Research On The Sexual Segregation Of Blue Sheep(Pseudois Nayaur) In The Helan Mountains, China

Sexual segregation, being traditionally considered as males and females live in separate groups and prefer different habitats outside the mating season, is common in wide range of group-living vertebrates. The sexual segregation ecology framework developed by many researchers proposed to explain the causes and effects, numerous hypotheses ranging from population ecology to morphology have arisen, and they can be broadly categorized as ecological, social and diet explanations. Main hypotheses were mainly accepted as follows, the forage selection hypothesis, the reproductive strategy-predation risk hypothesis, the indirect competition hypothesis, the activity budget hypothesis, the social factors hypothesis, and the nutritional demand hypothesis and so on.Blue sheep (Pseudois nayaur) is group-living animal, males and females have distinct body size and external attribute, and they live separately in different spatial and different habitat with different groups outside the rutting seasons. There is no doubt to find sexual segregation between male and female blue sheep, but for what extend and on which aspects does it exist? Which ecological factors or physiological factors affected it, and how? These questions arise to be the key points to make further understanding of the sexual segregation mechanism in blue sheep.From2010to2012, we conducted a series of surveys to study the difference and segregations between male and female blue sheep on their sexual dimorphism-body size, forage habitat, diet, home-range, group type and size, and activity rhythm, based on the hypothesis of sexual segregation. We came to some conclusions as follows:Significantly differences were found between male and female blue sheep on their physical and skull attributes, which were considered to be the fundamental of their sexual segregation. The Sexual Dimorphism (SD) of male and female blue sheep was1.52, highly above the threshold (1.2) of sexual segregation for ungulates, and the ratio of horn length for male and females was4.03, indicated a distinct sexual segregation of male and female blue sheep. Moreover, significantly sex and age differences were also found between male and female blue sheep on the depth and breadth of incisors. The result indicated that the sexual dimorphism-body size hypothesis and the indirect competition hypothesis have great effect on the sexual segregation of blue sheep.The forage habitat used by male and female blue sheep significantly segregated, and varied among seasons. Males preferred open habitats with sparse trees and shrub, and vegetation which located on steep hillside, while females preferred safe habitats not only with highly covered trees or shrub, but also close to water resource or cliffs. We also studied the habitat and diet diversity, evenness and niche width of male and female blue sheep during the non-rut seasons, the results showed that males have higher habitat diversity, higher evenness, and wider habitat niche during the non-rut seasons. Blue sheep consumed35plant species or genus from17families during the non-rut seasons in the study area, dominated by Gramineae, Fabaceae, Ulmaceae, Rosaceae, and Berberidaceae. Male blue sheep have significantly wider diet niche than females, though there is no significant difference between males and females on the diet diversity and evenness. Additionally, the segregation coefficient (SCforage) of diet indicated high segregation between male and female blue sheep, and also varied among seasons. The significant segregation of habitat and forage proved that the forage selection hypothesis and reproductive strategy hypothesis have great effect on the sexual segregation of blue sheep, and there is causal relationship between forage and habitat separation.The annual and non-rutting Minimum Convex Polygon (MCP) and Kernels Density Estimation (KDE) home-ranges and maximum moving distance for males and females were calculated and compared. We found significant difference (P<0.05) between sexes in the MCP home-ranges and maximum moving distances, but no significant difference (P>0.05) between sexes in the core (KDE50%) home-ranges. The results indicated that male and female P. nayaurs segregated slightly on the using of core areas (KDE50%), due to the resource availability and population density. Males were likely using significantly larger MCP home-ranges and traveling longer than females, because of their higher energy requirement and less vulnerability to predation. whereas females trade off higher quality diet for greater security from predators during sexual segregation, according to the forage selection hypothesis and reproductive strategy (predation risk) hypothesis.The study on the blue sheep groups shows that, the mean size of blue sheep is8.65(+10.07), mainly observed as small groups of2～6individuals. Significant difference was also detected between male and female blue sheep Typical Group Sizes (TGS), males have greater TGS than females. And the relative proportion of the amount of male, female and mixed groups varied by seasons, mixed groups mostly occurred during November to the following February, and male groups mostly occurred during May to September, while female groups mostly occurred during June to October. The mean sex ratio in mixed groups is2.07(±1.24), and varied by seasons. Male individuals take higher proportion than females in mixed groups during non-rut seasons. What’s more, the social segregation coefficient is0.69, indicated significant social segregation between male and female blue sheep. Significant sex and seasonal difference between male and female blue sheep was also detected on the activity rhythms, the forage activity took a greater proportion during all seasons. There is no significant difference between male and female blue sheep on the moving activity. For the diurnal rhythm, males and females spent more time in foraging and moving, but males spent more time in resting than females. The behavior synchronization index of groups indicated significant difference in the synchronization of male, female and mixed groups, higher degree of was found during the rut seasons for the individuals in mixed group, while males and females were just the reverse. Additionally, significant difference was also detected between males and females on their behavior synchronization index.