| Availability of food resources in the environment will affect the intensity of within-group competition,and the cost of competition among individuals will increase as the rising of group size.Most Asian colobines live in small groups to avoid intense intra-group competition.However,the golden snub-nosed monkey(Rhinopithecus roxellana),which distributed in North Temperate Zone with seasonal variation,share group living with more than hundreds of individuals.As the resources fluctuate with the drastic season changes,how these species maintain group stability in a large group to balance costs and benefits? Due to the limitation of technology and the lack of accurate information on ranging behavior,the seasonal adaptation strategy of large group has not been clearly understood.In this study,the northernmost of the R.roxellana was selected as the research object.There are two herds in the west ride troop of Zhouzhi National Nature Reserve(Shaanxi Province,China),which are GNG-herd(200 individuals)and DJF-herd(80 individuals).We collect accurate location data of the two herds for 5 years by using GPS collar,and obtain information about their food resources covering 480000 m2 in core area by quadrat method.Through investigating the relationship between the ranging behavior(home range,daily path length)and food resources(food diversity,food richness and food evenness)among different herds in different seasons,we expect to clarify that seasonal food resource changes impact on the ranging behavior of different herds.Thus explore the strategies for balancing costs and benefits are taken by different group sizes of R.roxellana during the seasonal change.The main results are as follows: 1.Home range of GNG-herd was 2 km2 larger than DJF-herd,daily path length was significantly longer than DJF-herd(P<0.01),core home range of GNG-herd had richer foods and main foods(P<0.01;P<0.05)2.Home range of summer were bigger than autumn and winter in two herds(P<0.05).Daily path length of spring and winter were shorter than summer and autumn in two herds(P<0.01).There were no food provisioning in summer and winter,home range of GNG-herd was 2 km2 smaller than DJF-herd,daily path length were longer than DJF-herd(P<0.01),core home range of GNG-herd had more abundant foods(P<0.05).The results indicate: 1.The home range and daily path length of the R.roxellana would respond to seasonal changes in food resources.In summer,food was widely distributed,and R.roxellana would increase the home range.In autumn and winter,they reduced the home range because of the concentrated distribution of food.In spring and winter,R.roxellana had high nutritional requirements and low proportion of main food intake,so their daily path length was reduced.Low nutritional requirements and high proportion of main food intake in summer and winter,R.roxellana increased daily path length.2.In the process of balancing the cost and benefit of R.roxellana,large herd would adopt the strategy of "high yield,high cost",while the small herd showed "low yield,low cost".The large herd needed more abundant food than small herd,so they would occupy a larger area as a home range which was richer in food resources.The longer daily path length may be the pressure of competition among individuals in the large herd.In summer and winter,large herd occupied areas with richer food resources,thus they reduced home range;but small groups needed to increase their home range and obtain sufficient food.In terms of daily path length,large herd would increase the daily path length to reduce the competition pressure of within-group;low competition pressure would reduce the daily path length in small herd.Therefore,R.roxellana responds to seasonal changes in food resources by adjusting the ranging behavior.The competitive advantage of large group for food may be an important factor,which provides an ecological evidence for the social fusion and evolution of Rhinopithecus. |
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