Spatial Pattern and Habitat Changes of Amphibian Species in the Priority Area for Biodiversity Conservation in the South Hengduan Mountains

Abstract

Amphibian species, as typical objects to study the evolution of vertebrates from aquatic to terrestrial, have faced serious threats in recent decades. This study revealed changes in the spatial distribution pattern of amphibians and their habitats in the priority area for biodiversity conservation in the south of the Hengduan Mountains based on remote sensing and field survey data. Results showed that 71 species of amphibians in 27 genera of 10 families of 2 orders were recorded in the study area, among which 46 species were endemic to China. In particular, there were four national protected species and two newly found species. The amphibian species richness was overall higher in the northern part and lower in the southern part of the study area. There was an obvious variation in the species composition in five major geographic zones in the study area, and the species richness, number, and endemism were all the highest in areas between 2000 and 3000 m. There was a higher abundance of some endemic species, i.e., the Amolops, Bufo, and Scutiger. The main habitats of amphibian species included the forest, farmland, and grassland. There was remarkable fragmentation of these habitats, which was mainly due to land use conversion. There are currently 14 national nature reserves in the study area, covering 39 amphibian species, but there are still 32 amphibian species outsides these nature reserves. It is recommended to carry out long-term located monitoring, improve the existing protection network, and fill the protection gaps to achieve effective protection of these valuable biological resources.

1. Introduction

Biodiversity plays a fundamental role in supporting the survival and development of human beings, and it is a focal and difficult issue to explore how to achieve sustainable use of biological resources in areas with increasing human activity disturbance [1,2,3]. Compared with other vertebrates, the amphibian species are characterized by smaller size, fewer species number, and sensitiveness of their distribution to the environment; however, they are very closely related to the production and living of human beings, and their species and population size are often used to characterize the ecosystem stability, which is pivotal in maintaining the ecosystem integrity and ensuring the ecosystem health [4,5]. In particular, the amphibian species can serve as important indicator taxa of the ecosystem health and can provide early warning signals of environmental changes [3,6]. Nevertheless, the global amphibian species have faced various serious threats, and their population size has declined rapidly in recent decades [7,8,9]. According to the latest results of IUCN [9], the percentage of threatened amphibian species has reached 41%, which is much higher than that of the birds (14%) and mammals (26%). It is notable that land use change is the most important factor leading to biodiversity loss, and the amphibian species are the vertebrates that are vulnerable to land use change around the world [10,11,12,13]. Scholars at home and abroad have carried out considerable exploration on the effects of agriculture, livestock farming, urbanization, deforestation, afforestation, and selective logging on the amphibian communities [14,15,16,17], and they find that land use change is the main factor leading to habitat degradation, which causing amphibian decrease [10]. Here, we defined amphibian habitats as forests, grasslands, waters, wetlands, etc.

The priority area for biodiversity conservation in the South Hengduan Mountains is one of the 25 biodiversity hotspots around the world [18]. Hengduan Mountains extend across eastern Tibet, western Sichuan Province, and northwest Yunnan Province of China, which are an important part of the Qinghai-Tibet Plateau, and there are a number of mountains and rivers extending from north to south in the priority area for biodiversity conservation with unique natural geographic conditions and various biota, making this region a key area of biodiversity research and conservation. The priority area is one of 35 biodiversity conservation priority areas in China. Priority areas are defined according to the richness, rarity, and endangerment of species, the representativeness of ecosystem types, and the irreplaceable nature of the region. They are the key areas for biodiversity protection in China.

The Amphibian and Reptile Report of the Hengduan Mountain Region is a systematic survey report of amphibians published in 1997, which is an important achievement of the scientific investigation in the Hengduan Mountain region of the Tibetan Plateau. In recent decades, the habitats in this region have undergone significant changes due to land use change, urbanization, infrastructure construction, and other factors, and there have also been significant changes in the species, number, and distribution of amphibians. However, the amphibian surveys in this region mainly include regional special surveys and reserve special surveys [19,20], with lower systematization and wholeness, leading to various problems such as unclear biodiversity background.

The amphibian survey in the priority area for biodiversity conservation in the south of the Hengduan Mountains in this study was a large-scale systematic survey in recent years, which could provide important data support for mapping the spatial distribution and population dynamics of amphibians in the priority area, which was very helpful in more effectively protecting amphibians. This study has explored the distribution pattern of amphibian species based on the amphibian survey data of the priority area during 2019~2020 and analyzed the influence of land use change on the amphibian biodiversity based on the land use data from 2000 to 2020, aiming to provide firm support for the sustainable use of biological resources.

2. Materials and Methods

2.1. Study Area

The priority area is located in southwest China, involving 40 counties in Yunnan Province, Sichuan Province, and Tibet autonomous region. This area is characterized by undulating terrain, where there are widespread high mountains and canyons, with an elevation between 271 and 6252 m, and the highest peak is located in Jade Dragon Snow Mountain. The priority area is the core area of Hengduan Mountain that can best represent its geomorphic characteristics. Jinsha River, Nujiang River, and Lancang River cross many mountain systems and form a three-river parallel flow area, alpine mountain area, and alpine river valley area.

The priority area was divided into five major geographical divisions, i.e., Tibetan-Shangri-La area, Gaoligong Mountain-Biluo Snow Mountain area, Yunling Mountain area, Shaluli Mountain area, and Daxue Mountain-Small Xiangling Mountain-Liang Mountain area, primarily according to the regional geographical differentiation characteristics.

The priority area is a representative area of the rare alpine landform in the world, which breeds very rich biodiversity. It is one of the areas with abundant biological resources in China, including 14 national nature reserves. Biodiversity distribution shows obvious vertical zonality; for example, species diversity and phylogenetic diversity reach the peak at an altitude of 1800~2000 m in the Gaoligong Mountain-Biluo Snow Mountain area. There are many animals and plants under special state protection in the priority area, e.g., alpine forest ecosystems, alpine wetland ecosystems, Alsophila spinulosa, Paradombeya sinensi, Ailuropoda melanoleuca, Rhinopithecus bieti, and other national key protected plants and animals [21].

2.2. Methods

2.2.1. Field Survey Methods

A scientific and feasible sampling scheme is proposed by using the systematic sampling method and considering the systematic integrity and spatial protection attributes of historical survey data. Firstly, the study area was divided into 1589 10 km × 10 km grid cells. Then, according to principles of the coverage of all ecosystem types in each elevation segment, the balance of survey points in five geographical divisions, typical habitat of amphibians, and road accessibility, 198 survey grid cells were selected. In each grid cell, we set 3 transect lines, with a length of 500 m for each sample line. The interval between transects is greater than 500 m, and all transects are investigated twice in the breeding season and non-breeding season. Considering the area of five geographical zones, sampling intensity, and road accessibility, we set 526, 245, 537, 239, and 502 transect lines in the Tibetan-Shangri-La area, Gaoligong Mountain-Biluo Snow Mountain area, Shaluli Mountain area, Yunling Mountain area, and the Daxue Mountain-Xiaoxiangling Mountain-Liangshan Mountain area, respectively. There were 334, 442, 737, 616, and 280 transect lines among five elevation gradients, respectively, and 395, 698, 671, 409, 158, and 78 among six habitat types. We conducted our surveys in a 10 m range around each sample line within 8:00−24:00 in habitats such as streams, lakes, ponds, and forest trails, and special attention was paid to some small habitats, e.g., piles of dead branches and leaves, small pools of water after rain, and caves, where amphibians could hide easily.

The amphibian survey in the priority area was conducted between June and September 2019 and 2020. In particular, each transect line was surveyed twice. In summary, there were 2049 sample lines in total, and the relevant survey results were recorded with the biodiversity survey mobile software during the survey. We used LED flashlights to find amphibians and recorded species name, number, latitude and longitude, and habitat.

2.2.2. Species Identification Methods

Species and protection ranks were identified based on standard references [22,23,24,25,26,27]. Individual specimens were collected for species that were difficult or unreliable to be identified in the field, which were firstly fixed in 8–10% Formalin solution in the field, then rinsed with water in the laboratory, and finally preserved in 75% alcohol. The molecular identification of these specimens was thereafter carried out in the laboratory.

2.2.3. Biodiversity Exploration Methods

The elevation, habitat types, and geographic conditions can greatly affect the distribution of the amphibian species. This study has accordingly categorized the priority zone into five elevation gradients (i.e., <1000 m, 1000–2000 m, 2000–3000 m, 3000–4000 m, and >4000 m) and five geographic zones and then summarized the species richness, number of individuals, and degree of dominance at different elevation gradients. Specifically, the species richness was calculated with the species number of amphibians. The degree of dominance was calculated with the Berger–Parker degree of dominance [28], i.e., P_i = N_i/N, where P_i denotes the degree of dominance; N_i represents the number of individuals of the ith species; N is the total number of individuals. The diversity index was calculated with the Shannon–Wiener index, Pielou evenness index, and Margalef abundance index as follows.

$$H^{\prime }=-{\displaystyle \sum }_{i=1}^S{P}_{i}ln{P}_i$$

(1)

$$E=\frac{H^{\prime }}{l{n}_S}$$

(2)

$$D_{MG}=\frac{S-1}{l{n}_N}$$

(3)

where H′ is the Shannon diversity index, E is the Pielou evenness index, D_MG is the Margalef abundance index, P_i is the frequency of species; S is the number of taxa; N_i is the number of individuals of the ith taxon; N is the total number of individuals of all taxa.

This study explored the relationship between the ecosystem type change and species information in the whole study area with the classified statistical tools in the ArcGIS software. This study set the maximum migration distance of amphibians to be 1500 m according to Smith et al. [29] and thereafter explored the influence of habitat change within the migration distance on the amphibian habitat as follows. Firstly, the buffer zone of 1500 m around the species point was generated with ArcGIS tools. Secondly, the buffer zone of multiple species points was dissolved to obtain the unique migration distance boundary. Thirdly, this boundary was used as a mask to extract the habitat type data in 2000, 2010, and 2020, which include farmland, forest, shrub, grassland, wetland, and built-up land.

Meanwhile, the correlation analysis between species richness and habitat type was carried out. If the result is significantly correlated, it indicates that habitat change will affect species richness. The analysis steps are as follows: firstly, the species richness of different habitats on different grids is obtained by using the statistical function of ArcGIS; then, the correlation analysis is carried out in SPSS 22.0 software.

3. Results

3.1. Species Composition

The recorded amphibian species in the priority area included 72 species in 27 genera of 10 families of 2 orders, including Lithobates catesbeiana as an exotic species, which was excluded in the subsequent analysis. Specifically, there were 3 genera and 6 species of Dicroglossidae, 2 genera and 7 species of Bufonidae, 3 genera and 4 species of Microhylidae, 4 genera and 18 species of Megophryidae, 1 genus and 1 species of Bombinatoridae, 1 genus and 3 species of Salamandridae, 4 genera and 7 species of Rhacophoridae, 7 genera and 22 species of Ranidae, 1 genus and 2 species of Hynobiidae, and 1 genus and 1 species of Hylidae. In terms of species richness, Ranidae and Megophryidae accounted for 30.99% and 25.35% of the total number of amphibian species, respectively. There were four protected species of national Class II, accounting for 5.63% of the total amphibian species number, including two newly recorded species, i.e., Odorrana dulongensis and Raorchestes dulongensis. In terms of the species number, Ranidae, Bufonidae and Megophryidae accounted for 30.74%, 25.05%, and 22.32% of the total number of amphibians, respectively. There were 46 endemic species in China, accounting for 64.79% of the total number of species, indicating a high level of amphibian endemism in the study area. According to the Red List of China’s Vertebrates [26], there was 1 endangered species, 12 vulnerable species, and 15 near threatened species in the study area, accounting for 39.43% of the total number of amphibian species and indicating the vulnerability of these amphibian species in the study area.

3.2. Species Distribution at Different Elevation Gradients

There was an obvious difference in the species richness, number of individuals, and degree of dominance among different elevation gradients (Figure 1). The results suggested the species richness, Shannon diversity index, and Margalef richness index were all the highest in the area between 2000 and 3000 m, where 46 species were recorded, accounting for 64.79% of the total number of amphibian species in the priority area. Moreover, 31 species were recorded in the area between 3000 and 4000 m, accounting for 43.66% of the total number of amphibian species, where the Margalef richness index ranked third, and the Pielou evenness index was the lowest. In addition, the area between 1000 and 2000 m ranked second in the Margalef richness index and third in the Shannon diversity index, where 27 species were recorded, accounting for 38.03% of the total number of amphibian species. In contrast, 20 amphibian species were recorded in the area <1000 m, where the Pielou evenness index was the highest and the Shannon diversity index ranked second. By contrast, only nine amphibian species were recorded in the area >4000 m, where both the Shannon diversity index and the Margalef richness index were the lowest.

The dominant species in the five elevation gradients were Microhyla fissipes, Hyla annectans, Bufo tibetanus, Rana chaochiaoensis, and Scutiger glandulatus, with the degree of dominance of 0.1443, 0.2974, 0.1865, 0.2799, and 0.3198, respectively. Overall, there are different dominant species at different elevations, reflecting the remarkable geographical differentiation of the mountainous area in the priority area. The number of individuals in the area between 2000–3000 m and 3000–4000 m accounted for 46.11% and 32.93% of the total number of individuals, respectively, i.e., most of the amphibian species in the priority area were distributed in these areas between 2000 and 4000 m. More specifically, most of the species in the priority area were distributed in the southern part of the priority area, e.g., the Gaoligong Mountain-Biluo Snow Mountain area, the southern part of the Shaluli Mountain area, the Liangshan Mountain area, and the Yunling Mountain area.

The number of endemic species in the five elevation areas was 8, 10, 28, 23, and 8, respectively (

Table 1. Metric characteristics of amphibian species in different elevation areas in the priority area.

Characteristics	<1000 m	1000–2000 m	2000–3000 m	3000–4000 m	>4000 m
Number of species	20	27	46	31	9
Number of individuals	97	427	1641	1172	222
Number of endemic species	8	10	28	23	8
Number of threatened species	2	6	10	5	1
Shannon diversity index	2.6610	2.3878	2.8904	2.3497	1.6913
Pielou evenness index	0.8883	0.7245	0.7549	0.6842	0.7697
Simpson degree of dominance	0.0762	0.1467	0.0859	0.1453	0.2241
Margalef richness index	4.1533	4.2927	6.0786	4.2454	1.4807

), and the proportion of endemic species was overall higher in the areas above 2000 m. Specifically, the proportion of endemic species in the area >4000 m was the highest, reaching 88.89%, where only one species was not endemic. In contrast, the proportion of endemic species reached 74.19% in the area between 3000 and 4000 m. Meanwhile, the proportion of endemic species reached 60.87% in the area between 2000 and 3000 m.

The Gynandropaa yunnanensis, an endangered species according to the Red List of China’s Vertebrates [26], was mainly distributed in areas between 1000 and 4000 m. Moreover, the vulnerable species were mainly distributed in areas between 2000 and 3000 m. Specifically, vulnerable species included Megophrys binchuanensis, Maculopaa chayuensis, Oreolalax jingdongensis, Odorrana andersonii, and Batrachuperus karlschmidti.

3.3. Species Distribution in Different Habitat Types

The habitats in the priority area were classified into forest, shrub, grassland, farmland, wetland, and built-up land, and the species richness and number of the amphibian species in different habitat types were thereafter summarized (

Table 2. Metric characteristics of amphibian species in different habitats in the priority area for biodiversity conservation in the Hengduan Mountains.

Characteristics	Farmland	Forest	Grassland	Shrub	Wetland	Built-Up Land
Number of species	21	32	26	14	5	6
Number of individuals	838	1408	690	369	53	110
Number of endemic species	21	32	26	14	5	6
Number of threatened species	6	12	8	4	/	1
Shannon diversity index	2.6785	3.0220	2.9521	2.3985	1.4486	1.2740
Pielou evenness index	0.7534	0.7381	0.8058	0.7759	0.7444	0.6126
Simpson degree of dominance	0.0951	0.0873	0.0715	0.1175	0.2642	0.4133
Margalef richness index	5.0512	8.1380	5.8133	3.5528	1.5112	1.4892

). The forest and shrubs were mainly distributed in the Gaoligong Mountain-Biluo Snow Mountain area, the southern part of the Shaluli Mountain area, and the Yunling Mountain area. The grassland was widespread in the Tibetan-Shangri-La area and the northern part of the Shaluli Mountain area with very high vegetation coverage, which were the main habitats of amphibians in the priority area. The farmland was mainly in the southeastern part of the priority area, where the elevation is generally below 2000 m.

The forest ranked the first in terms of the species richness, Margalef richness index and Shannon diversity index, where 60 species were recorded in this survey, accounting for 84.51% of the total number of amphibian species in the priority area. By contrast, the grassland ranked first in terms of the Pielou evenness index and second in terms of both the Margalef richness index and Shannon diversity index, where 39 amphibian species were recorded, accounting for 54.93% of the total number of amphibian species in the priority area. The farmland ranked third in terms of the Margalef richness index, Shannon diversity index, and Pielou evenness, with 35 amphibian species recorded in this survey, accounting for 49.30% of the total number of amphibian species in the priority area. The shrub ranked fourth in terms of the Margalef richness index and Shannon diversity, with 22 amphibian species recorded, accounting for 30.99% of the total number of amphibian species in the priority area. In contrast, only seven and eight amphibian species were recorded in the wetland and built-up land, respectively, where all the diversity indices were very low.

The dominant amphibian species in the forest, grassland, farmland, shrub, wetland, and built-up land were the Hyla annectans, Rana chaochiaoensis, Bufo gargarizans, Scutiger brevipes, Bufo tibetanus, and Hyla annectans, respectively, with the degree of dominance of 0.1575, 0.2244, 0.1652, 0.1924, 0.5660, and 0.6182, respectively. There are four amphibian species that could be found in all six habitat types, i.e., Amolops mantzorum, Odorrana grahami, Bufo tuberculatus, and Rana chaochiaoensis. Overall, the degree of dominance of amphibian species was higher in the wetland and built-up land and the lowest in the forest. The forest, farmland, and grassland ranked the top three in terms of the number of amphibian species, accounting for 40.60%, 24.16%, and 19.90% of the total number of amphibian species in the priority area, respectively. In other words, 84.66% of the amphibian species in the priority area can be found in these three habitat types, mainly including 15 amphibian species, e.g., the spotted-legged pan-tree frog, Chongan turbot frog, Scutiger mammatus, big webbed bell toad and Emei forest frog. Meanwhile, there were 32, 26, 21, 14, 5, and 6 Chinese endemic species in the forest, grassland, farmland, shrub, wetland, and built-up land, respectively. Additionally, Gynandropaa yunnanensis, which is an endangered species according to the Red List of China’s Vertebrates [26], was mainly distributed in areas between 1000 and 4000 m. Moreover, the vulnerable species could be found in farmland, forest, and grassland but could not be found in the shrub, wetland, and built-up land.

3.4. Spatial Distribution of Amphibian Species among Geographical Zones

There are remarkable differences between the five major geographic zones of the priority area in the distribution of species. Specifically, this survey recorded 21, 26, 19, 22, and 24 amphibian species in the Gaoligong Mountain-Biluo Snow Mountain area, Yunling Mountain area, Tibetan-Shangri-La area, Shaluli Mountain area, and the Daxue Mountain-Xiaoxiangling Mountain-Liangshan Mountain area, respectively. Moreover, the dominant amphibian species in these five major geographic zones were the Hyla annectans, Bufo gargarizans, Rana chaochiaoensis, Bufo tibetanus, and Bufo gargarizans, with a dominance index of 0.4599, 0.2769, 0.4138, and 0.300, respectively. In addition, Maculopaa chayuensis is widespread in the Gaoligong-Biluo Snow Mountain area, and Rana chaochiaoensis, Nanorana ventripunctata, and Amolops mantzorum are more widely distributed in the Yunling Mountain area. While Nanorana ventripunctata, Scutiger mammatus, and Amolops mantzorum are more widespread in the Tibetan-Shangri-La area. By contrast, the Scutiger boulengeri, Odorrana graham, and Bufo tuberculatus are widely distributed in the Shaluli Mountain area, and Rana chaochiaoensis and Hyla annectans are more widespread in the Daxue Mountain-Xiaoxiangling Mountain-Liangshan Mountain area.

There is also obvious heterogeneity in the distribution of amphibian species within the five major geographic zones of the priority area. Specifically, the amphibian species composition of the southern section differs greatly from that of the northern section in the Gaoligong Mountain-Biluo Snow Mountain area. There are mainly subtropical species in the southern section, e.g., Nidirana occidentalis, Rhacophorus rhodopus, Leptobrachella tengchongensis, Microhyla mukhlesuri, Quasipaa spinose, and Fejervarya multistriata. In contrast, there are mainly alpine species in the northern section, e.g., Liuhurana shuchinae and Scutiger gongshanensis. There were also a few narrowly distributed species in the Gaoligong Mountain-Biluo Snow Mountain area, e.g., Odorrana dulongensis, Raorchestes dulongensis, and Scutiger gongshanensis, which are only found in the northern Dulongjiang gorge. The Bombina maxima as a key species with high habitat requirements is only found in Tengchong County, where four samples were found in this survey. Moreover, the largest number of amphibian species in the Yunling Mountain area was recorded in Yulong County, and 25 red scrofulous newts were found in Yulong County and Yunlong County in this survey. In contrast, the number of amphibian species increased from the north to the south in the Tibetan-Shangri-La area, where the highest species richness was recorded in Shangri-La. In particular, the habitat elevation of the Maculopaa chayuensis, Amolops chayuensis, Gynandropaa yunnanensis, and Calluella yunnanensis in this area increased to some extent in comparison to the historical records, which is probably because climate warming induced the migration of these amphibian species extremely sensitive to the climate change. In addition, the number of amphibian species in the Shaluli Mountain area also increased from north to south, which was higher in Muli County and Yangyuan County. In particular, 14 were newly recorded in the counties in this area. On the one hand, this may be due to the taxonomic changes of some amphibian species, e.g., the Amolops. On the other hand, there were relatively few previous surveys in this area, where the biodiversity background was unclear, and this survey more clearly revealed the amphibian species composition in this area. Moreover, the amphibian species richness of Ebian County is the highest in the Daxueshan Mountain-Small Xiangling Mountain -Liang Shan Mountain area, where four species were newly recorded, i.e., Odorrana graminea, Odorrana junlianensis, Paramegophrys oshanensis, and Rhacophorus chenfui.

3.5. Spatial Distribution of Endemic Species of China

There are in total 46 endemic amphibian species of China in 9 families and 19 genera recorded in this survey. Most of these endemic species belonged to Amolops, Scutiger, and Bufo, with the number of species of 6, 5, and 4, respectively, jointly accounting for 31.61% of the total number of endemic species in the priority area (Figure 2). Specifically, species of the Amolops genus were mainly distributed in the Daxue Mountain-Small Xiangling Mountain-Liangshan Mountain area. These species of Amolops are generally in favor of a warm and humid climate, all belonging to the stream type and mainly inhabiting rocks and stones next to alpine streams. Meanwhile, these species of Amolops belong to the Himalayan-Hengduan Mountains type and Southern China type, reflecting the close relationship between the fauna in this area and the paleo geographic development history of the Hengduan Mountains, and the vertical distribution characteristics of the climate zones of the Hengduan Mountains. Most species of the Scutiger genus are distributed in the mountainous areas of southwest China, and Hengduan Mountains may be the center of their origin and differentiation [30]. The endemic species of the Scutiger genus in China recorded in this survey were mainly distributed in Mankang, Deqin, and Shangri-La in the Tibetan-Shangri-La area, Gongshan, and Lushui in the Gaoligong Mountain-Biluo Snow Mountain area, and Xiangcheng, Batang and Derong in the Shaluli Mountain. The abundance of the Scutiger genus in the northern part of the priority area was obviously higher than that in the southern part, which may be due to the preference of the Scutiger genus to live in the area between 3000 and 4500 m [23]. In fact, previous research has suggested that temperature and precipitation are the main influencing factors of the potential distribution of the Scutiger genus [31]. For example, the lower the precipitation in the wettest month is, the higher the probability of the presence of Scutiger mammatus is, and the more abundant the precipitation in the coldest season is, the higher the probability of the presence of Scutiger gongshanensis is. The Bufo genus is mainly distributed in the Shaluli Mountain area, Yangbi in the Yunling Mountain area, and Mangkang and Deqin in the Tibetan-Shangri-La area. In particular, the Bufo aspinius has a narrow distribution scope, mainly located in Yangbi of Yunnan Province. It is a second-class protected wildlife with a scarce population, which is one of the representative taxa of Himalayan amphibians [22].

The overall spatial distribution pattern of endemic species is generally consistent with that of the amphibian species, the abundance of which is higher in the northern and lower in the southern part of the priority area. There are generally two reasons for this distribution pattern: firstly, there is mainly forest and grassland in the northern part of the priority area, both of which are the main distribution habitats of amphibians. Secondly, the northern part of the priority area covers many areas with an elevation above 2000 m, which is a suitable area for the amphibian species, where both the species richness and the number of individuals are relatively higher.

3.6. Impacts of Habitat Change on Amphibian Species

The main habitat types of amphibian species in the priority area mainly included forest, grassland, farmland, shrub, wetland, and built-up land, and the changes during 2000–2020 are shown in Figure 3. Specifically, the shrub and wetland increased remarkably by 0.69% and 0.21% during 2000–2020, respectively. In contrast, the forest and grassland decreased slightly by 0.26% and 0.27%, respectively. Meanwhile the farmland and built-up land increased slightly by 0.16% and 0.13%, respectively.

There was obvious conversion among the main habitat types of amphibian species in the priority area. The farmland mainly decreased in Weixi, Lanping, Lushui, Tengchong, Mabian, and Muli during 2000–2020, 42.31% and 27.53% of which was converted into forest and grassland, respectively. Meanwhile, the forest was mainly converted into grassland (48.38%), shrub (38.29%), and farmland (10.57%), which primarily occurred in southeast Tibet, the Liangshan Moutain area, and the northern part of the Shaluli Mountain area. While the grassland was mainly converted into forest (63.06%), which mainly occurred in the Tibetan-Shangri-La area, Shaluli Mountain area, and the Daxueshan Mountain-Shapling Mountain-Liang Shan Mountain area, especially Deqin, Dacheng, and Jiulong. In addition, the conversion of the shrub to the forest and grassland dispersedly occurred in the central part of the priority area, with a very limited total area (Figure 4). Moreover, it is particularly notable that the built-up land showed a gradually expanding trend in the priority area, along with relatively intensive road construction, earth and rock mining, and other disturbance activities. Meanwhile, a large proportion of the forest was converted into farmland and orchards, resulting in obvious vegetation homogenization, and the large and medium-sized river channel regulation projects generally lasted for a long time, both of which had devastating effects on the habitat of stream-type amphibians [32]. Overall, the land use conversion has led to some fragmentation and re-variation of the amphibian habitats to some extent.

The trend of habitat changes within the 1500 m migration distance of amphibian species was shown in Figure 5. The forest accounted for over 60% of the habitats within the migration distance of amphibian species, but it decreased by 1.1% during 2000–2020. The grassland accounts for over 17% of the habitats within the migration distance of amphibian species and increased by 0.82% during 2000–2020. By contrast, the farmland decreased from 10.40% in 2000 to 10.17% in 2020, with a decrease of 0.23%. Additionally, the wetland overall increased by 0.3%, and the built-up land increased by 1.84 times, increasing from 0.54% in 2000 to 1.87% in 2020. Moreover, the habitat change influenced the amphibian population to some extent. For example, the Scutiger gongshanensis, an endemic species of Gaoligong Mountain and Biro Snow Mountain, generally live in habitats of high elevation streams. This survey found that there were some maintenance activities on the road (Gongshan to Dulongjiang Township) and grazing activities near the type locality of this species, which may have obvious impacts on the population of this endemic species.

4. Discussion

4.1. Deficiency in the Existing Conservation Sites

There are 14 national nature reserves in the priority area, covering 21,428.85 km² and accounting for 16.03% of the total area of the priority area (Figure 6). These nature reserves have covered 39 amphibian species in total, including 3 national second-class protected species, 24 endemic species of China, 1 endangered species, and 5 vulnerable species, accounting for 54.93% of the number of species recorded in this survey. Here, we defined the coverage as follows: if the species in the protected area, we think it is protected; then we divide the number of protected species by the total number of species. There are still 32 species out of the nature reserves, including 11 vulnerable species. In fact, these nature reserves mainly aim at protecting the forest, alpine wetland, and wildlife such as Yunnan golden monkey and water deer rather than the amphibian species. Xu et al. (2017) have suggested there is a high conservation deficiency in the protection of the amphibian species within the existing nature reserves [33]. The results of this survey also suggest there are some gaps in the existing protection network; for example, there are a number of populations of some regional endemic and endangered species outside the existing nature reserves, e.g., Gynandropaa sichuanensis, Gynandropaa yunnanensis, Batrachuperus daochengensis, and Tylototriton shanjing. According to the results, the extinction risk and the threat level of the amphibians in this region are much lower than the national level (43%) and global level (41%). So it is suggested to make a positive assessment first, then point out the deficiency.

4.2. Building the Monitoring Network and Carrying Out Long-Term Located Monitoring

It is very necessary to build a monitoring network and carry out long-term located monitoring of the amphibian species in the priority area. In particular, it is necessary to take into account the breeding season, breeding habitat types, and habitat environment of various amphibian species. According to the results of this survey, it is feasible to set up a few monitoring sample sites and sample lines to reinforce the long-term monitoring in some important habitats and ecological nodes, e.g., Gaoligong Mountain, Cang Mountain, Erhai Sea, Gesigou, and Gongga Mountain. It is also necessary to establish a big data-sharing platform and take full use of multiple source data to improve the capacity for monitoring amphibian diversity and provide support for the conservation and sustainable use of biological resources in the priority area. Moreover, this survey suggested there was a large population size of Rana catesbeiana in a few parts of the priority area, which is an exotic species. Rana catesbeiana may pose terrible threats to the eggs and larvae of Tylototriton shanjing and even seize the ecological niches from the latter. It is therefore recommended to set up some monitoring points in the southern part of Gaoligongshan National Nature Reserve, Lashihai Plateau Wetland Provincial Nature Reserve in Lijiang of Yunnan Province, Meiyu Town of Yangyuan County, and Lugu Lake to carry out special surveys of these exotic species. It is necessary to establish a monitoring and early warning system to implement regular monitoring of the population size, ecological habits, and potential risks of these exotic species and assess their impacts on the local environment and species. It is also necessary to take effective measures to eliminate the existing invasive exotic species and avoid the invasion of exotic species caused by reckless stocking and release.

4.3. Improving the Existing Conservation Network and Filling the Conservation Gaps

This survey showed that the habitats of most amphibian species only overlap slightly with most of the existing nature reserves, and there is a large proportion of conservation gaps in many regions, e.g., Yunlong, Ninglang, Yangyuan, and Muli (Figure 6). On the one hand, there are no nature reserves with the amphibian species as the conservation object in the priority area. On the other hand, the habitats of most amphibian species are narrowly distributed and highly fragmented, which generally expand across agricultural areas, forest areas, and even suburban edges, making it very difficult to establish special nature reserves. It is therefore recommended to establish a conservation network that encompasses all the minimum viable populations as soon as possible to maintain their existence [10]. As for the populations of some critically endangered species that are not covered by nature reserves, e.g., the Oreolalax liangbeiensis, which is only found in the Puxiong area of Daliang Mountain, Sichuan Province, it is necessary to carry out urgent relocation conservation by implementing artificial breeding programs and establishing nature reserves or conservation plots and so on. In addition, the survey suggested that road kill on some wide roads with high traffic flow might pose a potential threat to the survival of amphibian species, and the construction of biological corridors can solve this problem and improve the diversity of faunal communities near the roads [34]. Moreover, some notice boards should be set up at prominent locations to carry out the popularization of science and public education to reduce the impacts of tourism activities on amphibians and their habitats.