【摘要】 利用新疆等地区的597号麝鼠头骨标本和其它材料,研究种群年龄组成。主要依据左侧第一上臼齿齿根的形成、生长和齿冠磨损的程度,并分析了头骨的形态变化及测量数据,以及体重、体长、繁殖等和年龄的关系,初步得如下结果: 1.根据各方面的特征,划分为六个年龄组。 2.头骨、体重、体长有明显的年龄变化。 3.种群年龄组成有明显的季节变化,种群中性比随年龄而有差异。新疆地区一年繁殖2—3次。种群年龄组成的研究,为麝鼠资源的合理利用提供了资料。更多还原

【Abstract】 This study deals with age determination and age distribution of muskrat populations. A total of 597 skulls with notes on their reproduction, were collected from Kunges River at Sinkiang in 1964, and Changwu at Liao-ning from 1963-1964.Six age groups have been devised, based upon four criteria: (1) morphology of the tooth roots and enamel patterns of the molars, especially the height of the 2nd fluting on the left first upper molar; (2) degree of extrusion below the bona line of the anteriormost buccal fluting; (3) measurements of skulls and body lengths together with body weights; and (4) reproductive characters.Group 1. Without the tooth roots and the height of corona dentis of the 1st upper molar measuring 8.3-12.0mm, considered as juveniles, being about two months old after birth.Group 2. With the appearance of a band at the base of the molars, the height of fluting of the corona dentis measuring more than 9.0 mm, considered as being about two to six months old after birth.Group 3. With the appearance of the tooth roots, the height of the fluting of the corona dentis maesuring 7.0-8.9 mm, considered as subadults being five to nine months old after birth.Group 4. With well-developed tooth roots of molars, the height of the fluting of the corona dentis measuring 4.0-6.9 mm and the end of the fluting sitting just at the level of the alveolar socket limbus in most specimens, considered as adults of the 1st group being nine months to 1/2 years old.Group 5. Highly developed roots and the height of the fluting of the corona dentis measuring 2.0-3.9 mm and the end of the fluting sitting above the bone line in most specimens, considered as adult of the 2nd group, being 11/2-2 years old.Group 6. With long tooth roots, the height of the fluting measuring 0-1.9 mm, considered as aged group of over two years old.It is clear that the skull of this animal shows a considerable range of age variation in age groups 1-3. It grows intensively before group 4.It seems apparent that variations of the body weights and body length found are largely due to age, although there are overlaps in the measurements of the different age groups.The seasonal difference in the age distribution of the muskrat population is obvious. The sex ratio in the entire collection is 57 males to 43 females. There are generally two to three litters in a year from April to July, sometimes only one or four litters. The average litter size is 8.5 young. The yearling young, i.e., groups 1,2,3 are usually sexually inactive; the three other goups are capable of reproduction.更多还原