布氏田鼠种群生长指标的主分量分析

PRINCIPAL COMPONENT ANALYSIS OF GROWTHINDEX OF POPULATION FOR BRANDT'S VOLE(MICROTUS BRANDTI)

本文对布氏田鼠的体重、体长、尾长、颅全长、颅基长等１５项生长指标进行了主分量分析。结果表明：颅基长是最具有代表性的生长指标。同时，头骨的上齿隙宽因不存在性别差异，容易准确量度，可用作划分年龄组指标。根据上齿隙宽度，本文将布氏田鼠划分为５个年龄组。

To the purpose of age estimation, 15 growth indices in 560 specimens (males, 280; females,280 )of brandt's vole (Microtus brandti) were studied by principal component analysis (PCA).The 15growth indices are body weight,body length, tail length . greatest length of skull,basal length of skull,skull height.head back width,length of palatal bone,zygomatic width . interorbital width,nasal length,width between maxillary incisor and molar,length of maxillary molar row,length of mandibular molarrow and dry weight of lenses. All analyzed indices were arranged on the first principal component axis(Z1) which contribution rates are 74. 0/00 (female) and 75. 9% (male). The results are as follows,l. Interorbital width and tail length,as well skull height of female were regarded as poor growth in-dicators , because of their small projections on Z_1.2. Basal length of skull made the greatest projection on Z_1, so it reflected the growth best in bothmale and female.3. Other growth indicators made projections above 0. 829 and concentrated on Z_1, so they all can beused as age indicators of brandt's vole.4. Body weight and body length are the convenient indicators,butbody length is not easy to mea-sure accurately and body weight is affected by-pregnent females.5. Dry weight of eye lens is not a suitable age indicator for brandt's vole,because the eye lens is solight that the different between two age groups adjacent is less than 0. 1mg.6. Although skull indices (except interorbital width and female's skull height) can all be used as ageindicators, but they are not easy to obtain (except molar row and length between incisor and malar).Overall, the width between maxillary incisor and molar was used as the age indicator of brandt'svole based on both the results of PCA and practical circumstance. After further analysis, the populationof brandt's vole can be divided into five age groups. It is the juvenile (length between maxillary incisorand molar is less than 6. 49mm), subadult (6. 50-7. 33mm),adult 1 (7. 34-8. 38mm), adult Ⅱ(8. 39-9. 43mm) and old age group (over 9. 44mm).