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Double allee effects and extinction in the island fox

机译：岛上狐狸的双重阿利效应和灭绝

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An Allee effect (AE) occurs in populations when individuals suffer a decrease in fitness at low densities. If a fitness component is reduced (component AE), per capita population growth rates may decline as a consequence (demographic AE) and extinction risk is increased. The island fox (Urocyon littoralis) is endemic to six of the eight California Channel Islands. Population crashes have coincided with an increase in predation by Golden Eagles (Aquila chrysaetos). We propose that AEs could render fox populations more sensitive and may be a likely explanation for their sharp decline. We analyzed demographic data collected between 1988 and 2000 to test whether fox density (1) influences survival and reproductive rates; (2) interacts with eagle presence and affects fox fitness parameters; and (3) influences per capita fox Population trends. A double component AE simultaneously influenced survival (of adults and pups) and proportion of breeding adult females. The adult survival AE was driven by predation by eagles. These component AEs led to a demographic AE Multiple-component AEs, a predation-driven AE, and the simultaneous occurrence of both component and demographic AEs in a mammal are all previously unreported processes. Populations below 7 foxes/km(2) could have suboptimal population growth rates due to the demographic AE, and AEs may have contributed to the dramatic declines in three fox populations. Because fox densities in critically endangered populations are well below this level, removing Golden Eagles appears necessary to prevent a predation-driven AE Conservationists should also be aware of AEs when planning the release of captive foxes. More generally, our findings highlight the danger of overlooking AEs in the conservation of populations of rare or threatened species.
机译：当个体在低密度下体能下降时，会在人群中发生阿利效应（AE）。如果减少适应性成分（AE成分），结果人均人口增长率可能会下降（人口统计学AE），灭绝风险增加。狐狸（Urocyon littoralis）是八个加利福尼亚海峡群岛中的六个的特有物种。人口崩盘与金鹰（天鹰座chrysaetos）捕食增加有关。我们认为，不良事件可以使狐狸种群更加敏感，并且可能是其急剧下降的一种可能的解释。我们分析了1988年至2000年收集的人口数据，以检验狐狸密度（1）是否影响生存率和生殖率; （2）与鹰的存在相互作用并影响狐狸的适应性参数; （3）影响人均狐狸人口趋势。双组分AE同时影响（成年和成年幼犬的）成活率和成年雌性的比例。成年生存AE是由鹰捕食驱动的。这些成分AE导致了人口统计学AE多成分AE，被捕食驱动的AE，并且在哺乳动物中同时发生成分AE和人口统计学AE都是以前未报告的过程。人口AE导致低于7狐狸/ km（2）的人口增长率可能不理想，而AE可能导致了三个狐狸人口的急剧下降。由于极度濒危种群中的狐狸密度远低于此水平，因此有必要去除金鹰以防止被捕食驱动的AE。保护人员在计划释放圈养狐狸时也应意识到AE。更广泛地说，我们的发现突出了在保护稀有或受威胁物种的种群中忽视AE的危险。

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