T. H. Clutton-Brock

Red deer : behavior and ecology of two sexes

Red Deer: Behavior and Ecology of Two Sexes is the most extensive study yet available of reproduction in wild vertebrate. The authors synthesize data collected over ten years on a population of individually recognizable red deer, usually regarded as conspecific with the American elk. Their results reveal the extent of sex differences in behavior, reproduction, and ecology and make a substantial contribution to our understanding of sexual selection.

Inverse density dependence and the Allee effect

The Allee effect describes a scenario in which populations at low numbers are affected by a positive relationship between population growth rate and density, which increases their likelihood of extinction. The importance of this dynamic process in ecology has been under-appreciated and recent evidence now suggests that it might have an impact on the population dynamics of many plant and animal species. Studies of the causal mechanisms generating Allee effects in small populations could provide a key to understanding their dynamics.

Review Lecture: Mammalian Mating Systems

Male mammals show a diverse array of mating bonds, including obligate monogamy, unimale and group polygyny and promiscuity. These are associated with a wide variety of different forms of mate guarding, including the defence of feeding and mating territories, the defence of female groups and the defence of individual receptive females. Female mating bonds include long-term monogamy, serial monogamy, polyandry and promiscuity. Both male and female mating behaviour varies widely within species. Variation in male mating behaviour is related to the effect of male assistance in rearing young and to the defensibility of females by males. The latter is, in turn, related to female ranging behaviour and to the size and stability of female groups. Much of the variation in mammalian mating bonds and systems of mate guarding can be attributed to differences in these three variables.

The Roaring of Red Deer and the Evolution of Honest Advertisement

In many large animals, changes in fighting ability within breeding seasons or across the lifetime of individuals are related to changes in body condition but not to obvious changes in size. In situations where a conflict of interests is likely to lead to a fight, we might consequently expect opponents to assess each other on traits which are related to variation in body condition. This appears to be the case among red deer stags. Competing

The logical stag: Adaptive aspects of fighting in red deer (Cervus elaphus L.)

For red deer stags, fighting both has appreciable costs and yields considerable benefits. Up to 6 % of rutting stags are permanently injured each year, while fighting success and reproductive success are closely related, within age groups as well as across them. Fighting behaviour is sensitive to changes in the potential benefits of fighting: stags fight most frequently and most intensely where potential benefits are high and tend to avoid fighting with individuals they are unlikely to beat. The relevance of these findings to theoretical models of fighting behaviour is discussed. Anitn. Behav., 1979. 27, 21 I-225 THE LOGICAL STAG: ADAPTIVE ASPECTS OF FIGHTING IN RED DEER (CER VUS ELAPHUS L.) BY T. H. CLUTTON-BROCK, S. D. ALBON, R. M. GIBSON* & F. E. GUINNESS King’s College Research Centre, King’s College, Cambridge Abstract. For red deer stags, fighting both has appreciable costs and yields considerable benefits. Up to 6 % of rutting stags are permanently injured each year, while fighting success and reproductive success are closely related, within age groups as well as across them. Fighting behaviour is sensitive to changes in the potential benefits of fighting: stags fight most frequently and most intensely where potential benefits are high and tend to avoid fighting with individuals they are unlikely to beat. The relevance of these findings to theoretical models of fighting behaviour is discussed. For red deer stags, fighting both has appreciable costs and yields considerable benefits. Up to 6 % of rutting stags are permanently injured each year, while fighting success and reproductive success are closely related, within age groups as well as across them. Fighting behaviour is sensitive to changes in the potential benefits of fighting: stags fight most frequently and most intensely where potential benefits are high and tend to avoid fighting with individuals they are unlikely to beat. The relevance of these findings to theoretical models of fighting behaviour is discussed.

Reproductive Effort and Terminal Investment in Iteroparous Animals

Though it has been widely predicted that in animals in which reproductive value declines with age, reproductive effort should increase toward the end of the lifespan, analysis of changes in reproductive effort are impeded by fundamental difficulties in measuring the costs of reproduction. Energetic measures may not reflect the effects of breeding on subsequent survival and breeding success, especially in organisms in which body size increases with age, while attempts to estimate reproductive costs directly are complicated by positive correlations between breeding success and parental survival. Though the long-lived birds and mammals are among the most promising organisms on which to test the theory that reproductive effort increases with age, measures of fecundity commonly decline with increasing maternal age. Some recent evidence suggests, however, that offspring survival may improve toward the end of the lifespan.

LIFE HISTORY VARIATION IN PRIMATES

Extensive variation in life‐history patterns is documented across primate species. Variables included are gestation length, neonatal weight, litter size, age at weaning, age at sexual maturity, age at first breeding, longevity, and length of the estrous cycle. Species within genera and genera within subfamilies tend to be very similar on most measures, and about 85% of the variation remains when the subfamily is used as the level for statistical analysis. Variation in most life‐history measures is highly correlated with variation in body size, and differences in body size are associated with differences in behavior and ecology. Allometric relationships between life‐history variables and adult body weight are described; subfamily deviations from best‐fit lines do not reveal strong correlations with behavior or ecology. However, for their body size, some subfamilies show consistently fast development across life‐history stages while others are characteristically slow. One exception to the tendency for relative values to be positively correlated is brain growth: those primates with relatively large brains at birth have relatively less postnatal brain growth. Humans are a notable exception, with large brains at birth and high postnatal brain growth.

Sexual Selection in Males and Females

Research on sexual selection shows that the evolution of secondary sexual characters in males and the distribution of sex differences are more complex than was initially suggested but does not undermine our understanding of the evolutionary mechanisms involved. However, the operation of sexual selection in females has still received relatively little attention. Recent studies show that both intrasexual competition between females and male choice of mating partners are common, leading to strong sexual selection in females and, in extreme cases, to reversals in the usual pattern of sex differences in behavior and morphology.

Sex ratio variation in mammals.

Parents will increase their fitness by varying the sex ratio of their progeny in response to differences in the costs and benefits of producing sons and daughters. Sex differences in energy requirements or viability during early growth, differences in the relative fitness of male and female offspring, and competition or cooperation between siblings or between siblings and parents might all be expected to affect the sex ratio. Although few trends have yet been shown to be consistent, growing numbers of studies have demonstrated significant variation in birth sex ratios in non-human mammals. These are commonly cited as evidence of adaptive manipulation of the sex ratio. However, several different mechanisms may affect the birth sex ratio, and not all of them are likely to be adaptive. Valid evidence that sex ratio trends are adaptive must be based either on the overall distribution of those trends or on cases in which the sex ratio can be shown to vary with the relative fitness of producing sons and daughters. The distribution of observed sex ratio trends does not conform closely to the predictions of any single adaptive theory. Some recent studies, however, indicate that, within species, the sex ratio varies with the costs or benefits of producing male or female offspring.

Cooperation between non-kin in animal societies.

Explanations of cooperation between non-kin in animal societies often suggest that individuals exchange resources or services and that cooperation is maintained by reciprocity. But do cooperative interactions between unrelated individuals in non-human animals really resemble exchanges or are they a consequence of simpler mechanisms? Firm evidence of reciprocity in animal societies is rare and many examples of cooperation between non-kin probably represent cases of intra-specific mutualism or manipulation.