Studying mammals: The social climbers

# 4.3 Hierarchies within groups

Within multimale-multifemale groups of the type portrayed in Figure 7f, complex social relationships exist. These animals are 'forced together' to defend resources and to avoid predation, but competition for food and mates is substantially greater in large groups. This internal competition has led to males or females or both sexes forming kin or non-kin dominance hierarchies. In some groups, all the females are related (Figure 7d) and in this instance individuals inherit their rank from the mother - a so-called matrilineal dominance hierarchy. Some large groups consist of several matrilines (Figure 7e) and in these cases, all the females descended from one mother (i.e. of the same matriline) are dominant over another matriline, which in turn are dominant over a third, and so on.

As DA states in the TV programme, it pays to be 'high-born'. Females in the highest-ranking matriline will obtain the best food and most of the matings. You will recall that a female toque macaque in the programme was even able to remove food from the mouth of an older and bigger female because she outranked her. In years with low food availability, only the alpha male and alpha female (the most dominant male and female in the group) may produce any offspring. Individuals in male dominance hierarchies gain rank by fighting, and the alpha male is the strongest and fiercest male. Eventually, the alpha male is beaten by a younger male.

## Question 15

Question: From reading LoM and watching the TV programme, describe how rank is maintained and how disputes between individuals are settled.

## Answer

Generally a subordinate animal gives way to a higher-ranking individual. Subordinates forage at the least favoured positions and move position if a more dominant individual approaches, as is seen in vervets [p. 272]. They submissively present their hindquarters, or their chest in the case of gelada baboons [pp. 277-279], and the more dominant individual is appeased. Disputes do occur and they can escalate into a fight that may lead to injuries, but interestingly, once the dispute is settled, the individuals groom each other extensively. This reconciliatory behaviour is thought to help maintain the cohesion of the group.

Some societies are very complex; for example, hamadryas baboon troops herd together at night, but during the day, as they forage within their home range, the troop separates into bands, clans and even families, depending on food availability (Figure 7g). In order to succeed within multimale-multifemale groups, such as those found in baboons and macaques, individuals form coalitions (or alliances) to help each other. Alliances are often kin-bonded but they also form between non-kin. Such alliances cut across the hierarchies and enhance an individual's survival and reproductive success. Both males and females may defend food resources and females may join together to prevent infanticide. A male may form a lasting friendship with a female, playing with, feeding and protecting her infant in order to gain matings next time she comes into oestrus. Males may form temporary coalitions so that the alpha male is distracted while one male sneaks a mating. This strategy can be successful; in one population of langurs the alpha male was found to have sired only 57% of the offspring, the remainder being fathered by his subordinates. Alliances occasionally help individuals move up the ranking. For instance, if a subordinate male aids the alpha male, the alpha male may reward him by increasing his rank. You will recall from the TV programme (34.00-34.34) alpha male toque macaques forming alliances with other males who guard the rest of the females while the alpha male mates. These non-sexual relationships are maintained through grooming. Within the group are several grooming cliques. Kin are more willing to groom each other than non-kin, and subordinates spend more time grooming higher-ranking individuals than vice versa. In times of crisis, grooming partners come to each other's aid. Grooming releases a 'pleasure hormone', beta-endorphin, that may help to reduce stress and tension within the group.

## Question 16

Question: Why do you think kin are more willing to help each other than non-kin?

## Answer

Because kin share genes with each other. For example, each individual has two parents, giving rise to the statement that an individual inherits half its genes from its mother and half from its father. Continuing this line of reasoning, a parent and its infant share 50% of their genes, as do siblings, because they have the same parents. Each individual has four grandparents, so grandparents and grandchildren share 25% of their genes. When an individual helps a relative, it is helping to maintain some of its own genes in the population, thereby increasing its own inclusive fitness.

As noted in LoM, primates also show tactical deception [p. 271]. On that occasion, by making a snake call, an individual 'stole' a tuber from its owner, who had just painstakingly uncovered it, causing the tuber owner to leap for cover and abandon the tuber. Juveniles also 'steal' food by uttering distress calls close to an adult that has a food item. The calls attract kin to the caller's aid, who, assuming the adult was attacking the juvenile, attack the adult. The adult drops the food and runs away and the juvenile eats it. Subordinates may also keep quiet when they see a predator, presumably because this behaviour makes it more likely that a higher-ranking animal will be caught.

This course is too short to discuss all the nuances and subtleties of the social life of primates, but this description should give you an indication of the importance of social interactions and the necessity for each individual to recognise relationships between not only themselves and another individual but between that individual and a third party.

Section 4 introduced a lot of terminology that was probably new to you. You'll appreciate that terms of this sort have to be devised by scientists to describe accurately the very different social groupings evident in primates, and it's important that you're aware of how this is done. I don't expect you to remember all these terms, but you do need to be able to apply them and you should appreciate the type of variation that exists in primate societies and the logic behind the use of such terms; so that when you are given information about primate social groupings, you can devise diagrams of this type using appropriate symbols.

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