10a.docx

Behavioural zoologists are concerned with how two animals behave and why they behave in that way. 'How?' questions are concerned with immediate or proximate causation, and are studied experimentally, e.g. explaining the seasonal calling of male frogs in terms of hormonal or neural mechanisms. Altern...

Behavioural zoologists are concerned with how two animals behave and why they behave in that way. 'How?' questions are concerned with immediate or proximate causation, and are studied experimentally, e.g. explaining the seasonal calling of male frogs in terms of hormonal or neural mechanisms. Alternatively, the question might concern what function calling serves frogs, and then seek to understand those events in the ancestry of frogs that lead to this seasonal behaviour. These are 'Why?' questions, which focus on ultimate causation, the evolutionary origin and purpose of a behaviour. Questions of ultimate causation are answered using comparative methodology, applying phylogenetic analysis to understand evolutionary changes in behaviour and their associated morphological and environmental contexts. Comparative psychology aims to find universal laws of behaviour that would apply to many species, including humans. Early research depended heavily on inference, but was later replaced by experimental approaches concentrated on a few species, (readily available laboratory animals) such as rats, pigeons, dogs, and occasionally primates. Ethology aims to describe the behaviours of an animal in its natural habitat, data is gathered by field observation and experiments, e.g. playing recordings of animal vocalisations and altering habitats. Ethology emphasises the importance of ultimate factors affecting behaviour. One of the great contributions of animal behaviourists such as von Frisch, Lorenz, and Tinbergen, was to demonstrate that behavioural traits are identifiable and measurable entities like anatomical or physiological traits. Behavioural ecologists use both of the above methods to focus on how individuals are expected to behave to maximize reproductive success, and then concentrate on a particular aspect, such as mate choice, foraging, or parental investment. Sociobiology concerns the ethological study of social behaviours, which are defined as 'reciprocal communication of a cooperative nature that permits a group of the species to become organised in a cooperative manner'. In a complex system of social interactions, individuals are highly dependent on others for their daily living. Some basic concepts of animal behaviour can be illustrated by considering the egg-retrieval response of greylag geese, described by Lorenz and Tinbergen in 1939. A female greylag goose presented with an egg a short distance from her nest will rise, extend her neck until the bill is just over the egg, and then pull the egg into the nest. Although this behaviour appears to be intelligent, Tinbergen and Lorenz noticed that if they removed the egg once the goose had begun her retrieval, or if the egg being retrieved slipped away and rolled down the outer slope of the nest, the goose would continue the retrieval movement without the egg until she was again settled comfortably on her nest. Then, seeing that the egg had not been retrieved, she would begin the egg-rolling pattern again. Thus, the bird performed egg-rolling behaviour as if it were a program that, once initiated, had to run to completion. Behaviour of this type, performed in an orderly, predictable sequence is often called stereotypical behaviour. Further experiments by Tinbergen disclosed that the greylag goose was not particularly discriminating about what she retrieved, with any smooth and rounded object placed outside the nest triggering the egg-rolling sequence. The presence of an egg shaped object outside the nest acts as a stimulus, or trigger that releases egg-retrieval behaviour. Such a triggering stimulus (releaser or sign stimulus) is a simple signal in the environment that triggers a specific innate behaviour. Other sign stimuli include the alarm call of adult herring gulls, which results in a freeze-response in their chicks; nocturnal moths take evasive manoeuvres or drop to the ground on hearing ultrasonic bat calls. These examples illustrate the predictable and programmed nature of much animal behaviour. This is even more evident when stereotyped behaviour is released inappropriately. In spring, a territorial male three spined stickleback becomes aggressive to rival males. The red underside of the male serves as a releaser for aggression; this was confirmed by experiments involving presenting territorial males with models with red lower areas. Releases have the advantage of focusing an animal\'s attention on the relevant signal, and release of a pre programmed stereotyped behaviour will enable an animal to respond rapidly when speed may be essential for survival or reproductive success. From the beginning, the mostly invariable and predictable nature of stereotyped behaviour suggested that they were observing inherited, or innate, behaviour. Many kinds of pre-programmed behaviour appear suddenly in animals and are indistinguishable from similar behaviour performed by older, experi enced individuals, e.g. orb-weaving spiders build their webs without practice. It is easy to understand why programmed behaviour is important for survival, especially for animals that never know their parents. They must be equipped to respond to the world immediately and correctly as soon as they emerge into it. It is also evident that more complex animals with longer lives, with parental care or other opportunities for social interactions, may improve or change their behaviour by learning. Genetics of behaviour The hereditary transmission of most innate behaviour is complex; however, there are a few examples of behavioural differences within species that show simple Mendelian transmission from parents to offspring. Honey bees are susceptible to a bacterial disease, American foulbrood (Bacillus larvae). A bee larva that catches foul-brood dies. If the bees remove dead larvae from the hive, they reduce the chance of infection spreading. Some strains of bees, termed 'hygienic', uncap hive cells containing rotting larvae and remove them from the hive. There are two components to this behaviour: removal of cell caps, and then removal of larvae. Hygienic bees are homozygous recessive for two different genes. Uncapping behaviour is performed by individuals homozygous for the recessive allele; u at one gene, and removal behaviour is performed by homozygous bees with a recessive allele r at a second gene. Crossing hygienic bees (u/u r/r) with a non-hygienic strain (U/U R/), results in hybrids (U/u R/r) that exhibit non-hygienic behaviour. A 'backcross' between the hybrids and the hygienic parental strain resulted in the expected four different kinds of bees, a quarter homozygous recessive for both u/u and r/r (complete hygienic behaviour), a quarter (u/u R/r) uncapped, but did not remove dead bees, a quarter (U/u r/r) did not uncap, but removed the larvae of already uncapped cells, and a quarter (heterozygous for the dominant allele at both genes U/u R/r) do not perform either part of the cleaning behaviour. Unfortunately for behaviourists, most inherited behaviours do not show simple segregation and independence; instead, hybrids of subspecies or species commonly show intermediate or confused behaviours. Learning Learning is defined as 'modification of behaviour through experience'. An excellent model for studying learning processes is the marine 'sea hare' Aplysia, whose gills are partly covered by the mantle cavity and open to the outside by a siphon. If touched, its siphon and gills are withdrawn into the mantle cavity. This simple protective response, (gill withdrawal reflex) will decrease to extinction if touched repeatedly. This behavioural modification is called habituation. If the habituated Aplysia is given a noxious stimulus, (e.g. electric shock) to the head at the same time the siphon is touched, it becomes re-sensitised to the stimulus and withdraws its gills as before. Sensitisation can, therefore, reverse previous habituation. Receptors in the siphon are connected through sensor neurons to motor neurons controlling gill-withdrawal muscles. Repeated stimulation of the siphon diminishes the release of the synaptic transmitter from the sensory neurons. Sensory neurons continue to fire when the siphon is touched, but with less neurotransmitter being released into the synapse, the system becomes less responsive. Sensitisation requires the action of a different kind of neuron (facilitating interneuron), which makes connections between sensory neurons in the animal\'s head and motor neurons that control withdrawal. When sensory neurons in the head are stimulated by electric shock, they fire the facilitating interneurons, which end on the synaptic terminals of the sensory neurons. These endings cause an increase in the amount of transmitter released by the siphon sensory neurons, increasing the state of excitation in the excitatory interneurons and withdrawal motor neurons, leading to withdrawal. The motor neurons now fire more readily than before. These studies indicate that strengthening or weakening of the gill-withdrawal reflex involves changes in levels of transmitter, a physiological explanation of behavioural change. Another kind of learned behaviour is imprinting, 'imposition of a stable behaviour in a young animal by exposure to particular stimuli during a critical period in the animal\'s development'. As soon as a newly hatched gosling or duckling is strong enough to walk, it follows its mother away from the nest and will not follow another animal. However, this following behaviour is elicited by the first large object they see, regardless of whether it is a member of their own species. Natural selection favours evolution of a brain that imprints in this way. By following the mother, (the most likely large animate object a hatchling will encounter) and obeying her commands, survival is more likely. Social behaviour Any interaction resulting from the response of one animal to another of the same species represents social behaviour. Social aggregations such as herding or shoaling are only one kind of social behaviour, and not all aggregations of animals are social. For example, clouds of moths attracted to a light at night, barnacles attracted to a common float, or trout gathering in the coolest pool of a stream, are groupings of animals responding to environmental signals. Social aggregations, on the other hand, depend on signals from the animals themselves; remaining together and exhibiting co-ordinated mutually influence behaviours. While all sexually reproducing species must at least cooperate enough to achieve fertilisation, among other species breeding is the only adult social interaction. Other animals such as swans, albatrosses, and beavers form strong monogamous bonds that last a lifetime. The most persistent social bonds form between mothers and young, but these bonds usually terminate at fledging or weaning. Living together may be beneficial in many ways. One obvious benefit for aggregations is defence, both passive and active; from predators, e.g. musk-oxen that form a passive defensive circle when threatened by a wolf pack are less vulnerable than an individual. An example of active defence occurs in breeding colonies of gulls. When alarm calls of an individual results in the whole colony attacking the detected predators, a collective attack will discourage predators more effectively than an individual effort. Surveys of a wide variety of predators and prey show that the larger the group, the less likely any particular individual will be targeted. Sociality offers several reproductive benefits: it facilitates encounters between the sexes, which, for solitary animals, may consume much time and energy. Sociality also helps synchronise reproductive behaviour through mutual stimulation. Among colonial birds, the sounds and displays of courting individuals set in motion reproductive endocrine changes in other individuals. Because there is more social stimulation, large colonies of gulls produce more young per nest than small colonies. Indeed, some birds, e.g. flamingos will only breed if a large flock of their own species is present. Furthermore, parental care that social animals provide their offspring increases survival of young. Social living also provides opportunities for individuals to give aid and to share food. However, when animals live in groups, subordinates in any social order may be expendable. In many systems, they may never get a chance to reproduce, and are often the first to die. During times of food scarcity, death of weaker members protects resources for the stronger ones. Territoriality Territorial ownership is another facet of sociality in animal populations. A territory is defined as a fixed area from which intruders of the same species are excluded. This exclusion involves defending the area from intruders and spending long periods of time being conspicuous on the site. Territorial defence occurs in numerous animals: insects, crustaceans, fishes, amphibians, lizards, birds, and mammals, including humans. Sometimes, the space defended moves with the individual. 'Individual distance', can be observed in the spacing between swallows or pigeons on a wire, or gulls on a beach. Territoriality is generally an alternative to dominance behaviour, although both systems may be observed operating in the same species. A territorial system can work well with a low population, but may fail with increasing population density, being replaced with dominance hierarchies, with all animals occupying the same space. Like every other competitive endeavour, territoriality carries both costs and advantages. Specific benefits include uncontested foraging area; enhanced attractiveness to females (reducing problems of pair bonding, mating, and rearing young), reduced disease transmission, and predator vulnerability. However, advantages of holding a territory wane if an individual must spend most of its time in boundary disputes with its neighbours. Most of the time and energy required for territoriality is expended when the territory is first established. Once boundaries are established, they tend to be respected, and aggressive behaviours diminish as neighbours recognise each other. A 'beach master' seal (a dominant male with many females) seldom quarrels with neighbours, who have their own territories to defend. However, he must be constantly vigilant against bachelor bulls that challenge his mating privileges. Territorial behaviour is not as prominent with mammals as it is in birds. Mammals are less mobile than birds making it more difficult for them to patrol a territory for trespassers. Instead many mammals have home ranges. A lion's range is the total area an individual traverses in its activities. It is not an exclusive, defended preserve, but overlaps with home ranges of other individuals. Mating systems Animals display diverse mating systems, usually classified by the degree to which males and females associate during mating. Monogamy - one male and one female at a time. Polygamy - is a general term that incorporates all multiple mating systems where females and males have more than one mate. Polygyny - a male that mates with more than one female. Polyandry - a female that mates with more than one male. There are specific types of polygyny. Resource-defence polygyny occurs when males gain access to females indirectly by holding critical resources. For example, female bullfrogs prefer to mate with males holding more advantageous territories (better temperature regimes for tadpoles to grow or free of predatory leeches). Female-defence polygyny occurs when females aggregate and, consequently, are defendable. Thus, when female elephant seals occupy a small island, dominant males can defend and gain access to them for mating, relatively easily. Male-dominance polygyny occurs when females select mates from aggregations of males. For example, some animals (e.g. grouse) form leks (communal display ground where males congregate to attract and court females). Females choose and mate with the male having the most attractive qualities. In these systems, sexual selection is often intense, resulting in the evolution of bizarre courtship rituals and exaggerated morphological traits. Animal communication Only through communication can one animal influence the behaviour of another. Compared with the enormous communicative potential of human speech, however, non-human communication is severely restricted. Animals may communicate by sounds, scents, touch, and movement. In comparison to humans, communication skills of other animals consist of a limited repertoire of signals, each of which conveys a single message. A cricket\'s song announces to an unfertilised female the species of the sender (males of different species have different songs), his sex (only males sing), his location (source of the song), and social status (only a male, able to defend the area around his burrow, sings from one location). This information is crucial to a female and accomplishes a biological function. However, there is no way for a male to alter his song to provide additional information concerning food, predators, or habitat, which might improve his mate\'s chances of survival and thus enhance his own fitness. Phylogenetic studies have been important for testing hypotheses of the evolution of mating-behavioural and morphological characters by sexual selection. An important phylogenetic study of mating behaviour examines the evolution of male displays in leks of tropical bowerbirds. 44 behavioural characters have been identified that have been used to discover the historical sequence by which these displays evolved. The results show a general evolutionary trend towards increased complexity of displays and a tendency for behavioural changes to precede changes in plumage. A new behavioural display that highlights a particular area of plumage, subjects that plumage to sexual selection for morphological elabo ration. These studies suggest that behavioural evolution may be a major factor in determining the action of selection on morphological characters. Some evolutionists have proposed that behavioural evolution generally accelerates morphological evolution, and that a change in behaviour is often a critical factor permitting evolution of new adaptive features. There are many examples of animal communication, through various means. Mate attraction in silkworm moths illustrates an extreme case of stereotyped, single-message communication that has evolved to serve a single biological function: mating. Virgin female silkworm moths have special glands that produce a chemical attractant to which males are sensitive. Adult males detect this pheromone with large bushy antennae. To attract males, females merely sit quietly and emit a minute amount of pheromone, which is carried downwind. Only a few molecules reaching a male\'s antennae stimulate him to fly upwind in search of the female. Its effectiveness is ensured, because natural selection favours the evolution of males with antennal receptors sensitive enough to detect the attractant at great distances (several miles). Males with a genotype that produces a less sensitive sensory system fail to locate a female and, thus, are reproductively eliminated from the population. Displays A display is a kind of behaviour or series of behaviours that serves a communicative purpose. The release of sex attractant by a female moth and the dances of bees are examples of displays; so are alarm calls of herring gulls, songs of the white-crowned sparrow, courtship dances of the sage grouse, and 'eyespots' on the hind wings of certain moths that are exposed quickly to startle potential predators. The elaborate pair-bonding displays of blue-footed boobies are performed with maximum intensity when the birds come together after a period of separation. The exaggerated nature of the displays ensures that the message is not missed or misunderstood, thus ensuring the establishment and maintenance of a strong pair-bond between the male and the female. Repetitious displays maintain a state of mutual stimulation between the male and female, ensuring the degree of cooperation necessary for copulation and subsequent incubation and care of the young. Animal cognition One of the most fascinating subjects in animal behaviour deals with animal intelligence and awareness. Animal cognition is a general term for mental function, including perception, thinking and memory. Many biologists believe that mental processes of animals may be similar to those of humans. In fact, it has been possible to teach human language (sign language) to non-human primates. The chimpanzee, 'Washoe', could sign 132 words, which she could put into strings forming sentences, phrases, answer questions, make suggestions and convey moods. Washoe also taught signs to other chimpanzees. The biosphere An organism and its environment share a reciprocal relationship. The environment is modified by organisms, and populations of organisms are modified by their evolutionary process to adapt to the environment and its changes. As an open system, an animal is forever receiving and releasing materials and energy. Building materials for life are obtained from the physical environment, either directly by producers such as green plants or indirectly by consumers. A living form is a transient link built of environmental materials, which are then returned to the environment to be used again in the recreation of new life. Life, death, decay and recreation have been the cycle of existence since life began. The biosphere is defined as the thin outer layer of the Earth capable of supporting life. It is a global system that includes all life on Earth and the physical environments in which living organisms exist and interact. The non-living subdivisions of the biosphere include the lithosphere, hydrosphere, and atmosphere. The lithosphere is the rocky material of the Earth\'s outer crust. The hydrosphere is the water on or near the Earth\'s surface, and extends into the lithosphere and the atmosphere. Water is distributed over the Earth by a global hydrological cycle of evaporation, precipitation, and runoff. The gaseous component of the biosphere, the atmosphere, extends to some 3500km above the Earth\'s surface, but all life is confined to the lowest 8km to 15km (troposphere). Terrestrial environments: biomes A biome is a major biotic unit bearing a characteristic range of plant life. Botanists long ago recognised that the terrestrial environment of the Earth could be divided into large units with distinctive vegetation, such as forests, grasslands and deserts. Animal distribution has always been more difficult to map, because plant and animal distributions do not exactly coincide. A biome is identified by its dominant plant formation, but, because animals depend on plants, each biome supports a characteristic fauna. Each biome is distinctive, but plant communities grade into one another over broad areas. In North America, the moist deciduous forests of the Appalachians change gradually to drier oak forests of the Mississippi Valley, and then to oak woodlands with grassy clearings, which yield to tall and mixed grasslands, then to desert grasslands, and finally to desert shrublands. The indistinct boundaries where the dominant plants of adjacent biomes are mixed together form an almost continuous gradient called an ecocline. Distinctiveness of a biome is determined mainly by climate, the characteristic pattern of rainfall and the temperature of each region, and the amount of solar radiation it receives. Global variation in climate arises from the uneven heating of the atmosphere by the sun. Because of the lower angle of the sun\'s rays striking higher latitudes, atmospheric heating is less there than at the equator. Air warmed at the equator rises and moves toward the poles. It is replaced by cold air moving away from the poles at lower levels. The principal terrestrial biomes are temperate deciduous forests, temperate coniferous forests, tropical forests, grasslands, tundras, and deserts. Terrestrial biomes The temperate deciduous forest was developed in eastern North America, and Europe. Deciduous, broad leaved trees such as oak, maple, and beech that shed their leaves in winter predominate. The deciduous habitat is an adaptation of dormancy for low-energy levels from the sun in winter and freezing winter temperatures. In summer, the relatively dense forests form a closed canopy that creates deep shade below, resulting in undergrowth plants that grow rapidly in the spring and flower early before the canopy develops. The mean annual precipitation is relatively high, and rain falls periodically throughout the year. The mean annual temperatures range between 5° C and 18° C. Animal communities in deciduous forests respond to seasonal changes in various ways. Some, such as insect-eating warblers, migrate. Others, e.g. woodchucks, hibernate in winter. Others survive by using available food (deer) or stored food supplies (squirrels). Hunting and habitat loss have eliminated virtually all large carnivores (bears and wolves) that once roamed these forests. Insect and invertebrate communities are abundant as decaying logs and forest-floor debris provide excellent shelter. Coniferous forests form a broad, continuous, belt, stretching across Northern Europe, the former USSR, Canada and Alaska, making it one of the largest plant formations on Earth. It is dominated by evergreens (pine, fir. spruce, and cedar), which are adapted to withstand freezing temperatures and take full advantage of short summer growing seasons. Conical trees with their flexible branches shed snow easily. These boreal (northern) forests, often called taiga, are dominated by white and black spruce, balsam fir, pine, larch, and birch. The mean annual precipitation is less than 100cm and average temperatures range from -5° C to +3° C. Mammals of boreal forests include deer, moose, caribou, snowshoe hares, a variety of rodents, and carnivores such as wolves, foxes, wolverines, lynxes, weasels, martins, and omnivorous bears. They are adapted physiologically or behaviourally for long, cold, snowy winters. Common birds are nuthatches, warblers, and jays. One bird, the crossbill, has a beak specialised for picking seeds from cones. Mosquitoes and flies are pests to both animals and humans in this biome. The worldwide equatorial belt of tropical forests is an area of high rainfall (more than 200cm per year), high humidity, relatively high and constant temperatures averaging more than 17° C, and little seasonal variation in day length. These conditions produce luxurious growth that reaches its greatest intensity in rainforests. In sharp contrast to temperate deciduous forests, dominated by relatively few tree species, tropical forests contain thousands of species, none of which is dominant. Climbing plants and epiphytes are common. A distinctive feature of tropical forests is the stratification of life into six, and occasionally as many as eight, feeding strata. Insectivorous birds and bats occupy the air above the canopy; below it birds, fruit bats, and mammals feed on leaves and fruit. In the middle zones are arboreal mammals (monkeys and sloths), numerous birds, insectivorous bats, insects, and amphibians. Climbing animals, such as squirrels and civets, feed from all strata. On the ground are large mammals lacking climbing ability, e.g. rodents of South America (for example, capybara) and members of the pig family. Finally, a mixed group of small insectivorous, carnivorous, and herbivorous animals search the litter and lower tree trunks for food. Food webs are intricate and difficult to unravel. It may seem paradoxical that a biome as luxuriant as a tropical forest should have poor soil, but this occurs because nutrients released by decomposition are rapidly recycled by plants, leaving no reservoir of humus. In many areas, once the plants are removed, the soil rapidly becomes a hard, crust, called laterite, which tropical plants cannot colonise. The grasslands of central Asia and North America are one of the most extensive biomes in the world. Original grassland associations of plants and animals have been almost completely destroyed by humans in North America; 'prairies' today are dominated by monocultures of cereal grains. In grazing lands virtually all major native grasses have been replaced by alien species. Of the once dominant herbivore, bison, few survive, but jackrabbits, prairie dogs, ground squirrels, and antelope remain. Mammalian predators include coyotes, ferrets, and badgers. Rainfall on the North American prairie ranges from about 80cm in the east to 40cm in the west. Average annual temperatures range between 10° C and 20° C. Tundra is characteristic of severe, cold climatic regions, especially treeless Arctic regions and high mountain tops. Plant life is adapted to a short growing season of about 60 days and soil that remains frozen for most of the year. The average annual precipitation is less than 2cm with annual temperatures averaging about -10° C. Most tundra regions are covered with bogs, marshes, ponds, and a spongy mat of decayed vegetation, although mountain tundra may only be covered with lichens and grasses. Despite thin soil and a short growing season, the vegetation of dwarf woody plants, grasses, sedges, and lichens may be quite profuse.