Hill M Forrest, Hastings Alan, Botsford Louis W
Institute of Theoretical Dynamics, University of California, Davis, California 95616, USA.
Am Nat. 2002 Sep;160(3):389-402. doi: 10.1086/341526.
Habitat destruction is a critical factor that affects persistence in several taxa, including Pacific salmon. Salmon are noted for their ability to home to their natal streams for reproduction. Since straying (i.e., spawners reproducing in nonnatal streams) is typically low in salmon, its effects have not been appreciated. In this article, we develop both a general analytical model and a simple simulation model describing structured metapopulations to study how weak connections between subpopulations affect the ability of a species to tolerate habitat destruction and/or declines in habitat quality. Our goals are to develop general principles and to relate these principles to salmon population dynamics. The analytical model describes the dynamics of two density-dependent subpopulations, connected by dispersal, whose growth rates fluctuate in response to environmental and demographic stochasticity. We find that, for moderate levels of environmental variability, small dispersal rates can significantly increase mean extinction times. This effect declines with increasing habitat quality, increasing temporal correlation, and increasing spatial correlation, but it is still significant for realistic parameter values. The simulation model shows there is a threshold rate of dispersal that minimizes extinction probabilities. These results cannot be seen in classical metapopulation models and provide new insights into the rescue effect.
栖息地破坏是影响包括太平洋鲑鱼在内的多个分类群种群存续的关键因素。鲑鱼因其能够洄游到它们出生的溪流中进行繁殖而闻名。由于鲑鱼的离群现象（即产卵者在非出生溪流中繁殖）通常较少，其影响尚未得到重视。在本文中，我们开发了一个通用分析模型和一个简单的模拟模型来描述结构化集合种群，以研究亚种群之间的弱连接如何影响物种耐受栖息地破坏和/或栖息地质量下降的能力。我们的目标是制定通用原则，并将这些原则与鲑鱼种群动态联系起来。分析模型描述了两个通过扩散相连的密度依赖亚种群的动态，其增长率会因环境和人口统计学随机性而波动。我们发现，对于中等程度的环境变异性，较小的扩散率可以显著增加平均灭绝时间。随着栖息地质量的提高、时间相关性的增加和空间相关性的增加，这种影响会减弱，但对于实际参数值来说仍然很显著。模拟模型表明，存在一个使灭绝概率最小化的扩散阈值率。这些结果在经典集合种群模型中无法看到，并为救援效应提供了新的见解。
