4.1 Maxent model and environmental variables
Maxent model can connect the distribution data of species with
geographic and ecological information, and calculate the maximum entropy
value of species distribution, so as to predict the potential
distribution area of species(Giannakopoulos et al., 2019). Maxent model
can achieve a good prediction effect only by using limited species
distribution data. Therefore, it is often used to simulate the potential
distribution area of species, drift of potential distribution area,
suitability evaluation and other studies on global climate change
involving species distribution and genetic diversity in conservation
biology and invasion biology(Hannah et al., 2007; Mays, Hung, Shaner,
Denvir, & Primerano, 2018; Prieto-Torres, Navarro-Sigüenza,
Santiago-Alarcon, & Rojas-Soto, 2016).
Environmental variables commonly used for Maxent model analysis include
climate variables, landscape variables such as topography and landform,
and the impact of human factors on species distribution is rarely
considered (Pearson, Raxworthy, Nakamura, & Townsend, 2010; Penman,
Pike, Webb, & Shine, 2010). However, the influence of human factors on
ecological environment is extensive and continuous, and its role cannot
be ignored(Li et al., 2014). From the contribution of the four
environmental factors selected in this study, the climate factor is
still the main factor affecting distribution of B. gargarizans in
China. Among them, the contribution of Bio9 and Bio14 is relatively
large, the contribution was 38.4% and 16.2%, and the optimal
distribution range of B. gargarizans was -1.85℃ ~
13.01℃ and 3.59mm ~ 145.20mm, respectively. Secondly,
human influence also has a certain degree of contribution, and the
overall influence trend shows that, within a certain range, the
distribution probability of B. gargarizans increases with the
enhancement of human influence (Table S5, Fig.3), this is caused by the
overlap of the ecological niche of the B. gargarizans and the
area of human activities and some human infrastructure is more conducive
to the distribution of amphibians(Tytar, Sobolenko, Nekrasova, &
Mezhzherin, 2015). Compared with other environmental factors, the
overall contribution of topographic and geomorphic factors is relatively
low, and see Fig.7 for details.