Sand Håkan
Grimsö Research Station, Swedish University of Agricultural Sciences, S-730 91, Riddarhyttan, Sweden.
Oecologia. 1996 Apr;106(2):212-220. doi: 10.1007/BF00328601.
I examined the relationship between age, body size and fecundity in 833 female moose (Alces alces) from 14 populations in Sweden sampled during 1989-1992. Data on population density, food availability and climatic conditions were also collected for each population. Age and body mass were both significantly positively related to fecundity, measured as ovulation rate, among female moose. The relationship between the probability of ovulation and body mass was dependent on age with (1) a higher body mass needed in younger females for attaining a given fecundity, and (2) body mass having a stronger effect on fecundity in yearling (1.5 year) than in older (≥2.5 year) females. Thus, a 40 kg increase in yearling body mass resulted in a 42% increase in the probability of ovulation as compared to a 6% increase in older females. The lower reproductive effort per unit body mass, and the relatively stronger association between fecundity and body mass in young female moose compared to older ones, is likely to primarily represent a mechanism that trades off early maturation against further growth, indicating a higher cost of reproduction in young animals. In addition to age and body mass, population identity explained a significant amount of the individual variation in fecundity, showing that the relationship between body mass and fecundity was variable among populations. This variation was in turn related to the environment, in terms of climatic conditions forcing female moose living in relatively harsh/more seasonal climatic conditions to attain a 22% higher body mass to achive the same probability of multiple ovulation (twinning) as females living in climatically milder/less seasonal environments. The results suggests that the lower fecundity per unit body mass in female moose living in climatically harsh/more seasonal environments may be an adaptive response to lower rates of juvenile survival, compared to females experiencing relatively milder/less seasonal climatic conditions.
我研究了1989年至1992年期间在瑞典14个种群中采样的833头雌性驼鹿（驼鹿属）的年龄、体型与繁殖力之间的关系。还收集了每个种群的种群密度、食物可利用性和气候条件数据。在雌性驼鹿中，年龄和体重均与以排卵率衡量的繁殖力显著正相关。排卵概率与体重之间的关系取决于年龄，（1）年轻雌性达到给定繁殖力所需的体重更高，（2）一岁（1.5岁）雌性的体重对繁殖力的影响比年龄较大（≥2.5岁）的雌性更强。因此，一岁雌性体重增加40千克，排卵概率增加42%，而年龄较大的雌性仅增加6%。与年龄较大的雌性相比，年轻雌性驼鹿单位体重的繁殖投入较低，且繁殖力与体重之间的关联相对更强，这可能主要代表了一种在早熟与进一步生长之间进行权衡的机制，表明幼龄动物的繁殖成本更高。除了年龄和体重外，种群特征也解释了繁殖力个体差异的很大一部分，表明体重与繁殖力之间的关系在不同种群中存在差异。这种差异反过来又与环境有关，就气候条件而言，生活在相对恶劣/季节性更强气候条件下的雌性驼鹿需要达到比生活在气候更温和/季节性更弱环境中的雌性高22%的体重，才能获得相同的多次排卵（双胎）概率。结果表明，与经历相对温和/季节性较弱气候条件的雌性相比，生活在气候恶劣/季节性更强环境中的雌性驼鹿单位体重繁殖力较低，可能是对幼崽存活率较低的一种适应性反应。
