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behavioral ecology.docx

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McMaster University
Laura Parker

Behavioral Ecology 1. Behavior is everything an animal does and how it does it. Behavioral has both proximate and ultimate causes. a. Proximate questions are concerned with the environmental stimuli that trigger a behavior, as well as the genetic, physiological, and anatomical mechanisms underlying it. Proximate questions are referred to as “how?” questions. i. Proximate mechanisms produce behaviors that evolved because they increase fitness in some way. b. Ultimate questions address the evolutionary significance of a behavior and why natural selection favors this behavior. Ultimate questions are referred to as “why?” questions. 2. Four questions must be answered to fully understand any behavior. The first two, which concern mechanism and development, are proximate questions, while the second two are ultimate, or evolutionary, questions. a. What is the mechanistic basis of the behavior, including chemical, anatomical, and physiological mechanisms? b. How does development of the animal, from zygote to mature individual, influence the behavior? c. What is the evolutionary history of the behavior? d. How does the behavior contribute to survival and reproduction (fitness)? 3. A fixed action pattern (FAP) is a sequence of unlearned behavioral acts that is essentially unchangeable and, once initiated, is usually carried to completion. a. A FAP is triggered by an external sensory stimulus called a sign stimulus. i. In the red-spined stickleback, the male attacks other males that invade his nesting territory. The stimulus for the attack is the red underside of the intruder. ii. A male stickleback will attack any model that has some red visible on it. (1) A proximate explanation for this aggressive behavior is that the red belly of the intruding male acts as a sign stimulus that releases aggression in a male stickleback. (2) An ultimate explanation is that by chasing away other male sticklebacks, a male decreases the chance that eggs laid in his nesting territory will be fertilized by another male. b. Imprinting is a type of behavior that includes learning and innate components and is generally irreversible. i. Imprinting has a sensitive period, a limited phase in an animal’s behavior that is the only time that certain behaviors can be learned. ii. An example of imprinting is young geese following their mother. (1) A proximate explanation for young geese following and imprinting on their mother is that during an early, critical developmental stage, the young geese observe their mother moving away from them and calling. (2) An ultimate explanation is that, on average, geese that follow and imprint on their mother receive more care and learn necessary skills, and thus have a greater chance of surviving, than those that do not follow. 4. Behavioral traits, like other aspects of a phenotype, are the result of complex interactions between genetic and environmental factors. In biology, the nature-versus-nurture issue is not about whether genes or environment influence behavior, but about how both are involved. All behaviors are affected by both genes and environment. a. In some cases, the behavior is variable, depending on environmental experience. b. In other cases, nearly all individuals in the population exhibit identical behavior, despite internal and external environmental differences during development and throughout life. i. Behavior that is developmentally fixed is called innate behavior. ii. Such behaviors are under strong genetic influence. iii. The range of environmental differences among individuals does not appear to alter innate behavior. 5. Many animal movements are under substantial genetic influence. a. A kinesis is a simple change in activity or turning rate in response to a stimulus. b. A taxis is an automatic, oriented movement toward or away from a stimulus. c. Migration is the regular movement of animals over relatively long distances. 6. Much of the social interaction between animals involves transmitting information through specialized behaviors called signals. a. In behavioral ecology, a signal is a behavior that causes a change in another animal’s behavior. b. Some features of animal communication are under strong genetic control, although the environment makes a significant contribution to all communication systems. c. Many signals are efficient in energy costs. d. Animals communicate using visual, auditory, chemical, tactile, and electrical signals. The type of signal is closely related to an animal’s lifestyle and environment. i. For example, nocturnal species use olfactory and auditory signals. ii. Birds are diurnal and have a poor olfactory sense. They communicate primarily by visual and auditory signals. iii. Humans are more attentive to the colors and songs of birds than the rich olfactory signals of many other animals because of our own senses. e. Many animals secrete chemical substances called pheromones, chemicals which alter the behavior of other animals. 7. Mating and parental behavior by male prairie voles (Microtus ochrogaster) are under strong genetic control. a. Prairie voles and a few other vole species are monogamous, a social trait found in only 3% of mammalian species. b. Male prairie voles help their mates care for young, a relatively uncommon trait among male mammals. Male prairie voles form a strong pair-bond with a single female after they mate, engaging in grooming and huddling behaviors. c. Mated males are intensely aggressive to strange males or females, while remaining nonaggressive to their mate and pups. d. Arginine-vasopressin (AVP), a nine-amino-acid neurotransmitter released in mating, mediates both pair-bond formation and aggression in male prairie voles. i. In the CNS, AVP binds to a receptor called the V receptor. 1a ii. There are significant differences in the distribution of V rec1ators between the brains of monogamous prairie voles and related promiscuous montane voles. iii. When the prairie vole V rec1ator gene was inserted into laboratory mice the mice developed the same distribution of V recep1ars as the prairie voles and also showed many of the mating behaviors of the voles. iv. Thus, a single gene appears to mediate much of the complex mating and parental behavior of the prairie vole. 8. Environment, interacting with an animal’s genetic makeup, influences the development of behavior. a. Diet plays an important role in mate selection by Drosophila mojavensis, which mates and lays its eggs in rotting cactus tissues. i. The food eaten by male flies as larvae strongly influenced mate selection by female flies. (1) The proximate cause in the female mate choices was in the exoskeletons of the flies, assessed by the sense of taste in female flies. (2) When males from the other population were “perfumed” with hydrocarbons extracted from males of the same population, they were accepted by female flies. b. The California mouse (Peromyscus californicus) is monogamous and, like male prairie voles, male California mice are highly aggressive to other mice and provide considerable parental care. i. Unlike prairie voles, even unmated California mice are aggressive. ii. Researchers placed newborn California mice in the nests of white-footed mice (and vice versa). iii. White-footed mice are not monogamous and provide little parental care. iv. This cross-fostering changed the behavior of both species. (1) Cross-fostered California mice provided less parental care and were less aggressive toward intruders when they grew up and reared their own young. (2) Their brains had reduced levels of AVP, compared with California mice raised by their own parents. (3) White-footed mice reared by California mice were more aggressive as parents than those raised by their own parents. 9. One of the most powerful ways that environmental conditions can influence behavior is through learning, the modification of behavior based on specific experiences. a. Habituation involves a loss of responsiveness to unimportant stimuli or stimuli that do not provide appropriate feedback. i. For example, some animals stop responding to warning signals if signals are not followed by a predator attack (the “cry wolf” effect). ii. In terms of ultimate causation, habituation may increase fitness by allowing an animal’s nervous system to focus on meaningful stimuli, rather than wasting time on irrelevant stimuli. b. The fitness of an organism may be enhanced by the capacity for spatial learning. i. It may be advantageous for animals to modify their behavior based on experience with the spatial structure of their environment, including the locations of nest sites, hazards, food, and prospective mates. (1) Digger wasps found their nest entrances by using landmarks, or location indicators, in their environment. ii. Because some environments are more stable than others, animals may use different kinds of information for spatial learning in different environments. (1) Sticklebacks from a river learned a maze by learning a pattern of movements. (2) Sticklebacks from a more stable pond environment used a combination of movements and landmarks to learn the maze. (3) The degree of environmental variability influences the spatial learning strategies of animals. iii. Some animals form cognitive maps, complex arrangements of spatial relationships of objects in their environment. c. Associative learning is the ability of animals to learn to associate one stimulus with another. i. For example, a mouse may have an unpleasant experience with a colorful, poisonous caterpillar and learn to avoid all caterpillars with that coloration. ii. Classical conditioning is when an animal learns to associate a meaningless stimulus with a significant one. iii. Operant conditioning is also called trial-and-error learning. An animal learns to associate one of its own behaviors with a reward or a punishment. Note that this refers to voluntary behavior. 10. Varying degrees of genetic and environmental factors contribute to the learning of complex behavior. a. Animal cognition is the ability of an animal’s nervous system to perceive, store, process, and use information gathered by sensory receptors. It connects behavior with nervous system function. i. Chimpanzees learn to solve problems by copying the behavior of other chimpanzees. ii. The development of songs by birds has revealed varying degrees of genetic and environmental influence on the learning of complex behavior. (1) For instance, New World flycatchers that are reared away from adults of their own species will sing the song characteristic of their own species without every having heard it. (2) Individual white-crowned sparrows reared in silence perform abnormal songs, but if recordings of the proper songs are played early in the life of the bird, normal songs develop. 11. Because of the influence of genes on behavior, natural selection can result in the evolution of behavioral traits in populations. a. When behavioral variation within a species corresponds to variation in environmental conditions, it may be evidence of past evolution. b. Experiments have provided evidence for behavioral evolution. i. e.g., a polymorphism in a gene for foraging in Drosophila melanogaster. The gene is called for, and it has two alleles. R (1) One allele, for , results in a “rover” phenotype in which the fly larva moves more thansusual. (2) The other allele, for , results in a “sitter” phenotype in which the fly larva moves less than usual. ii. Researches reared Drosophila at high and low population densities for 74 generatsons. R iii. The for allele increased in low-density populations, while for increased in high-density populations. (1) At low densities, short-distance foraging yielded sufficient food. (2) At high densities, long-distance foraging helped the larvae to move beyond areas of food depletion. c. Natural selection favors behaviors that increase survival and reproductive success. Two of the most direct ways that behavior can affect fitness are through influences on foraging and mate choice. i. Foraging includes not only eating, but also any mechanisms that an animal uses to recognize, search for, and capture food items. (1) Optimal foraging theory views foraging behavior as a compromise between the benefits of nutrition and the costs of obtaining food, such as the energy expenditure and risk of predation while foraging. (a) Natural selection should favor foraging behavior that minimizes the costs of foraging and maximizes the benefits. (2) Researchers have carried out a cost-benefit analysis of feeding behavior in crows in BC. (a) Crows search tide pools for snails. (b) A crow flies up and drops the snail onto the rocks to break its shell. (c) If the drop is successful
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