4.1 The variables selected for the MaxEnt model
Table S1 shows seven environmental and human population densities and eight bioclimatic variables were selected to establish MaxEnt models describing macaques’ evolutionary changes and future distribution profiles. Three of them, the precipitation of the warmest quarter (var8), the mean temperature of the driest quarter (var5), and the human population density (var16), are those playing a decisive role in setting up the models for the current (1970-2000) and future (the 2050s) distribution profiles (Figure S5).
Rainfall and other water sources are crucial for animals’ survival, which can constrain their geographical environment and habitat selections; such as, elephants’ movement closely tracks precipitation-driven vegetation dynamics in a Kenyan forest-savanna landscape (Bohrer et al., 2014). One of the main reasons causing many mammal species to become extinct is the drought in the Later Pleistocene and the early Holocene (Jukar et al., 2021), such as that occurred in some macaque species, Macaca sylvanus in Norfolk (Elton and O’Regan, 2014) and Greece (Konidaris et al., 2022), Macaca majori in Italy (Zoboli et al., 2016),Macaca cf. M. cyclopis and Macaca anderssoni in China (Chang et al., 2012; Ito et al., 2014). Studies of climate impacts on the distribution of extant non-human primates have been few (Bernard and Marshall, 2020; Stewart et al., 2020); regarding that related to the taxa in China, it is reported that isothermality and temperature of the driest quarter are critically affecting the distribution of the gray-white snub-nosed monkey (Rhinopithecus bieti ) – temperature might act as a reproductive regulator for the onset of estrus and mating season (Zhao et al., 2019).
The extant macaque taxa now primarily reside in tropic-subtropic and temperate regions in North Africa and Asia (Mittermeier et al., 2013; Galán-Acedo et al., 2019), less tolerating droughty climates (Fleagle and Gilbert, 2006). A positive relationship between habitat suitability and precipitation for Macaca (Figure S6) is like what was described in primate species in Southeast Asia (Wang et al., 2013); less rainfall would limit their access to food sources due to poor leaf and fruit production (Rosenzweig, 1968; Wang’ondu et al., 2013). This study implies that climatic conditions or fluctuation would continue to be essential in driving macaques’ diversity and distribution.
Unsurprisingly, the human population density variable is the primary driving force shaping macaques’ future geographical changes by reducing habitat suitability (Figure S6). Intensified anthropogenic activities have also followed human population growth, leading to significant increases in cropland, pasture, and rangeland since the 1950s in China – the human population size increased from 540 million in 1949 to 1.4 billion in 2020 (Jo Huth, 1990) in which, cropland increased by 2549.2×104 hm2 from 1949 to 2003, increasing 47.2×104hm2/year (Bi and Zheng, 2000; Feng et al., 2005). Pastures and croplands have separated suitable distributions and migration paths, which have blocked genetic exchanges and caused population reduction and extinction (Forman and Alexander, 1998; Saxena et al., 2020). Such a scenario applies explicitly to some macaque populations in Shanxi (Zhou, 2014).