摘要:

A study of the Great Argus pheasantArgusianus argusis described. Cleared display sites are owned each by a single male which calls to attract females, while other adult and subadult males maintain no such sites. Evidence is presented to show that vocal differences between males at display sites are slight and unstable, and are therefore unlikely to be used by females in mate choice. No evidence was obtained to suggest that females wander from display site to site and mate with the best male chosen by visual comparison of subtle plumage variation, although the classical assumption has been that such choice accounts for the evolution of the males' extravagant plumage. Females may by chance meet males without display sites at random in the forest, but the displays of such males are probably insufficiently stimulating to induce the female to copulate. Choice between males with or without display sites, on gross plumage and display differences, provides an alternative explanation for the evolution of the males' plumage.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1981.tb00751.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

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, we combine several previous hypotheses with some new ideas.Owing to their structural and behavioural 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; one parent guards the offspring while the other forages for the family. Further, among predators hunting alert prey such as vertebrates, two mates because of interference may not procur much more food than would one mate hunting alone. By contrast, two mates feeding on less alert prey may together obtain almost twice as much food as one mate hunting alone. For these reasons, partitioning of breeding labours might be adaptive only in predatory birds.An initial imbalance favours 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 five of six aspects explored. The male must therefore 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 one 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. Further, 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 therefore 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

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1981.tb00752.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The genetic relationships among 30 populations of 11 species and five genera of North American Unionidae were assessed by using standard allozyme procedures. Emphasis was on relationships among populations and species ofElliptioandFusconaia.Multi‐dimensional scaling based on a matrix of Nei's (1972) genetic distances substantiated the immunoelectrophoretic results of Davis&Fuller 1981, which demonstrated the distinct and divergent taxonomic groups Anodontinae, Margaritiferinae, and Ambleminae, plus die close relationship ofElliptio and Fusconaia, which justifies their inclusion within the same tribe. Genetic distance appears to increase regularly with time since divergence of taxa. TheE. complanataspecies group is an apparently recent radiation and probably is actively radiating today. The I values among species of this group range from 0.90 to 0.99. Considerable heterozygosity, numerous polymorphic loci, and much interpopuladon phenotypic diversity was also recorded for this group. Some taxa mat have been considered synonyms are demonstrated to be valid species. Reasons for the low genetic distances among unionid taxa are discussed. Standard allozyme analyses are shown to be of great value for assessing relationships among unionid tax

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1981.tb00753.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Observations of several plant species suggest that individuals incur greater herbivore damage in shaded than in nearby sunny areas. Two hypotheses are presented to explain this pattern of herbivory; a preliminary test of one suggests that plants growing in the sun are usually tastier, although eaten less, than those in the shade. The phenomenon has several implications for the nature of plant‐herbivore interactions in terrestrial communitie

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1981.tb00754.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Recently discovered correspondence between Charles Darwin and David Moore shows the latter's role in providing fresh material of importance to Darwin's studies on insectivorous plants. One letter relates to Moore's experimental work on potatoes. This research, probably concerned with resistance of selected varieties of potato to blight, is apparently not supported by Glasnevin Botanic Garden (Dublin) records or contemporary literature.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1981.tb00755.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Linnaeus described eleven species in the generaMuscaandConopsthat are now placed in the Fanniidae, Anthomyiidae and Muscidae. A study is presented of the types and other material of these three families in his collection.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1981.tb00756.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY