在年龄结构化动物种群的分析过程中常见的几种错误

分析动物各年龄组的种群数据有助于推断影响动物种群发展趋势的诸因素,而且便于设计出种群层次。然而,在研究近期文献资料时,我们发现存在三种错误。这些错误均可导致非正确的解释。即:1)在生命表分析中,将Sx与lx等同(Sx由各死亡年龄组推导而出,lx为存活率);2)在综合跨年龄组的成雌生育率时,不计算该年龄组的成雌死亡数;3)在用Leslie矩阵计算周限增长率时,以mx取代Fx。我们将探讨上述错误的含义及后果,并提出解决方法。

ON SOME COMMON ERRORS IN ANALYSIS OF AGE-STRUCTURED POPULATIONS

Analyzing age-structured population data can be ufeful in deducing factors affecting population trend, and projecting future population levels. However, in a review of recent literature, we noted 3 errors in analyses, all of which may lead to erroneous inferences.( 1 ) In life-table analyses, it is incorrect to equate Sx(the proportion of animals in each age-class x) with lx (the proportion of a cohort surviving to the beginning of age-class x) ,unless it is known that r = 0 and the population has achieved a stable age distribution. However, if these two conditions hold, the lifetable cannot 'calculate' r; rather, knowledge of r is a prerequisite to building the life-table.( 2 ) In building a life-table, problems can arise when pooling birth rates across age-categories of mothers without accounting for mortality of mothers within the pooled age category.If resultant birth rates are not discounted in some way, resulting estimates of r will be biased in a positive direction.( 3 ) When calculating the finite growth rate A using a Leslie matrix, it is incorrect to substitute mx for Fx. The former is the more commonly obtained term (number of female young per female of age x just after the birth season) ; the latter is Leslie's term, which is more complex and difficult to gather in the field.We discuss implications of these errors and suggest ways to avoid making them.