Higgins Kevin
Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, United States.
Theor Popul Biol. 2009 Sep;76(2):146-55. doi: 10.1016/j.tpb.2009.05.006. Epub 2009 Jun 6.
Metapopulation extinction risk is the probability that all local populations are simultaneously extinct during a fixed time frame. Dispersal may reduce a metapopulation's extinction risk by raising its average per-capita growth rate. By contrast, dispersal may raise a metapopulation's extinction risk by reducing its average population density. Which effect prevails is controlled by habitat fragmentation. Dispersal in mildly fragmented habitat reduces a metapopulation's extinction risk by raising its average per-capita growth rate without causing any appreciable drop in its average population density. By contrast, dispersal in severely fragmented habitat raises a metapopulation's extinction risk because the rise in its average per-capita growth rate is more than offset by the decline in its average population density. The metapopulation model used here shows several other interesting phenomena. Dispersal in sufficiently fragmented habitat reduces a metapopulation's extinction risk to that of a constant environment. Dispersal between habitat fragments reduces a metapopulation's extinction risk insofar as local environments are asynchronous. Grouped dispersal raises the effective habitat fragmentation level. Dispersal search barriers raise metapopulation extinction risk. Nonuniform dispersal may reduce the effective fraction of suitable habitat fragments below the extinction threshold. Nonuniform dispersal may make demographic stochasticity a more potent metapopulation extinction force than environmental stochasticity.
集合种群灭绝风险是指在固定时间框架内所有局部种群同时灭绝的概率。扩散可能通过提高集合种群的平均人均增长率来降低其灭绝风险。相比之下，扩散可能通过降低集合种群的平均种群密度来提高其灭绝风险。哪种效应占主导由栖息地破碎化控制。在轻度破碎化的栖息地中扩散，通过提高平均人均增长率而不会使其平均种群密度出现任何明显下降，从而降低集合种群的灭绝风险。相比之下，在严重破碎化的栖息地中扩散会增加集合种群的灭绝风险，因为其平均人均增长率的上升被平均种群密度的下降所抵消。这里使用的集合种群模型还展示了其他几个有趣的现象。在足够破碎化的栖息地中扩散会将集合种群的灭绝风险降低到恒定环境的灭绝风险水平。只要局部环境不同步，栖息地片段之间的扩散就会降低集合种群的灭绝风险。成群扩散会提高有效栖息地破碎化水平。扩散搜索障碍会增加集合种群的灭绝风险。不均匀扩散可能会使适合的栖息地片段的有效比例降低到灭绝阈值以下。不均匀扩散可能会使人口统计学随机性成为比环境随机性更强大的集合种群灭绝力量。
