The Coexistence Mechanism Of Two Sympatric Macaques In Nabanhe Natural Reserve In Yunnan

The coexistence of species is a basic question in ecology and one of the most interesting issues for primate researchers.Niche differentiation is the core of classical coexistence theory and is considered as a stable mechanism to reduce competition and promote coexistence.Based on the infrared camera data obtained during 2012 to 2016,we found that the northern pig-tailed macaque(Macaca leonina)and rhesus macaque(M.mulatta)were sympatric in the Nabanhe River Watershed National Nature Reserve(NRW-NNR),a tropical forest in Xishuangbanna(Yunnan,China).We first investigated the non-human primate resources in the reserve,using camera trapping and social survey.M.leonina and M.mulatta were identified as the dominant species in the NRW-NNR.We applied the species distribution model(MaxEnt)to predict the distribution of two macaques,to understand the key environmental factors for each of them.The niche indices were analyzed in three dimensions of elevation,vegetation and activity rhythm,in order to reveal how the niche differentiation mechanism worked for their stable coexistence.The main conclusions are as follows:(1)Of six non-human primate species recorded in NRW-NNR,only four were investigated during 2012-2018.The M.leonina,M.mulatta and Assam macaque(M.assamensis)were captured by the camera trapping,with relative abundance ratio of1:0.7:0.04,which identified the former two as the dominant species in this region.The M.assamensis was scarce and detected in only two camera sites.The existence of the greater slow loris(Nycticebus bengalensis)was confirmed by local residents.No news about the stump-tailed macaque(M.arctoides)and Phayre's leaf-monkey(Trachypithecus phayrei).The road and farmland divided the reserve into small patches,resulting reduced forest area and serious fragmentation,which might be the main reason for the reduction of non-human primate diversity in this region.(2)Predicted by species distribution model(MaxEnt),M.leonina was predominantly in cooler and wetter areas at higher elevation,while M.mulatta in hotter and drier areas at lower elevation.The broadleaved evergreen forest was mainly predicted as suitable area for both of them.The unsuitable area was bordered by the rubber forest,which restricting the spread of macaques.(3)The two sympatric macaques coexist with a high niche overlap value in both space and time dimensions.The niche differentiation varies with areas and seasons,and occurs in at least one dimension for their stable sympatry.Habitat,including elevation and vegetation,is tended to be mainly differed by M.leonina and M.mulatta for their sympatry.Driven by space limitation in the overlapping area,the differentiation of activity time is significant.The M.leonina exhibits impressively a wider distribution and niche breadth.Listed as Class I Protected Animals in the Chinese Wildlife Conservation Law,M.leonina is worthy to be the icon of conservation in the tropical forest of southwestern China.More comparative studies between these two macaques in other dimensions are needed in the future.