50-54 Flashcards
CONCEPT: Sensory receptors transduce stimulus energy and transmit signals to the central nervous system
(pp. 1085–1090) - Sensory receptors - sensory transduction - transmission - Mechanoreceptors - Chemoreceptors - Electromagnetic receptors - thermoreceptors - nociceptors
Sensory receptors
are usually specialized neurons or epithelial cells that detect external or internal stimuli
sensory transduction
The detection of a stimulus by sensory cells precedes sensory transduction, the change in the membrane potential of a sensory receptor in response to a stimulus
transmission
The resulting receptor potential controls transmission of action potentials to the CNS, where sensory information is integrated to generate perceptions
stimulus strength.
The frequency of action potentials in an axon and the number of axons activated determine stimulus strength
five basic types of sensory receptors
Mechanoreceptors: respond to stimuli such as pressure, touch, stretch, motion, and sound. Chemoreceptors: detect either total solute concentrations or specific molecules. Electromagnetic receptors: detect different forms of electromagnetic radiation. Thermoreceptors signal: surface and core temperatures of the body Nociceptors: Pain is detected by a group of nociceptors that respond to excess heat, pressure, or specific classes of chemicals
CONCEPT: The mechanoreceptors responsible for hearing and equilibrium detect moving fluid or settling particles
(pp. 1090–1094) • Most invertebrates sense their orientation with respect to gravityby means of statocysts. Specialized hair cells form thebasis for hearing and balance in mammals and for detection of water movement in fishes and aquatic amphibians. In mammals, the tympanic membrane (eardrum) transmits sound waves to three small bones of the middle ear, which transmit the waves through the oval window to the fluid in the coiled cochlea of the inner ear. Pressure waves in the fluid vibrate the basilar membrane, depolarizing hair cells and triggering action potentials that travel via the auditory nerve to the brain. Each region of the basilar membrane vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex. Receptors in the inner ear function in balance and equilibrium.
Statocysts.
Most invertebrates sense their orientation with respect to gravity by means of statocysts. Specialized hair cells form the basis for hearing and balance in mammals and for detection of water movement in fishes and aquatic amphibians
Tympanic membrane
In mammals, the tympanic membrane (eardrum) transmits sound waves to three small bones of the middle ear, which transmit the waves through the oval window to the fluid in the coiled cochlea of the inner ear.
basilar membrane
Pressure waves in the fluid vibrate the basilar membrane, depolarizing hair cells and triggering action potentials that travel via the auditory nerve to the brain. Each region of the basilar membrane vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex. Receptors in the inner ear function in balance and equilibrium.
CONCEPT Visual receptors in diverse animals depend on light-absorbing pigments
(pp. 1095–1101) • Invertebrates have varied light detectors, including simple lightsensitive eyespots, image-forming compound eyes, and singlelens eyes. In the vertebrate eye, a single lens is used to focus light on photoreceptors in the retina. Both rods and cones contain a pigment, retinal, bonded to a protein (opsin). Absorption of light by retinal triggers a signal transduction pathway that hyperpolarizes the photoreceptors, causing them to release less neurotransmitter. Synapses transmit information from photoreceptors to cells that integrate information and convey it to the brain along axons that form the optic nerve.
CONCEPT The senses of taste and smell rely on similar sets of sensory receptors
(pp. 1101–1103) Both taste (gustation) and smell (olfaction) depend on the stimulation of chemoreceptors by small dissolved molecules that bind to proteins on the plasma membrane. In humans, sensory cells within taste buds express a single receptor type specific for one of the five taste perceptions—sweet, sour, salty, bitter, and umami (elicited by glutamate). Olfactory receptor cells line the upper part of the nasal cavity and extend axons to the olfactory bulb of the brain. More than 1,000 genes code for membrane proteins that bind to specific classes of odorants, and each receptor cell appears to express only one of those genes.
CONCEPT The physical interaction of protein filaments is required for muscle function
(pp. 1103–1110) The muscle cells (fibers) of vertebrate skeletal muscle contain myofibrils composed of thin filaments of (mostly) actin and thick filaments of myosin. Motor neurons release acetylcholine, triggering action potentials that penetrate the muscle fiber along the T tubules and stimulate the release of Ca2 from the sarcoplasmic reticulum. When the Ca2 binds the troponin complex, tropomyosin repositions on the thin filaments, exposing the myosin-binding sites on actin and thus initiating cross-bridge formation. A motor unit consists of a motor neuron and the muscle fibers it controls. Recruiting multiple motor units results in stronger contractions. A twitch results from a single action potential in a motor neuron. Cardiac muscle, found only in the heart, consists of striated cells that are electrically connected by intercalated disks and that can generate action potentials without input from neurons.
CONCEPT Skeletal systems transform muscle contraction into locomotion
(pp. 1110–1115) Skeletal muscles, often in antagonistic pairs, bring about movement by contracting and pulling against the skeleton. Skeletons may be hydrostatic and maintained by fluid pressure, as in worms; hardened into exoskeletons, as in insects; or in the form of endoskeletons, as in vertebrates. • Each form of locomotion—swimming, movement on land, or flying—presents a particular challenge. For example, swimmers need to overcome friction, but face less of a challenge from gravity than do animals that move on land or fly. Animals specialized for swimming expend less energy per distance traveled than similarly sized animals specialized for flying or running. For any of the three major modes of locomotion, larger animals are more efficient than smaller ones.
50:1 test Which of the following sensory receptors is incorrectly paired with its category? a. hair cell—mechanoreceptor b. muscle spindle—mechanoreceptor c. taste receptor—chemoreceptor d. rod—electromagnetic receptor e. olfactory receptor—electromagnetic receptor
e
50:1 test The middle ear converts a. air pressure waves to fluid pressure waves. b. fluid pressure waves to air pressure waves. c. air pressure waves to nerve impulses. d. fluid pressure waves to nerve impulses. e. pressure waves to hair cell movements.
a
50:1 test During the contraction of a vertebrate skeletal muscle fiber, calcium ions a. break cross-bridges by acting as a cofactor in the hydrolysis of ATP. b. bind with troponin, changing its shape so that the myosin-binding sites on actin are exposed. c. transmit action potentials from the motor neuron to the muscle fiber. d. spread action potentials through the T tubules. e. re-establish the polarization of the plasma membrane following an action potential.
b
50:2 test Which sensory distinction is not encoded by a difference in neuron identity? a. white and red d. salty and sweet b. red and green e. spicy and cool c. loud and faint
c
50:2 test The transduction of sound waves into action potentials takes place: a. within the tectorial membrane as it is stimulated by the hair cells. b. when hair cells are bent against the tectorial membrane, causing them to depolarize and release neurotransmitter that stimulates sensory neurons. c. as the basilar membrane becomes more permeable to sodium ions and depolarizes, initiating an action potential in a sensory neuron. d. as the basilar membrane vibrates at different frequencies in response to the varying volume of sounds. e. within the middle ear as the vibrations are amplified by the malleus, incus, and stapes.
b
50:3 test Although some sharks close their eyes just before they bite, their bites are on target. Researchers have noted that sharks often misdirect their bites at metal objects and that they can find batteries buried under sand. This evidence suggests that sharks keep track of their prey during the split second before they bite in the same way that: a. a rattlesnake finds a mouse in its burrow. b. a male silkworm moth locates a mate. c. a bat finds moths in the dark. d. a platypus locates its prey in a muddy river. e. a flatworm avoids light places.
d
CONCEPT Earth’s climate varies by latitude and season and is changing rapidly
(pp. 1144–1150) • Global climate patterns are largely determined by the input of solar energy and Earth’s revolution around the sun. • The changing angle of the sun over the year, bodies of water, and mountains exert seasonal, regional, and local effects on macroclimate. •Fine-scale differences in abiotic (nonliving) factors, such as sunlight and temperature, determine microclimate. • Increasing greenhouse gas concentrations in the air are warming Earth and altering the distributions of many species. Some species will not be able to shift their ranges quickly enough to reach suitable habitat in the future.
climate
Global climate patterns are largely determined by the input of solar energy and Earth’s revolution around the sun.
macroclimate.
changing angle of the sun over the year, bodies of water, and mountains exert seasonal, regional, and local effects
abiotic
abiotic (nonliving) factors. Fine-scale differences in abiotic (nonliving) factors, such as sunlight and temperature, determine microclimate.
Suppose global air circulation suddenly reversed, with most air ascending at 30° north and south latitude and descending at the equator. At what latitude would you most likely find deserts in this scenario?
Because dry air would descend at the equator instead of at 30° north and south latitude (where deserts exist today), deserts would be more likely to exist along the equator (see Figure 52.3
CONCEPT The structure and distribution of terrestrial biomes are controlled by climate and disturbance
(pp. 1150–1156) • Climographs show that temperature and precipitation are correlated with biomes. Because other factors also play roles in biome location, biomes overlap. • Terrestrial biomes are often named for major physical or climatic factors and for their predominant vegetation. Vertical layering is an important feature of terrestrial biomes. • Disturbance, both natural and human-induced, influences the type of vegetation found in biomes. Humans have altered much of Earth’s surface, replacing the natural terrestrial communities described and depicted in Figure 52.12 with urban and agricultural ones.
Climographs
show that temperature and precipitation are correlated with biomes
biomes
?? Because other factors also play roles in biome location, biomes overlap.
Terrestrial biomes
are often named for major physical or climatic factors and for their predominant vegetation. Vertical layering is an important feature of terrestrial biomes
Disturbance
both natural and human-induced, influences the type of vegetation found in biomes. Humans have altered much of Earth’s surface, replacing the natural terrestrial communities described and depicted in Figure 52.12 with urban and agricultural ones.
CONCEPT Aquatic biomes are diverse and dynamic systems that cover most of Earth
(pp. 1157–1163) •Aquatic biomes are characterized primarily by their physical environment rather than by climate and are often layered with regard to light penetration, temperature, and community structure. Marine biomes have a higher salt concentration than freshwater biomes. • In the ocean and in most lakes, an abrupt temperature change called a thermocline separates a more uniformly warm upper layer from more uniformly cold deeper waters.
Aquatic biomes
characterized primarily by their physical environment rather than by climate and are often layered with regard to light penetration, temperature, and community structure. Marine biomes have a higher salt concentration than freshwater biomes.
Thermocline
an abrupt temperature change separating a more uniformly warm upper layer from more uniformly cold deeper waters
In which aquatic biomes might you find an aphotic zone?
An aphotic zone is most likely to be found in the deep waters of a lake, the oceanic pelagic zone, or the marine benthic zone.
CONCEPT Interactions between organisms and the environment limit the distribution of species
(pp. 1163–1167) Ecologists want to know not only where species occur but also why those species occur where they do. The distribution of species may be limited by dispersal, the movement of individuals away from their area of origin; behavior; biotic (living) factors; and abiotic factors, such as temperature extremes, salinity, and water availability.
dispersal
the movement of individuals away from their area of origin;
52:1 TEST Which of the following areas of study focuses on the exchange of energy, organisms, and materials between ecosystems? a. population ecology b. organismal ecology c. landscape ecology d. ecosystem ecology e. community ecology
c
52:1 TEST Which lake zone would be absent in a very shallow lake? a. benthic zone b. aphotic zone c. pelagic zone d. littoral zone e. limnetic zone
b
52:1 TEST Which of the following is true with respect to oligotrophic lakes and eutrophic lakes? a. Oligotrophic lakes are more subject to oxygen depletion. b. Rates of photosynthesis are lower in eutrophic lakes. c. Eutrophic lake water contains lower concentrations of nutrients. d. Eutrophic lakes are richer in nutrients. e. Sediments in oligotrophic lakes contain larger amounts of decomposable organic matter.
d
52:1 TEST Which of the following biomes is correctly paired with the description of its climate? a. savanna—low temperature, precipitation uniform during the year b. tundra—long summers, mild winters c. temperate broadleaf forest—relatively short growing season, mild winters d. temperate grasslands—relatively warm winters, most rainfall in summer e. tropical forests—nearly constant day length and temperature
e
52:2 TEST Which of the following is characteristic of most terrestrial biomes? a. annual average rainfall in excess of 250 cm b. a distribution predicted almost entirely by rock and soil patterns c. clear boundaries between adjacent biomes d. vegetation demonstrating vertical layering e. cold winter months
d
52:2 TEST The oceans affect the biosphere in all of the following ways except a. producing a substantial amount of the biosphere’s oxygen. b. removing carbon dioxide from the atmosphere. c. moderating the climate of terrestrial biomes. d. regulating the pH of freshwater biomes and terrestrial groundwater. e. being the source of most of Earth’s rainfall
d
52:2 TEST Which statement about dispersal is false? a. Dispersal is a common component of the life cycles of plants and animals. b. Colonization of devastated areas after floods or volcanic eruptions depends on dispersal. c. Dispersal occurs only on an evolutionary time scale. d. Seeds are important dispersal stages in the life cycles of most flowering plants. e. The ability to disperse can expand the geographic distribution of a species.
c
52:2 TEST When climbing a mountain, we can observe transitions in biological communities that are analogous to the changes a. in biomes at different latitudes. b. at different depths in the ocean. c. in a community through different seasons. d. in an ecosystem as it evolves over time. e. across the United States from east to west.
a
52:2 TEST Suppose that the number of bird species is determined mainly by the number of vertical strata found in the environment. If so, in which of the following biomes would you find the greatest number of bird species? a. tropical rain forest b. savanna c. desert d. temperate broadleaf forest e. temperate grassland
a
52:3 TEST If the direction of Earth’s rotation reversed, the most predictable effect would be a. no more night and day. b. a big change in the length of the year. c. winds blowing from west to east along the equator. d. a loss of seasonal variation at high latitudes. e. the elimination of ocean currents.
c
CONCEPT Discrete sensory inputs can stimulate both simple and complex behaviors
(pp. 1118–1122) • Behavior is the sum of responses to external and internal stimuli and includes muscular as well as nonmuscular activity. Tinbergen developed a set of questions that highlight the complementary nature of two perspectives. Proximate, or “how,” questions focuson the environmental stimuli, if any, that trigger a behavior, as well as the genetic, physiological, and anatomical mechanisms underlying a behavioral act. Ultimate, or “why,” questions address the evolutionary significance of a behavior. • A fixed action pattern is a largely invariant behavior triggered by a simple cue known as a sign stimulus. Migratory movements involve navigation, which can be based on orientation relative to the sun, the stars, or Earth’s magnetic field. Animal behavior is sometimes synchronized to the daily, or circadian, cycle of light and dark in the environment or to environmental cues that cycle over the seasons. • The transmission and reception of signals constitute animal communication. Animals use visual, auditory, chemical (usually olfactory), and tactile signals, sometimes as part of a stimulus-response chain that governs a complex behavior. Chemical substances called pheromones transmit species-specific information through the environment in behaviors ranging from foraging to courtship.
Behavior
the sum of responses to external and internal stimuli and includes muscular as well as nonmuscular activity
fixed action pattern
a largely invariant behavior triggered by a simple cue known as a sign stimulus
animal communication
The transmission and reception of signals constitute animal communication. Animals use visual, auditory, chemical (usually olfactory), and tactile signals, sometimes as part of a stimulus-response chain that governs a complex behavior
How is migration based on circannual rhythms poorly suited for adaptation to global climate change?
Circannual rhythms are typically based on the cycles of light and dark in the environment. As the global climate changes, animals that migrate in response to these rhythms may shift to a location before or after local environmental conditions are optimal for reproduction and survival.
CONCEPT Learning establishes specific links between experience and behavior
(pp. 1123–1128) Cross-fostering studies can be used to measure the influence of social environment and experience on behavior. • Learning, the modification of behavior based on experience, can take many forms: Imprinting, cognition, spatial learning, associative learning, social learning
Imprinting
?
cognition
?
spatial learning
?
associative learning
?
social learning
?
How do imprinting in geese and song development in sparrows differ with regard to the resulting behavior?
For the goose, all that is acquired is an object at which the behavior is directed. In the case of the sparrow, learning takes place that will give shape to the behavior itself.
CONCEPT Selection for individual survival and reproductive success can explain most behaviors
(pp. 1128–1134) • An optimal foraging model is based on the idea that natural selection should favor foraging behavior that minimizes the costs of foraging and maximizes the benefits. • Sexual dimorphism correlates with the type of mating relationship between males and females. These include monogamous and polygamous mating systems. Variation in mating system and variation in the mode of fertilization affect certainty of paternity, which in turn has a significant influence on mating behavior and parental care. • Game theory provides a way of thinking about evolution in situations where the fitness of a particular behavioral phenotype is influenced by other behavioral phenotypes in the population.
optimal foraging model
based on the idea that natural selection should favor foraging behavior that minimizes the costs of foraging and maximizes the benefits
monogamous
?? Sexual dimorphism correlates with the type of mating relationship between males and females.
polygamous
?? Sexual dimorphism correlates with the type of mating relationship between males and females.
Game theory
way of thinking about evolution in situations where the fitness of a particular behavioral phenotype is influenced by other behavioral phenotypes in the population.
CONCEPT Inclusive fitness can account for the evolution of behavior, including altruism
(pp. 1134–1139) • Genetic studies in insects have revealed the existence of master regulatory genes that control complex behaviors. Within the underlying hierarchy, multiple genes influence specific behaviors, such as a courtship song. Research with two species of voles has revealed that variation in a single gene can determine differences in complex behaviors involved in both mating and parenting. • When behavioral variation within a species corresponds to variation in environmental conditions, it may be evidence of past evolution. Field and laboratory studies have documented the genetic basis for a change in migratory behavior of certain birds and revealed behavioral differences in snakes that correlate with geographic variation in prey availability. • On occasion, animals exhibit altruism. This behavior can be explained by the concept of inclusive fitness, the total effect an individual has on proliferating its genes by producing its own offspring and by providing aid that enables close relatives to produce offspring. The coefficient of relatedness and Hamilton’s rule provide a way of measuring the strength of the selective forces favoring altruism against the potential cost of the “selfless” behavior. Kin selection favors altruistic behavior by enhancing the reproductive success of relatives. Altruistic behavior toward unrelated individuals can be adaptive if the aided individual returns the favor in the future, an exchange of aid called reciprocal altruism.
altruism
DEF: Altruism or selflessness is the principle or practice of concern for the welfare of others.
inclusive fitness
the total effect an individual has on proliferating its genes by producing its own offspring and by providing aid that enables close relatives to produce offspring
The “coefficient of relatedness” & “Hamilton’s rule”
a way of measuring the strength of the selective forces favoring altruism against the potential cost of the “selfless” behavior.
Suppose you studied the genetics of the lacewing courtship song, but not the effects of courtship mutations in flies or of variation in the vasopressin receptor gene of voles. What insight about the genetic basis of behavior would you likely have missed?
You would likely have missed the idea that changes in a single gene can have large-scale effects on even complex behaviors.
51:1 TEST Which of the following is true of innate behaviors? a. Their expression is only weakly influenced by genes. b. They occur with or without environmental stimuli. c. They are limited to invertebrate animals. d. They are expressed in most individuals in a population. e. They occur in invertebrates and some vertebrates but not mammals.
d
51:1 TEST According to Hamilton’s rule, a. natural selection does not favor altruistic behavior that causes the death of the altruist. b. natural selection favors altruistic acts when the resulting benefit to the beneficiary, corrected for relatedness, exceeds the cost to the altruist. c. natural selection is more likely to favor altruistic behavior that benefits an offspring than altruistic behavior that benefits a sibling. d. the effects of kin selection are larger than the effects of direct natural selection on individuals. e. altruism is always reciprocal.
b
51:1 TEST Female spotted sandpipers aggressively court males and, after mating, leave the clutch of young for the male to incubate. This sequence may be repeated several times with different males until no available males remain, forcing the female to incubate her last clutch. Which of the following terms best describes this behavior? a. monogamy b. polygyny c. polyandry d. promiscuity e. certainty of paternity
c
51:2 TEST A region of the canary forebrain shrinks during the nonbreeding season and enlarges when breeding season begins. This change is probably associated with the annual a. addition of new syllables to a canary’s song repertoire. b. crystallization of subsong into adult songs. c. sensitive period in which canary parents imprint on new offspring. d. renewal of mating and nest-building behaviors. e. elimination of the memorized template for songs sung the previous year.
a
51:2 TEST Although many chimpanzees live in environments containing oil palm nuts, members of only a few populations use stones to crack open the nuts. The likely explanation is that a. the behavioral difference is caused by genetic differences between populations. b. members of different populations have different nutritional requirements. c. the cultural tradition of using stones to crack nuts has arisen in only some populations. d. members of different populations differ in learning ability. e. members of different populations differ in manual dexterity.
C
51:2 TEST Which of the following is not required for a behavioral trait to evolve by natural selection? a. In each individual, the form of the behavior is determined entirely by genes. b. The behavior varies among individuals. c. An individual’s reproductive success depends in part on how the behavior is performed. d. Some component of the behavior is genetically inherited. e. An individual’s genotype influences its behavioral phenotype.
A
CONCEPT Dynamic biological processes influence population density, dispersion, and demographics
(pp. 1170–1175) • Population density—the number of individuals per unit area or volume—reflects the interplay of births, deaths, immigration, and emigration. Environmental and social factors influence the dispersion of individuals. • Populations increase from births and immigration and decrease from deaths and emigration. Life tables, survivorship curves, and reproductive tables summarize specific trends in demography.
Population density
the number of individuals per unit area or volume—reflects the interplay of births, deaths, immigration, and emigration.
Population dispersion types
clumped, uniform, random
immigration
Populations increase from births
emigration.
Populations decrease from deaths
Life tables,
? summarize specific trends in demography.
survivorship curves
? summarize specific trends in demography.
reproductive tables
? summarize specific trends in demography.
Gray whales (Eschrichtius robustus) gather each winter near Baja California to give birth. How might such behavior make it easier for ecologists to estimate birth and death rates for the species?
Ecologists can potentially estimate birth rates by counting the number of young born each year, and they can estimate death rates by seeing how the number of adults changes each year.
CONCEPT The exponential model describes population growth in an idealized, unlimited environment
(pp. 1175–1177) • If immigration and emigration are ignored, a population’s growth rate (the per capita rate of increase) equals its birth rate minus its death rate. • The exponential growth equation dN/dt rmaxN represents a population’s potential growth in an unlimited environment, where rmax is the maximum per capita rate of increase and N is the number of individuals in the population.
exponential growth
dN/dt = r/max N represents a population’s potential growth in an unlimited environment, where rmax is the maximum per capita rate of increase and N is the number of individuals in the population.
Suppose one population has an rmax that is twice as large as the rmax of another population. What is the maximum size that both populations will reach over time, based on the exponential model?
Under the exponential model, both populations will continue to grow to infinite size, regardless of the specific value of rmax (see Figure 53.7).
CONCEPT The logistic model describes how a population grows more slowly as it nears its carrying capacity
(pp. 1177–1179) • Exponential growth cannot be sustained for long in any population. A more realistic population model limits growth by incorporating carrying capacity (K), the maximum population size the environment can support.
• According to the logistic growth equation dN/dt rmaxN(K – N)/K, growth levels off as population size approaches the carrying capacity.
• The logistic model fits few real populations perfectly, but it is useful for estimating possible growth.
carrying capacity
the maximum population size the environment can support.
logistic growth
dN/dt = rmaxN(K – N)/K,
As an ecologist who manages a wildlife preserve, you want to increase the preserve’s carrying capacity for a particular endangered species. How might you go about accomplishing this?
There are many things you can do to increase the carrying capacity of the species, including increasing its food supply, protecting it from predators, and providing more sites for nesting or reproduction
CONCEPT
Life history traits are products of natural selection
(pp. 1179–1181)
• Life history traits are evolutionary outcomes reflected in the development, physiology, and behavior of organisms.
• Big-bang, or semelparous, organisms reproduce once and die. Iteroparous organisms produce offspring repeatedly.
• Life history traits such as brood size, age at maturity, and
parental caregiving represent trade-offs between conflicting demands for time, energy, and nutrients. Two hypothetical life history patterns are K-selection, or density-dependent selection, and r-selection, or density-independent selection.
Life history traits
evolutionary outcomes reflected in the development, physiology, and behavior of organisms.
Big-bang, or semelparous
Big-bang, or semelparous, organisms reproduce once and die.
Iteroparous organisms
Iteroparous organisms produce offspring repeatedly.
Two hypothetical life history patterns
- *K-selection**, or density-dependent selection,
- *r-selection**, or density-independent selection
What two factors likely contribute to the evolution of semelparity versus iteroparity?
Two key factors appear to be the survival rate of the offspring and the chance that adults will live long enough to reproduce again
CONCEPT
Many factors that regulate population growth are density
dependent
(pp. 1182–1187)
• In density-dependent population regulation, death rates rise and birth rates fall with increasing density. In density-independent population regulation, birth and death rates do not vary with density.
- Density-dependent changes in birth and death rates curb population increase through negative feedback and can eventually stabilize a population near its carrying capacity. Density-dependent limiting factors include intraspecific competition for limited food or space, increased predation, disease, stress due to crowding, and buildup of toxic substances.
- Because changing environmental conditions periodically disrupt them, all populations exhibit some size fluctuations. Manypopulations undergo regular boom-and-bust cycles that are influenced by complex interactions between biotic and abiotic factors. A metapopulation is a group of populations linked by immigration and emigration.
density-dependent population regulation,
death rates rise
and birth rates fall with increasing density
density-independent population
In density-independent
population regulation, birth and death rates do not
vary with density
Density-dependent limiting factors include
- intraspecific competition for limited food or space,
- increased predation,
- disease,
- stress due to crowding,
- and buildup of toxic substances
boom-and-bust cycles
all populations exhibit some size fluctuations.
regular boom-and-bust cycles that are influenced
by complex interactions between biotic and abiotic
factors.
metapopulation
a group of populations linked by immigration and emigration.
Give an example of one biotic and one abiotic factor that contribute to yearly fluctuations in the size of the human population.
An example of a biotic factor would be disease caused by a pathogen; natural disasters, such as floods and storms, are examples of abiotic factors.
CONCEPT
The human population is no longer growing exponentially
but is still increasing rapidly
(pp. 1187–1191)
• Since about 1650, the global human population has grown exponentially, but within the last 50 years, the rate of growth has fallen by nearly half. Differences in age structure show that while some nations’ populations are growing rapidly, those of others are stable or declining in size. Infant mortality rates and life expectancy at birth differ markedly between industrialized and less industrialized countries.
•The carrying capacity of Earth for humans is uncertain.
Ecological footprint is the aggregate land and water area
needed to produce all the resources a person or group of people consume and to absorb all of their wastes. It is one measure of how close we are to the carrying capacity of Earth. With a world population of more than 6.8 billion people, we are already using many resources in an unsustainable manner.
Ecological footprint
the aggregate land and water area needed to produce all the resources a person or group of people consume and to absorb all of their wastes.
How are humans different from other species in the ability to
“choose” a carrying capacity for their environment?
Humans are unique in our potential ability to reduce global population through contraception and family planning.
Humans also are capable of consciously choosing their diet and personal lifestyle, and these choices influence the number of people Earth can support.
53:1 TEST
Population ecologists follow the fate of same-age cohorts to
a. determine a population’s carrying capacity.
b. determine the birth rate and death rate of each group in a
population.
c. determine if a population is regulated by density-dependent processes.
d. determine the factors that regulate the size of a population.
e. determine if a population’s growth is cyclic.
b
53:1 TEST
A population’s carrying capacity
a. may change as environmental conditions change.
b. can be accurately calculated using the logistic growth model.
c. generally remains constant over time.
d. increases as the per capita growth rate (r) decreases.
e. can never be exceeded.
a
53:1
Scientific study of the population cycles of the snowshoe hare and its predator, the lynx, has revealed that
a. the prey population is controlled by predators alone.
b. hares and lynx are so mutually dependent that each
species cannot survive without the other.
c. multiple biotic and abiotic factors contribute to the cycling
of the hare and lynx populations.
d. both hare and lynx populations are regulated mainly by
abiotic factors.
e. the hare population is r-selected and the lynx population is K-selected
c
53:1
Based on current growth rates, Earth’s human population in
2012 will be closest to
a. 2 million.
d. 7 billion.
b. 3 billion.
e. 10 billion.
c. 4 billion.
d
53:1
A recent study of ecological footprints concluded that
a. Earth’s carrying capacity for humans is about 10 billion.
b. Earth’s carrying capacity would increase if per capita meat consumption increased.
c. current demand by industrialized countries for resources
is much smaller than the ecological footprint of those
countries.
d. it is not possible for technological improvements to increase Earth’s carrying capacity for humans.
e. the ecological footprint of the United States is large because per capita resource use is high.
e
53:2
The observation that members of a population are uniformly
distributed suggests that
a. the size of the area occupied by the population is increasing.
b. resources are distributed unevenly.
c. the members of the population are competing for access to a resource.
d. the members of the population are neither attracted to nor repelled by one another.
e. the density of the population is low
c
53:2
According to the logistic growth equation
a. the number of individuals added per unit time is greatest
when N is close to zero.
b. the per capita growth rate (r) increases as N approaches K.
c. population growth is zero when N equals K.
d. the population grows exponentially when K is small.
e. the birth rate (b) approaches zero as N approaches K.
c
53:2
Which pair of terms most accurately describes life history
traits for a stable population of wolves?
a. semelparous; r-selected
b. semelparous; K-selected
c. iteroparous; r-selected
d. iteroparous; K-selected
e. iteroparous; N-selected
d
53:2
During exponential growth, a population always
a. grows by thousands of individuals.
b. grows at its maximum per capita rate.
c. quickly reaches its carrying capacity.
d. cycles through time.
e. loses some individuals to emigration
b
53:2
Which of the following statements about human population
in industrialized countries is incorrect?
a. Life history is r-selected.
b. Average family size is relatively small.
c. The population has undergone the demographic transition.
d. The survivorship curve is Type I.
e. Age distribution is relatively uniform.
a
CONCEPT
Community interactions are classified by whether they
help, harm, or have no effect on the species involved
(pp. 1194–1200)
• A variety of interspecific interactions affect the survival
and reproduction of the species that engage in them. These
interactions include interspecific competition, predation,
herbivory, symbiosis, and facilitation. Parasitism, mutualism, and commensalism are types of symbiotic interactions.
• Competitive exclusion states that two species competing for the same resource cannot coexist permanently in the same place. Resource partitioning is the differentiation of species niches that enables species to coexist in a community.
Competition (-/-)
Two or more species compete for a resource
that is in short supply.
Predation (+/-)
One species, the predator, kills and eats the
other, the prey. Predation has led to diverse
adaptations, including mimicry.
Herbivory (+/-)
An herbivore eats part of a plant or alga. Plants
have various chemical and mechanical defenses
against herbivory, and herbivores have
specialized adaptations for feeding.
Symbiosis
Individuals of two or more species live in close
contact with one another. Symbiosis includes
parasitism, mutualism, and commensalism.
Parasitism (+/-)
The parasite derives its nourishment from a
second organism, its host, which is harmed.
Mutualism (+/+)
Both species benefit from the interaction.
Commensalism (+/0)
One species benefits from the interaction,
while the other is unaffected by it.
Facilitation (+/+ or0/+)
Species have positive effects on the survival
and reproduction of other species without
the intimate contact of a symbiosis.
CONCEPT
Diversity and trophic structure characterize biological
communities
(pp. 1200–1206)
• Species diversity measures the number of species in a
community—its species richness—and their relative
abundance. A community with similar abundances of
species is more diverse than one in which one or two species are abundant and the remainder are rare.
• More diverse communities typically produce more biomass and show less year-to-year variation in growth than less diverse communities and are more resistant to invasion by exotic species.
• Trophic structure is a key factor in community dynamics.
Food chains link the trophic levels from producers to top carnivores. Branching food chains and complex trophic interactions form food webs. The energetic hypothesis suggests that the length of a food chain is limited by the inefficiency of energy transfer along the chain.
• Dominant species are the most abundant species in a community and possess high competitive abilities. Keystone
species are usually less abundant species that exert a disproportionate influence on community structure because of their ecological niche. Ecosystem engineers influence community structure through their effects on the physical environment.
• The bottom-up model proposes a unidirectional influence
from lower to higher trophic levels, in which nutrients and
other abiotic factors primarily determine community structure, including the abundance of primary producers. The top-down model proposes that control of each trophic level comes from the trophic level above, with the result that predators control herbivores, which in turn control primary producers.
Species diversity
measures the number of species in a community
Species diversity** / relative abundance**
A community with similar abundances of
species is more diverse than one in which one or two species
are abundant and the remainder are rare.
Based on indexes such as Shannon diversity, is a community of higher species richness always more diverse than a community of lower species richness? Explain.
Not necessarily if the more species-rich community is dominated by only one or a few species
CONCEPT
Disturbance influences species diversity and composition
(pp. 1207–1210)
• Increasing evidence suggests that disturbance and lack of
equilibrium, rather than stability and equilibrium, are the
norm for most communities. According to the intermediate
disturbance hypothesis, moderate levels of disturbance can
foster higher species diversity than can low or high levels of
disturbance.
• Ecological succession is the sequence of community and
ecosystem changes after a disturbance. Primary succession
occurs where no soil exists when succession begins; secondary succession begins in an area where soil remains after a disturbance. Mechanisms that produce community change during succession include facilitation and inhibition.
• Humans are the most widespread agents of disturbance, and their effects on communities often reduce species diversity. Humans also prevent some naturally occurring disturbances, such as fire, which can be important to community structure.
intermediate disturbance hypothesis
moderate levels of disturbance can foster higher species diversity than can low or high levels of disturbance.
Ecological succession
the sequence of community and ecosystem changes after a disturbance.
- Primary succession occurs where no soil exists when succession begins
- secondary succession begins in an area where soil remains after a disturbance.
Mechanisms that produce community change during
succession include facilitation and inhibition.
CONCEPT
Biogeographic factors affect community diversity
- Species richness generally declines along a latitudinal gradient from the tropics to the poles. The greater age of tropical environments may account for the greater species richness of thetropics. Climate also influences the diversity gradient through energy (heat and light) and water.
- Species richness is directly related to a community’s geographic size, a principle formalized in the species-area curve.
- Species richness on islands depends on island size and distance from the mainland. The island equilibrium model maintains that species richness on an ecological island reaches an equilibrium where new immigrations are balanced by extinctions. This model may not apply over long periods, during which abiotic disturbances, evolutionary changes, and speciation may alter community structure.
Top-down model
Proposes that control of each trophic level comes from
the trophic level above, with the result that predators control
herbivores, which in turn control primary producers.
Based on indexes such as Shannon diversity, is a community of higher species richness always more diverse than a community of lower species richness? Explain.
Not necessarily if the more species-rich community
is dominated by only one or a few species
CONCEPT
Disturbance influences species diversity and composition
(pp. 1207–1210)
• Increasing evidence suggests that disturbance and lack of
equilibrium, rather than stability and equilibrium, are the
norm for most communities. According to the intermediate
disturbance hypothesis, moderate levels of disturbance can
foster higher species diversity than can low or high levels of
disturbance.
• Ecological succession is the sequence of community and
ecosystem changes after a disturbance. Primary succession
occurs where no soil exists when succession begins; secondary succession begins in an area where soil remains after a disturbance. Mechanisms that produce community change during succession include facilitation and inhibition.
• Humans are the most widespread agents of disturbance, and their effects on communities often reduce species diversity. Humans also prevent some naturally occurring disturbances, such as fire, which can be important to community structure.
intermediate disturbance hypothesis
moderate levels of disturbance can foster higher species diversity than can low or high levels of disturbance.
CONCEPT
Biogeographic factors affect community diversity
(pp. 1211–1213)
- Species richness generally declines along a latitudinal gradient from the tropics to the poles. The greater age of tropical environments may account for the greater species richness of the tropics. Climate also influences the diversity gradient through energy (heat and light) and water.
- Species richness is directly related to a community’s geographic size, a principle formalized in the species-area curve.
- Species richness on islands depends on island size and distance from the mainland. The island equilibrium model maintains that species richness on an ecological island reaches an equilibrium where new immigrations are balanced by extinctions. This model may not apply over long periods, during which abiotic disturbances, evolutionary
species-area curve
Species richness is directly related to a community’s geographic size, a principle formalized in the species-area curve.
How have periods of glaciation influenced latitudinal patterns of diversity?
Glaciations have severely reduced diversity in northern temperate, boreal, and Arctic ecosystems, compared to tropical ecosystems.
CONCEPT
Pathogens alter community structure locally and globally
(pp. 1213–1215)
• Recent work has highlighted the role that pathogens play in
structuring terrestrial and marine communities.
• Zoonotic pathogens are transferred from other animals to humans and cause the largest class of emerging human diseases. Community ecology provides the framework for identifying key species interactions associated with such pathogens and for helping us track and control their spread.
pathogens
Recent work has highlighted the role that pathogens play in
structuring terrestrial and marine communities
Zoonotic pathogens
Zoonotic pathogens are transferred from other animals to humans and cause the largest class of emerging human diseases
In what way can a vector of a zoonotic pathogen differ from a
host of the pathogen?
A host is required to complete the pathogen’s life cycle, but a vector is not. Vectors are intermediate species that merely transport a pathogen to its host.
54:1
The feeding relationships among the species in a community
determine the community’s
a. secondary succession.
b. ecological niche.
c. species richness.
d. species-area curve.
e. trophic structure.
e
54:1
The principle of competitive exclusion states that
a. two species cannot coexist in the same habitat.
b. competition between two species always causes extinction or emigration of one species.
c. competition in a population promotes survival of the bestadapted individuals.
d. two species that have exactly the same niche cannot coexist in a community.
e. two species will stop reproducing until one species leaves the habitat.
d
54:1
Based on the intermediate disturbance hypothesis, a community’s species diversity is increased by
a. frequent massive disturbance.
b. stable conditions with no disturbance.
c. moderate levels of disturbance.
d. human intervention to eliminate disturbance.
e. intensive disturbance by humans.
c
54:1
According to the equilibrium model of island biogeography,
species richness would be greatest on an island that is
a. large and close to a mainland.
b. large and remote.
c. small and remote.
d. small and close to a mainland.
e. environmentally homogeneous.
a
54:1
Keystone predators can maintain species diversity in a community if they
a. competitively exclude other predators.
b. prey on the community’s dominant species.
c. allow immigration of other predators.
d. reduce the number of disruptions in the community.
e. prey only on the least abundant species in the community.
b
54:1
Food chains are sometimes short because
a. only a single species of herbivore feeds on each plant
species.
b. local extinction of a species causes extinction of the other species in its food chain.
c. most of the energy in a trophic level is lost as it passes to
the next higher level.
d. predator species tend to be less diverse and less abundant than prey species.
e. most producers are inedible.
c
54:1
Which of the following could qualify as a top-down control
on a grassland community?
a. limitation of plant biomass by rainfall amount
b. influence of temperature on competition among plants
c. influence of soil nutrients on the abundance of grasses versus wildflowers
d. effect of grazing intensity by bison on plant species diversity
e. effect of humidity on plant growth rates
d
54:1
The most plausible hypothesis to explain why species richness
is higher in tropical than in temperate regions is that
a. tropical communities are younger.
b. tropical regions generally have more available water and
higher levels of solar radiation.
c. higher temperatures cause more rapid speciation.
d. diversity increases as evapotranspiration decreases.
e. tropical regions have very high rates of immigration and
very low rates of extinction.
b
54:1
Community 1 contains 100 individuals distributed among
four species (A, B, C, and D). Community 2 contains 100 individuals distributed among three species (A, B, and C).
Community 1: 5A, 5B, 85C, 5D
Community 2: 30A, 40B, 30C
- Calculate the Shannon diversity (H) for each community.*
- Which community is more diverse?*
Community 1:
H (0.05 ln 0.05 0.05 ln 0.05 0.85 ln 0.85 0.05 ln 0.05) 0.59.
Community 2:
H (0.30 ln 0.30 0.40 ln 0.40 0.30 ln 0.30) 1.1.
Community 2 is more diverse.
Another important species in the Chesapeake Bay estuary (see Figure 54.15) is the blue crab (Callinectes sapidus). It is an omnivore, eating eelgrass and other primary producers as well as clams. It is also a cannibal. In turn, the crabs are eaten by humans and by the endangered Kemp’s Ridley sea turtle. Based on this information, draw a food web that includes the blue crab. Assuming that the top-down model holds for this system, what would happen to the abundance of eelgrass if humans stopped eating blue crabs?
