Angert Amy Lauren
Department of Plant Biology, 166 Plant Biology Building, Michigan State University, East Lansing, Michigan 48824, USA.
Ecology. 2006 Aug;87(8):2014-25. doi: 10.1890/0012-9658(2006)87[2014:docamp]2.0.co;2.
Every species occupies a limited geographic area, but how spatiotemporal environmental variation affects individual and population fitness to create range limits is not well understood. Because range boundaries arise where, on average, populations are more likely to go extinct than to persist, range limits are an inherently population-level problem for which a demographic framework is useful. In this study, I compare demographic parameters and population dynamics between central and marginal populations of monkeyflowers, Mimulus cardinalis and M. lewisii, along an elevation gradient spanning both species' ranges. Central and marginal populations of both species differed in survival and fecundity. For M. lewisii, these components of fitness were higher in central than in marginal populations, but for M. cardinalis the converse was true. To assess spatiotemporal variation in population dynamics, I used transition matrix models to estimate asymptotic population growth rates (lambda) and found that population growth rates of M. lewisii were highest at the range center and reduced at the range margin. Population growth rates of M. cardinalis were highest at the range margin and greatly reduced at the range center. Life table response analysis decomposed spatiotemporal variation in lambda into contributions from each transition between life stages, finding that transitions from large nonreproductive and reproductive plants to the seed class and stasis in the reproductive class made the largest contributions to spatial differences in lambda. These transitions had only low to moderate sensitivities, indicating that differences in projected population growth rates resulted mainly from observed differences in transition matrix parameters and their underlying vital rates.
每个物种都占据着有限的地理区域，但时空环境变化如何影响个体和种群适应性以形成分布范围界限，目前还没有得到很好的理解。由于分布范围边界出现在平均而言种群更有可能灭绝而非持续存在的地方，分布范围界限本质上是一个种群水平的问题，对此人口统计学框架很有用。在本研究中，我沿着跨越这两个物种分布范围的海拔梯度，比较了猴面花（Mimulus cardinalis和M. lewisii）中心种群和边缘种群的人口统计学参数及种群动态。两个物种的中心种群和边缘种群在存活率和繁殖力方面存在差异。对于M. lewisii，适应性的这些组成部分在中心种群中高于边缘种群，但对于M. cardinalis则相反。为了评估种群动态的时空变化，我使用转移矩阵模型来估计渐近种群增长率（λ），发现M. lewisii的种群增长率在分布范围中心最高，在分布范围边缘降低。M. cardinalis的种群增长率在分布范围边缘最高，在分布范围中心大幅降低。生命表响应分析将λ的时空变化分解为生命阶段之间每次转移的贡献，发现从大型非繁殖和繁殖植物到种子类别的转移以及繁殖类别的停滞对λ的空间差异贡献最大。这些转移只有低到中等的敏感性，表明预测的种群增长率差异主要源于观察到的转移矩阵参数及其潜在生命率的差异。
