Of course, there is variation among high-rankers in the quality of the services they can provide to subordinates; the higher their rank, the more valuable their service. Among females, the alpha female is the most valuable partner. Low-ranking females compete with and try to outbid one another to obtain the services of their queen. They do so by trying to groom the alpha female whenever they get a chance, and for as long as possible. The value of grooming as a commodity increases with its amount, so that the more grooming the alpha female receives from a particular female, the more she should be willing to tolerate and protect that female.
Compared to the two-sided mating market in which both males and females select each other as partners, the monkey grooming market is rather one-sided, because, to a high-ranking female, the benefits of receiving grooming are pretty much the same regardless of who does the grooming. All low-rankers are the same—it’s just labor. In addition, since there is usually a large supply of low-ranking females in the group eager to groom all day, high-rankers don’t have to compete with one another to obtain their services. Even high-rankers, however, have their own preferences for social partners. They prefer to hang out with kin, for example, rather than with nonkin. So if the daughter of the alpha female and the lowest-ranking female simultaneously offer to groom the alpha female, there is a good chance that the alpha female will accept her daughter’s offer and refuse the other’s. The alpha female’s daughter ranks just below her mother in the hierarchy, and in general kin are closer to each other in rank than nonkin. This means that, in the competition to groom the alpha female, the bargaining power of low-ranking females decreases as their distance in rank from the alpha increases. Biological market theory predicts that individuals in weak bargaining positions will become less selective and lower their demands. Thus, even though every female in the group would be happy to give all of her grooming to the alpha female, in reality the probability of this happening decreases the lower the female’s rank.
In the 1970s, long before biological market theory was developed, primatologist Robert Seyfarth speculated that competition between low-ranking females to groom the alpha female and the constraints imposed by supply and demand should result in every female having to compromise and groom the female that ranks just above her in the hierarchy. His observations of a group of baboons confirmed his intuitions: while most female grooming was directed up the hierarchy, each female groomed the female one notch above her in the hierarchy most often.11 These observations have been replicated many times, not only in other primates such as macaques and vervet monkeys but also in other animals, such as the spotted hyenas I discussed in Chapter 7.
Spotted hyenas have a social structure similar to that of baboons, macaques, and vervet monkeys. Even though they don’t groom one another, they express their social preferences by joining subgroups that contain particular individuals. Jennifer Smith, Kay Holekamp, and their colleagues at Michigan State University studied the social preferences of spotted hyenas from the perspective of biological market theory.12 They concluded that although the highest-ranking hyenas in the clan could offer more goods and better services to subordinates, market forces lead subordinates to associate most closely with the animals that hold a rank immediately above them rather than with the highest-ranking females in the clan. Again, this is the result of supply and demand and of competition among low-ranking individuals. But what happens if the market value of an individual as a social partner changes suddenly and dramatically? How is the market affected by this change?
To address this question, a group of researchers led by Dutch primatologist Ronald Noë—a pioneer in the development of biological market theory and its application to animal behavior—conducted an ingenious experiment with wild vervet monkeys in South Africa.13
After creating artificial markets in two groups of these monkeys by making certain individuals valuable as cooperation partners, the researchers recorded how much grooming other group members were willing to pay them to benefit from their services. Then they experimentally changed the market value of these individuals and looked at what happened to the grooming trade. But let me describe what the researchers did step by step.
At the beginning of their study, Noë and his colleagues simply recorded who groomed whom and for how long in order to show that, as is always the case in vervet monkeys, high-ranking individuals receive a lot more grooming than low-ranking ones. Low-ranking females, unless they are in estrus or have a newborn infant, are not attractive social partners because they have no power and therefore have low value as potential coalition partners. Then the researchers taught a low-ranking female in each of the two groups to press a lever that opened a container full of food. The container contained enough pieces of apple for every group member to have a good chance of getting some apple to eat, even though, as usual, the high-rankers got more than the others. The opening of the container was repeated sixteen times over a period of nine weeks (phase 1). During this period, the researchers recorded all grooming interactions involving the food-delivering female and other monkeys in the hour after she opened the food container.
In phase 2 of the experiment, Noë and his colleagues trained another low-ranking female within each group to open a second food container. The same amount of food was now divided between the two containers, which were made available simultaneously. The researchers again recorded all grooming exchanges between individuals after the introduction of the second skilled individual. They were especially interested in the ratio of grooming given relative to grooming received by the two food providers because they expected that other monkeys would behave nicely to them and offer grooming without demanding any in return. It turned out that before phase 1 of the experiment, the first low-ranking female that was subsequently trained did a lot of grooming but received little in return. During the period in which she opened the food container for everyone, this changed dramatically: she became popular and received a lot of grooming while giving very little. Interestingly, she opened the food container preferentially in the presence of those who groomed her the most, thus giving them the chance to grab a lot of apple pieces. When the other monkey started opening the second food container, however, the market value of the first food provider dropped by half: she was still getting more grooming than she had initially received, but the effect was half as strong as before. These changes were observed in both groups. Thus, the trading of commodities in primate grooming markets varies in relation to changes in the value of the individuals as trading partners, exactly as predicted by biological market theory.
Trading Between Species: Mutualistic Markets
Mutualism is a cooperative relationship between two organisms of different species in which both benefit from their association. Unlike cooperation, in which altruistic acts are reciprocated with a time delay, in mutualism the same interaction simultaneously benefits both partners. A wide range of mutualistic relationships, not only between animals but also between animals and plants, have been studied from the perspective of biological markets. To illustrate the approach, I first describe the business between ants and the larvae of Lycaenid butterflies, and then the cleaner-client fish market.
THE ANTS-BUTTERFLY LARVAE MARKET
Many species of ants protect Lycaenid butterfly larvae against predators and parasites. In exchange, the larvae offer the ants a sugar-rich nectar, which is produced by a gland called the nectar organ. The only function of the nectar is to attract ants and reward them for their protection. Researchers have discovered that the butterfly larvae adjust the amount of nectar offered depending on the number of ants protecting them. When only a few ants are present, the larvae produce more nectar to attract additional ants; when many ants are present, they reduce their nectar production. Thus, this appears to be a biological market in which the larvae compete with one another to attract ants and adjust their supply of nectar in relation to the demand. When ants are few, intense competition between larvae results in increased bidding and nectar product
ion; when there are many ants on the market, the larvae can afford to reduce their bids and produce less nectar (which is costly to produce). In an interesting twist, larvae that do not produce nectar (free riders that try to benefit from the ants’ protection without providing anything in return) sometimes end up being eaten by the ants: if a larva produces little or no nectar, her body becomes valuable as food to the ants. So, by eating these unproductive larvae, the ants kill two birds with one stone: they get their food, even though it tastes less sweet than nectar, and they also eliminate the free riders from the population.14
THE CLEANER-CLIENT FISH MARKET
There is a lot more to the story of cleaner fish and their clients than what I briefly covered in Chapter 5. Research conducted by biologist Redouan Bshary and his colleagues has shown that the mutualistic interactions between cleaners and their clients, like those of ants and butterfly larvae, are regulated by the laws of the market.15 To recap, cleaners are small fish called bluestreak wrasses (their scientific name is Labroides dimidiatus) that inspect the body surface and the inside of the gill chambers and mouths of larger fish—the clients—in search of skin parasites and dead or infected tissue. As I mentioned earlier, cleaners sometimes “cheat” and also eat mucus, scales, and fleshy tissues inside the mouths of their clients. These fish are found in the Red Sea and in the Pacific and Indian Oceans, from the east coast of Africa all the way to the Great Barrier Reef in northeastern Australia. Bshary and his colleagues observed these fish at Ras Mohammed National Park in Egypt and did laboratory experiments with them at the Lizard Island research station at Australia’s Great Barrier Reef.
The cleaners live in small territories, called cleaning stations. Clients visit these cleaning stations and often use special postures (such as spreading their pectoral fins and stopping their swimming, maintaining a head-up or head-down posture) to signal their desire to be serviced. Individual clients visit cleaners and seek inspection from them five to thirty times per day, sometimes up to one hundred times per day. Cleaners may perform more than two thousand inspections per day. Clients can discriminate among different cleaners directly, or indirectly, depending on the location of the cleaning station where they meet them. Cleaners seem to be able to recognize their clients just from the way they look.
The cleaner-client system can be thought of as a market in which two classes of traders offer different commodities: hygiene in exchange for food. Cleaners usually stay in their territory; in other words, they stand behind the counter in their shop waiting for the clients to arrive. Clients can decide whether or not to visit a particular cleaning station. Cleaners, in turn, can accept the request for cleaning or ignore the client. There is competition among clients: they often form lines at cleaning stations, waiting to be served. Cleaners have clients from the immediate neighborhood as well as from the open sea. The “resident” clients never leave the neighborhood in which they live and therefore have access to only one cleaning station, while “floater” clients normally swim over larger areas that include several cleaning stations. The cleaners have exclusive access to resident clients in their territory without competition from other cleaners: they are the choosing class. The resident clients are the chosen class, which means that sometimes they have no choice but to accept poor service because poor service is better than no service at all; they wait longer, get a shorter cleaning, and occasionally have to put up with being bitten by their cleaners. In contrast, the floaters have access to different cleaning stations, so they can select the cleaner that gives the best service. As clients, the floaters can afford to be choosy, so cleaners try to outbid each other by providing better service to attract them.
Figure 8.1. The cleaner wrasse at work with one of its clients.
Two floater clients or a resident and a floater can compete for services from the same cleaner. Sometimes a client arrives at a cleaning station while the cleaner is inspecting another client; other times, two or more clients seek inspection from the same cleaner simultaneously and the cleaner has to choose between them. Competition between clients occurs only through invitations to the cleaner for inspection, not through aggression. When a cleaner chooses between clients, biological market theory predicts that it will choose the more valuable client, the floater, over the resident, because if the cleaner ignores the floater it will lose it as a client, possibly for good, whereas the resident will continue visiting the shop—it has nowhere else to go—even if it is temporarily ignored. So if a resident needs cleaning but a floater has already occupied the station, the resident has no option but to wait in line for service or to come back later. In contrast, if a floater doesn’t get immediate attention from a cleaner, it can go to another station and never come back.
Observations and experimental results show that cleaners do indeed give preferential treatment to the floaters over the resident clients. In one study, cleaners switched from a resident to a floater client fifty-one times, but switched only once from a floater to a resident. When a floater and a resident client requested service simultaneously, the cleaners inspected the choosy client in sixty-five out of sixty-six instances. Finally, floaters got better service: they got cleaned early in the morning (a favorite time for all client fish, since nothing is better than a shower before going to work); they never waited in line; they were cleaned for longer durations; and most importantly, they didn’t get bitten by a cleaner. When a floater was occasionally ignored or bitten by a careless cleaner, he immediately went to a different station and was never seen again in the shop.
It’s interesting that the cleaners prefer the floater over the resident clients even though sometimes the residents are larger and presumably have more parasites (which means more food for the cleaners). Bshary did some very careful experiments with fake floaters and residents to make sure that cleaners didn’t always simply choose the “fat” clients. When cleaners have to choose between two floaters, however, they typically choose the larger one, which has more parasites as well as more mucus they can chew on. Because Bshary always examined cleaners’ preferences for clients of different species, however, it is possible that other differences between these species accounted for his results. This possibility was addressed by Thomas Adam, a behavioral ecologist at the University of California–Santa Barbara, who recently published an article with the clever title “Competition Encourages Cooperation: Client Fish Receive Higher-Quality Service When Cleaner Fish Compete.”16 Instead of examining cleaners’ partner choice between clients of different species, Adam focused on a single client species, the ornate butterflyfish, Chaetodon ornatissimus. Some individuals of this species have small territories containing only one cleaning station, and others have larger territories with multiple cleaning stations. Multiple cleaning stations means competition for the cleaners; market theory predicts that cleaners should provide higher-quality service to clients with multiple cleaner stations in their territory. Adam’s study showed just that. The clients with more options were cleaned more quickly and for longer periods of time, while clients without options were forced to wait in line.
Back to Bshary’s work. There is an interesting twist in his story of the cleaner-client fish market. It turns out that, although the majority of client fish are vegetarian and only eat algae, about 15 percent of client species are carnivorous and eat other fish. This means that when cleaners get into the mouths of these predators, they risk being swallowed and digested, especially if they don’t do a good cleaning job and inadvertently (or intentionally) hurt the client. When a cleaner cheats with a vegetarian client, the client simply “gets mad” and swims off or chases the cleaner, but when a predatory client gets mad, the consequences can be far more serious. In terms of market dynamics, the cleaners simply trade hygiene for food with harmless clients, but with the predators they also trade their safety. Consequently, biological market theory predicts that the predatory clients—whether floaters or residents—should receive better treatment than the harmless clients. And lo and behold, it turns out t
hat predators are bitten less often than harmless clients. As mentioned in Chapter 5, a cleaner’s biting (cheating) makes a client “jolt,” so how often a client jolts is a good indicator of how often a cleaner fish cheats. The predator clients don’t jolt as much during cleaning as the harmless clients do.
What can the clients do to prevent their cleaner partner from cheating? First of all, as mentioned in Chapter 5, clients tend to go to cleaners that have a reputation for not cheating. Second, if they are fooled and go to a cleaner with a good reputation who then cheats, they can try to punish the cheater by attacking or trying to eat it. If the cheater is eaten, you might say that the punishment is effective. But even if the cheating cleaner is simply chased away by the client, this seems to affect the cleaner’s future behavior. Clearly, when “thinking” about cheating, the cleaners take the possibility of punishment into consideration. If the punishment option is eliminated, cheating gets out of control. This was shown by an experiment in which clients were slightly anesthetized; with the client half-asleep, the cleaners cheated like crazy and mainly fed on their mucus and tissues instead of removing parasites.
Biological market theory predicts that nonpredatory clients have to accept more frequent cheating by the cleaner than predatory clients, and this turns out to be the case: as mentioned before, while in the cleaning station, the former jolted more frequently than the latter, and this was true for both resident and floater clients. Resident clients’ punishment of cheating cleaners is about as effective as the switching strategy of choosy clients. In the language of game theory, the predator’s option to kill the cleaner leads the cleaner to engage in an unconditional cooperative strategy with the predator. So, biological market effects influence partner choice, but partner control mechanisms are also important. Specifically, partner choice options determine which pairs form first. When it comes to the frequency of cheating by cleaner fish, however, partner choice options are overrun by client control mechanisms: predatory clients are far less often cheated than nonpredatory clients, irrespective of choice options.
Games Primates Play: An Undercover Investigation of the Evolution and Economics of Human Relationships Page 25