Kanda L Leann, Fuller Todd K, Sievert Paul R, Kellogg Robert L
Department of Biology, Ithaca College, Ithaca, New York 14850, USA.
Ecology. 2009 Jun;90(6):1574-85. doi: 10.1890/08-1263.1.
The roles of dispersal and population dynamics in determining species' range boundaries recently have received theoretical attention but little empirical work. Here we provide data on survival, reproduction, and movement for a Virginia opossum (Didelphis virginiana) population at a local distributional edge in central Massachusetts (USA). Most juvenile females that apparently exploited anthropogenic resources survived their first winter, whereas those using adjacent natural resources died of starvation. In spring, adult females recolonized natural areas. A life-table model suggests that a population exploiting anthropogenic resources may grow, acting as source to a geographically interlaced sink of opossums using only natural resources, and also providing emigrants for further range expansion to new human-dominated landscapes. In a geographical model, this source-sink dynamic is consistent with the local distribution identified through road-kill surveys. The Virginia opossum's exploitation of human resources likely ameliorates energetically restrictive winters and may explain both their local distribution and their northward expansion in unsuitable natural climatic regimes. Landscape heterogeneity, such as created by urbanization, may result in source-sink dynamics at highly localized scales. Differential fitness and individual dispersal movements within local populations are key to generating regional distributions, and thus species ranges, that exceed expectations.
扩散和种群动态在决定物种分布范围边界方面所起的作用，近来受到了理论上的关注，但实证研究却很少。在此，我们提供了关于美国马萨诸塞州中部一个局部分布边缘的弗吉尼亚负鼠（Didelphis virginiana）种群的生存、繁殖和移动的数据。大多数明显利用人为资源的幼年雌性负鼠度过了它们的第一个冬天，而那些利用相邻自然资源的负鼠则死于饥饿。在春天，成年雌性负鼠重新定居到自然区域。一个生命表模型表明，一个利用人为资源的种群可能会增长，成为仅利用自然资源的负鼠地理交错分布的汇的源，并且还为进一步向新的人类主导景观的范围扩张提供移民。在一个地理模型中，这种源 - 汇动态与通过道路死亡调查确定的局部分布是一致的。弗吉尼亚负鼠对人力资源的利用可能缓解了能量限制的冬季，并且可能解释了它们的局部分布以及它们在不适合的自然气候条件下向北扩张的现象。景观异质性，如城市化所造成的，可能在高度局部的尺度上导致源 - 汇动态。局部种群内不同的适合度和个体扩散移动是产生超出预期的区域分布以及物种分布范围的关键。
