Fig.7 Results of jackknife train of relative importance of predictor variables forB. gargarizans
4.2 Future distribution change and barycenter migration ofB. gargarizans
Many studies suggest that global temperatures are rising and will continue to do so for some time to come, with an expected increase of 0.6℃ in the 20th century and 1.4℃ ~ 5.8℃ by the 21th century (Budikova, 2009; Mccarthy, Canziani, Leary, Dokken, & White, 2007). The rising global temperature will inevitably affect the change of species distribution, which will eventually lead to two results: one is the reduction of species distribution, which will eventually lead to extinction of species; the other is the migration of species to previously undistributed areas, which will expand the distribution (Bellard, Bertelsmeier, Leadley, Thuiller, & Courchamp, 2012; Morueta-Holme, Camilla, & Svenning, 2010; Thomas et al., 2004).
In this study, under the background of climate change, the suitable distribution area of B. gargarizans will continue to decrease in the next 30~50 years. In comparison to three other global Change Scenarios, we can see the smallest reduction in suitable habitat for B. gargarizans under RCP2.6 Scenarios (The most optimistic scenario is that greenhouse gas emissions peak between 2010 and 2020, then continue to decline, with a negative value by the end of the century). And the suitable habitat ofB. gargarizans will be further reduced Under the scenarios of RCP4.5 and RCP6.0(That represents a decline after greenhouse gas emissions peaked in 2040 and 2080, respectively). the suitable habitat of B. gargarizans of China decreased to the maximum extent under the condition of RCP8.5(Greenhouse gas emissions continue to rise in this century). The results show that with the increase of greenhouse gas emission concentration, the area of suitable habitat of B. gargarizans decreases more, on the other hand, it suggests the importance of energy conservation and emission reduction to the maintenance of ecological balance.
As show in Fig. 4 and Fig. S5, the suitable habitat ofB. gargarizans will decrease in the south, southeast coast and central part of China, and correspondingly increase in the central and western part of China from now to 2050. And the trend will become more pronounced by 2070. In the next 30 to 50 years, the distribution centers of B. gargarizanswill gradually move from Yunyang County in northeast Chongqing City to Wanyuan County, Tongjiang County and Xuanhan County in northeast Sichuan Province and Langao County, Ziyang County, Zhenba County, Nanzheng County and Chenggu County in southwest Shaanxi Province. Compared with the present, the distribution focus has gradually shifted to the northwest, and this trend has not weakened with time. In addition, it can be seen from Figure 1 that Bio9 and Bio14, two climatic factors that have a great influence on the distribution of B. gargarizans . are increasing from 2050 to 2070 compared with the present, and the growth trend is more obvious in eastern and southern China. And these are the areas where B. gargarizans , will be less concentrated in the future. And the reason for this phenomenon is that the average temperature and precipitation in these regions are higher at present, and the further increase of temperature and precipitation in the future will make the values of these factors beyond the range suitable for the distribution of B. gargarizans (Table S6) .
Four GCMs under four RCPs were used in this study, and the results show that under the global climate change, like other species that have been reported, the distribution area of B. gargarizans will migrate to the high latitude and high altitude area (China’s terrain is low in the east)(Kelly & Goulden, 2008; Parmesan & Yohe, 2003). On the other hand, this paper is more inclined to think that the current distribution pattern of B. gargarizans , is caused by the dispersion, because from the perspective of the current distribution, there is no obvious geographical isolation between the distribution areas of different regions of B. gargarizans ,, and the future distribution ofB. gargarizans , showed that the future distribution of B. gargarizans , would gradually break up, and the geographical separation would gradually form between different regions (Fig.2, Fig. S1). The results of this study indicated that the distribution area of B. gargarizans would be reduced in the future, and the habitat connectivity, resilience and gene exchange between the populations would be reduced with the serious habitat fragmentation year by year, finally leading to the gradual decline of B. gargarizans population(Duan et al., 2016). And it suggests that some amphibians, which are more sensitive to environmental changes and narrower than B. gargarizans , the changes to their niches from climate change will be even more dramatic and even devastating. Due to the influence of the resolution of the environmental layer, the prediction results cannot be very accurate. However, we still believe that this study will provide theoretical support for the direction of conservation and ecological management of B. gargarizans , and it is believed that it can provide a research direction for other amphibians to cope with climate change.