Introduction to Animal Behavior
Behavior is the change in activity of an organism in response to a stimulus and can be grouped as innate or learned.
Distinguish between innate and learned behaviors
- Behavioral biology is the study of the biological and evolutionary bases for changes in activity in response to a stimulus.
- Comparative psychology is an extension of work done in human and behavioral psychology. Ethology is an extension of genetics, evolution, anatomy, physiology, and other biological disciplines.
- Innate behaviors have a strong genetic component and are largely independent of environmental influences; they are “hard wired.”
- Learned behaviors result from environmental conditioning; they allow an organism to adapt to changes in the environment and are modified by previous experiences..
- behavioral biology: A systematic approach to the understanding of human and animal behavior assuming that the behavior of a human or animal is a consequence of that individual’s history.
- comparative psychology: The scientific study of the behavior and mental processes of non-human animals, especially as these relate to the phylogenetic history, adaptive significance, and development of behavior.
Behavior is the change in activity of an organism in response to a stimulus. Behavioral biology is the study of the biological and evolutionary bases for such changes. The idea that behaviors evolved as a result of the pressures of natural selection is not new.
Animal behavior has been studied for decades, by biologists in the science of ethology, by psychologists in the science of comparative psychology, and by scientists of many disciplines in the study of neurobiology. Although there is overlap between these disciplines, scientists in these behavioral fields take different approaches. Comparative psychology is an extension of work done in human and behavioral psychology. Ethology is an extension of genetics, evolution, anatomy, physiology, and other biological disciplines. One cannot study behavioral biology without touching on both comparative psychology and ethology.
One goal of behavioral biology is to distinguish the innate behaviors, which have a strong genetic component and are largely independent of environmental influences, from the learned behaviors, which result from environmental conditioning.
Innate behavior, or instinct, is important because there is no risk of an incorrect behavior being learned. These behaviors are “hard wired” into the system. In contrast, learned behaviors are flexible, dynamic, and can be altered relative to changes in the environment. Learned behaviors, even though they may have instinctive components, allow an organism to adapt to changes in the environment and are modified by previous experiences. Simple learned behaviors include habituation and imprinting—both are important to the maturation process of young animals.
Movement and Migration
Innate behaviors, such as kinesis, taxis, and migration, are instinctual responses to external stimuli.
Distinguish between kinesis, taxis, and migration in response to stimuli
- Innate behaviors are instinctual, relying on responses to stimuli.
- Kinesis is the undirected movement in response to a stimulus, which can include orthokinesis (related to speed) or klinokinesis (related to turning).
- Taxis is the directed movement towards or away from a stimulus, which can be in response to light (phototaxis), chemical signals ( chemotaxis ), or gravity (geotaxis).
- Migration is an innate behavior characterized as the long-range seasonal movement of animals; it is an evolved, adapted response to variation in resource availability.
- Migration is a variable innate behavior as some migrating species always migrate (obligate migration) while in other animals, only a portion of the population migrates (incomplete migration).
- orthokinesis: the speed of movement of the individual is dependent upon the intensity of the stimulus
- taxis: the movement of an organism in response to a stimulus; similar to kinesis, but more direct
- kinesis: the undirected movement of an organism in response to an external stimulus
Innate behaviors: movement and migration
Innate or instinctual behaviors rely on response to stimuli. The simplest example of this is a reflex action: an involuntary and rapid response to stimulus. To test the “knee-jerk” reflex, a doctor taps the patellar tendon below the kneecap with a rubber hammer. The stimulation of the nerves there leads to the reflex of extending the leg at the knee. This is similar to the reaction of someone who touches a hot stove and instinctually pulls his or her hand away. Even humans, with our great capacity to learn, still exhibit a variety of innate behaviors.
Kinesis and taxis
Another activity or movement of innate behavior is kinesis: undirected movement in response to a stimulus. Orthokinesis is the increased or decreased speed of movement of an organism in response to a stimulus. Woodlice, for example, increase their speed of movement when exposed to high or low temperatures. This movement, although random, increases the probability that the insect spends less time in the unfavorable environment. Another example is klinokinesis, an increase in turning behaviors. It is exhibited by bacteria such as E. coli which, in association with orthokinesis, helps the organisms randomly find a more hospitable environment.
A similar, but more-directed version of kinesis is taxis: the directed movement towards or away from a stimulus. This movement can be in response to light (phototaxis), chemical signals (chemotaxis), or gravity (geotaxis). It can be directed toward (positive) or away (negative) from the source of the stimulus. An example of a positive chemotaxis is exhibited by the unicellular protozoan Tetrahymena thermophila. This organism swims using its cilia, at times moving in a straight line and at other times making turns. The attracting chemotactic agent alters the frequency of turning as the organism moves directly toward the source, following the increasing concentration gradient.
Migration as innate behavior
Migration is the long-range seasonal movement of animals. An evolved, adapted response to variation in resource availability, it is a common phenomenon found in all major groups of animals. Birds fly south for the winter to get to warmer climates with sufficient food, while salmon migrate to their spawning grounds. The popular 2005 documentary March of the Penguins followed the 62-mile migration of emperor penguins through Antarctica to bring food back to their breeding site and to their young. Wildebeests migrate over 1800 miles each year in search of new grasslands.
Although migration is thought of as an innate behavior, only some migrating species always migrate (obligate migration). Animals that exhibit facultative migration can choose to migrate or not. Additionally, in some animals, only a portion of the population migrates, whereas the rest does not migrate (incomplete migration). For example, owls that live in the tundra may migrate in years when their food source, small rodents, is relatively scarce, but not migrate during the years when rodents are plentiful.
Animal Communication and Living in Groups
Animals communicate using signals, which can be chemical (pheromones), aural (sound), visual (courtship displays), or tactile (touch).
Differentiate among the ways in which animals communicate
- Animals need to communicate with one another in order to successfully mate, which usually involves one animal signaling another; the energy-intensive behaviors or displays associated with mating are called mating rituals.
- Animal signaling is not the same as the communication we associate with language, which has been observed only in humans, but may also occur in some non-human primates and cetaceans.
- Animal communication by stimuli known as signals may be instinctual, learned, or a combination of both.
- pheromone: a chemical secreted by an animal that affects the development or behavior of other members of the same species, functioning often as a means of attracting a member of the opposite sex
Innate behaviors: living in groups
Not all animals live in groups, but even those that live relatively-solitary lives (with the exception of those that can reproduce asexually) must mate. Mating usually involves one animal signaling another so as to communicate the desire to mate. There are several types of energy-intensive behaviors or displays associated with mating called mating rituals. Other behaviors found in populations that live in groups are described in terms of which animal benefits from the behavior. In selfish behavior, only the animal in question benefits; in altruistic behavior, one animal’s actions benefit another animal; cooperative behavior occurs when both animals benefit. All of these behaviors involve some sort of communication between population members.
Communication within a species
Animals communicate with each other using stimuli known as signals. These signals are chemical ( pheromones ), aural (sound), visual (courtship and aggressive displays), or tactile (touch). These types of communication may be instinctual, learned, or a combination of both. These are not the same as the communication we associate with language, which has been observed only in humans and, perhaps, in some species of primates and cetaceans.
A pheromone is a secreted, chemical signal used to obtain a response from another individual of the same species. The purpose of pheromones is to elicit a specific behavior from the receiving individual. Pheromones are especially common among social insects, but they are used by many animal species to attract the opposite sex, to sound alarms, to mark food trails, and to elicit other, more-complex behaviors. Even humans are thought to respond to certain pheromones called axillary steroids. These chemicals influence human perception of other people. In one study, they were responsible for a group of women synchronizing their menstrual cycles. The role of pheromones in human-to-human communication is still somewhat controversial and continues to be researched.
Songs are an example of an aural signal: one that needs to be heard by the recipient. Perhaps the best known of these are songs of birds, which identify the species and are used to attract mates. Other well-known songs are those of whales, which are of such low frequency that they can travel long distances underwater. Dolphins communicate with each other using a wide variety of vocalizations. Male crickets make chirping sounds using a specialized organ to attract a mate, repel other males, and to announce a successful mating.
Courtship displays are a series of ritualized visual behaviors (signals) designed to attract and convince a member of the opposite sex to mate. These displays are ubiquitous in the animal kingdom. They often involve a series of steps, including an initial display by one member followed by a response from the other. If at any point the display is performed incorrectly or a proper response is not given, the mating ritual is abandoned and the mating attempt will be unsuccessful.
Aggressive displays are also common in the animal kingdom. As, for example, when a dog bares its teeth to get another dog to back down. Presumably, these displays communicate not only the willingness of the animal to fight, but also its fighting ability. Although these displays do signal aggression on the part of the sender, it is thought that they are actually a mechanism to reduce the amount of fighting that occurs between members of the same species: they allow individuals to assess the fighting ability of their opponent and thus decide whether it is “worth the fight.”
Distraction displays are seen in birds and some fish. They are designed to attract a predator away from the nest that contains their young. This is an example of an altruistic behavior: it benefits the young more than the individual performing the display, which is putting itself at risk by doing so.
Many animals, especially primates, communicate with other members in the group through touch. Activities such as grooming, touching the shoulder or root of the tail, embracing, lip contact, and greeting ceremonies have all been observed in the Indian langur, an Old World monkey. Similar behaviors are found in other primates, especially in the great apes.
Altruism and Populations
Altruistic behaviors may be explained by the natural instinct to improve the chances of passing on one’s genes.
Explain how altruistic behaviors can benefit populations
- Behaviors that lower the fitness of the individual, but increase the fitness of another individual are termed altruistic; why altruistic behaviors exist has been the topic of some debate.
- One explanation for altruistic-type behaviors is found in the genetics of natural selection and the “selfish gene ” theory: although a gene cannot be selfish in the human sense, it may appear that way if the sacrifice of an individual benefits related individuals that share genes that are identical.
- Even less-related individuals, those with less genetic identity than that shared by parent and offspring, benefit from seemingly-altruistic behavior, such as sterile worker bees protecting the queen.
- Unrelated individuals may also act altruistically to each other, which seems to defy the “selfish gene” explanation; however, this altruism is typically reciprocal, in that both benefit from the interaction.
- Most of the behaviors described when speaking of altruism do not seem to satisfy the definition of “pure” altruism; some evolutionary game theorists suggest that we get rid of the terms “altruistic” and “selfish” altogether since they describe human behavior.
- kin selection: an evolutionary mechanism by which an organism’s behavior benefits the reproductive success of its relatives, including at the expense of its own survival or reproduction
- altruism: devotion to the interests of others; brotherly kindness; opposed to egoism or selfishness
- game theory: a branch of applied mathematics that studies strategic situations in which individuals or organizations choose various actions in an attempt to maximize their returns
Behaviors that lower the fitness of the individual engaging in the behavior, but increase the fitness of another individual, are termed altruistic. Examples of such behaviors are seen widely across the animal kingdom. Social insects, such as worker bees, have no ability to reproduce, yet they maintain the queen so she can populate the hive with her offspring. Meerkats keep a sentry standing guard to warn the rest of the colony about intruders, even though the sentry is putting itself at risk. Wolves and wild dogs bring meat to pack members not present during a hunt. Lemurs take care of infants unrelated to them. Although on the surface these behaviors appear to be altruistic, it may not be so simple.
Why Does Altruism Exist?
There has been much discussion over why altruistic behaviors exist. Do these behaviors lead to overall evolutionary advantages for their species ? Do they help the altruistic individual pass on its own genes? And what about such activities between unrelated individuals? One explanation for altruistic-type behaviors is found in the genetics of natural selection. In the 1976 book, The Selfish Gene, scientist Richard Dawkins attempted to explain many seemingly-altruistic behaviors from the viewpoint of the gene itself. Although a gene obviously cannot be selfish in the human sense, it may appear that way if the sacrifice of an individual benefits related individuals that share genes that are identical by descent (present in relatives because of common lineage). Mammal parents make this sacrifice to take care of their offspring. Emperor penguins migrate miles in harsh conditions to bring food back for their young. Selfish gene theory has been controversial over the years and is still discussed among scientists in related fields.
Even less-related individuals (those with less genetic identity than that shared by parent and offspring) benefit from seemingly altruistic behavior. The activities of social insects such as bees, wasps, ants, and termites are good examples. Sterile workers in these societies take care of the queen because they are closely related to it; as the queen has offspring, she is passing on genes from the workers indirectly. Thus, it is of fitness benefit for the worker to maintain the queen without having any direct chance of passing on its genes due to its sterility. The lowering of individual fitness to enhance the reproductive fitness of a relative and, thus, one’s inclusive fitness evolves through kin selection. This phenomenon can explain many superficially-altruistic behaviors seen in animals. However, these behaviors may not be truly defined as altruism in these cases because the actor is actually increasing its own fitness either directly (through its own offspring) or indirectly (through the inclusive fitness it gains through relatives that share genes with it).
Unrelated individuals may also act altruistically to each other; this seems to defy the “selfish gene” explanation. An example of this is observed in many monkey species where a monkey will present its back to an unrelated monkey to have that individual pick the parasites from its fur. After a certain amount of time, the roles are reversed and the first monkey now grooms the second monkey. Thus, there is reciprocity in the behavior. Both benefit from the interaction and their fitness is raised more than if neither cooperated or if one cooperated and the other did not. This behavior is still not necessarily altruism, as the “giving” behavior of the actor is based on the expectation that it will be the “receiver” of the behavior in the future; a concept termed reciprocal altruism. Reciprocal altruism requires that individuals repeatedly encounter each other, often the result of living in the same social group, and that cheaters (those that never “give back”) are punished.
Evolutionary Game Theory and Altruism
According to evolutionary game theory, a modification of classical game theory in mathematics, many of these so-called “altruistic behaviors” are not altruistic at all. The definition of “pure” altruism, based on human behavior, is an action that benefits another without any direct benefit to oneself. Most of the behaviors previously described do not seem to satisfy this definition; game theorists are good at finding “selfish” components in them. Others have argued that the terms “selfish” and “altruistic” should be dropped completely when discussing animal behavior, as they describe human behavior and may not be directly applicable to instinctual animal activity. What is clear, though, is that heritable behaviors that improve the chances of passing on one’s genes or a portion of one’s genes are favored by natural selection and will be retained in future generations as long as those behaviors convey a fitness advantage.
Mating Systems and Sexual Selection
In mating, there are two types of selection (intersexual, intrasexual) and three mating systems (monogamous, polygynous, polyandrous).
Differentiate among monogamous, polygynous, and polyandrous mating systems, and distinguish between intersexual and intrasexual mate selection
- Two types of mate selection occur: intersexual selection (the choice of a mate where individuals of one sex choose mates of the other sex) and intrasexual selection (the competition for mates between species members of the same sex).
- Three general mating systems, all involving innate as opposed to learned behaviors, are seen in animal populations: monogamous ( monogamy ), polygynous ( polygyny ), and polyandrous (polyandry).
- In monogamous systems, one male and one female are paired for at least one breeding season; although in some animals, these partnerships can last even longer, sometimes an entire lifetime; males provide substantial parental care.
- Polygynous mating refers to one male mating with multiple females; in these situations, the female must be responsible for most of the parental care as the single male is not capable of providing care to that many offspring.
- In polyandrous mating systems, one female mates with many males; these types of systems are much rarer than monogamous and polygynous mating systems.
- polyandry: the mating pattern whereby a female copulates with several males
- polygyny: the mating patterns whereby a male copulates with several females
- monogamy: a form of sexual bonding involving an exclusive pair bond between two individuals
Finding Sexual Partners
Not all animals reproduce sexually, but many that do have the same challenge: they need to find a suitable mate and often have to compete with other individuals to obtain one. Significant energy is spent in the process of locating, attracting, and mating with a sex partner.
Types of Mate Selection
Two types of selection that occur during the process of choosing a mate may be involved in the evolution of reproductive traits called secondary sexual characteristics. These types are: intersexual selection (the choice of a mate where individuals of one sex choose mates of the other sex) and intrasexual selection (the competition for mates between species members of the same sex). Intersexual selection is often complex because choosing a mate may be based on a variety of visual, aural, tactile, and chemical cues. An example of intersexual selection is when female peacocks choose to mate with the male with the brightest plumage. This type of selection often leads to traits in the chosen sex that do not enhance survival, but are those traits most attractive to the opposite sex (often at the expense of survival). Intrasexual selection involves mating displays and aggressive mating rituals such as rams butting heads; the winner of these battles is the one that is able to mate. Many of these rituals use up considerable energy, but result in the selection of the healthiest, strongest, and/or most dominant individuals for mating.
Three general mating systems, all involving innate as opposed to learned behaviors, are seen in animal populations: monogamous (monogamy), polygynous (polygyny), and polyandrous (polyandry).
In monogamous systems, one male and one female are paired for at least one breeding season. In some animals, such as the gray wolf, these associations can last much longer, even a lifetime. Several explanations have been proposed for this type of mating system. The “mate-guarding hypothesis” states that males stay with the female to prevent other males from mating with her. This behavior is advantageous in such situations where mates are scarce and difficult to find. Another explanation is the “male-assistance hypothesis,” where males that remain with a female to help guard and rear their young will have more and healthier offspring. Monogamy is observed in many bird populations where, in addition to the parental care from the female, the male is also a major provider of parental care for the chicks. A third explanation for the evolutionary advantages of monogamy is the “female-enforcement hypothesis.” In this scenario, the female ensures that the male does not have other offspring that might compete with her own, so she actively interferes with the male’s signaling to attract other mates.
Polygynous mating refers to one male mating with multiple females. In these situations, the female must be responsible for most of the parental care as the single male is not capable of providing care to that many offspring. In resourced-based polygyny, males compete for territories with the best resources. They then mate with females that enter the territory, drawn to its resource richness. The female benefits by mating with a dominant, genetically-fit male; however, it is at the cost of having no male help in caring for the offspring. An example is seen in the yellow-rumped honeyguide, a bird whose males defend beehives because the females feed on the wax. As the females approach, the male defending the nest will mate with them. Harem mating structures are a type of polygynous system where certain males dominate mating while controlling a territory with resources. Elephant seals, where the alpha male dominates the mating within the group, are an example. A third type of polygyny is a lek system. Here there is a communal courting area where several males perform elaborate displays for females; the females choose their mate from this group. This behavior is observed in several bird species.
In polyandrous mating systems, one female mates with many males. These types of systems are much rarer than monogamous and polygynous mating systems. In pipefishes and seahorses, males receive the eggs from the female, fertilize them, protect them within a pouch, and give birth to the offspring. Therefore, the female is able to provide eggs to several males without the burden of carrying the fertilized eggs.