenas-Navarro et al. 2020). Additionally, lower elevations offer ample light but lower humidity, while higher elevations have better humidity but insufficient light (Jiang 2015), explaining the concentration of habitats at 500–1,200 m.

Soil nutrients also significantly affect the distribution of plants. Soil organic matter, containing the essential nutrients for plant growth, serves as a comprehensive indicator of soil fertility. Low soil fertility affects plant growth, reducing the number of individuals a habitat can support (Wang et al. 2014), and affecting the soil gas-water exchange as well as nutrient availability (Schoenholtz et al. 2000). Nitrogen and phosphorus are crucial for plant diversity, and deficits severely affect photosynthesis and water use strategies (Bucci et al. 2006). Although phosphorus was not a primary factor, it is often a limiting nutrient in tropical regions (Baribault et al. 2012), warranting further investigation.

Annual mean temperature, annual precipitation, and precipitation seasonality also play crucial roles in plant distribution and the phenology of food plants (Crimmins et al. 2011; Engler et al. 2011; Potter et al. 2013; Du et al. 2020). The main food resources for gibbons are fruits and tender leaves, and changes in the phenology of food plants directly affect their survival and distribution (Deng and Zhou 2018; Naher et al. 2021). Therefore, future restoration efforts of the Hainan gibbon habitat should carefully consider the effects of climatic conditions on food plants.

4.3. The effects of key drivers vary among food plant types and elevations: conservation insight

Our research revealed that the driving factors for different food plant types varied significantly. For example, Bio1 and TN primarily affected the distribution of food plants. The C/N ratio and TP are more crucial for preferred food plants, whereas the N/P ratio and Bio15 mainly drive the distribution of dry-season food plants (Fig. 5). These differences are due to the specific habitat preferences of various food plant species, such as Ficus spp., which thrive in low C/N environments (Zhang et al. 2022), whereas Liquidambar formosana prefers higher N/P ratios (Lin et al. 2006). Restoration efforts must consider these specific factors to avoid creating ecological traps.

Additionally, the key driving factors affected the distribution of food plants differently at different elevations (Fig. 6), confirming Hypothesis 3. Linear regression analysis indicated that higher soil phosphorus (TP) levels were associated with a lower abundance of preferred food plants. This may be because high phosphorus levels promote the growth of competitive plant species, which suppresses the growth of preferred food plants. Therefore, in high-altitude areas, it may be necessary to control soil phosphorus levels to prevent them from becoming too high. However, increasing soil phosphorus levels could improve growing conditions in low-altitude areas. This underscores the importance of implementing elevation-specific strategies when restoring habitats. Future conservation plans should integrate these insights to enhance the effectiveness of habitat restoration and ensure the sustainability of the Hainan gibbon population.

4.4. Integrating comprehensive factors for effective conservation

This study considered soil nutrients, topographic factors, and climatic factors, but plant species distribution patterns are affected by both external ecological factors (Chanthorn et al. 2018; Libalah et al. 2020) and internal plant interactions (Fibich et al. 2016; Zhou et al. 2019). Future research should consider human disturbances and plant interactions to provide a comprehensive understanding. Long-term monitoring is needed to assess the effectiveness of habitat restoration and explore low-altitude secondary forests as viable habitats through natural succession.

This study quantified the spatial distribution of food plants in the Hainan gibbon habitat and identified key driving factors, providing a scientific basis for habitat restoration. The high-altitude habitats exhibited greater food plant diversity and were the most suitable habitats for Hainan gibbons. Although the low-altitude secondary forests supported gibbons and had sufficient small food plants, they lacked the large food plants necessary for gibbons. To improve these habitats, targeted management practices, such as thinning, are recommended to enhance plant diversity and ensure a stable food supply. Elevation, the C/N ratio, annual mean temperature, and precipitation significantly affected the plant distribution, with varying effects across different altitudes and food plant types. These findings underscore the necessity of considering specific ecological factors in conservation strategies to ensure the long-term survival and habitat expansion of the critically endangered Hainan gibbon. Future research should consider additional factors, such as human disturbances and plant interactions, to achieve a comprehensive understanding. Long-term monitoring is essential to assess the effectiveness of habitat restoration efforts.

Competing Interests

None of the authors has any conflicts of interest to report.

Funding

This work was supported by the Key Project of the National Natural Science Foundation of China (U22A20503), and the grant of the Hainan Province Innovation of Science and Technology Talents (KJRC2023C13) as well as the grant of the Institute of Hainan National Park (HD-KYH-2021001).

Author Contribution

All authors contributed to the study’s conception and design. Material preparation, data collection, and analysis were performed by SL, AZ, and DZ. The first draft of the manuscript was written by SL, with WL and YC providing comments on early versions. GW provided suggestions on the manuscript before submission. All authors have read and approved the final manuscript.

Acknowledgments

This work was supported by the Key Project of the National Natural Science Foundation of China Regional Innovation and Development Joint Fund“Habitat maintenance and restoration mechanism of Hainan gibbon” (U22A20503), and a grant from the Institute of Hainan National Park, “Establishment of a monitoring system for Hainan gibbon habitats”(HD-KYH-2021001). We thank the staff of the Bawangling Branch of HTRNP for their support. We also appreciate the assistance of Rucai Li, Jinqiang Wang, and Ming Wu with help in identifying plant species.

Data Availability

The datasets generated during and/or analyzed during this study are available from the corresponding author upon reasonable request.

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Effects of Ecological Factors on the Spatial Distribution of Food Plants in Hainan Gibbon (Nomascus hainanus) Habitat: Conservation and Habitat Restoration Insights

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Abstract

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Highlights

1. Introduction

2. Materials and methods

2.1. Study site

2.2. Delineation of the home range

2.3. Grid-plot layout and investigation

2.4. Classification of food plants

2.5. Ecological factor data

2.6. Data analysis

2.6.1. Calculation of food plant diversity

2.6.2. Distribution patterns of the food plants

2.6.3. Abiotic factors influencing the food plant distribution

3. Results

3.1. Spatial distribution of ecological factors

3.2. Spatial distribution patterns of the food plants

3.2.1. Distributions of the different diameter classes of food plants

3.2.2. Distribution of preferred food plants

3.2.3. Distribution of dry-season food plants

3.3. Factors affecting the spatial distribution pattern of the food plants

4. Discussion

4.1. Spatial distribution of food plants varies among altitudes and family groups

4.2. Factors affecting the food plant distribution

4.3. The effects of key drivers vary among food plant types and elevations: conservation insight

4.4. Integrating comprehensive factors for effective conservation

5. Conclusions

Declarations

Competing Interests

Funding

Author Contribution

Acknowledgments

Data Availability

References

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