Pérez-Barbería F J, Gordon I J
The Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB15 8QH, Scotland, UK e-mail:
Oecologia. 1999 Aug;120(2):258-267. doi: 10.1007/s004420050856.
Sexual segregation in Soay sheep (Ovis aries) was investigated using an experimental approach in order to test the sexual dimorphism-body size hypothesis. Two corollaries of the sexual dimorphism-body size hypothesis were tested: (1) in dimorphic species males, the larger sex, have relatively smaller bite sizes on short swards because of the scaling of incisor arcade with body weight, and (2) they move off earlier to feed on taller but poorer-quality swards when such swards are patchily distributed on a scale which enables the spatial segregation of individuals. Patch choice between sexes was estimated using a matrix of grass patches which differed in both quality and biomass of grass on offer (HQ: high-quality-low-biomass; LQ: low-quality-high-biomass). Sex differences in patch choice and grazing behaviour were tested in short-term preference trials. Incisor breadth showed no significant difference between sexes. On the other hand, muzzle width was dimorphic, with females having a narrower muzzle than males. Bite size was significantly different between the sexes, being smaller in females than in males, although it was not significantly different between sward types. Females had a higher bite rate than males and the bite rate was higher in the HQ sward type than the LQ sward type. When the effect of body mass was removed, no sex differences in muzzle size, bite size or bite rate were found. The intake rate did not differ between the sexes or between sward types. Whilst both sexes preferred the HQ sward type, females spent a significantly longer time feeding on the LQ sward type than did males. The difference detected between the sexes in patch choice was not consistent directly with the sexual dimorphism-body size hypothesis. Alternative explanations based on sex differences in foraging behaviour in relation to body mass sexual dimorphism are discussed to explain the result.
为了验证性二态性-体型假说，采用实验方法对索艾羊（Ovis aries）的性别隔离进行了研究。对性二态性-体型假说的两个推论进行了检验：（1）在两性异形的物种中，雄性作为较大的性别，由于切齿弓与体重的比例关系，在矮草地上的咬口相对较小；（2）当这种较高但质量较差的草地呈斑块状分布且分布规模足以使个体进行空间隔离时，它们会更早离开去采食此类草地。使用提供的草质量和生物量不同的草斑块矩阵来估计性别间的斑块选择。在短期偏好试验中测试了斑块选择和放牧行为的性别差异。切齿宽度在两性之间没有显著差异。另一方面，口吻宽度存在两性异形，雌性的口吻比雄性窄。咬口大小在两性之间存在显著差异，雌性比雄性小，尽管在不同草皮类型之间没有显著差异。雌性的咬食率高于雄性，且在高质量草皮类型中的咬食率高于低质量草皮类型。去除体重影响后，在口吻大小、咬口大小或咬食率方面未发现性别差异。采食量在性别之间或草皮类型之间没有差异。虽然两性都更喜欢高质量草皮类型，但雌性在低质量草皮类型上采食的时间比雄性显著更长。在斑块选择中检测到的性别差异与性二态性-体型假说并不直接一致。讨论了基于与体重性二态性相关的觅食行为性别差异的其他解释来解释这一结果。
