EVOLUTION OF REVERSED SEXUAL SIZE DIMORPHISM AND ROLE PARTITIONING AMONG PREDATORY BIRDS, WITH A SIZE SCALING OF FLIGHT PERFORMANCE
EVOLUTION OF REVERSED SEXUAL SIZE DIMORPHISM AND ROLE PARTITIONING AMONG PREDATORY BIRDS, WITH A SIZE SCALING OF FLIGHT PERFORMANCE
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DOI：
10.1111/j.1095-8312.1981.tb00752.x
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发表时间：
1981-01-01
影响因子：
1.9
通讯作者：
NORBERG, RA
中科院分区：
文献类型：
--
作者：
ANDERSSON, M;NORBERG, RA
为了解释猛禽、猫头鹰和贼鸥（雌性通常大于雄性）中性别角色划分和逆转性别体型二态性的适应性意义，之前的几个假设与一些新想法相结合。由于掠食性鸟类对捕获猎物的结构和行为适应，它们比其他鸟类更有可能保护其后代免受巢穴捕食者的侵害。这使得性别角色划分变得有利；父母一方负责保护后代，另一方则为家人寻找食物。在捕猎脊椎动物等警觉猎物的捕食者中，由于干扰，2个配偶可能不会比1个配偶单独捕猎获得更多的食物。相比之下，两个以不太警觉的猎物为食的配偶所获得的食物可能几乎是一个单独狩猎的配偶所获得的食物的两倍。由于这些原因，繁殖劳动的分配可能只适用于掠食性鸟类。最初的不平衡有利于雌性守卫巢穴和雄性觅食：如果雌性攻击猎物，正在发育的卵可能会受到损害；它们的质量可能会降低她的飞行性能；她必须去鸟巢产蛋；雄性在她产下之前喂养她（求爱喂养）。雌性体型的增加会增强产蛋量、孵化能力、撕裂幼鸟猎物的能力，特别是对掠食性鸟类的后代的保护。对于雄性来说，繁殖期间的高效觅食变得最为重要。这对雄性的空中敏捷性提出了很高的要求，特别是对于敏捷猎物的捕食者。在所探索的 6 个方面中，有 5 个方面的飞行性能随着尺寸的增加而降低。相对于最重要的猎物而言，雄性的体型不能太大。由于这些原因，他应该比雌性小。在掠食性鸟类中，体型二态性随着鸟类在饮食中所占比例的增加而增加，这可以解释如下。成年鸟类主要有一种捕食者：其他掠食性鸟类。因为几乎只有这些专家才会利用成年鸟类，所以他们负责捕食这种猎物的大部分工作。捕食较容易猎物的捕食者会与许多其他种类的捕食者竞争，这会大大减少其领地内的猎物丰度。对于成年鸟类的捕食者来说，情况并非如此。由于鸟类极其敏捷，专门的捕食者只能在有限的体型范围内有效地捕猎，而它的飞行技能却可以与鸟类相媲美。因此，这些捕食者之间体型二态性的增加对于扩大这对捕食者的食物基础尤为重要。在繁殖期间，鸟类专家可能会吃掉大部分合适大小范围内的可用猎物。当捕食者的幼崽足够大以保护自己时，雌性通过狩猎来提供比保护幼崽更好的帮助。对于鸟类专家来说，如果雌性捕食与雄性不同大小的猎物，这对鸟类专家来说是有利的，因为雄性此时已经减少了其猎物尺寸类别中的猎物丰度。但在捕猎更容易的猎物的掠食性鸟类中，雌性通过在雄性猎物范围之外狩猎而获得的收益很少，因为其他种类的捕食者会减少雄性偏好的体型范围之外和内部的猎物丰度。通过大的性别大小二态性进行的配对内食物分离对于鸟类的捕食者来说应该特别有利。这可能是鸟类体型二态性程度随鸟类饮食比例增加而增加的主要原因。
To explain the adaptive significance of sex role partitioning and reversed sexual size dimorphism among raptors, owls and skuas, where females are usually larger than males, several previous hypotheses are combined with some new ideas. Owing to their structural and behavioral adaptations for prey capture, predatory birds have better prospects than other birds of defending their offspring against nest predators. This makes sex role partitioning advantageous; 1 parent guards the offspring while the other forages for the family. Among predators hunting alert prey such as vertebrates, 2 mates because of interference may not procure much more food than would 1 mate hunting alone. By contrast, 2 mates feeding on less alert prey may together obtain almost twice as much food as 1 mate hunting alone. For these reasons, partitioning of breeding labors might be adpative only in predatory birds. An initial imbalance favors female nest guarding and male foraging: the developing eggs might be damaged if the female attacks prey; their mass might reduce her flight performance; she must visit the nest to lay; and the male feeds her before she lays (courtship feeding). Increased female body size should enhance egg production, incubation, ability to tear apart prey for the young and in particular, offspring protection in predatory birds. Efficient foraging during the breeding period then becomes most important for the male. This imposes great demands on aerial agility in males, particularly among predators of agile prey. Flight performance decreases with increasing size in 5 of 6 aspects explored. The male must not be too large in relation to the most important prey. For these reasons, he should be smaller than the female. Among predatory birds, size dimorphism increases with the proportion of birds in the diet, which may be explained as follows. Adult birds have mainly 1 type of predators: other predatory birds. Because almost only these specialists exploit adult birds, they carry out most of the cropping of this prey. A predator of easier prey competes with many other kinds of predators, which considerably reduce prey abundance in its territory. This is not so for predators of adult birds. Because birds are extremely agile, the specialized predator can hunt efficiently only within a limited size range of birds, whose flight skill it can match. Increased size dimorphism among these predators therefore should be particularly important for enlarging the combined food base of the pair. A bird specialist may consume much of the available prey in the suitable size range during the breeding period. When the predator''s young are large enough to defend themselves, the female aids better by hunting than by guarding the chicks. It is advantageous among bird specialists if she hunts prey of other sizes than does the male, who has by then reduced prey abundance in his prey size class. But among predatory birds hunting easier prey the female gains little by hunting outside the male''s prey spectrum because other kinds of predators will have reduced the prey abundance outside as well as inside the male''s preferred size range. Intra-pair food separation through large sexual size dimorphism should be particularly advantageous among predators of birds. This may be the main reason why the degree of size dimorphism increases with the dietary proportion of birds.