Abstract: In the analysis of social dominance in groups of animals, linearity has been used by many researchers as the main structural characteristic of a dominance hierarchy. In this paper we propose, alongside linearity, a quantitative measure for another property of a dominance hierarchy, namely its steepness. Steepness of a hierarchy is defined here as the absolute slope of the straight line fitted to the normalized David's scores (calculated on the basis of a dyadic dominance index corrected for chance) plotted against the subjects' ranks. This correction for chance is an improvement of an earlier proposal by de Vries (appendix 2 in de Vries, Animal Behaviour, 1998, 55, 827-843). In addition, we present a randomization procedure for determining the statistical significance of a hierarchy's steepness, which can be used to test the observed steepness against the steepness expected under the null hypothesis of random win chances for all pairs of individuals. Whereas linearity depends on the number of established binary dominance relationships and the degree of transitivity in these relationships, steepness measures the degree to which individuals differ from each other in winning dominance encounters. Linearity and steepness are complementary measures to characterize a dominance hierarchy.

Abstract: The dominance score (number of wins divided by the total number of interactions) is the most widely used procedure in field studies to rank individuals. Its reliability depends on the number of interactions on which it is calculated. However, most authors use it without any estimate of the associated error. We describe the precision associated with a dominance score estimate as a function of the number of interactions on which it is based, and hence provide a tool to plan field protocols and effort. The precision error decreases according to a power function with increasing number of interactions, but with more precision for extreme scores for any given number of interactions. We discuss the fact that the minimum number of interactions should be based on the precision associated with the 50% score, the least precise of all scores. We also emphasize the trade-off between recording effort and precision of the estimator, and give an example of our choice of 26 interactions for fieldwork on ducks and geese. When comparing individual ranks based on dominance scores with ranks given by the dominance matrix, we found a good correlation, with more mismatches around the middle of the hierarchy. This was consistent with the precision calculated with our model. We conclude that dominance score is a reliable tool, but conclusions must take into account the number of interactions on which the calculations are done. We also discuss the importance of initial assumptions and sources of bias in field studies.

Abstract: In a wide range of animal species, males coerce females to mate with them, either by physically forcing them to mate, by harassing them until they mate or by punishing persistent refusal to mate. The first section of this paper argues that the possibility of forced copulation can generate arms races between males and females that may have substantial costs to both sexes. In the second section, it is suggested that sexual harassment commonly represents a `war of attrition' between the sexes; existing game theory models that may apply to sexual conflict over mating decisions are reviewed. The third section develops a simple prospective model for the evolution of intimidation by punishment in situations where males can raise the probability that females will accept their advances in future by punishing them for refusal to mate. Where the benefits of sexual coercion to males are high, all three male strategies may develop to a point where they have substantial costs to females. In the final section, evidence that female behaviour is adapted to minimizing these costs is reviewed.

Abstract: Individuals in a foraging group of brown capuchin monkeys choose different spatial positions relative to the rest of the group. An individual's choice of spatial positiion affects its foraging success and perceived predation risk (as measured by vigilance behaviour). The two most dominant group members preferred to forage where their expected forwaging success was greatest. Juveniles chose to forage where their perceived predation risk was least, not where they would achieve the highest foraging success. The positions used by non-dominant adults neither maximized foraging success nor minimized predation risk. It is likely that subordinate adults accept spatial positions with suboptimal ecological consequences to avoid the costs of frequent confrontations with the dominant members of the group over foraging sites in poreferred positions.

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.