Biodiversity hotspot assessment in the Altai Mountains transboundary region based on Mammals and Aves

environmental variations that influence species distributions. Elevation affects temperature and precipitation patterns, while slope influences soil stability and water drainage. These fac- tors are critical in mountainous regions like the Altai Mountains, where altitude can create diverse microhabitats. Landscape variables, including land use and land cover (LULC), were selected to reflect the spatial structure and composition of the habitat. The landscape heteroge- neity was measured using Shannon’s Diversity Index (SHDI) to represent habitat diversity, and the landscape contagion index (CONTAG) to depict landscape connectivity. These indices are crucial for understanding habitat fragmentation and connectivity, which are important for species movement and survival [35]. Human activity variables, such as population density, road distance, and night light data, were chosen to represent anthropogenic pressures on the environment. These variables are indicators of human presence and infrastructure develop- ment, which can lead to habitat loss, degradation, and fragmentation. Including these variables helps in assessing the impact of human activities on species distributions and identifying areas that require conservation interventions. Bioclimatic (BIO1~BIO19) variables were collinearly eliminated using Band Collection Sta- tistic in ArcGIS 10.8 (selection range -0.7~0.7). We selected a certain number of species occur- rence data and used the built-in tool [Spatially Rarefy Occurrence Data for SDMs (reduce

spatial autocorrelation)] of SDM Toolbox v2.5 (http://www.sdmtoolbox.org/) to reduce the resolution to rarefy. The data frame was set to 1 km to avoid spatial autocorrelation caused by species distribution points being too close, which could affect the accuracy of prediction results [36, 37]. Finally, we eliminated the data with AUC less than 0.8 and obtained a total of 20 spe- cies of Mammals (Detailed procedures are provided in S1 File), including 7 threatened species, such as Snow leopard (Panthera uncia), Siberian Ibex (Capra sibirica), etc., and 13 species of least concern, such as Siberian Chipmunk (Eutamias sibiricus), etc. There are 605 species of Aves, including 20 threatened species, such as Cinereous Vulture (Aegypius monachus), and 585 non-threatened species, such as Chuckar (Alectoris chukar) (Fig 2). Results Distribution characteristics of BHs Fig 3 shows the BHs of AMTR Mammals and Aves respectively. There is a certain spatial simi- larity in BHs between TM and AM species. High richness (HR) is mainly distributed in the Russian-Mongolian border areas and near-border areas of Mongolia. Medium richness (MR) also has obvious distribution characteristics along the National boundaries and covers most of the Altai Mountains. Low richness (LR) is mainly distributed in MAR. From an area perspec- tive, the HR of TM is approximately 9943.29km2, the MR is approximately 94589.96km2, and the LR is approximately 131667.55km2. The HR of AM is approximately 22877.47 km2, and the HR is larger than the HR of AM.

The spatial distribution of HR of AA is also similar to AM and is mainly distributed in the Russian-Mongolian border areas and the near-border areas of Mongolia. Similarly, the area of MR (38482.06km2) for TA was larger than the area (35976.61km2) for AA. The HR (6012.66km2) and LR (6918.04km2) of TA are smaller than that of AA (HR area: 615955.75km2, LR area: 636102.77km2), and there is spatial overlap between AA distribution and water sources. This difference may be due to the fact that most AA have similar suitable habitat areas and there are differences in spatial distribution among AM. From the perspective of each partition, AA diversity is mainly concentrated in the RAR (the HR ratio of TA is 82.40%, and the HR ratio of AA is 83.19%; the MR ratio of TA is 64.30%, and the MR ratio of AA is 72.44%). AM diversity is mainly distributed in the MAR (the HR of TM proportion is 54.84%, the HR of PLOS ONE Biodiversity hotspot assessment in the Altai Mountains transboundary region PLOS ONE | https://doi.org/10.1371/journal.pone.0314075 December 4, 2024 6 / 20