Comparing plant life histories using elasticity analysis: the importance of life span and the number of life-cycle stages
Comparing plant life histories using elasticity analysis: the importance of life span and the number of life-cycle stages
复制标题
使用弹性分析比较植物生命史：寿命的重要性和生命周期阶段的数量
作者：
Neal J. Enright;Miguel Franco;J. Silvertown
近年来，人们利用转移矩阵弹性分析方法研究了多年生植物种群生存率（L）、生长率（G）和繁殖力（F）在估计种群增长率中的相对作用。这三个变量的相对重要性，然后被用来作为一个框架，在一个三角形参数空间中的植物生活史模式进行比较。在这里，我们分析的方式，选择来描述一个物种（过渡矩阵维数）的生命周期阶段的数量可能会影响这种比较的解释。由于描述生存（“停滞”）和生长的过渡矩阵元素不是独立的，用于描述一个物种的阶段数影响它们对种群增长率的相对贡献。阶段数量的减少增加了停滞相对于生长的明显重要性，因为每个阶段变得更广泛，每个单位时间内进入下一阶段的个体更少。一个假设的树种分为4-32个生命周期阶段的测试矩阵的分析证实了这一点。如果阶段的数量与物种寿命有关，使得每个阶段的平均停留时间近似恒定，那么G的弹性将反映相对增长率对λ的重要性。另一种确保物种之间结果可比性的更简单的方法可能是使用相同数量的阶段，而不管物种的寿命。已发表的关于草本和木本物种的研究倾向于使用相对较少的阶段来描述生命周期（草本：n=45，
$$ar x =下午六时十六分
木本植物：n=21，
$$ar x =晚上八时三十八分3.57$$
），因此近似于这种方法。通过使用相同数量的阶段，而不管寿命，物种的位置沿着三角形参数空间的G-L侧很大程度上反映了寿命的差异。弹性的变化程度为L，G和F内和物种之间也可能与演替状态和栖息地等因素。例如，耐荫木本树种南洋杉（Araucaria cunninghamii）对郁闭（L）表现出更大的重要性，而间隙期同类树种南洋杉（Araucaria hunsteinii）则表现出更高的G值（尽管G值可能随林分发展阶段而变化）。
AbstractRecent studies have used transition matrix elasticity analysis to investigate the relative role of survival (L), growth (G) and fecundity (F) in determining the estimated rate of population increase for perennial plants. The relative importance of these three variables has then been used as a framework for comparing patterns of plant life history in a triangular parameter space. Here we analyse the ways in which the number of life-cycle stages chosen to describe a species (transition matrix dimensionality) might influence the interpretation of such comparisons. Because transition matrix elements describing survival (“stasis”) and growth are not independent, the number of stages used to describe a species influences their relative contribution to the population growth rate. Reduction in the number of stages increases the apparent importance of stasis relative to growth, since each becomes broader and fewer individuals make the transition to the next stage per unit time period. Analysis of a test matrix for a hypothetical tree species divided into 4–32 life-cycle stages confirms this. If the number of stages were defined in relation to species longevity so that mean residence time in each stage were approximately constant, then the elasticity of G would reflect the importance of relative growth rate to λ. An alternative, and simpler, approach to ensure comparability of results between species may be to use the same number of stages regardless of species longevity. Published studies for both herbaceous and woody species have tended to use relatively few stages to describe life cycles (herbs: n=45,
$$ar x = 6.16 pm 4.63$$
; woody plants: n=21,
$$ar x = 8.38 pm 3.57$$
) and so approximate this approach. By using the same number of stages regardless of longevities, the position of species along the G-L side of the triangular parameter space largely reflects differences in longevity. The extent of variation in elasticity for L, G and F within and between species may also be related to factors such as successional status and habitat. For example, the shade-tolerant woody species, Araucaria cunninghamii, shows greater importance for stasis (L), while the gap-phase congener species, Araucaria hunsteinii, shows higher values for G (although values are likely to vary with the stage of stand development).