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Chapter 1

Essential Animal Behaviour Chapter 1.doc

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Robert Gerlai

ESSENTIAL ANIMAL BEHAVIOUR: AN INTRODUCTION • People have probably always been fascinated by the behavior of animals. Indeed an understanding of the behavior of prey animals must have been essential to our early ancestors; their paintings on the walls of caves suggest that they could have been fairly familiar with behavioral concepts such as herd size and migration. • The earliest stock-farmers would have needed to understand the behavior of the charges in their care just as their modern counterparts do today. • The field of animal behavior is diverse and may be studied from a variety of perspectives. • It is useful to consider behaviors as adaptations. • A single behavior will not serve, or serve the same purpose in all situations, and behaviors are adapted to be effective in the environment of the animal performing them. • It is wrong to think of animal behavior as a general interest or a purely academic subject. The study of animal behavior is an important science which has a clear applied context. Cephalopod inking behaviour • Many species of octopus and squid are known to exhibit a particularly effective behavior that enables them to escape from predators. • In the region of their intestines the animals have a special sac-like organ. In the wall of this sac there is a gland which secretes a brown or black liquid rich in the pigment melanin, this is ink. • When threatened the animal has the ability to compress the ink sac and squirt a jet of the liquid from its anus. • It is thought that the cloud of ink hanging in the water forms a dummy squid termed a pseudomorph, which attracts and holds the attention of the predator allowing the animal to dart away to safety. • The deception is made all the more effective because long thin species produce long thin pseudomorphs and more round species produce rounder clouds of ink. • Squid and octopus are molluscs, taxonomic relatives of the garden slug and snail. • Can you imagine a slug squirting out ink to leave a pseudomorph hanging in the air to decoy a bird predator while the slug made its escape? • Of course you can’t, for the simple reason that this behavioral strategy can only work when the animal is surrounded by a medium that will support the ink cloud for a sufficient period to allow the escape. In water this works, but in the less dense medium of air it would not. • Some species of octopus and squid are inhabitants of the ocean depths. Here light penetration from the surface is minimal or zero and the seawater is a constant inky black. • Obviously the ink-dummy strategy would be no more effective here than it would be in air. The pseudomorph would hang in the water column, but it is unlikely that an ink-black shape would be seen against the inky-black backdrop. • In this situation species such as the deep-water squid Heteroteuthis secrete a luminescent ink, creating a brief flash of light which is thought to confuse a potential predator just long enough for an escape to be affected. • From this example I hope that I have made a few key points about behavior. • Firstly, that behaviors are adaptations which serve specific functions, and we will consider this point further later in this chapter. • Secondly, that a single behavior may not serve, or serve the same function, in all situations (a point to be borne in mind throughout this book). • Finally, behaviors are adapted to be effective in the environment of the animal performing them. What is behaviour? • Before investigating the amazing diversity of behaviors that animals exhibit, it is necessary for us to gain some insight into the concept of behavior itself. • We need to decide what the word behavior means to us in the current context and to examine the various avenues open to us for the study of animal behavior. • So what is behavior? Dictionary definitions of the word typically include phrases such as “acting or functioning in a specified or usual way.” This suggests to us that behavior is a predictable thing. • Another common phrase is “the response of an organism to a stimulus.” This suggests that behaviors are made to happen by something. In the case of this definition the “something” concerned is not specified, and may be internal or external to the animal involved. • Each of these ideas is in its own way an adequate response to the question. Behaviors are in many cases predictable given sufficient information concerning their context (although many appear initially to be highly unpredictable). Similarly behaviors are often linked to a stimulus in an immediate sense at some level. • The shortcoming of such definitions, however, is that they attempt to narrowly confine behavior in an easily described and highly specific way. Given the diversity of behavior such an approach may not be appropriate, because as humans we often think of different behaviors in very different terms. • Take for example breathing, swimming, and learning. Each of these words describes a behavior for which the definitions presented above would be sufficient. However as humans we would probably not think of them as being equivalent conceptually. • We would consider breathing to be an involuntary process and may not even consider it to be a behavior at all because of that. • Swimming, on the other hand, is clearly an active process, we tend to think of it as having a motivation or goal. • Learning we think of in different terms again. We have a tendency to place it into a higher class of processes, which require a higher level of mental ability. • So as a result of our own preconceptions about the words we use to label behaviors, and their obvious diversity, it will be much more useful for us to adopt a very broad definition of behavior in this book. • Put more simply then behavior is a property of all living things and whenever we observe an animal to be engaged in any activity (voluntary or involuntary) we are witnessing behavior. Indeed it could be said that the only animal not behaving is a dead animal! • This is an important point to remember. Although we may feel that a sleeping seal or a motionless sea-snake are doing nothing, they are in fact behaving. The act of sleep is a behavior in its own right, and the snake is quite probably poised to strike at passing prey, tensing a host of muscles in readiness and taking in and processing a wealth of information about its environment. There can be no doubt that it is behaving. Focus on anthropomorphism • Anthropomorphism is the attribution of human feelings and emotional states to animals. As humans we are aware of three mental experiences: feelings (pain, pleasure, etc.), motivations (the purposes of our actions), and thought. • Our current understanding of nonhuman animal species does not allow us to say that they experience the same (of course nor does it preclude common mental experiences). • Throughout the development of the field of animal behavior anthropomorphism and the use of anthropomorphic language has been frowned upon by some as a bar to clarity of expression, and in the extreme as a bar to the progression of science. • However, given the “human baggage” associated with many of the words we use in describing behavior (e.g. aggression, hierarchy, motivation), it is inevitable that a degree of anthropomorphism will occur. • Throughout this text I have endeavored to avoid unwarranted anthropomorphism; in reading it I would ask that you do the same. Concept: The scientific method • The scientific method is a four-stage approach that we can use to explore animal behavior. • First we make observations of a behavioral phenomenon. • Then we use these observations to formulate a hypothesis to explain the behavior. • This may lead us to make further predictions concerning the behavior. • Finally we design, carry out, and evaluate experiments to test our hypothesis and predictions. Approaches to the study of animal behaviour • The effective study of animal behavior requires observation and experimentation. Before we have any chance of understanding a behavior fully we must observe that behavior, in its natural context, and in its entirety. • The careful description of a behavior pattern or a sequence of behaviors allows us to identify all of the relevant components and to link their performance to the wider context of the physical and biological environment of the animal. • From such a knowledge base we are able to develop our own ideas about that behavior, to speculate upon its function, and upon the factors which control it. • In the language of science we are able to generate testable hypotheses. • These are carefully worded questions that we hope to answer via carefully designed experiments where specific factors surrounding behavioral performances are monitored and manipulated. • Animal behavior can be studied at two key levels. • At the physiological level we might be interested in the mechanism by which a behavior actually occurs. By this I mean in what way do the biochemistry, nerves, muscles, and senses of an animal interact to result in a particular behavior? • Equally interesting, however, are questions related to the whole animal and the world external to it. At this level we might consider the performance of a behavior in relation to the environment in which it is performed, to the wider ecology of the animal, or to its social experiences. • This kind of whole animal observation could be carried out in the field – in the natural environment of the animal – or it could be carried out in the laboratory where a controlled environment more readily permits experimentation. • In recent times, however, these distinctions have blurred and it is now commonplace to have “field” simulations in the laboratory and experimental manipulations in the field. • The most significant recent development in the process of the study of animal behavior must however be the advent of powerful user-friendly computers. Via computer models behavior can be simulated, and “experiments” carried out and evaluated without the involvement of any animal (other than the human operator) and often at a fraction of the cost of a more traditional line of investigation. • Such an approach undoubtedly has value, but a model is only as good as the data provided to it, and it will never replace the study of living animals. Asking questions in the study of behaviour • We further the study of animal behavior by posing (and hopefully answering) questions, which are carefully constructed to take into account previous observations (and the answers to previous questions). Although the actual number of specific questions that we can ask is huge, there are a relatively small number of types of question that need concern us: • What is behavior X? • The simplest way to answer this question would be to provide a description of the behavior. A more sophisticated answer might consider the raison d’être of the behavior, and in doing so the question would overlap with those below. • When does behavior X occur? • We might address this question in a number of ways. Perhaps we are asking at what time of year/day does it occur? Alternatively the question could relate to a life stage (is the behavior performed by mature animals only?). We could also be interested in the position of this behavior within a behavioral sequence (does the animal always do X after Y? or does one animal always do X if another animal has just done Z?). • Why does behavior X occur? • This is perhaps the most often asked question during studies of animal behavior and it is certainly the question which is given the most weight. Tinbergen’s four question • In 1963 Niko Tinbergen, a recognized pioneer of the study of animal behavior, suggested that there are four ways in which we can ask the question “why?” • Such is the importance afforded to Tinbergen’s four questions that it is worth spending some time on them so that we can be sure that we understand the subtleties of the distinctions between these four ways of asking “why?” • It is also important to remember that no one of the possible answers to the question “why?” that we might discuss is more important than any other. They complement one another and together help us to appreciate the wider picture. Why do cephalopods ink? • We started this chapter with a description of the way in which some species of cephalopod mollusc eject a cloud of ink as part of their antipredator behavior. • As enquiring animal behaviorists we should not be satisfied with a description of the behavior, we should ask the question why does it happen? • Tinbergen suggested that to fully explore the behavior we should ask why? in terms of the causation of the behavior, in terms of its evolution, of its function, and of its ontogeny. Causation • What causes a cephalopod to ink? The highly developed sensory organs of the cephalopods allow an animal to continually receive a wealth of information regarding its environment. The animal processes this information and specific environmental stimuli elicit specific responses. • If the animal is threatened with immediate danger a sequence of nerve impulses trigger the activity of the ink sac, an effector organ (i.e. an organ which carries out the response to a stimulus). Upon stimulation the ink sac compresses and the duct sealing it from the rectum opens. A jet of ink is expelled through the rectum and out of the anus. In the environment the ink forms either a pseudomorph or a diffuse cloud, depending upon the species involved. • In thinking about the roles of sense organs, nerves, and muscles we have already considered the mechanics of inking behavior, and so we have begun to examine the causal mechanisms of this behavior in an immediate sense. We might go further, however, to better understand the role of the recent experiences of the animal in the process. • Inking is relatively costly because it involves the production of an energetically expensive substance. For this reason it is usually a behavior of last resort. Typically an individual may have attempted to remain undetected through camouflage (crypsis behavior) or to frighten or confuse its attacker by performing one of a range of diematic behaviors. • Examples of diematic behavior include changing color rapidly to startle a predator or adopting a threatening body posture. We should therefore consider failure of crypsis and diematic behavior as being causal factors of inking. Evolution • Behaviors do not fossilize in the same way that body parts do. For this reason we can say little about the very recent evolution of inking behavior, or about its continuing development in the face of improvements in the ability of predators to detect the bluff, as must surely happen. • However, by looking at the family tree of the molluscs, and at that of the cephalopods particularly, we can say something about the longer-term evolution of the behavior. • Inking is not a general property of the molluscs, it is restricted to the class Cephalopoda. This tells us that the behavior has evolved more recently than at the point at which the cephalopods diverged from the other molluscs. • Further investigation reveals that not all cephalopods have an ink sac. The order is subdivided into two subclasses, the Nautilioidea (none of the species of nautilus has an ink sac) and the Coleoidea (most of which have an ink sac). Inking must thus be a relatively recent evolution within the subclass Coleoidea, the squids and octopuses. • Further examinations of differences and similarities in inking behavior between the various octopus and squid families would allow us to gain yet more insights into the evolution of the behavior, and may help us to better understand why it has evolved. Function • The function of inking behavior is very easy to understand. The behavior allows an animal to escape, thereby ensuring its survival and contributing to its fitness. (Fitness in this context equates to reproductive fitness and is a measure of the organism’s success in passing on its genes – after all a dead animal cannot pass on its genes.) • If inking is so effective why do some octopus and squid use it only as a last resort? As we have already mentioned inking probably has a high cost associated with it, whereas the behaviors involved in crypsis are probably far less costly. It would be better for an individual to rely on less costly behaviors where possible, because by doing so it may save energy with which its fitness might be enhanced. For example, we could speculate that by not using and replacing ink an animal may be able to spend more energy producing a greater number of eggs or sperm. Ontogeny • We might expect such a useful behavior as inking to be performed by all animals throughout their lives. After all the cephalopods have many predators. However, this is not always the case. The young of the blue-ringed octopus (Hapalochlaena lunulata) eject ink during the first few weeks of life, but after that they never do. H. lunulata is highly venemous – perhaps this proves a sufficient detterent to predators of adults, but not to those preying upon the young animals. • Antipredator behavior must therefore continue to develop and be refined throughout the lifetime of the animal in at least some species. The cover of this book shows just how striking the blue-ringed octopus is. Focus on heredity and natural selection: • That there is considerable variation among the individuals within a species. • That this variation is passed from parents to their offspring through their genes. • That many more individuals are produced than can ever survive to mature and reproduce. • From these basic building blocks, together with a prodigious amount of patient work and probably a touch of genius, Charles Darwin was able to construct his theory of evolution by natural selection. • Long before the importance of genes was appreciated he realized that some heritable property of certain individuals placed them at an advantage relative to others of their kind. Through time the diffe
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