Adler G H, Levins R
Department of Population Sciences, School of Public Health, Harvard University, Boston, Massachusetts 02115.
Q Rev Biol. 1994 Dec;69(4):473-90. doi: 10.1086/418744.
Populations of rodents isolated on islands often show systematic differences in demography, reproduction, behavior, and morphology when compared to mainland populations. These differences, termed the island syndrome, include higher and more stable densities, better survival, increased body mass, and reduced aggressiveness, reproductive output, and dispersal. We synthesize information in the literature on island rodent populations and construct a conceptual model to explain the island syndrome. Population density and other manifestations of the island syndrome are predicted to increase with island isolation and to decrease with island area. The effect of isolation is direct by limiting dispersal, while the effect of area is less direct. As area increases, predators, competitors, and habitat structure increase in diversity. We suggest that the intensity or absence of density-depressing factors (primarily predation in communities comprised of only a few morphologically and trophically divergent species) is primarily responsible for the area effect and serves as a principal factor differentiating island from mainland populations of rodents. Other characteristics associated with the island syndrome may be the result of both short-term and long-term processes or responses. Short-term responses include reproductive, body size, and behavioral changes that may be phenotypic reaction norms in response to higher island densities. Thus, higher densities lead to reduced reproductive output, which then leads to greater body size. Initial behavioral differences may be owing to better survival and reduced dispersal, which result in less population turnover, greater neighbor familiarity, and less aggression. Long-term changes may be due to directional selection for reduced dispersal, increased body size in response to increased intraspecific competition, reduced reproductive output (smaller litters and delayed maturation) in response to reduced mortality schedules, and reduced aggressiveness. While the model is specific to rodent populations, the conclusions may be applicable to other systems if characteristics such as body size, vagility, and community composition are considered.
与大陆种群相比，隔离在岛屿上的啮齿动物种群在人口统计学、繁殖、行为和形态学方面常常表现出系统性差异。这些差异被称为岛屿综合征，包括更高且更稳定的密度、更好的存活率、增加的体重以及降低的攻击性、繁殖产出和扩散能力。我们综合了文献中有关岛屿啮齿动物种群的信息，并构建了一个概念模型来解释岛屿综合征。预计岛屿综合征的种群密度和其他表现会随着岛屿隔离程度的增加而上升，随着岛屿面积的增大而下降。隔离的影响是直接的，它限制了扩散，而面积的影响则不那么直接。随着面积增加，捕食者、竞争者和栖息地结构的多样性也会增加。我们认为，密度抑制因素（主要是在仅由少数形态和营养差异较大的物种组成的群落中的捕食）的强度或缺失是造成面积效应的主要原因，也是区分岛屿和大陆啮齿动物种群的主要因素。与岛屿综合征相关的其他特征可能是短期和长期过程或反应的结果。短期反应包括繁殖、体型和行为变化，这些可能是对较高岛屿密度的表型反应规范。因此，较高的密度导致繁殖产出减少，进而导致体型增大。最初的行为差异可能是由于更好的存活率和减少的扩散，这导致种群更替减少、邻居熟悉度增加以及攻击性降低。长期变化可能是由于对减少扩散的定向选择、对种内竞争增加的反应而导致的体型增大、对死亡率降低的反应而导致的繁殖产出减少（产仔数减少和成熟延迟）以及攻击性降低。虽然该模型是针对啮齿动物种群的，但如果考虑体型、迁移能力和群落组成等特征，其结论可能适用于其他系统。
