Identification of Suitable Habitats in different biogeographic provinces of IHR
Identifying suitable habitats that support the long-term survival of species under changing climatic scenarios is crucial for timely management and conservation efforts. This study represents the first effort to predict the distribution of Barking deer under current and future climate and land use patterns, utilizing Shared Socioeconomic Pathways (SSPs) SSP2.6 and SSP8.5 for the years 2050 and 2090 in three provinces of the Indian Himalayan Region (IHR), as well as across the IHR as a whole. The distribution of vegetation in the Himalayas, heavily influenced by variations in topographic and climatic factors (Salick et al. 2014), leads to diverse phytogeographic zones that significantly impact the distribution and ecology of species like the Barking deer (Singh and Kumar 1997).
Acknowledging the distinctiveness of the different biogeographic provinces in the IHR, we conducted region-wise modeling to understand how climatic, topographic, and land use variables influence the distribution of Barking deer in each province—Western, Central, and Eastern Himalayas—and in a combined model of the entire IHR. Forest presence, a key variable, showed a positive association with the probability of Barking deer occurrence in the Western and Central Himalayas, corroborating with previous studies that suggest good canopy cover and leaf litter provide vital food sources for Barking deer (Lekagul and McNeely 1977; Armstrong et al. 1983; Takahashi and Kaji 2001; Ilyas et al. 2003; Teng et al. 2004; Odden and Wegge 2007; Neupane et al. 2022). Among topographic variables, slope was particularly influential, with the probability of occurrence decreasing with increased steepness in the Central Himalayan landscape, where moderate levels of slope positively influence the presence of Barking deer (Singh and Kushwaha 2011; Paudel and Kindlmann 2012; Pokharel et al. 2015; Neupane et al. 2022). In this study, the species was found using a habitat up to the 3650-meter elevation in Eastern and Central Himalayas, whereas the species was found using an elevation up to 3300 meters in Western Himalayas (Fig. 5). This study also predicts that the species in the future will neither move upwards or lower in elevation.
Anthropogenic variables also showed a positive association with Barking deer occurrence up to a Human Influence Index value of 30%, after which a significant decrease was observed, indicating tolerance towards human presence (Oka 1998; Jathanna et al. 2003; Paudel and Kindlmann 2012). This tolerance is likely facilitated by agroforestry practices that provide ample food and other resources, which are easily accessible at forest edges or agricultural fields (Hofmann 1989; Ilyas 2003).
Spatial distribution prediction of Barking deer in three biogeographic province of IHR suggest that the species occupies the habitat outside the protected areas (territorial forest, community forest etc) more than the PAs corroborated with the findings of previous studies (Lekagul and McNeely 1977; Kitamura et al. 2010; Trisurat et al. 2014). The Barking deer distribution range in CH and EH will decline under future land use and climate change scenarios, which could be due to habitat loss, habitat fragmentation and habitat degradation. Whereas the prediction is just the opposite in WH, it was observed that currently, the species occupies the dense canopy forest, but in future, the species may occupy a habitat close to human settlement or cropland or open forest; hence, there will be a shift rather loss of distribution range.
The probability of occurrence of Barking deer across all three biogeographic provinces of the Indian Himalayan Region (IHR) is strongly associated with bioclimatic variables. Notably, in the Western Himalaya (WH) and throughout the IHR, the distribution of Barking deer is significantly influenced by the mean temperature of the wettest quarter (bio8 up to 18°C). The peak growing season for plants coincides with this period of high precipitation and optimal temperatures, which enhances vegetation growth, nutrient availability, forage quality, and water availability—key factors for meeting the deer’s nutritional needs for survival and reproduction (O’donnell et al. 2012; Richardson 2000; Hanley et al. 2012; Felton et al. 2020).
Conversely, the mean monthly temperature (bio2) negatively impacts Barking deer distribution in both Eastern (EH) and Central Himalayas (CH). In EH, Isothermality (bio3) which measures the diurnal temperature oscillations relative to the annual oscillations significantly influences Barking deer occurrences. This variable supports the availability of feeding resources in different seasons and suits the microclimatic preferences of Barking deer, providing a consistent food supply throughout the year (Odden and Wegge 2007; Habiba et al. 2020). Previous studies confirm these observations, noting no seasonal differences in habitat selection, home range size, or elevation shifts among Barking deer (Odden and Wegge 2007; Habiba et al. 2020). However, in the Eastern Himalayas, precipitation seasonality (Coefficient of Variation) (bio15) shows a negative association with the occurrence of Barking deer. Here, an increase in monthly precipitation fluctuation correlates with a sharp decrease in the likelihood of Barking deer presence, suggesting that the species struggles with high variability in precipitation. This finding underlines the critical role of stable hydrological conditions in determining Barking deer distribution at local and landscape levels throughout the IHR.
This study assumes that both temperature and precipitation significantly affect the probability of Barking deer presence, which may extend to other species in the IHR. Such inferences are supported by broader ecological studies documenting similar responses to climatic variables (Dai et al. 2019; Mukherjee et al. 2021). Under the three scenarios (M1, M2, and M3), WH shows a considerable gain in suitable habitat for Barking deer by 2050 and 2090 under both low and high emission and development conditions. Notably, the habitat expansion is most pronounced toward the southern regions, which are currently unsuitable, with the greatest increase projected under the M3 scenario in 2050. This suggests that Barking deer in WH are effectively adapting to changing climatic and land-use conditions, tracking adaptive environmental niches.
In contrast, the suitable habitat for Barking deer in Central (CH) and Eastern Himalaya (EH) is expected to decrease under the combined effects of climate and land-use changes (M1) for both the 2050 and 2090 projections, across all emission and development scenarios. However, isolated impacts of climate change (M2) or land-use change (M3) alone show less detrimental effects on habitat than the combined scenario (M1). Future shifts in Barking deer habitat in CH are anticipated to move from degraded and sparsely forested areas—currently used for agriculture or agroforestry—toward denser forests, driven by the availability of food, water sources, predation pressure, and human activities. Similarly, in EH, the habitat is expected to shift toward mid-altitudes (1000–2000 m), aligning with the species' preference for mid-elevation zones (Bhattacharya et al. 2010; Pokharel and Chalise 2010; Neupane et al. 2022). This habitat transition in CH and EH is directly tied to anticipated changes in climate and land use. The study underscores the Barking deer's difficulty in coping with these projected changes, particularly under both low and high emission and development scenarios. Moreover, overall distribution modeling across the IHR indicates a decrease in suitable habitat under all scenarios (M1, M2, and M3), reinforcing the importance of the middle elevations, which offer adequate resources for the Barking deer.
Landscape metrics reveal that habitat patches in WH, CH, and EH are expected to decrease in number and fragment into smaller sizes in future scenarios. This fragmentation suggests that Barking deer in Central and Eastern Himalayan regions may not effectively track climate change, facing greater habitat loss than their counterparts in Western Himalayas. This study provides significant baseline information on the habitat suitability of Barking deer in the Indian Himalayan Region (IHR). Our findings reveal that the distribution and environmental predictors vary across different provinces of the IHR, necessitating region-specific conservation planning. The models predict that the majority of suitable habitats for Barking deer are clustered at mid-altitudes across all three biogeographic provinces (WH, EH, and CH).
The presence of Barking deer is crucial for ecosystem functioning, particularly in governing the populations of large carnivores in the Himalayas (Anup 2017; Kandel 2019; Baral et al. 2023). This is in contrast to mainland habitats, where diverse sympatric species such as sambar, chital, Indian gazelle, and mouse deer are abundant (Selvan et al. 2013; Rather et al. 2020). In the mid-Himalayas, Barking deer emerge as the dominant ungulate species, thus forming a major component of the diet for large carnivores, including the common leopard (Sathyakumar et al. 2011; Shrestha 2015; Kandel 2019).
Furthermore, our study highlights a concerning trend: most Barking deer habitats are located outside protected areas. These areas are at risk of degradation and fragmentation due to rapid development, emphasizing the urgent need for enhanced conservation efforts to designate these vulnerable areas as Protected Areas (PAs). Specifically, the loss of suitable habitat in the Eastern and Central Himalayas is predominantly at the forest edge, making these regions particularly susceptible to the impacts of rapid development and anthropogenic activities.