Fluctuations in age structure and their variable influence on population growth
Fluctuations in age structure and their variable influence on population growth
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DOI：
10.1111/1365-2435.13431
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发表时间：
2019-08-30
影响因子：
5.2
通讯作者：
Vucetich, John A.
中科院分区：
文献类型：
--
作者：
Hoy, Sarah R.;MacNulty, Daniel R.;Vucetich, John A.
增长率的时间波动可能来自特定年龄的生命率变化和年龄结构的时间波动（即每个年龄组中个体的相对丰度）。然而，对年龄结构的时间波动及其对人口增长率的影响进行的经验性评估相对较少。大多数研究侧重于了解不断变化的生命率对人口增长率的贡献，这些分析通常假定：（a）人口具有稳定的年龄分布，（B）环境对生命率和年龄结构的影响是固定的（即这些过程的均值和/或方差不随时间变化），（c）动态与密度无关。在这里，我们量化了年龄结构的波动，并评估了它们是否是固定的四个种群的自由放养的脊椎动物：驼鹿（观察48年），麋鹿（15年），茶色猫头鹰（15年）和灰狼（17年）。我们还评估了年龄结构的波动在多大程度上是有用的预测年人口增长率的模型，占密度依赖。年龄结构的波动与丰度的波动幅度相似。对于三个种群（驼鹿，麋鹿，猫头鹰），年龄分布的平均值和偏度波动，在所观察到的时间段内不稳定。更确切地说，年龄结构指数的样本方差（年际方差）随着研究期的延长而增加，这表明这些人口的年龄结构波动是不稳定的-至少在所分析的15至48年期间是如此。年龄结构的波动与两个种群的种群增长率有关。特别是，随着成年人的平均年龄在其观察范围内增加，驼鹿的人口增长从正到负，麋鹿的人口增长从接近零到负。年龄结构的非平稳性可能是一个重要的机制，丰富的变得非平稳的-因此难以预测-随着时间的推移，野生动物管理者关注的尺度。总的来说，我们的研究结果强调需要脊椎动物种群建模的方法，考虑瞬态动力学和密度依赖性，不依赖于假设环境过程是静止的。可以在本文的支持信息中找到免费的简明语言摘要。
Temporal fluctuations in growth rates can arise from both variation in age-specific vital rates and temporal fluctuations in age structure (i.e. the relative abundance of individuals in each age-class). However, empirical assessments of temporal fluctuations in age structure and their effects on population growth rate are relatively rare. Most research has focused on understanding the contribution of changing vital rates to population growth rates and these analyses routinely assume that: (a) populations have stable age distributions, (b) environmental influences on vital rates and age structure are stationary (i.e. the mean and/or variance of these processes does not change over time), and (c) dynamics are independent of density. Here we quantified fluctuations in age structure and assessed whether they were stationary for four populations of free-ranging vertebrates: moose (observed for 48 years), elk (15 years), tawny owls (15 years) and grey wolves (17 years). We also assessed the extent that fluctuations in age structure were useful for predicting annual population growth rates using models which account for density dependence. Fluctuations in age structure were of a similar magnitude to fluctuations in abundance. For three populations (moose, elk, owls), the mean and the skew of the age distribution fluctuated without stabilizing over the observed time periods. More precisely, the sample variance (interannual variance) of age structure indices increased with the length of the study period, which suggests that fluctuations in age structure were non-stationary for these populations - at least over the 15- to 48-year periods analysed. Fluctuations in age structure were associated with population growth rate for two populations. In particular, population growth varied from positive to negative for moose and from near zero to negative for elk as the average age of adults increased over its observed range. Non-stationarity in age structure may represent an important mechanism by which abundance becomes non-stationary - and therefore difficult to forecast - over time-scales of concern to wildlife managers. Overall, our results emphasize the need for vertebrate populations to be modelled using approaches that consider transient dynamics and density dependence and that do not rely on the assumption that environmental processes are stationary. A free Plain Language Summary can be found within the Supporting Information of this article.