Food Competition In A Provisioned Free-ranging Band Of The Golden Snub-nosed Monkeys (Rhinopithecus Roxellana)

Cooperation is the basic social relationship to animals,especially when group living animals are under the pressure of food resource competition,and the cooperation also is fundamental issue of evolution of social system.Food resources pressure hypothesis is widely used to explain the mechanisms of grouping in primates and other mammals,but this rarely get real field validation.Multilevel society appeared in society of few non-human primates and the human,which is a complex social system and have multiple social structures.How this human liked social system start and evolution in non-human primates is a big question before primatologists and anthropologist for this issue might help people understand the origin of our society.In such multilevel society,individuals live together in a group,but food resource allocation obviously presents small collectivization among structures.To explore the response of different structures in the society to the food pressure will help us understand the path way of food pressure transfer in the society,and then find an evolutionary and ecological clues in forming a multilevel society and whether and how a group keeps its form of the multilevel society under the nature pressure.Polygynous unit(One-male multi-female unit,OMU)is composed of golden snub-nosed monkeys(Rhinopithecus roxellana)layer of the basic organization of social structure,food competition exists among both individuals and units and the cooperation would occur among both individuals and units.Such social model is an ideal model to be studied on the issue of cooperation among groups(OMUs).Our study aim is to study the patterns of cooperation among basic structure of the group – OMUs and its driving forces in two types of food patch: scattered and clustered.From October 2013 to December 2013 and October 2015 to December 2015,we designed two experiments of food distribution models: the scattered distribution(Experiment 1,E1)and clustered distribution(Experiment 2,E2).We chose a provisioning R.roxellana band living in Zhouzhi National Nature Reserve as the study subject.We used focal sampling,all-occurrences recording and instantaneous sampling methods to record and analysis the behavior including aggressive-yield behavior,spatial foraging sequence during dietary event and occupied time for food patch.During the study period,we observed twelve OMUs and ten OMUs,respectively.We collected hair and feces samples of focal individuals as genetic samples and we analyzed STR genotypes to calculate relative coefficient of each individual based on 18 high polymorphism microsatellite loci information.We compared the spatial and temporal data of occupying patterns in food patch grids and analyzed cooperation relationships of OMUs and we classified cooperation behavior as some OMUs enter into food patches together,share food,and allied attack against other units.We analyze the correlation between Euclidean distance matrix and rank difference matrix,Euclidean distance matrix and kinship coefficient matrix.The results showed that:(1)In both food scattered experiment(E1)and food clustered experiment(E2),all of OMUs in the band clearly form spatial and temporal two groups when use the food patches,units and individuals of the firstly entering group always occupy higher quality provisioned foods and feeding time are significantly higher than the second entering group(E1: t-test,t = 3.880,df = 10,P = 0.003;E2: t-test,t = 5.640,df = 8,P < 0.001);(2)we used David Score to calculate the rank order of all OMUs,those units belong to first group show higher rank than second group;(3)The matching analysis of spatial and temporal data of occupying patterns with kinship among OMUs and social hierarchies produced the result that kinds of possible kinship among OMUs had no effect on relationships of cooperation between OMUs(E1: Mental test: r = [-0.162~0.205],P > 0.05),but the social rank clustering matches with space-time cooperative matrix between units(E1: Mental test: r = 0.545,P < 0.001;E2: Mental test: r = 0.329,P = 0.025).We argue that the competition for food among sub-groups formed by rank probably force OMUs the cluster sub-groups in the band.Rank orders of units indicated different cost and benefit in feeding competition.We can see that golden snub-nosed monkey community forms directional structure break down under the pressure of food resources is increasing — OMUs bands spilt into OMU subgroups but OMU still keep its form.Social dominance is the main factor to form the subgroup not based kinship,and the subgroups which formed of high rank OMUs has more advantages in competition of food resources.Therefore,the study suggested that the groups which formed during foraging is determined by the social rank,and the social rank promote cooperation among OMUs.