Chapter 50 Ecology is the scientific study of the interactions between organisms and their environment. Concept 50. 1 Ecology is the study of interactions between organisms and the environment Ecology and evolutionary biology are closely related sciences. * Ecology has a long history as a descriptive science. * Modern ecology is also a rigorous experimental science. * Ecology and evolutionary biology are closely related sciences. * Events that occur over ecological time (minutes to years) translate into effects over evolutionary time (decades to millennia). For example, hawks feeding on field mice kill certain individuals (over ecological time), reducing population size (an ecological effect), altering the gene pool (an evolutionary effect), and selecting for mice with fur color that camouflages them in their environment (over evolutionary time). Ecological research ranges from the adaptations of individual organisms to the dynamics of the biosphere. * The environment of any organism includes the following components: * Abiotic components: nonliving chemical and physical factors such as temperature, light, water, and nutrients. Biotic components: all living organisms in the individual’s environment. * Ecology can be divided into a number of areas of study. * Organismal ecology is concerned with the behavioral, physiological, and morphological ways individuals interact with the environment. * A population is a group of individuals of the same species living in a particular geographic area. Population ecology examines factors that affect population size and composition. * A community consists of all the organisms of all the species that inhabit a particular area.
Community ecology examines the interactions between species and considers how factors such as predation, competition, disease, and disturbance affect community structure and organization. * An ecosystem consists of all the abiotic factors in addition to the entire community of species that exist in a certain area. Ecosystem ecology studies energy flow and cycling of chemicals among the various abiotic and biotic components. * A landscape or seascape consists of several different ecosystems linked by exchanges of energy, materials, and organisms. Landscape ecology deals with arrays of ecosystems nd their arrangement in a geographic region. * The biosphere is the global ecosystem, the sum of all of the planet’s ecosystems. Ecology provides a scientific context for evaluating environmental issues. * In 1962, Rachel Carson’s book Silent Spring warned that the use of pesticides such as DDT was causing population declines in many nontarget organisms. * Today, acid precipitation, land misuse, toxic wastes, habitat destruction, and the growing list of endangered or extinct species are just a few of the problems that threaten the Earth. * Our ecological information is always incomplete.
The precautionary principle (essentially “an ounce of prevention is worth a pound of cure”) can guide decision making on environmental issues. Concept 50. 2 Interactions between organisms and the environment limit the distribution of species * Biogeography is the study of past and present distributions of individual species in the context of evolutionary theory. Species dispersal/transplant contributes to the distribution of organisms * The movement of individuals away from centers of high population density or from their area of origin is called dispersal. The dispersal of organisms is crucial to understanding geographic isolation in evolution and the broad patterns of geographic distribution of species. * One way to determine if dispersal is a key factor limiting distribution is to observe the results when humans have accidentally or intentionally transplanted a species to areas where it was previously absent. * For the transplant to be considered successful, the organisms must not only survive in the new area, but also reproduce there. * If the transplant is successful, then the potential range of the species is larger than its actual range. Species introduced to new geographic locations may disrupt the communities and ecosystems to which they are introduced. * Consequently, ecologists rarely conduct transplant experiments today. * Instead, they study the outcome when a species has been transplanted accidentally or for another purpose. Behavior and habitat selection contribute to the distribution of organisms. * Habitat selection is one of the least-understood ecological processes, but it appears to play an important role in limiting the distribution of many species. Biotic factors affect the distribution of organisms. Negative interactions with other organisms in the form of predation, parasitism, disease, or competition may limit the ability of organisms to survive and reproduce. * Predator-removal experiments can provide information about how predators limit distribution of prey species. * Absence of other species may also limit distribution of a species. * For example, the absence of a specific pollinator or prey species may limit distribution of an organism. Abiotic factors affect the distribution of organisms. * The global distribution of organisms broadly reflects the influence of abiotic factors such as temperature, water, and sunlight. The environment is characterized by spatial and temporal heterogeneity. * Environmental temperature is an important factor in the distribution of organisms because of its effect on biological processes. * Very few organisms can maintain an active metabolism at very high or very low temperatures. * Some organisms have extraordinary adaptations to allow them to live outside the temperature range habitable for most other living things. * The variation in water availability among habitats is an important factor in species distribution. Most aquatic organisms are restricted to either freshwater or marine environments. * Terrestrial organisms face a nearly constant threat of desiccation and have adaptations to allow them to obtain and conserve water. * Sunlight provides the energy that drives nearly all ecosystems. * Intensity of light is not the most important factor limiting plant growth in most terrestrial environments, although shading by a forest canopy makes competition for light in the understory intense. * In aquatic environments, light intensity limits distribution of photosynthetic organisms. Every meter of water depth selectively absorbs 45% of red light and 2% of blue light passing through it. * As a result, most photosynthesis in aquatic environments occurs near the surface. * Photoperiod, the relative length of daytime and nighttime, is a reliable indicator of seasonal events and is an important cue for the development or behavior of many organisms. * Wind amplifies the effects of temperature by increasing heat loss due to evaporation and convection. It also increases water loss by increasing the rate of evaporative cooling in animals and transpiration in plants. The physical structure, pH, and mineral composition of soils and rocks limit distribution of plants and, thus, of the animals that feed upon them, contributing to the patchiness of terrestrial ecosystems. * In streams and rivers, substrate composition can affect water chemistry, affecting distribution of organisms. * In marine environments, the structure of substrates in the intertidal areas or seafloor limits the organisms that can attach to or burrow in those habitats. Four abiotic factors are the major components of climate. * Climate is the prevailing weather conditions in an area. Four abiotic factors—temperature, water, sunlight, and wind—are the major components of climate. * Climate patterns can be described on two scales. Macroclimate patterns are on global, regional, or local levels, and microclimate patterns are very fine patterns such as the conditions experienced by a community of organisms under a fallen log. * Climate determines the makeup of biomes, the major types of ecosystems. * Annual means for temperature and rainfall are reasonably well correlated with the biomes found in different regions. * Global climate patterns are determined by sunlight and Earth’s movement in space. The sun’s warming effect on the atmosphere, land, and water establishes the temperature variations, cycles of air movement, and evaporation of water that are responsible for latitudinal variations in climate. * Bodies of water and topographic features such as mountain ranges create regional climatic variations, while smaller features of the landscape affect local climates. * Ocean currents influence climate along the coast by heating or cooling overlying air masses, which may pass over land. * Coastal regions are generally moister than inland areas at the same latitude. In general, oceans and large lakes moderate the climate of nearby terrestrial environments. * In certain regions, cool, dry ocean breezes are warmed when they move over land, absorbing moisture and creating a hot, rainless climate slightly inland. * This Mediterranean climate pattern occurs inland from the Mediterranean Sea. * Ocean currents also influence climate in coastal areas. * Mountains have a significant effect on the amount of sunlight reaching an area, as well as on local temperature and rainfall. * In the Northern Hemisphere, south-facing slopes receive more sunlight than north-facing slopes, and are therefore warmer and drier. These environmental differences affect species distribution. * At any given latitude, air temperature declines 6°C with every 1,000-m increase in elevation. * This temperature change is equivalent to that caused by an 880-km increase in latitude. * As moist, warm air approaches a mountain, it rises and cools, releasing moisture on the windward side of the peak. * On the leeward side of the mountain, cool, dry air descends, absorbing moisture and producing a rain shadow. * Deserts commonly occur on the leeward side of mountain ranges. * The changing angle of the sun over the course of a year affects local environments. Belts of wet and dry air on either side of the equator shift with the changing angle of the sun, producing marked wet and dry seasons around 20° latitude. * Seasonal changes in wind patterns produce variations in ocean currents, occasionally causing the upwelling of nutrient-rich, cold water from deep ocean layers. * Lakes are also sensitive to seasonal temperature changes. * During the summer and winter, many temperate lakes are thermally stratified or layered vertically according to temperature. * These lakes undergo a semiannual mixing, or turnover, of their waters in spring and fall.
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Turnover brings oxygenated water to the bottom and nutrient-rich water to the surface. * Many features in the environment influence microclimates. * Forest trees moderate the microclimate beneath them. * Cleared areas experience greater temperature extremes than the forest interior. * A log or large stone shelters organisms, buffering them from temperature and moisture fluctuations. * Every environment on Earth is characterized by a mosaic of small-scale differences in abiotic factors that influence the local distribution of organisms. * Long-term climate changes profoundly affect the biosphere. One way to predict possible effects of current climate changes is to consider the changes that have occurred in temperate regions since the end of the last Ice Age. * Until about 16,000 years ago, continental glaciers covered much of North America and Eurasia. * As the climate warmed and the glaciers melted, tree distribution expanded northward. * A detailed record of these migrations is captured in fossil pollen in lake and pond sediments. * If researchers can determine the climatic limits of current geographic distributions for individual species, they can predict how that species distribution will change with global warming. A major question for tree species is whether seed dispersal is rapid enough to sustain the migration of the species as climate changes. * Consider the American beech, Fagus grandifolia. * Climate models predict that the northern and southern limit of the beech’s range will move 700–900 km north over the next century. * ? The beech will have to migrate 7–9 km per year to maintain its distribution. * However, since the Ice Age, the beech has migrated into its present rage at a rate of only 0. 2 km per year. * Without human assistance, the beech will become extinct. Concept 50. Abiotic and biotic factors influence the structure and dynamics of aquatic biomes * Varying combinations of biotic and abiotic factors determine the nature of the Earth’s biomes, major types of ecological associations that occupy broad geographic regions of land or water. Aquatic biomes occupy the largest part of the biosphere. * Ecologists distinguish between freshwater and marine biomes on the basis of physical and chemical differences. * Marine biomes generally have salt concentrations that average 3%, while freshwater biomes have salt concentrations of less than 1%. Marine biomes cover approximately 75% of the earth’s surface and have an enormous effect on the biosphere. * The evaporation of water from the oceans provides most of the planet’s rainfall. * Ocean temperatures have a major effect on world climate and wind patterns. * Photosynthesis by marine algae and photosynthetic bacteria produce a substantial proportion of the world’s oxygen. Respiration by these organisms consumes huge amounts of atmospheric carbon dioxide. * Freshwater biomes are closely linked to the soils and biotic components of the terrestrial biomes through which they pass. The pattern and speed of water flow and the surrounding climate are also important. * Most aquatic biomes are physically and chemically stratified. * Light is absorbed by the water and by photosynthetic organisms, so light intensity decreases rapidly with depth. * There is sufficient light for photosynthesis in the upper photic zone. * Very little light penetrates to the lower aphotic zone. * The substrate at the bottom of an aquatic biome is the benthic zone. * This zone is made up of sand and sediments and is occupied by communities of organisms called benthos. A major food source for benthos is dead organic material or detritus, which rains down from the productive surface waters of the photic zone. * Sunlight warms surface waters, while deeper waters remain cold. * As a result, water temperature in lakes is stratified, especially in summer and winter. * In the ocean and most lakes, a narrow stratum of rapid temperature change called a thermocline separates the more uniformly warm upper layer from more uniformly cold deeper waters. * In marine communities, phytoplankton, zooplankton, and many fish species live in the relatively shallow photic zone. The aphotic zone contains little life, except for microorganisms and relatively sparse populations of luminescent fishes and invertebrates. * The major aquatic biomes include lakes, wetlands, streams, rivers, estuaries, intertidal biomes, oceanic pelagic biomes, coral reefs, and marine benthic biomes. * Freshwater lakes vary greatly in oxygen and nutrient content. * Oligotrophic lakes are deep, nutrient poor, oxygen rich, and contain little life. * Eutrophic lakes are shallow, nutrient rich, and oxygen poor. * In lakes, the littoral zone is the shallow, well-lit water close to shore. * The limnetic zone is the open surface water. Wetlands are areas covered with sufficient water to support aquatic plants. * Wetlands include marshes, bogs, and swamps. * They are among the most productive biomes on Earth and are home to a diverse community of invertebrates and birds. * Because of the high organic production and decomposition in wetlands, their water and soil are low in dissolved oxygen. * Wetlands have a high capacity to filter dissolved nutrients and chemical pollutants. * Humans have destroyed many wetlands, but some are now protected. * Streams and rivers are bodies of water moving continuously in one direction. Headwaters are cold, clear, turbulent, and swift. * They carry little sediment and relatively few mineral nutrients. * As water travels downstream, it picks up O2 and nutrients on the way. * Nutrient content is largely determined by the terrain and vegetation of the area. * Many streams and rivers have been polluted by humans, degrading water quality and killing aquatic organisms. * Damming and flood control impairs the natural functioning of streams and rivers and threatens migratory species such as salmon. * Estuaries are areas of transition between river and sea. The salinity of these areas can vary greatly. * Estuaries have complex flow patterns, with networks of tidal channels, islands, levees, and mudflats. * They support an abundance of fish and invertebrate species and are crucial feeding areas for many species of waterfowl. * An intertidal zone is a marine biome that is periodically submerged and exposed by the tides. * The upper intertidal zone experiences longer exposure to air and greater variation in salinity and temperature than do the lower intertidal areas. * Many organisms live only at a particular stratum in the intertidal. The oceanic pelagic biome is the open blue water, mixed by wind-driven oceanic currents. * The surface waters of temperate oceans turn over during fall through spring. * The open ocean has high oxygen levels and low nutrient levels. * This biome covers 70% of the Earth’s surface and has an average depth of 4,000 meters. * Coral reefs are limited to the photic zone of stable tropic marine environments with high water clarity. They are found at temperatures between 18°C and 30°C. * They are formed by the calcium carbonate skeletons of coral animals. * Mutualistic dinoflagellate algae live within the tissues of the corals. Coral reefs are home to a very diverse assortment of vertebrates and invertebrates. * Collecting of coral skeletons and overfishing for food and the aquarium trade have reduced populations of corals and reef fishes. * Global warming and pollution contribute to large-scale coral mortality. * The marine benthic zone consists of the seafloor below the surface waters of the coastal or neritic zone and the offshore pelagic zone. * Most of the ocean’s benthic zone receives no sunlight. * Organisms in the very deep abyssal zone are adapted to continuous cold (about 3°C) and extremely high pressure. Unique assemblages of organisms are associated with deep-sea hydrothermal vents of volcanic origin on mid-ocean ridges. * The primary producers in these communities are chemoautotrophic prokaryotes that obtain energy by oxidizing H2S formed by a reaction of volcanically heated water with dissolved sulfate (SO42? ). Concept 50. 4 Climate largely determines the distribution and structure of terrestrial biomes * Because there are latitudinal patterns of climate over the Earth’s surface, there are also latitudinal patterns of biome distribution. A climograph denotes the annual mean temperature and precipitation of a region. * Temperature and rainfall are well correlated with different terrestrial biomes, and each biome has a characteristic climograph. * Most terrestrial biomes are named for major physical or climatic features or for their predominant vegetation. * Vertical stratification is an important feature of terrestrial biomes. * The canopy of the tropical rain forest is the top layer, covering the low-tree stratum, shrub understory, ground layer, litter layer, and root layer. * Grasslands have a canopy formed by grass, a litter layer, and a root layer. Stratification of vegetation provides many different habitats for animals. * Terrestrial biomes usually grade into each other without sharp boundaries. The area of intergradation, called the ecotone, may be narrow or wide. * The species composition of any biome differs from location to location. * Biomes are dynamic, and natural disturbance rather than stability tends to be the rule. * Hurricanes create openings for new species in tropical and temperate forests. * In northern coniferous forests, snowfall may break branches and small trees, producing gaps that allow deciduous species to grow. As a result, biomes exhibit patchiness, with several different communities represented in any particular area. * In many biomes, the dominant plants depend on periodic disturbance. * For example, natural wildfires are an integral component of grasslands, savannas, chaparral, and many coniferous forests. * Human activity has radically altered the natural patterns of periodic physical disturbance. * Fires are now controlled for the sake of agricultural land use. * Humans have altered much of the Earth’s surface, replacing original biomes with urban or agricultural ones. The major terrestrial biomes include tropical forest, desert, savanna, chaparral, temperate grassland, coniferous forest, temperate broadleaf forest, and tundra. * Tropical forests are found close to the equator. * Tropical rain forests receive constant high amounts of rainfall (200 to 400 cm annually). * In tropical dry forests, precipitation is highly seasonal. * In both, air temperatures range between 25°C and 29°C year round. * Tropical forests are stratified, and competition for light is intense. * Animal diversity is higher in tropical forests than in any other terrestrial biome. Deserts occur in a band near 30° north and south latitudes and in the interior of continents. * Deserts have low and highly variable rainfall, generally less than 30 cm per year. * Temperature varies greatly seasonally and daily. * Desert vegetation is usually sparse and includes succulents such as cacti and deeply rooted shrubs. * Many desert animals are nocturnal, so they can avoid the heat. * Desert organisms display adaptations to allow them to resist or survive desiccation. * Savanna is found in equatorial and subequatorial regions. * Rainfall is seasonal, averaging 30–50 cm per year. The savanna is warm year-round, averaging 24–29°C with some seasonal variation. * Savanna vegetation is grassland with scattered trees. * Large herbivorous mammals are common inhabitants. * The dominant herbivores are insects, especially termites. * Fire is important in maintaining savanna biomes. * Chaparrals have highly seasonal precipitation with mild, wet winters and dry, hot summers. * Annual precipitation ranges from 30 to 50 cm. * Chaparral is dominated by shrubs and small trees, with a high diversity of grasses and herbs. * Plant and animal diversity is high. * Adaptations to fire and drought are common. Temperate grasslands exhibit seasonal drought, occasional fires, and seasonal variation in temperature. * Large grazers and burrowing mammals are native to temperate grasslands. * Deep fertile soils make temperate grasslands ideal for agriculture, especially for growing grain. * Most grassland in North America and Eurasia has been converted to farmland. * Coniferous forest, or taiga, is the largest terrestrial biome on Earth. * Coniferous forests have long, cold winters and short, wet summers. * The conifers that inhabit these forests are adapted for snow and periodic drought. * Coniferous forests are home to many birds and mammals. These forests are being logged at a very high rate and old-growth stands of conifers may soon disappear. * Temperate broadleaf forests have very cold winters, hot summers, and considerable precipitation. * A mature temperate broadleaf forest has distinct vertical layers, including a closed canopy, one or two strata of understory trees, a shrub layer, and an herbaceous layer. * The dominant deciduous trees in Northern Hemisphere broadleaf forests drop their leaves and become dormant in winter. * In the Northern Hemisphere, many mammals in this biome hibernate in the winter, while many bird species migrate to warmer climates. Humans have logged many temperate broadleaf forests around the world. * Tundra covers large areas of the Arctic, up to 20% of the Earth’s land surface. * Alpine tundra is found on high mountaintops at all latitudes, including the tropics. * The plant communities in alpine and Arctic tundra are very similar. * The Artic tundra winter is long and cold, while the summer is short and mild. The growing season is very short. * Tundra vegetation is mostly herbaceous, consisting of a mixture of lichens, mosses, grasses, forbs, and dwarf shrubs and trees. A permanently frozen layer of permafrost prevents water infiltration and restricts root growth. * Large grazing musk oxen are resident in Arctic tundra, while caribou and reindeer are migratory. * Migratory birds use Arctic tundra extensively during the summer as nesting grounds. * Arctic tundra is sparsely settled by humans but has recently become the focus of significant mineral and oil extraction. Chapter 51 * The modern scientific discipline of behavioral ecology studies how behavior develops, evolves, and contributes to survival and reproductive success. Concept 51. Behavioral ecologists distinguish between proximate and ultimate causes of behavior * Scientific questions that can be posed about any behavior can be divided into two classes: those that focus on the immediate stimulus and mechanism for the behavior and those that explore how the behavior contributes to survival and reproduction. * What is behavior? * Behavioral traits are an important part of an animal’s phenotype. * Many behaviors result from an animal’s muscular activity, such as a predator chasing a prey. * In some behaviors, muscular activity is less obvious, as in bird song. Some nonmuscular activities are also behaviors, as when an animal secretes a pheromone to attract a member of the opposite sex. * Learning is also a behavioral process. * Put simply, behavior is everything an animal does and how it does it. * Proximate questions are mechanistic, concerned with the environmental stimuli that trigger a behavior, as well as the genetic, physiological, and anatomical mechanisms underlying a behavioral act. * Proximate questions are referred to as “how? ” questions. * Ultimate questions address the evolutionary significance of a behavior and why natural selection favors this behavior. Ultimate questions are referred to as “why? ” questions. * These two levels of causation are related. * Proximate mechanisms produce behaviors that evolved because they increase fitness in some way. * For example, increased day length has little adaptive significance for red-crowned cranes, but because it corresponds to seasonal conditions that increase reproductive success, such as the availability of food for feeding young birds, breeding when days are long is a proximate mechanism that has evolved in cranes. Classical ethology presaged an evolutionary approach to behavioral biology. In the mid-20th century, a number of pioneering behavioral biologists developed the discipline of ethology, the scientific study of animal behavior. * In 1963, Niko Tinbergen suggested four questions that must be answered to fully understand any behavior. 1. What is the mechanistic basis of the behavior, including chemical, anatomical, and physiological mechanisms? 2. How does development of the animal, from zygote to mature individual, influence the behavior? 3. What is the evolutionary history of the behavior? 4. How does the behavior contribute to survival and reproduction (fitness)? Tinbergen’s list includes both proximate and ultimate questions. 1. The first two, which concern mechanism and development, are proximate questions, while the second two are ultimate, or evolutionary, questions. * 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 FAP is triggered by an external sensory stimulus called a sign stimulus. 2. In the red-spined stickleback, the male attacks other males that invade his nesting territory. 3.
The stimulus for the attack is the red underside of the intruder. 4. A male stickleback will attack any model that has some red visible on it. * 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. * 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. * Imprinting is a type of behavior that includes learning and innate components and is generally irreversible. . Imprinting has a sensitive period, a limited phase in an animal’s behavior that is the only time that certain behaviors can be learned. * An example of imprinting is young geese following their mother. 6. In species that provide parental care, parent-offspring bonding is a critical time in the life cycle. * During the period of bonding, the young imprint on their parent and learn the basic behavior of the species, while the parent learns to recognize its offspring. 7. Among gulls, the sensitive period for parental bonding on young lasts one or two days. If bonding does not occur, the parent will not initiate care of the infant, leading to certain death of the offspring and decreasing the parent’s reproductive success. * How do young gulls know on whom—or what—to imprint? 8. The tendency to respond is innate in birds. 9. The world provides the imprinting stimulus, and young gulls respond to and identify with the first object they encounter that has certain key characteristics. * In greylag geese, the key stimulus is movement of the object away from the young. * A proximate explanation for young eese 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. * 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. * Early study of imprinting and fixed action patterns helped make the distinction between proximate and ultimate causes of behavior. 10.
They also helped to establish a strong tradition of experimental approaches in behavioral ecology. Concept 51. 2 Many behaviors have a strong genetic component Behavior results from both genes and environmental factors. * 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. * Behavior can be viewed in terms of the norm of reaction. We can measure the behavioral phenotypes for a particular genotype that develop in a range of environments. * In some cases, the behavior is variable, depending on environmental experience. * In other cases, nearly all individuals in the population exhibit identical behavior, despite internal and external environmental differences during development and throughout life. * Behavior that is developmentally fixed is called innate behavior. * Such behaviors are under strong genetic influence. * The range of environmental differences among individuals does not appear to alter innate behavior.
Many animal movements are under substantial genetic influence. * A kinesis is a simple change in activity or turning rate in response to a stimulus. * For example, sowbugs are more active in dry areas and less active in humid areas. * This increases the chance that they will leave a dry area and encounter a moist area. * A taxis is an automatic, oriented movement toward or away from a stimulus. * For example, many stream fishes exhibit positive rheotaxis, automatically swimming or orienting themselves in an upstream direction (toward the current). This keeps them from being swept away and keeps them facing in the direction in which food is coming. * Ornithologists have found that many features of migratory behavior in birds are genetically programmed. * Migration is the regular movement of animals over relatively long distances. * One of the best-studied migratory birds is the blackcap (Sylvia atricapilla), a small warbler that ranges from the Cape Verde Islands off the coast of West Africa to northern Europe. Animal communication is an essential component of interactions between individuals. Much of the social interaction between animals involves transmitting information through specialized behaviors called signals. * In behavioral ecology, a signal is a behavior that causes a change in another animal’s behavior. * The transmission, reception, and response to signals constitute animal communication. * Some features of animal communication are under strong genetic control, although the environment makes a significant contribution to all communication systems. * Animals communicate using visual, auditory, chemical, tactile, and electrical signals. The type of signal is closely related to an animal’s lifestyle and environment. * For example, nocturnal species use olfactory and auditory signals. * Birds are diurnal and have a poor olfactory sense. * They communicate primarily by visual and auditory signals. * 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. * Many animals secrete chemical substances called pheromones. * These chemicals are especially common in mammals and insects and often relate to reproductive behaviors. In honeybees, pheromones produced by the queens and her daughters (workers) maintain the hive’s very complex social order. * Male drones are attracted to the queen’s pheromone when they are outside the hive. * Pheromones can also function in nonreproductive behavior. * When a minnow is injured, an alarm substance is released from glands in the fish’s skin, inducing a fright response among other fish in the area. * They become more vigilant and group in tightly packed schools. * Pheromones are effective at very low concentrations. * The songs of most birds are at least partly learned. In contrast, in many species of insect, mating rituals include characteristic songs that are under direct genetic control. * Some insect species are morphologically identical and can be identified only through courtship songs or behaviors. Prairie vole mating and parental behaviors are under strong genetic influence. * Mating and parental behavior by male prairie voles (Microtus ochrogaster) are under strong genetic control. * Prairie voles and a few other vole species are monogamous, a social trait found in only 3% of mammalian species. 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. * Mated males are intensely aggressive to strange males or females, while remaining nonaggressive to their mate and pups. * Research by Thomas Insel at Emory University suggests that arginine-vasopressin (AVP), a nine-amino-acid neurotransmitter released in mating, mediates both pair-bond formation and aggression in male prairie voles. In the CNS, AVP binds to a receptor called the V1a receptor. * The researcher found significant differences in the distribution of V1a receptors between the brains of monogamous prairie voles and related promiscuous montane voles. * Insel inserted the prairie vole V1a receptor gene into laboratory mice. * The mice developed the same distribution of V1a receptors as the prairie voles and also showed many of the mating behaviors of the voles. * Thus, a single gene appears to mediate much of the complex mating and parental behavior of the prairie vole. Concept 51. Environment, interacting with an animal’s genetic makeup, influences the development of behaviors * Environmental factors modify many behaviors. * Diet plays an important role in mate selection by Drosophila mojavensis, which mates and lays its eggs in rotting cactus tissues. * Two populations of this fruit fly species use different species of cactus for their eggs. * Flies from each population were raised on artificial media in the lab. * Females would mate only with males from their own population. * The food eaten by male flies as larvae strongly nfluenced mate selection by female flies. * The proximate cause in the female mate choices was in the exoskeletons of the flies, assessed by the sense of taste in female flies. * When males from the other population were “perfumed” with hydrocarbons extracted from males of the same population, they were accepted by female flies. * The California mouse (Peromyscus californicus) is monogamous. * Like male prairie voles, male California mice are highly aggressive to other mice and provide considerable parental care. * Unlike prairie voles, even unmated California mice are aggressive. Researchers placed newborn California mice in the nests of white-footed mice (and vice versa). * White-footed mice are not monogamous and provide little parental care. * This cross-fostering changed the behavior of both species. * Cross-fostered California mice provided less parental care and were less aggressive toward intruders when they grew up and reared their own young. * Their brains had reduced levels of AVP, compared with California mice raised by their own parents. * White-footed mice reared by California mice were more aggressive as parents than those raised by their own parents. One of the most powerful ways that environmental conditions can influence behavior is through learning, the modification of behavior based on specific experiences. * Learned behaviors can be very simple, such as imprinting, or highly complex. * Habituation involves a loss of responsiveness to unimportant stimuli or stimuli that do not provide appropriate feedback. * For example, some animals stop responding to warning signals if signals are not followed by a predator attack (the “cry wolf” effect). 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. The fitness of an organism may be enhanced by the capacity for spatial learning. * Every natural environment shows spatial variation. * As a consequence, 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. * The fitness of an animal may be enhanced by the capacity for spatial learning. Niko Tinbergen found that digger wasps found their nest entrances by using landmarks, or location indicators, in their environment. * Landmarks must be stable within the time frame of the activity. * Because some environments are more stable than others, animals may use different kinds of information for spatial learning in different environments. * Sticklebacks from a river learned a maze by learning a pattern of movements. * Sticklebacks from a more stable pond environment used a combination of movements and landmarks to learn the maze. * The degree of environmental variability influences the spatial learning strategies of animals. Some animals form cognitive maps, internal codes of spatial relationships of objects in their environment. * It is difficult to distinguish experimentally between the use of landmarks and the development of a true cognitive map. * Researchers have obtained good evidence that corvids (a bird family including ravens, crows, and jays) use cognitive maps. * Many corvids store food in caches and retrieve it later. * Pinyon jays may store nuts in as many as a thousand widely dispersed caches, keeping track of location and food quality (based on time since the food was stored). Birds can learn that caches are halfway between two landmarks. Many animals can learn to associate one stimulus with another. * Associative learning is the ability of animals to learn to associate one stimulus with another. * Classical conditioning is a type of associative learning. * Researchers trained Drosophila melanogaster to avoid air carrying a particular scent by coupling exposure to the odor with an electrical shock. * Drosophila has a surprising capacity for learning. * Associative learning may play an important role in helping animals to avoid predators. Zebra fish, an Asian minnow, and pike, an American predatory fish, do not occur together in the wild. * Researchers exposed zebra fish in an experimental group to an influx of 20 mL of water containing an alarm substance and then, 5 minutes later, to 20 mL of water with pike odor. * Zebra fish had no innate negative reaction to pike odor, but learned to associate pike odor with the alarm substance. * The zebra fish were conditioned to associate pike odor with the alarm substance. * 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. An example is the mouse eating the poisonous caterpillar and learning to avoid such caterpillars in the future. The study of cognition connects behavior with nervous system function. * The term cognition is variously defined. * In a narrow sense, it is synonymous with consciousness or awareness. * In a broad sense, animal cognition is the ability of an animal’s nervous system to perceive, store, process, and use information gathered by sensory receptors. * The study of animal cognition, called cognitive ethology, examines the connection between an animal’s nervous system and its behavior. One area of research investigates how an animal’s brain represents physical objects in the environment. * Cognitive ethnologists have discovered that many animals, including insects, categorize objects in their environment as “same” or “different. ” * Primates, dolphins, and corvids (crow, ravens, and jays) are capable of novel problem-solving behavior. * Individual animals may show great individual variation in the way they attempt to solve a problem. * Many animals solve problems by observing the behavior of other individuals. * Chimpanzees learn to solve problems by copying the behavior of other chimpanzees. Concept 51. Behavioral traits can evolve by natural selection * Because of the influence of genes on behavior, natural selection can result in the evolution of behavioral traits in populations. Behavior varies in natural populations. * Behavioral differences between closely related species are common. * Males of different Drosophila species sing different courtship songs. * Species of voles differ in paternal care. * Although less obvious, significant differences in behavior can be found within animal species. * When behavioral variation within a species corresponds to variation in environmental conditions, it may be evidence of past evolution. One of the best-known examples of genetically based variation in behavior within a species is prey selection by the garter snake Thamnophis elegans. * Coastal garter snakes feed on salamanders, frogs, and toads, but mainly on slugs. * Inland snakes eat frogs, leeches, and fish, but not slugs. * Stevan Arnold investigated this variation. * He offered slugs to snakes from both populations, but only coastal snakes readily accepted the slugs. * He tested newborn snakes born in the laboratory and found that 73% of young snakes from coastal mothers attacked slugs they were offered. Only 35% of naive snakes from inland mothers attacked the slugs. * Arnold proposed that when inland snakes colonized coastal environments 10,000 years ago, a small fraction of the population had the ability to recognize slugs by chemoreception. * These snakes took advantage of the abundant food source that slugs represented and had higher fitness than snakes that ignored slugs. * The capacity to recognize slugs as prey increased in frequency in coastal populations. * The funnel web spider Agelenopsis aperta lives in riparian zones and the surrounding arid environment in the western United States. The spider’s web is a silken sheet ending in a hidden funnel, where the spider sits and watches for food while foraging. * When prey strikes the web, the spider runs out across the web to make its capture. * Riechert and her colleagues found a striking contrast in the behavior of spiders in riparian forests and those in arid habitats. * In arid, food-poor habitats, A. aperta is more aggressive to potential prey and to other spiders in defense of its web, and it returns to foraging more quickly following disturbance. Hedrick and Riechert reared spiders in the lab and found that the differences in aggressiveness between desert and riparian spiders are genetic. * Highly productive riparian sites are rich in prey for spiders, but the density of bird predators is also high. * The timid behavior of A. aperta in riparian habitats was selected for by predation risk. Experiments provide evidence for behavioral evolution. * Researchers are carrying out experiments on organisms with short life ps, looking for evidence of evolution in laboratory populations. * Marla Sokolowski studied a polymorphism in a gene for foraging in Drosophila melanogaster. The gene is called for, and it has two alleles. * One allele, forR, results in a “rover” phenotype in which the fly larva moves more than usual. * The other allele, forS, results in a “sitter” phenotype in which the fly larva moves less than usual. * Sokolowski reared Drosophila at high and low population densities for 74 generations. * The forS allele increased in low-density populations, while forR increased in high-density populations. * At low densities, short-distance foraging yielded sufficient food. * At high densities, long-distance foraging helped the larvae to move beyond areas of food depletion. Peter Berthold and his colleagues captured 20 male and 20 female blackcaps wintering in Britain and transported them to southwest Germany. * The birds were caged in glass-covered funnel cages lined with carbon paper. * As the birds moved around the funnels, the marks they made on the paper showed the direction they were trying to migrate. * The migratory orientation of wintering adult birds captured in Britain was similar to their laboratory-reared offspring. * Young birds originally from Germany had a very different migratory orientation. This study indicates a genetic basis for migratory orientation of the young birds. * Has the behavior evolved over time? * Berthold’s study suggests that the change in migratory behavior of the blackcaps is recent and rapid, having taken place over the past 50 years. * Before 1960, there were no westward-migrating blackcaps in Germany. * By the 1990s, westward migrants made up 7–11% of the blackcap populations of Germany. * Berthold suggested that westward migrants benefited from their new behavior, due to the milder winter climate and greater abundance of bird feeders in Britain. Concept 51. Natural selection favors behaviors that increase survival and reproductive success * The genetic components of behavior evolve through natural selection favoring traits that enhance survival and reproductive success in a population. * Two of the most direct ways that behavior can affect fitness are through influences on foraging and mate choice. * Foraging includes not only eating, but also any mechanisms that an animal uses to recognize, search for, and capture food items. * 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 nd risk of predation while foraging. * Natural selection should favor foraging behavior that minimizes the costs of foraging and maximizes the benefits. * Behavioral ecologists apply cost-benefit analysis to study the proximate and ultimate causes of diverse foraging strategies. * Reta Zach of the University of British Columbia carried out a cost-benefit analysis of feeding behavior in crows. * Crows search the tide pools of Mandarte Island, B. C. , for snails called whelks. * A crow flies up and drops the whelk onto the rocks to break its shell. * If the drop is successful, the crow eats the snail’s soft body. If it is not successful, the crow flies higher and tries again. * Zach predicted—and found—that crows would, on average, fly to a height that would provide the most food relative to the total amount of energy required to break the whelk shells. * Bluegill sunfish feed on small crustaceans called Daphnia, selecting larger individuals that supply the most energy per unit time. * Smaller individuals will be selected if larger prey are too far away. * Optimal foraging theory predicts that the proportion of small to large prey captured will vary with prey density. At high densities, it is efficient for bluegill sunfish to feed only on large crustaceans. * At low densities, bluegill sunfish should exhibit little size selectivity because all prey are needed to meet energy requirements. * In experiments, young bluegill sunfish forage efficiently but not as close to optimum as older individuals. * Perhaps younger fish do not judge size and distance as accurately because their vision is not yet completely developed. * Learning may also improve the foraging efficiency of bluegill sunfish as they age. * Risk of predation is one of the most significant potential costs to a forager. Mule deer are preyed on by mountain lions throughout their range. * Researchers studied mule deer populations in Idaho to determine if they forage in a way that reduces their risk of falling prey to mountain lions. * The researchers found that food available to mule deer was fairly uniform across the potential foraging area. * Risk of predation varied greatly, however. * Mountain lions killed most mule deer at forest edges. * Few were killed in open areas and forest interiors. * How does mule deer feeding behavior respond to the differences in feeding risk? Mule deer feed predominantly in open areas, avoiding forest edges and forest interiors. * When deer are at the forest edge, they spend significantly more time scanning their surroundings than when they are in other areas. * Mating behavior, which includes seeking and attracting mates, choosing among potential mates, and competing for mates, is the product of a form of natural selection called sexual selection. * The mating relationship between males and females varies a great deal from species to species. * In many species, mating is promiscuous, with no strong pair-bond or lasting relationships. In species where the mates remain together for a longer period, the relationship may be monogamous (one male mating with one female) or polygamous (one individual mating with several partners). * Polygamous relationships may involve a single male and many females (polygyny) or a single female and many males (polyandry). * Among monogamous species, males and females are often so much alike morphologically that they are impossible to distinguish based on external characteristics. * Polygynous species are generally dimorphic, with males being larger and more showy. In polyandrous species, females are ornamented and larger than males. * The needs of young are an important factor constraining the evolution of mating systems. * Parental investment refers to the time and resources expended for the raising of offspring. * Most newly hatched birds cannot care for themselves and require a large, continuous food supply that a single parent cannot provide. * In such cases, a male will have more successful offspring if he helps his partner to rear their chicks than if he goes off to seek more mates. * This is why most birds are monogamous. Birds with young that can feed and care for themselves from birth, such as pheasant and quail, have less need for parents to stay together. * Males of these species can maximize their reproductive success by seeking other mates. * In mammals, the lactating female is often the only food source for the young, and males play no role in caring for them in most mammal species. * In some mammal species, males protect many females and their young. * Certainty of paternity can influence mating systems and parental care. * If the male is unsure if offspring are his, parental investment is likely to be lower. Females can be sure that they contributed to an offspring when they give birth or lay eggs. * Males do not have that assurance because the acts of mating and birth are separated over time. * Males in many species with internal fertilization engage in behaviors that appear to increase their certainty of paternity, including guarding females, removing sperm from the female’s reproductive tract before copulation, and introducing large numbers of sperm to displace the sperm of other males. * Certainty of paternity is much higher when egg laying and mating occur together, in external fertilization. Parental care in aquatic invertebrates, fishes, and amphibians, when it occurs, is as likely to be by males as females. * Male parental care occurs in only 7% of fish and amphibian families with internal fertilization and in 69% of families with external fertilization. * The expression certainty of paternity does not imply conscious awareness of paternity by the father. Sexual selection is a form of natural selection. * Sexual dimorphism within a species results from sexual selection, a form of natural selection in which differences in reproductive success among individuals are a consequence of differences in mating success. Sexual selection can take the form of intersexual selection, in which members of one sex choose mates on the basis of particular characteristics of the other sex—such as courtship songs, or intrasexual selection, which involves competition among members of one sex for mates. * Mate preferences by females may play a central role in the evolution of male behavior and anatomy through intersexual selection. * Witte and Sawka experimented to see whether imprinting by young zebra finches on their parents influenced their choice of mates when they matured. They taped a red feather to the heads of both parents, male parent only, or female parent only, before the young chicks opened their eyes. * Control zebra finches were reared by unadorned parents. * When the chicks matured, they were given a choice of ornamented or unornamented mate finches. * Males showed no preference, but females reared by ornamented fathers preferred ornamented mates. * These results suggest that females imprint on their fathers and that mate choice by female zebra finches has played a key role in evolution of ornamentation in male zebra finches. Courtship behaviors of stalk-eyed flies are fascinating. * Males have elongated eyestalks, which they display to females during courtship. * Females prefer to mate with males with relatively long eyestalks. * How is this preference adaptive for females? * Researchers have correlated certain genetic disorders in male flies with an inability to develop long eyestalks. * Males with long eyestalks may be demonstrating their genetic quality to females. * In general, ornaments such as long eyestalks and brightly colored feathers correlate with a male’s health and vitality. A female that chooses a healthy male increases the chance that her offspring will be healthy. * Males compete with each other by (often ritualized) agonistic behaviors that determine which competitors gain access to resources. * The outcome of such contests may be determined by strength or size. * In some species, more than one mating behavior can result in successful reproduction. * In such cases, intrasexual selection has led to the evolution of alternative male mating behavior and morphology. Alternative male mating behaviors have been documented in the marine intertidal isopod Paracerceis sculpta, which lives in sponges in the Gulf of California. * This species includes three genetically distinct male types—alpha, beta, and gamma. * Large alpha males defend harems of females within intertidal sponges, largely against other alpha males. * Beta males mimic female morphology and behavior and gain access to guarded harems. * Tiny gamma males invade and live within large harems. * The mating success of each type of isopod depends on the relative density of males and females in the sponges. The alpha males sire the majority of young when defending a single female. * If more than one female is present, beta males father 60% of the offspring. * The reproductive rate of gamma males increases linearly with harem size. * Overall, all three types of males have approximately equal mating success, and variation among males in this species is sustained by natural selection. Game theory can model behavioral strategies. * Game theory evaluates alternative strategies in situations where the outcome depends on each individual’s strategies and the strategies of other individuals. Barry Sinervo and Curt Lively used game theory to account for the existence of three different male phenotypes in populations of side-blotched lizards (Uta stansburiana). * Males have three genetically controlled colors: orange throats, blue throats, and yellow throats. * Orange-throat males are the most aggressive and defend large territories with many females. * Blue-throat males are also aggressive but defend smaller territories with fewer females. * Yellow-throat males are nonterritorial and use sneaky tactics to mimic females and sneak copulations. Frequency of the three types of males varies from year to year. * Modeling showed that the relative success of different males varies with the abundance of other types of males. * When blue-throat males are abundant, they can defend their few females from the sneaky yellow-throat males. * However, they cannot defend their territories against the aggressive orange-throat males. * Orange-throat males take over large territories but cannot defend large numbers of females against the sneaky yellow-throat males. * Yellow-throat males then increase in numbers but are defeated by the blue-throat males. The cycle continues. Concept 51. 6 The concept of inclusive fitness can account for most altruistic social behavior * Most social behaviors are selfish, meaning that they benefit the individual at the expense of others, especially competitors. * Behavior that maximizes an individual’s survival and reproductive success is favored by selection, regardless of its effect on other individuals. * How do we account for behaviors that help others? * Altruism is defined as behavior that appears to decrease individual fitness but increases the fitness of others. Belding’s ground squirrel lives in some mountainous regions of the western United States. * The squirrel is vulnerable to predators such as coyotes and hawks. * If a squirrel sees a predator approach, it often gives a high-pitched alarm call, which alerts unaware individuals. * The alerted squirrels then retreat to their burrows. * This conspicuous alarm behavior calls attention to the caller, who has a greater risk of being killed. * In honeybees, workers are sterile but labor on behalf of a single fertile queen. * Workers will sacrifice themselves to sting intruders in defense of the hive. Naked mole rats are highly social rodents that live in underground chambers and tunnels in Africa. * These rodents are hairless and nearly blind and live in colonies of 75–250 individuals. * Each colony has only one reproducing female, the queen, who mates with one to three males, called kings. * The rest of the colony consists of nonreproductive females and males who forage for underground roots and tubers and care for the kings, queen, and young rats. * How can a naked mole rat (or a honeybee or a ground squirrel) enhance its fitness by helping other members of the population? * How is altruistic behavior maintained by evolution? If related individuals help each other, they are, in effect, helping keep their own genes in the population. * Inclusive fitness is defined as the effect an individual has on proliferating its own genes by reproducing and by helping relatives raise offspring. * William Hamilton proposed a quantitative measure for predicting when natural selection should favor altruistic acts. * Hamilton’s rule states the conditions under which altruistic acts will be favored by natural selection. * The three key variables are as follows: * The benefit to the recipient is B. * The cost to the altruist is C. The coefficient of relatedness is r, which equals the probability that a particular gene present in one individual will also be inherited from a common parent or ancestor in a second individual. * The rule is as follows: * rB > C * The more closely related two individuals are, the greater the value of altruism. * Kin selection is the mechanism of inclusive fitness, where individuals help relatives raise young. * Some animals behave altruistically toward others who are not close relatives. * Such behavior can be adaptive if the aided individual can be counted on to return the favor in the future. This exchange of aid is called reciprocal altruism and is commonly used to explain altruism between unrelated humans. * Reciprocal altruism is limited to species with stable social groups in which individuals have many opportunities to exchange aid and where there would be negative social consequences for those who “cheat” and refuse to return favors to those who have helped them in the past. * However, because cheating may provide a large benefit to cheaters, behavioral ecologists have questioned how reciprocal altruism could arise. * To answer this question, behavioral ecologists have turned to game theory. Axelrod and Hamilton found that reciprocal altruism can evolve and persist in a population where individuals adopt a behavioral strategy called tit for tat. * In this strategy, an individual treats another individual the same way it was treated the last time they met. * Individuals are always altruistic, or cooperative, on the first encounter, and will remain so as long as their altruism is reciprocated. * When it is not, they will retaliate immediately but will return to cooperative behavior as soon as the other individual becomes cooperative. Animals learn by observing others. Social learning is learning through observing others. * Social learning forms the roots of culture, which can be defined as a system of information transfer through social learning or teaching. * Cultural transfer of information has the potential to alter behavioral phenotypes and influence the fitness of individuals. * Social learning is not restricted to humans. * In many species, mate choice is strongly influenced by social learning. * Mate choice copying, a behavior in which individuals in a population copy the mate choices of others, has been extensively studied in the guppy Poecilia reticulata. Female guppies prefer to mate with males having a high percentage of orange coloration. * However, if a female sees another female engaging in courtship with a male with relatively little orange, she will choose a male with little orange herself. * Below a certain threshold of difference in mate color, mate choice copying by female guppies can mask genetically controlled female preference for orange males. * What is the advantage for females? * A female that mates with males that are attractive to other females may increase the probability that her male offspring will also be attractive and have high reproductive success. In their studies of vervet monkeys in Amboseli National Park, Kenya, Dorothy Cheny and Richard Seyfarth found that performance of a behavior can improve through learning. * Vervet monkeys (Cercopithecus aethiops) produce a complex set of alarm calls. * Distinct alarm calls warn of leopards, eagles, or snakes, all of which prey on the small vervets. * Vervets react to each alarm differently, depending on the threat. * Infant vervets give alarm calls but in an undiscriminating way. * For example, they call “eagle” for any bird. With age, they improve their accuracy. * Vervets learn how to give the right call by observing other members of the group and by receiving social confirmation for accurate calls. Sociobiology places social behavior in an evolutionary context. * Human culture is related to evolutionary theory in the discipline of sociobiology, whose main premise is that certain behavioral characteristics exist because they are expressions of genes that have been perpetuated by natural selection. * In his seminal 1975 book Sociobiology: The New Synthesis, E. O.
Wilson speculated about the evolutionary basis of certain kinds of social behavior in nonhuman animals, but he also included human culture, sparking a heated debate. * The spectrum of possible human social behaviors may be influenced by our genetic makeup, but that is very different from saying that genes are rigid determinants o
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