Accuracy of the Maxent model and importance of environmental factors
The testing and training AUCs of the models for 10 plants eaten by Tibetan antelope were more than 0.8, demonstrating that the model performance was good. The testing and training AUCs of the models for Tibetan antelope were higher than 0.9, showing that the model performance was excellent. In a word, the model accuracy indicated that all the model performances were acceptable.
The main environmental variables influencing the Tibetan antelope and 10 forage plants distribution and their contribution rates were obtained from the jackknife analysis. The important variables affecting the distribution of Tibetan antelope as follows: elevation, mean temperature of wettest quarter (Bio8), slope, mean temperature of warmest quarter (Bio10), landcover, max temperature of warmest month (Bio5), precipitation of driest month (Bio14), Stipa capillata, Oxytropis ochrocephala and human influence index (HII) (Table 3). All the contribution of these variables was 97.6%, indicating that the Tibetan antelope distribution was strongly affected by these factors. The contribution rate of the three terrain variables was 40.6%. All the contribution rate of bioclimatic variables was 39.8%. The contribution rate of the landcover and human influence index were 10.3%. The total contribution rate of plant variables was 7.9%. It indicated that the influence of the topography and bioclimatic variables on the Tibetan antelope distribution was much greater than that of plants, landcover and human influence index. The important variables affecting the distribution of 10 plants eaten by Tibetan antelope as follows: elevation, annual precipitation (Bio12), mean temperature of coldest quarter (Bio11), slope, precipitation of wettest month (Bio13), mean temperature of driest quarter (Bio9), aspect, T_BULK_DEN and max temperature of warmest month (Bio5). The contribution rate of the three terrain variables was 63.53%. All the contribution rate of the bioclimatic variables was 33.8%. The results indicated that the distribution of the 10 plants eaten by the Tibetan antelope was strongly influenced by climatic and terrain variables.
Current potential distribution of 10 plants eaten by the Tibetan antelope
The potential distribution area for 10 plants with the richness of 4–8 under current climate scenario was 181,626 km2, and mainly scattered in the southern of QTP (Fig. 3). The mean elevation for 10 plants with the richness of 4–8 under current climate scenario was 3879 m. The potential distribution area for 10 plants with the richness of 2–3 under current climate scenario was 539,638 km2. The mean elevation for 10 plants with the richness of 2–3 under current climate scenario was 4358 m. The average altitude of all the potential distribution of 10 plants under current climate circumstance was between 3879 m and 4262 m.
Table 3
The contribution percentage of environmental variables.
Tibetan antelope
|
10 forage plants
|
Variables
|
Contribution (%)
|
Variables
|
Mean contribution (%)
|
Elevation
|
25.1
|
Elevation
|
55.05
|
Bio8
|
16.6
|
Bio12
|
18.08
|
Slope
|
15.5
|
Bio11
|
6.69
|
Bio10
|
12.1
|
Slope
|
5.86
|
Landcover
|
8.5
|
Bio13
|
3.09
|
Bio5
|
5.9
|
Bio9
|
2.64
|
Bio14
|
5.2
|
Aspect
|
2.62
|
Stipa capillata
|
5
|
T_BULK_DEN
|
1.89
|
Oxytropis ochrocephala
|
1.9
|
Bio5
|
1.72
|
Human influence index
|
1.8
|
Bio10
|
0.75
|
Poa crymophila
|
0.9
|
T_CEC_CLAY
|
0.72
|
Bio7
|
0.5
|
Bio8
|
0.41
|
Stipa purpurea
|
0.1
|
T_CEC_SOIL
|
0.25
|
Androsace integra
|
0.1
|
|
|
Aspect
|
0.1
|
|
|
Current potential distribution of the Tibetan antelope
The current potential suitable habitat of Tibetan antelope covered a total area of 502,906 km2 (about accounting for 20% of QTP), and were mostly concentrated in Shenza County, Nima county and Zhongba County of Tibet Automonous Region, Zhiduo County and Qumalai County of Qinghai province and Ruoqiang County of Xinjiang Uygur Autonomous (Fig. 4). The areas of high, moderately and low potential suitable habitat were 65,119 km2, 130,426 km2 and 307,361 km2, respectively. Qiangtang National Nature Reserve, Kekexili National Nature Reserve and Altun National Nature Reserve were the main suitable habitats for Tibetan antelope.
Future potential distribution of Tibetan antelope
Under the four climate scenarios, the distribution changes in potential suitable habitats for Tibetan antelope during the two future periods were different. Yet there were some similarities in the trends. Under the four future climate scenarios in 2050s, the area of high, moderately and low suitable habitats all increased compared with current value. Under the four future climate scenarios in 2070s, the area of low suitable habitats all decreased compared with current value. In 2050s, the tatal area of high, moderately and low suitable habitats increased from SSP1-2.6 to SSP2-4.5, decreased from SSP2-4.5 to SSP3-7.0, and increased from SSP3-7.0 to SSP5-8.5. However, the total area of high, moderately and low suitable habitats decreased from SSP1-2.6 to SSP2-4.5, increased from SSP2-4.5 to SSP3-7.0, and decreased from SSP3-7.0 to SSP5-8.5 in 2070s (Table 4, Fig. 5).
The mean elevation of the high, moderately and low suitable habitats all increased compared with current value under the four future scenarios in 2050s and 2070s. The mean elevation of the high suitable habitats climbed from SSP1-2.6 (4767 m) to SSP5-8.5 (4838 m) in 2050s. The mean elevation of the high suitable habitats declined from SSP1-2.6 (4771 m) to SSP3-7.0 (4736 m), and increased from SSP3-7.0 to SSP5-8.5 (4778 m) in 2070s. The mean elevation of the moderately suitable habitats increased from SSP2-4.5 to SSP5-8.5 in 2050s and 2070s. The mean elevation of the low suitable habitats also increased from SSP2-4.5 to SSP5-8.5 in 2050s. The minimum mean elevation (4698 m) was at the high suitable habitat under current climate circumstance. The maximum mean elevation (4838 m) was at the high suitable habitat under the SSP5-8.5 circumstance in 2050s (Table 5).
Table 4. The area of the potential suitable habitats under different climate scenarios.
Habitat Suitability
|
The area of suitable habitats under different climate scenario (km2)
|
|
2050s
|
2070s
|
Current
|
SSP1-2.6
|
SSP2-4.5
|
SSP3-7.0
|
SSP5-8.5
|
SSP1-2.6
|
SSP2-4.5
|
SSP3-7.0
|
SSP5-8.5
|
High suitable habitat
|
71,825
|
73,151
|
72,743
|
80,694
|
86,939
|
68,312
|
59,639
|
81,756
|
65,119
|
Moderately suitable habitat
|
151,919
|
154,935
|
155,246
|
158,990
|
161,197
|
124,947
|
154,821
|
147,399
|
130,426
|
low suitable habitat
|
320,213
|
318,869
|
294,409
|
351,395
|
303,661
|
279,579
|
302,231
|
271,786
|
307,361
|
Total suitable habitat
|
543,957
|
546,955
|
522,398
|
591,079
|
551,797
|
472,838
|
516,691
|
500,941
|
502,906
|
Table 5
The mean elevation of the potential suitable habitats under different climate scenarios.
Habitat Suitability
|
The mean elevaton of suitable habitats under different climate scenario
|
The mean elevation of suitable habitats under current climate
|
2050s
|
2070s
|
SSP1-2.6
|
SSP2-4.5
|
SSP3-7.0
|
SSP5-8.5
|
SSP1-2.6
|
SSP2-4.5
|
SSP3-7.0
|
SSP5-8.5
|
High suitable habitat
|
4767
|
4771
|
4780
|
4838
|
4771
|
4739
|
4736
|
4788
|
4698
|
Moderately suitable habitat
|
4775
|
4760
|
4776
|
4834
|
4781
|
4767
|
4783
|
4826
|
4749
|
low suitable habitat
|
4794
|
4786
|
4791
|
4826
|
4795
|
4801
|
4789
|
4807
|
4770
|
Area changes of suitable habitats under different climate scenarios
We used the tool of “Distribution Changes Between Binary SDMs” by ArcGis to obtain the area changes of suitable habitats under different climate scenarios from current to 2050s and from current to 2070s, The results demonstrated that the area of suitable habitats under SSP2-4.5 from current to 2070s would shrink largest than other climate scenarios (Fig. 6). The SSP2-4.5 in 2070s was regarded as the worst scenario for Tibetan antelope. The area of suitable habitats under SSP1-2.6 from current to 2070s would expand largest than other climate scenarios. The SSP1-2.6 in 2070 was regarded as the best suitable habitats for Tibetan antelope. The results showed that the expanded habitat areas were basically larger than the predicted shrinking areas. This potential expanded habitats would be regarded as a new refuge for Tibetan antelope.
The Intersection Distribution Changes With The Forage Plants And Tibetan Antelope
We analyzed the intersection distribution changes of the 10 plants and Tibetan antelope under future climate scenarios. The results demonstrated that the area of the intersection distribution expanded most under the SSP5-8.5 scenario which were suitable for Tibetan antelope and main forge plants. The area of the intersection distribution shrank from SSP1-2.6 (72,081 km2) to SSP2-4.5 (44,900 km2) and gone on expanding to SSP5-8.5 (78,436 km2) in 2050s. The area of the intersection distribution expanded from SSP1-2.6 (32,979 km2) to SSP2-4.5 (70,712 km2), shrank from SSP2-4.5 to SSP3-7.0 (58,986 km2) and expanded to SSP5-8.5 (88,568 km2) in 2070s. The smallest area of the intersection distribution was 44,900 km2 under SSP2-4.5 in 2050s. The largest area of the intersection distribution was 88,568 km2 under SSP5-8.5 in 2070s. If there was grass, there would not be sheep, and where there were sheep, there would not be grass (Fig. 7).