Jurmain et al. Chapter 7. Primate Behavior

Transcription

1 Jurmain et al. Chapter 7 Primate Behavior

2 Primate Studies Primate studies often use an ecological approach to explain variation in primate behavior between different species and within a single species. The focus is on habitat, specifically contrasting terrestrial and arboreal species At the same time, ethological studies address animal behaviors in a scientific fashion. Behavior is anything organisms do that involves action in response to internal or external stimuli. The response can be that of an individual, group, or species to its environment. Such responses may or may not be deliberate, and they aren t necessarily the results of conscious decision making. Many basic behaviors have been shaped by the evolutionary history of the species. We must be careful not to anthropomorphize the behaviors of other animals. In mammals and birds, the percentage of behavior that is caused by learning, as compared to genetics, is larger than seen in insects and other invertebrates. This allows for greater behavioral plasticity (the capacity to change). In a physiological context, plasticity is the ability of systems or organisms to make alterations in order to respond to differing conditions. An evolutionary approach creates a valuable framework within which primatologists can analyze data to generate and test hypotheses concerning behavioral patterns.

3 The Evolution of Behavior 1 The ecological perspective pertains to relationships between organisms and all aspects of their environment (temperature, predators, vegetation, availability of food and water, types of food, disease organisms, parasites, and so forth). Primate studies by the mid-1980 s had shifted toward behavioral ecology and so the science of behavioral ecology is the focus of this chapter. Behavioral ecology studies the relationship between behaviors, natural environment, and biological traits of the species. Behaviors and behavioral patterns have been selected because they increase reproductive fitness in individuals in specific ecological contexts. These studies are based on the assumption that animals, plants, and microorganisms evolved together. Behavioral genetics, the study of how genes influence behavior, is a fairly new field. This lands right in the middle of the nature-nurture question in that complex relationships exist between genetic and environments components. The evolution of behavior: Behavior constitutes a phenotype and so individuals whose behavioral phenotypes increase reproductive fitness pass on their genes at a faster rate. Genes do not code for specific behaviors, however (i.e. aggression, cooperation, etc.). Species vary in their limits and potentials for learning and behavioral flexibility, set by genetic factors. Natural selection acts on genetic factors shaped by ecological setting of past and present.

4 The Evolution of Behavior 2 A major goal of primatology is to determine how behaviors influence reproductive fitness and how ecological factors have shaped the evolution of these behaviors. Because primates are among the most social of animals, social behavior is a major topic in primate research. Technically, what we are talking about is the study of primate social structure A social structure is defined as the composition, size, and sex ratio of a group of animals. Social structures guide individual interactions and social relationships. The subject is broad, including all aspects of behavior that occur in social settings Why be a part of a social group? There are advantages: facilitation of reproduction; predator avoidance and defense; help with foraging for food; help with learning; and a division of labor: males and females do slightly different things. Savannah baboons are an excellent example of these advantages. Social evolution (sociality) has occurred among several forms of life, but by no means all. Social life, to have evolved at all, must have enhanced the chances of individual organisms to survive and reproduce.

5 Factors That Influence Social Structure

6 The Evolution of Behavior 3 Some Factors that Influence Social Structure Body size: As a rule, larger animals require fewer calories per unit of weight than smaller animals. Heat loss at the surface is the explanation. Larger animals are better able to retain heat and their overall energy requirements are less than for smaller animals. (Remember Bergmann s rule?). Basal Metabolic Rate (BMR) and diet: Metabolism is the set of chemical processes within cells that breakdown nutrients and release energy for the body to use. (When nutrients are broken down into their component parts, such as amino acids, energy is released and made available for the cell to use in a variety of ways). The BMR is the rate that energy is used during a resting state in an external temperature that does not require either heating or cooling. Smaller animals have a higher BMR. Smaller primates tend to need an energy-rich diet (such as proteins, fats, and carbohydrates). Some larger primates can survive on lower energy-rich diets (more leaves, bamboos and such).

7 The Evolution of Behavior 4 Some Factors that Influence Social Structure (continued) Diet: Nutritional requirements of animals are related to both body size and BMR. Therefore, diet, body size and BMR evolved together. One then looks at the relationship of calories (benefits) to energy expended (costs). Smaller animals concentrate on high-energy foods, but large animals do not necessarily need to do so (think of gorillas). Distribution of resources: Leaves, which are plentiful, tend to support large groups of animals, amalgamations of several subunits can merge into multi-male-multi-female groups. Insects are more sparsely distributed so you see primates in small groups or solitary Where foods are distributed in small clumps (such as seen with fruits, nuts and berries): Primates tend to break into smaller social groups (subunits), such as one-male-multi-female groups (baboons) or matrilines (macaques). There is more likely to be defense of the foods that are clumped. Think how different the dietary needs of this mouse lemur are as compared to a gorilla.

8 The Evolution of Behavior 5 Some Factors that Influence Social Structure (continued) Predation: Primates are vulnerable to many types of predators, including snakes, birds of prey, leopards, wild dogs, lions, and even other primates. Leopards are the most serious nonhuman threat to terrestrial primates. This means a larger community is an advantage when predation pressure is high. These may be multi-male, multi-female groups or congregations of one-male groups. Relationships with nonpredatory species: Many primates group with other species of primates (or non-primates) for predator protection. When this occurs, there is a pattern of exploiting different resources to reduce competition. Dispersal: One of the sexes tends to leave the natal group about the time they become sexually active. Male dispersal is common. Female dispersal is less common but found in some colobus species, hamadryas baboons, gorillas, and frequently chimps. This type of behavior decreases the incidence of inbreeding. Those that remain in natal group benefit from the creation of long-term bonds within the group.

9 The Evolution of Behavior 6 Some Factors that Influence Social Structure (continued) Life histories: Life history traits (also called life history strategies) include those characteristics and developmental stages that influence rates of reproduction. (Strategies are the behaviors or behavioral complexes that have been favored by natural selection to increase individual reproductive fitness). Examples include length of gestation, length between pregnancies, period of infant dependency, and age at weaning, age at sexual maturity and life expectancy. Distribution and types of sleeping sites: Gorillas are the only non-human primates to sleep on the ground. The spacing of sleeping sites can be associated with social structure, predator avoidance, and how many of the sites are available. Activity patterns: Influences whether a species is diurnal or nocturnal. Most primates are diurnal, but several small-bodied prosimians and the owl monkey are nocturnal. Also influences whether they forage together in groups or alone. Nocturnal primates tend to forage for food alone or in groups of 2 or 3, and use concealment to avoid predators. Human activities: Both hunting and forest clearing are affecting all primate species. I am seeing more and more reporting of diseases in non-human primates due to exposure to humans (even in controlled tourist activities).

10 Primate Social Behavior 1 Dominance Many primate societies are organized into dominance hierarchies Dominance hierarchies are systems of social organization in which individuals within a group are ranked relative to one another. Sometimes called pecking orders. All primates learn their position in the hierarchy. And while violence can be used to maintain one s position, dominance hierarchies also serve to reduce the overall violence in the troop. Higher-ranking animals have greater access to preferred food items and mating partners than do lower-ranking individuals. Access to reproduction and survival of offspring are most likely the key to dominance hierarchies. Among Gombe chimpanzees, the offspring of higher ranked females were more likely to survive. They also produced more offspring during their lifetimes as they matured faster. Position in the hierarchy is not permanent. Factors that influence dominance status: include the primate s sex, age, aggression, time in the group, intelligence, motivation, and one s mother s social position. In most primate groups were multiple females are present, the males dominant them. There is a separate dominance hierarchy among the females. Chimpanzees are one example In species where there is pair bonding, the two partners are co-dominant. Gibbons are an example.

11 Primate Social Behavior 2 Communication Is universal among animals and includes much that is non-verbal, even autonomic. Can be any act that conveys information, in the form of a message, to another individual. Autonomic responses are physiological responses not under voluntary control. Examples: Chimpanzee: Erection of body hair during excitement. Humans: blushing Frequently, the result of communication is a change in the recipient s behavior. Communication may not be deliberate, but may instead be the result of involuntary processes or a secondary consequence of an intentional action. Deliberate behaviors that convey information include gestures, facial expressions and vocalizations. Mounting can signal dominance, while submission can be signaled by taking a crouched position Grooming does the same, signal submission or reassurance A wide variety of facial expressions are used as well as vocalization. Here are a few chimpanzee vocalizations and their meanings. In 2011, it was revealed for instance, that chimpanzees use 66 different gestures to communicate. Displays are another way primates communicate. Displays are complicated, frequently elaborate combinations of behaviors. Examples: Exaggerated courtship dances of male birds, often enhanced by colorful plumage. Chest slapping and tearing of vegetation are common gorilla threat displays.

12 Primate Social Behavior 3 Within primate societies, there is an interplay between affiliative behaviors, which promote group cohesion, and aggressive behaviors, which can lead to group disruption. Aggressive Interactions Conflict within a group develops out of competition for mating partners and food items. This can be as serious as death or more display-based. Most intragroup aggression occurs in the form of signals and displays within the context of a dominance hierarchy. Primates resolve the majority of tense situations using submissive and appeasement behaviors. Between groups, aggression is used to protect territories. Primate groups are associated with a home range (area where they remain permanently) Within the home range is a core area. The core area is portion of a home range containing the highest concentration and most reliable supplies of food and water. The core area is defended. Generally, territoriality is associated with species whose ranges are small enough to be patrolled and protected. Some species are not territorial. Some are not aggressive to other primate species.

13 Primate Social Behavior 4 Aggressive Interactions (continued) When it gets nasty Chimpanzees can be highly aggressive. Jane Goodall documented brutal attacks, several ending in death. She also documented the killing and eating of infants by one female and her son. Affiliation and grooming Affiliative behaviors reinforce bonds between individuals, and enhance group stability. Common affiliative behaviors include reconciliation, consolation, and simple amicable interactions between friends and relatives. Types of affiliative behaviors. Grooming is one of the most important affiliative behaviors in primate species, and it plays an important role in day-to-day life. Altruism is behavior that benefits another while involving some risk or sacrifice to the performer. Altruistic acts sometimes contain elements of what might be interpreted as compassion and cooperation. Among primates, recipients of altruistic acts may include individuals who aren t offspring and who may not even be closely related to the performer. Can include protection during a predator attack or even adoption among nonhuman primates.

14 Reproduction/Reproductive Behaviors 1 In most primate species, sexual behavior is tied to the female reproductive cycle of estrus. Reproductive Strategies The complex of behavioral patterns that contributes to individual reproductive success. The behaviors need not be deliberate, and they often vary considerably between males and females. Among the mammals, primates are among the most K- selected in their reproductive strategies. An adaptive strategy whereby individuals produce relatively few offspring, in whom they invest increased parental care. Although only a few infants are born, chances of survival are increased for each one because of parental investments in time and energy. Examples of K-selected nonprimate species are birds and canids. Other mammals are more r-selected: Adaptive strategy that emphasizes relatively large numbers of offspring and reduced parental care. Among mammals, more r-selected examples would be mice and rabbits. Macaca nigri female in estrus Macaca nigri selfie

15 Reproduction/Reproductive Behaviors 2 Female and Male Reproductive Strategies When it comes to investment in the young, in most primate species males and females have different strategies. In the majority of primate species, the mother carries the burden. Female primates spend almost half of their adult lives pregnant, lactating and/or caring offspring with a heavy metabolic toll. This suggests that a female should guard her resources from other females It also suggests females should be most choosy in mate selection. Males, given their lesser investment, should maximize the number of mates Old biological adage: Choosy females, competitive males. Sexual Selection Sexual selection is the result of the differing mating strategies of female and male primates. Operates on only one of the sexes, usually males. Most likely more common when males have more than one mate ( polygyny ). and there is male competition. Generally see as significant sexual dimorphism; where there is pair bonding do not see this significant sexual dimorphism.

16 Reproduction/Reproductive Behaviors 3 Infanticide as a Reproductive Strategy? Reproductive advantage for the male A male can increase his own reproductive success if he kills all the offspring of the male he vanquished. He does not kill his own offspring. DNA samples verify this among Hamuman langurs study. This sends the females back into estrus. While advantageous for the individual male, is counterproductive for the species There has been a lot of debate over this explanation and alternative explanations include competition for resources, aberrant behavior, and accidental death during aggressive episodes. Other species commonly known to commit infanticide include lions (males), meerkats (females), and chimpanzees (both males and females; first observed by Jane Goodall). Hamuman langurs Meerkats

17 Mothers, Fathers & Infants The basic social unit of all primates is the female and her infants. Except in those species that are both monogamous and polyandrous, the male is not greatly invested in the care of offspring. Polyandry is a mating system wherein a female continuously associates with more than one male (usually two or three) with whom she mates. Among nonhuman primates, polyandry is seen only in marmosets and tamarins. It also occurs in a few human societies. Marmoset and tamarin males assume most of the responsibility for infant care (except for nursing). A female with normal exposure to experiences with infant seems be predisposed to bonding with her infant. This does not mean she is skilled, but attracted The exact nature of the bonding process is not yet well understood In the 1950s, there was a set of experiments conducted on the mother-infant bond. Harlow s experiments clearly demonstrated the importance of social contact with peers, showing abnormal behaviors in monkeys kept from other infants. The isolated primates lacked both the opportunity to learn and the important experiences associated with physical contact.

18 Primate Cultural Behavior 1 Cultural behavior is learned, passed from generation to generation. Humans deliberately teach their young, but it appears that free-ranging primates do not Nonhuman primate infants, by observation, learn about food items, appropriate behaviors, and how to use and modify objects to achieve certain ends. Tool Use What emerges is a cultural tradition that may typify an entire group or even a species. In 1952, researchers observed macaques on the coast of Kyushu in Japan who learned to wash sweet potatoes in the ocean (and the fad spread!). One study of orangutans noted 19 behaviors that were labeled as likely culturallyconnected Among the areas of study among non-human primates has been tool use. By now we all know about the use of twigs for termite fishing as seen by chimpanzees In 2005, gorillas were observed using sticks as tools (levers). Chimpanzees are now know to create spears to hunt galagos. Chimpanzees in several West African groups use hammer stones to crack nuts and hard fruits. What is particularly interesting is that these behaviors among chimpanzees show regional variations, both in type and methods of tool use. Chimpanzees also show regional differences in dietary preferences. One bonobo, Kanzi, a captive ape, has created stone tools by striking two stones together. Kanzi then used the sharp pieces to open a container of food.

19 Primate Cultural Behavior 2 Communication Vervet monkeys use specific vocalizations to refer to particular categories of predators, such as snakes, birds of prey, and leopards. Other studies have shown that numerous nonhuman primates use distinct calls that have specific references. Language Humans use language, a set of written and/or spoken symbols that refer to concepts, other people, objects, and so on. Language has always been considered a uniquely human achievement, setting humans apart from the rest of the animal kingdom. Humans can recombine symbols in an infinite number of ways to create new meanings, and use language to refer to events, places, objects, and people removed in space and time. Language is described as an open system of communication, based on the human ability to think symbolically. Work with captive apes has shown they can learn to interpret visual signs and use them to communicate. The fact that apes can t speak has less to do with lack of intelligence than with the anatomy of the vocal tract and language-related structures in the brain.

20 Evolution of Human Language

21 The Primate Continuum Remember the term, biological continnum: Refers to the fact that organisms are related through common ancestry and that behaviors and traits seen in one species are seen also in others to varying degrees. The differences between human and other primates (especially chimpanzees) are more quantitative and not qualitative. This has also been described as a matter of degree and not kind. Continuum: Human brains are larger than other primate brains, but the neurological processes are functionally the same. The necessity of close bonding with at least one parent Need for physical contact Developmental stages and dependence on learning Capacity for cruelty, aggression, compassion, altruism, with humans more adept at cruelty and compassion and capability to reflect on behavior Differences Humans better at symbolic communication and may be only species capable of true language (hot debate) Humans are interested in teaching others for the purpose of shared goals Human women go through menopause decades before they die; not true of other species.