摘要:

Summary(A) There are data showing beyond question a gender gap, with women living longer than men, especially in economically developed societies. There is greater male vulnerability to the major causes of human death.(B) In lower animals there are data suggesting a female survival advantage to adult life in many species, but the observations do not consider longevity or survival to an advanced age.(C) In laboratory rodents kept under controlled conditions the relationship of sex to longevity is variable, with males sometimes showing greater longevity than females and with life span being dependent on factors like breeding and diet.(D) Similar genetic and hormonal processes operate in humans and in non‐human mammals including the genetic mechanism of sex determination, the hormonal consequences of sex determination, and the effects of hormones on processes which affect longevity such as cholesterol levels and immune functions.(E) Causes of death in humans and animals are different, and it seems unlikely, therefore, that the same mechanisms could be determinants of longevity in all mammalian species.(F) Human male and female longevity continue to change, and it is likely that the gender gap will narrow, with societal and medical changes in post‐industrial societies reducing the male disadvantages in behaviour and in the handling of cholesterol.(G) It remains an important question whether part of the gender gap seen in humans is based on other differences in the basic biology of males and fema

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00635.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryOne commonly cited benefit to animals that forage in groups is an increase in the probability of detecting a predator, and a decrease in the time spent in predator detection. A mathematical model (Pulliam 1973) predicts a negative relationship between group size and vigilance rates. Over fifty studies of birds and mammals report a negative correlation between group size and vigilance behaviour and most conclude that the relationship at least partly explains why individuals forage in groups. This review evaluates the strength of these conclusions based on their evidence. Those variables that may confound the relationship between vigilance and group size are outlined, and their control is assessed for each study. The variables I consider to be important include the density and type of food; competition between individuals; the proximity to both a safe place and the observer; the presence of predators; the visibility within the habitat; the composition of the group; the ambient temperature and the time of day. Based on these assessments, most of the studies fail to adequately demonstrate an unambiguous relationship between vigilance behaviour and group size. Nevertheless, many studies reveal interesting features of the relationship between vigilance and group size that should provide fruitful avenues for future research.

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00636.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00637.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryJuvenile birds differ from conspecific adults in their diet and methods of prey capture and prey handling. Juvenile‐adult differences in foraging result from (1) immaturity of the beak, skeleto‐muscular and neurological systems and (2) the time required to learn foraging skills. These conclusions are largely based on field observations. More experimental studies to assess the relative importance of the various constraints are needed.Juvenile birds appear to be under strong selection to reach adult form and function as rapidly as possible. Remaining differences between juveniles and adults are largely attributable to constraints. In contrast to many other taxa there are few examples in which juvenile‐adult differences in foraging have been accentuated by selection on the juvenile behav

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00638.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00639.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY