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AP Biology Ecology Unit Chapters 5054


May increase fitness by allowing an animal's nervous system to focus on stimuli ... Life Tables and Survivorship Curves. Reproductive Rates ... – PowerPoint PPT presentation

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Title: AP Biology Ecology Unit Chapters 5054

AP Biology Ecology UnitChapters 50-54
Intro to Ecology
  • Ecology the study of the interactions between
    organisms and their environment
  • Uses descriptive observations and manipulative
  • Organisms are open systems that interact
    continuously with their environments
  • The environment of any organism includes
  • Biotic Components living members of the same
    species, prey or predator species, competing
  • Abiotic Components non-living chemical and
    physical factors

Levels of Ecology
  • Organismal Ecology concerned with the
    morphological, physiological, and behavioral ways
    in which individual organisms meet the challenges
    of its environment
  • Population Ecology concentrates on factors that
    affect how many individuals of a species live in
    an area
  • Population group of individuals of the same
    species living in a particular geographic area
  • Community Ecology deals with the array of
    interacting species in a community. Focuses on
    interactions such as predation, competition, and
  • Community all the organisms of all the species
    that inhabit a particular area

Levels of Ecology
  • Ecosystem Ecology studies energy flow and
    cycling of chemicals among the biotic and abiotic
  • Ecosystem all the abiotic factors in addition to
    the community of a species in a certain area
  • Landscape Ecology deals with arrays of
    ecosystems and how they are arranged in a
    geographic region.
  • Biome group of similar ecosystem having similar
    abiotic characteristics and biotic populations
  • Biosphere the global ecosystemsum of all the
    planets ecosystems
  • Ranges from several kilometers into the
    atmosphere and at least 3,000m belowground

Factors Affecting the Distribution of Organisms
  • Biogeography is the study of past and present
    distributions of individual species, which
    provides a good starting point to understanding
    what limits geographic distributions.
  • Factors include
  • Dispersal
  • Potential vs. Actual range
  • Behavior
  • Habitat Selection
  • Biotic Factors (predator-prey relationships)
  • Abiotic Factors (Temp, water, sunlight, wind,

Flowchart of factors limiting geographic
Species Transplant Experiments
  • If the transplant was successful, then the
    potential range of the species is larger than the
    actual range.
  • If the transplant was unsuccessful, then
    distribution is limited by other species or
    abiotic factors.
  • Problems with Introduced Species.
  • Transplanted species often explode to occupy a
    new area.
  • The African honeybee and Zebra mussel are good
    examples of this explosion.

The African Honeybee
  • The African Honeybee is a very aggressive
    subspecies of honeybee that was brought to Brazil
    in 1956 to breed a variety that would produce
    more honey.
  • The bees escaped by accident in 1957 and have
    been spreading through the Americas ever since
  • Because they are aggressive they drive out the
    native bees.
  • They have been moving 110 km north every year
  • Will they be able to continue north?

The Zebra Mussel
  • In 1988 the zebra mussel (small mollusk native to
    Caspian Sea of Asia) was discovered in Lake St.
    Claire (Detroit)
  • It reproduces rapidly and forms dense clusters.
  • Have reached densities of 750,000 per square
    meter in Lake Erie
  • Clog sewer and water intake pipes
  • Suspension feedersare cleaning the waters
  • In the Hudson River, NY
  • Phytoplankton was decreased by 85
  • Zooplankton was decreased by 70
  • Zebra mussels are crowding out native mollusks
    leading toward extinction

  • Biomes, the major types of ecosystems.
  • Determined by Climate, the prevailing weather
    conditions in an area.
  • Temperature, water, light, and wind are major
    components of climate.
  • Climate determines the makeup of Annual means for
    temperature and rainfall are reasonably well
    correlated with the biomes we find in different
  • Global climate patterns are largely determined by
    sunlight and the planets movement in space.
  • The suns 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.

Aquatic Biomes
  • Aquatic biomes occupy the largest part of the
  • Marine biomes have a salt concentration of
    approximately 3 and cover approximately 75 of
    the earths surface.
  • Freshwater biomes are usually characterized by
    salt concentration of less than 1 and are
    closely linked to the soils and biotic components
    of the terrestrial biomes through which they
  • Vertical stratification of aquatic biomes.
  • The photic zone is the zone through which light
    penetrates and photosynthesis can occur.
  • The aphotic zone is where very little light can
  • The benthic zone is the bottom of any aquatic
    biome and contains detritus, dead organic matter.

Freshwater Biomes
  • Oligotrophic lakes are deep, nutrient-poor and do
    not contain much life.
  • Eutrophic lakes are shallower and have increased
  • Mesotrophic lakes have a moderate amount of
    nutrients and phytoplankton productivity.
  • Over long periods of time, oligotrophic lakes may
    become mesotrophic as runoff brings in nutrients.
  • Pollution from fertilizers can cause explosions
    in algae population and cause a decrease in
    oxygen content.

Lake Stratification and Turnover
Distribution of Major Terrestrial Biomes
Tropical Forests
Temperate Grassland
Temperate Deciduous Forest
Coniferous Forest
  • Chapter 51 Behavioral Biology

What is Behavior?
  • Behavior is what an animal does and how it does
  • has both proximate and ultimate causes
  • Proximate questions are mechanistic, concerned
    with the environmental stimuli that trigger a
    behavior, as well as the genetic and
    physiological mechanisms underlying a behavioral
  • Ultimate questions address the evolutionary
    significance for a behavior and why natural
    selection favors this behavior.
  • Behavior results from both genes and
    environmental factors
  • Ethology is the study of how animals behave in
    their natural habitat

Fixed Action Patterns
  • Fixed action pattern (FAP) A sequence of
    behavioral acts that is essentially unchangeable
    and usually carried to completion once initiated.
  • triggered by an external sensory stimulus known
    as a sign stimulus (stimuli are usually obvious
    and from another species).
  • Example Moths drop when they sense bats
  • occurs in a series of actions the same way every
  • Many animals tend to use a relatively small
    subset of the sensory information available to
    them and behave stereotypically.
  • They do not read the entire situation
  • Can be easily tricked
  • Some simple behaviors can be explained with FAPs,
    they are too simplicstic to account for much of
    animal behavior

FAP Experiments
  • Male stickleback fish will attack any objects
    with a red belly in attempt to defend their
    territory. The realistic fish is not attacked
    because it lacks the red.

Behavioral Ecology
  • Behavioral ecology is the research field that
    views behavior as an evolutionary adaptation to
    the natural ecological conditions of animals.
  • We expect animals to behave in ways that maximize
    their fitness (this idea is valid only if genes
    influence behavior).
  • Songbird repertoires provide us with examples.
  • Why has natural selection favored a multi-song
  • It may be advantageous for males attracting
  • Cost-benefit analysis of foraging behavior.
  • Foraging is food-obtaining behavior.
  • The optimal foraging theory states that natural
    selection will benefit animals that maximize
    their energy intake-to-expenditure ratio.

Foraging Behavior Example
  • In feeding on Daphnia the bluegill sunfish do not
    feed randomly but tend to select prey based on
    apparent size information about both prey size
    and distance.
  • Fish will pursue the one that looks largest
  • Small prey at close distance may be taken with
    small energy expenditure
  • More distant but larger prey will require more
    energy to catch, but provide higher energy

Types of Behaviors Learning
  • Learning is the modification of behavior
    resulting from specific experiences.
  • Involves both innate or developmentally fixed
    behaviors and environmental experience
  • Example The alarm calls of vervet monkeys are
    different for different types of predators
    (leopards, eagles, snakes) along with the
    confirmation call and physical response of others
    for the call
  • With age infant monkeys learn to give the proper
    call and elicit the proper behavior for each
  • Maturation is the situation in which a behavior
    may improve because of ongoing developmental
    changes in neuromuscular systemsnot true
  • Example Flight in birds As a bird continues to
    develop its muscles and nervous system, it is
    able to fly.
  • Habituation involves a loss of responsiveness to
    unimportant stimuli or stimuli that do not
    provide appropriate feedback.
  • May increase fitness by allowing an animals
    nervous system to focus on stimuli that signal
    food, mates, or real danger instead of wasting
    time and energy on other irrelevant stimuli
  • Example some animals stop responding to warning
    signals if signals are not followed by a predator
    attack (the cry-wolf effect).

Types of Behaviors Learning
  • Imprinting is the recognition, response, and
    attachment of young to a particular adult or
  • Konrad Lorenz experimented with geese that spent
    the first hours of their life with him and after
    time responded to him as their parent.
  • Lorenz isolated geese after hatching and found
    that they could no longer imprint on anything.
  • What is innate in these birds is the ability to
    respond to a parent figure, while the outside
    world provides the imprinting stimulus.
  • The sensitive period is a limited phase in an
    individual animals development when learning
    particular behaviors can take place
  • Development of behavior can be explained using
    bird songs
  • Some songbirds have a sensitive period for
    developing their songs.
  • Individuals reared in silence perform abnormal
    songs, but if recordings of the proper songs are
    played early in the life of the bird, normal
    songs develop.
  • Canaries exhibit open-ended learning where they
    add new syllables to their song as the get older.
  • Also seen in humans as children can learn a
    second language very easily

Types of Behaviors Learning
  • Associative learning is the ability of many
    animals to learn to associate one stimulus with
  • Classical conditioning is a type of associative
  • Ivan Pavlov exposed dogs to a bell ringing and at
    the same time sprayed their mouths with powdered
    meat, causing them to salivate.
  • Soon, the dogs would salivate after hearing the
    bell, even if they were not getting any powdered
  • Operant conditioning or trial-and-error
    learningan animal learns to associate one of its
    own behaviors with a reward or a punishment.
  • Example predators learn to associate certain
    types of potential prey with painful experiences
    and modify behavior
  • Play as a behavior has no apparent external goal,
    but may facilitate social development or practice
    of certain behaviors and provide exercise.
  • Involves movements closely associated with
    goal-directed behaviorsstalking and attacking

Types of Behaviors Cognition
  • Cognition is the ability of an animals nervous
    system to perceive, store, process, and use
    information gathered by sensory receptors.
  • connects nervous system function with behavior
  • Using tools, problem solving, feigning injuries
  • Cognitive ethology study of animal cognition
  • Animals use various cognitive mechanisms during
    movement through space
  • Kinesis is a change in activity rate in response
    to a stimulus.
  • For example, sowbugs are more active in dry areas
    and less active in humid areas.
  • Taxis is an automatic, oriented movement toward
    or away from a stimulus.
  • For example, phototaxis, chemotaxis, and
  • Some organisms move in response to a recognized
    object, a landmark, or an environmental cue.
  • Some animals form cognitive maps (internal codes
    of spatial relationships of objects in the

Types of Behaviors Cognition
  • Migration is the regular movement of animals over
    relatively long distances.
  • Piloting an animal moves from one familiar
    landmark to another until it reaches its
  • Orientation animals can detect directions and
    travel in particular paths until reaching
  • Navigation involves determining ones present
    location relative to other locations, in addition
    to detecting compass directions

Types of Behaviors Cognition
  • The study of consciousness poses a unique
    challenge for scientists
  • Besides humans, are animals aware of themselves?
  • Some would argue that certain behaviors are a
    result of conscious processing.
  • Sociobiology places social behavior in an
    evolutionary context
  • Social behavior is any kind of interaction
    between two or more animals, usually of the same
  • Competitive social behaviors often represent
    contests for resources
  • Cooperation when a social group carries out
    behavior more efficiently than a single
  • Agonistic behavior is a contest involving both
    threats and submissive behavior. Determines who
    gets access to some resource (food, mates, etc)
  • Most of the behaviors are Ritual the use of
    symbolic activity, without serious harm done
  • Degree of combat that is ritual depends on
    scarcity of the resource

Types of Behaviors Cognition
  • Reconciliation behavior often happens between
    conflicting individuals after agnostic behavior
    who live in close social groups
  • Dominance hierarchies involve a ranking of
    individuals in a group (a pecking order).
  • Alpha, beta rankings exist.
  • The alpha organisms control the behavior of
  • Top ranking animal is assured access to food and

Types of Behaviors Cognition
  • Territoriality is behavior where an individual
    defends a particular area, called the territory.
  • Territories are typically used for feeding,
    mating, and rearing young and are fixed in
  • Benefits are exclusive access to food, breeding
    areas, and places to raise young. Familiarity
    with territory makes it easier to avoid
    predators. Helps to stabilize population density
  • Drawbacks are that territoriality uses a great
    deal of an individuals energy an individual
    might die or miss a reproductive opportunity as a
    result of defending a territory.
  • Ownership of territories is continually
  • Songs or noises
  • Spraying behavior is where an individual marks
    its territory.
  • Defense of territories are directed at

Types of Behaviors Mating Behaviors
  • Natural selection favors mating behavior that
    maximizes the quantity or quality of mating
  • Courtship behavior consists of patterns that lead
    to copulation and consists of a series of
    displays and movements by the male or female.
  • Parental investment refers to the time and
    resources expended for raising of offspring.
  • Generally lower in males because they are capable
    of producing more gametes (which are also
    smaller), therefore making each one less
  • Females usually invest more time into parenting
    because they make fewer, larger gametes, a
    process which is energetically more expensive,
    thus making each gamete more valuable.
  • Mate choice females are usually more
    discriminating in terms of the males with whom
    they choose to mate.
  • Females look for more fit males (i.e., better
    genes), the ultimate cause of the choice.

Types of Behaviors Mating Behaviors
  • Mating systems differ among species.
  • Usually based on the needs of the young and the
    certainty of paternity
  • Example baby birds require large amount of
    continuous care a male is more likely to leave
    more viable offspring if he sticks around and
    helps raise the young then if he goes off seek
    more mates
  • Promiscuous no strong pair-bond between males
    and females.
  • Monogamous one male mating with one female.
  • Polygamous an individual of one sex mating with
    several of the other sex.
  • Polygyny is a specific example of polygamy, where
    a single male mates with many females.
  • Polyandry occurs in some species where one female
    mates with several males.

Types of Behavior Communication
  • Social interactions depend on diverse modes of
  • A signal is a behavior that causes a change in
    the behavior of another animal.
  • The transmission of, reception of, and response
    to signals make up communication.
  • Examples include the following
  • Displays such as singing and howling.
  • Visual, chemical, tactile, electrical signals
  • Pheromones are chemicals released by an
    individual that bring about mating and other
  • Used to attract mates, leave trails (ants),
    outline territory
  • Example The Dance of the Honeybee.
  • If an individual finds a good food source, it
    will communicate the location to others in the
    hive through an elaborate dance.

Types of Behaviors Altruistic
  • Most social behaviors are selfish, so how do we
    account for behaviors that help others?
  • Altruism is defined as behavior that might
    decrease individual fitness, but increase the
    fitness of others.
  • Inclusive fitness How can a naked mole rat
    enhance its fitness by helping other members of
    the population?
  • How is altruistic behavior maintained by
  • If related individuals help each other, they are
    in affect helping keep their own genes in the
  • Inclusive fitness is defined as the effect an
    individual has on proliferating its own genes by
    reproducing and by helping relatives raise
  • Hamiltons Rule and Kin Selection a quantitative
    measure for predicting when natural selection
    would favor altruistic acts.
  • Hamiltons rule states that natural selection
    favors altruistic acts.
  • 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
  • Reciprocal altruism, where an individual aids
    other unrelated individuals without any benefit,
    is rare, but sometimes seen in primates (often in

Examples of Altruism
  • Belding Ground Squirrels signal alarm calls to
    warn others of dangergiving signal increases
    chance of being eaten
  • Mole Rats live in colonies with only one
    reproducing female queen who mates with one to
    three kings . Nonreproductive members of the
    colony forage and care for queen, kings, and
    offspring. Will sacrifice lives to protect the

Humans and Sociobiology
  • Sociobiology maintains that much of human social
    behavior and cultures can be understood on
    evolutionary and basic biological terms

AP Biology
  • Chapter 52 Population Ecology

  • A population is a group of individuals of a
    single species that simultaneously occupy the
    same general area.
  • The characteristics of populations are shaped by
    the interactions between individuals and their
  • Two important characteristics of any population
    are density and the spacing of individuals
  • Populations have size and geographical
  • The density of a population is measured as the
    number of individuals per unit area.
  • The dispersion of a population is the pattern of
    spacing among individuals within the geographic

Measuring Density
  • Measuring density of populations is a difficult
  • We can count individuals we can estimate
    population numbers.
  • Unfortunately, it is usually impractical to
    attempt to count individuals in a population.
  • One sampling technique that researchers use is
    known as the mark-recapture method.
  • Individuals are trapped in an area and captured,
    marked with a tag, recorded, and then released.
  • After a period of time has elapsed, traps are set
    again, and individuals are captured and
  • This information allows estimates of population
    changes to be made.

Patterns of Dispersion
  • Within a populations geographic range, local
    densities may vary considerably.
  • Different dispersion patterns result within the
  • Overall, dispersion depends on resource
  • Clumped dispersion is when individuals aggregate
    in patches.
  • By contrast, uniform dispersion is when
    individuals are evenly spaced.
  • In random dispersion, the position of each
    individual is independent of the others.

  • Demography is the study of factors that affect
    the growth and decline of populations
  • Additions occur through birth, and subtractions
    occur through death.
  • Demography studies the vital statistics that
    affect population size.
  • A life table is an age-specific summary of the
    survival pattern of a population.
  • The best way to construct life table is to follow
    a cohort, a group of individuals of the same age
    throughout their lifetime.
  • A graphic way of representing the data is a
    survivorship curve.
  • This is a plot of the number of individuals in a
    cohort still alive at each age.
  • Type I curve shows a low death rate early in life
  • Type II curve shows constant mortality
  • Type III curve shows a high death rate early in
    life (oysters).

Life Tables and Survivorship Curves
Reproductive Rates
  • Demographers that study populations usually
    ignore males, and focus on females because only
    females give birth to offspring.
  • A reproductive table is an age-specific summary
    of the reproductive rates in a population.
  • For sexual species, the table tallies the
    number of female offspring produced by each
    age group.

Life Histories
  • The traits that affect an organisms schedule of
    reproduction and survival make up its life
  • Life histories are highly diverse, but they
    exhibit patterns in their variability
  • Life histories are a result of natural
    selection, and often parallel environmental
  • big-bang reproduction or semelparity where large
    numbers of offspring are produced in each
    reproduction, after which the individual often
    dies. (ex. Agave plant)
  • repeated reproduction or iteroparity some
    organisms produce only a few eggs during yearly

Life Histories
  • What factors contribute to the evolution of
    semelparity and iteroparity?
  • Limited resources mandate trade-offs between
    investments in reproduction and survival
  • Life-histories represent an evolutionary
    resolution of several conflicting demands.
  • The number of offspring produced at each
    reproductive episode exhibits a trade-off between
    number and quality of offspring.

Population Growth
  • We define a change in population size based on
    the following verbal equation.Change in
    Population Births during - Deaths during
    Size during time interval time interval
    time interval
  • Using mathematical notation, we can express this
    relationship as follows
  • If N represents population size, and t represents
    time, then ? N is the change is population size
    and ?t represents the change in time, then
  • ? N/? t B-D
  • Where B is the number of births and D is the
    number of deaths
  • We can simplify the equation and use r to
    represent the difference in per capita birth and
    death rates.
  • ? N/ ? t rN OR dN/dt rN
  • If B D then there is zero population growth

Exponential Growth
  • Under ideal conditions, a population grows
    rapidly Exponential population growth
  • Under these conditions, we may assume the maximum
    growth rate for the population (rmax) to give us
    the following exponential growth equation
  • dN/dt rmaxN

Logistic Growth
  • Typically, unlimited resources are rare.
    Population growth is therefore regulated by
    carrying capacity (K), which is the maximum
    stable population size a particular environment
    can support.
  • The logistic population growth model incorporates
    the effect of population density on the rate of
  • Mathematically, we start with the equation for
    exponential growth, creating an expression that
    reduces the rate of increase as N increases
  • dN/dt rmaxN((K-N)/K)
  • The graph of this equation shows an S-shaped

Logistic Growth
  • Logistic model assumes that the population growth
    rate dN/dt decreases as N increases
  • When N is close to 0, population grows rapidly
  • As N approaches K, the growth rate approaches 0
    and the population growth slows
  • If N is greater than K, population growth rate
    is negative, and size decreases
  • Equilibrium reached at the white line when NK

How well does Logistic Model fit the growth of
Real Populations?
  • The growth of laboratory populations of some
    animals fits the S-shaped curves fairly well.
  • Some of the assumptions built into the logistic
    model do not apply to all populations.
  • It is a model which provides a basis from which
    we can compare real populations.

The logistic population growth model and life
  • This model predicts different growth rates for
    different populations relative to carrying
  • Resource availability depends on the situation.
  • The life-history traits that natural selection
    favors may vary with population density and
    environmental conditions.
  • In K-selection, or density-dependent selection,
    organisms live and reproduce around K, and are
    sensitive to population density.
  • In r-selection, or density-independent selection,
    organisms exhibit high rates of reproduction and
    occur in variable environments in which
    population densities fluctuate well below K.

Population Limiting Factors
  • Why do all populations eventually stop growing?
  • What environmental factors stop a population from
  • The first step to answering these questions is to
    examine the effects of increased population
  • Density-dependent factors increase their affect
    on a population as population density increases.
  • This is a type of negative feedback.
  • Density-independent factors are unrelated to
    population density, and there is no feedback to
    slow population growth.

Negative Feedback
  • Negative feedback prevents unlimited population
  • Resource limitation in crowded populations can
    stop population growth by reducing reproduction.
  • Intraspecific competition for food can also cause
    density-dependent behavior of populations.
  • Territoriality, defense of a space, may set a
    limit on density.
  • Predation may also be a factor because it can
    cause mortality of prey species.
  • Waste accumulation is another component that can
    regulate population size.
  • Disease can also regulate population growth,
    because it spreads more rapidly in dense
  • Population dynamics reflect a complex interaction
    of biotic and abiotic influences
  • Carrying capacity can vary.
  • Some populations fluctuate erratically, based on
    many factors.
  • Some populations have regular boom-and-bust
  • Example the lynx and snowshoe hare that cycle on
    a ten year basis.

Figure 52.17 Long-term study of the moose (Alces
alces) population of Isle Royale, Michigan
Figure 52.19 Population cycles in the snowshoe
hare and lynx
Human Population Growth
  • The human population has been growing almost
    exponentially for three centuries but cannot do
    so indefinitely
  • The human population increased relatively slowly
    until about 1650 when the Plague took an untold
    number of lives.
  • Ever since, human population numbers have doubled
  • How might this population increase stop?

The Demographic Transition.
  • A regional human population can exist in one of 2
  • Zero population growth high birth rates high
    death rates.
  • Zero population growth low birth rates low
    death rates.
  • The movement from the first toward the second
    state is called the demographic transition.

Age Structures
  • Age structure is the relative number of
    individuals of each age.
  • Age structure diagrams can reveal a populations
    growth trends, and can point to future social

Estimating Earths Carrying Capacity
  • Estimating Earths carrying capacity for humans
    is a complex problem
  • Predictions of the human population vary from 7.3
    to 10.7 billion people by the year 2050.
  • Will the earth be overpopulated by this time?
  • Wide range of estimates for carrying capacity.
  • What is the carrying capacity of Earth for
  • This question is difficult to answer.
  • Estimates are usually based on food, but human
    agriculture limits assumptions on available

Ecological footprint.
  • Humans have multiple constraints besides food.
  • The concept an of ecological footprint uses the
    idea of multiple constraints.
  • For each nation, we can calculate the aggregate
    land and water area in various ecosystem
  • Six types of ecologically productive areas are
    distinguished in calculating the ecological
  • Land suitable for crops.
  • Pasture.
  • Forest.
  • Ocean.
  • Built-up land.
  • Fossil energy land.

AP Biology
  • Chapter 53Community Ecology

What is a community?
  • A community is defined as an assemblage of
    species living close enough together for
    potential interaction.
  • Communities differ in their species richness, the
    number of species they contain, and the relative
    abundance of different species.
  • Contrasting views of communities are rooted in
    the individualistic and interactive hypotheses
  • An individualistic hypothesis depicts a community
    as a chance assemblage of species found in the
    same area because they happen to have similar
    abiotic requirements.
  • An interactive hypothesis depicts a community as
    an assemblage of closely linked species locked in
    by mandatory biotic interactions.
  • These two very different hypotheses suggest
    different priorities in studying biological
  • In most actual cases, the composition of
    communities does seem to change continuously.

Interspecific Interactions and Community
  • There are many different interspecific
    interactions, relationships between the species
    of a community.
  • Populations may be linked by
  • Competition
  • Predation
  • Mutualism
  • Commensalism

  • Interspecific competition for resources can occur
    when resources are in short supply.
  • There is potential for competition between any
    two species that need the same limited resource.
  • The competitive exclusion principle two species
    with similar needs for same limiting resources
    cannot coexist in the same place.
  • two species cannot coexist in a community if
    their niches are identical.
  • The ecological niche is the sum total of an
    organisms use of abiotic/biotic resources in the
    environment or its role in the environment.
  • Resource partitioning is the differentiation of
    niches that enables two similar species to
    coexist in a community.
  • Character displacement is the tendency for
    characteristics to be more divergent in sympatric
    populations of two species than in allopatric
    populations of the same two species.

Gauses Paramecium Experiment
  • The two species of Paramecium used by Gause grew
    well by them selves but P. caudium was out
    competed by P. aurelia when the two were grown
  • Experiment supports Competition Exclusion

Competitive Exclusion Principle
Resource Partitioning
Character Displacement
  • A predator eats prey
  • Herbivory, in which animals eat plants.
  • In parasitism, predators live on/in a host and
    depend on the host for nutrition.
  • Predator adaptations many important feeding
    adaptations of predators are both obvious and
  • Ex Claws, teeth, fangs, poison, heat-sensing
    organs, speed, and agility.
  • Prey have adaptations to avoid being eaten
  • Plant defenses against herbivores include
    chemical compounds that are toxic.
  • Animals behavioral defenses include fleeing,
    hiding, self-defense, noises, and mobbing.
  • Camouflage includes cryptic coloration, deceptive
  • Mechanical defenses include spines.
  • Chemical defenses include odors and toxins
  • Aposematic coloration is indicated by warning
    colors, and is sometimes associated with other
    defenses (toxins).
  • Mimicry is when organisms resemble other species.
  • Batesian mimicry is where a harmless species
    mimics a harmful one.
  • Müllerian mimicry is where two or more
    unpalatable species resemble each other.

Aposematic (warning) coloration
Deceptive Coloration
Batesian Mimicry Harmless caterpillar mimics
dangerous snake
Mullerian Mimicry Harmful species resemble each
Symbiotic Relationships
  • Parasitism one organism benefits and one is
  • Parasites and pathogens as predators.
  • A parasite derives nourishment from a host, which
    is harmed in the process.
  • Endoparasites live inside the host and
    ectoparasites live on the surface of the host.
  • Parasitoidism is a special type of parasitism
    where the parasite eventually kills the host.
  • Pathogens are disease-causing organisms that can
    be considered predators.

  • Mutualism is where two species benefit from their
  • Examples Rhino birds Rhinos, Ants Acacias
  • Commensalism is where one species benefits from
    the interaction, but other is not affected.
  • Example barnacles on a whale.
  • Coevolution refers to reciprocal evolutionary
    adaptations of two interacting species.
  • When one species evolves, it exerts selective
    pressure on the other to evolve to continue the

Summary of Interspecific Interactions
Trophic Structure
  • The trophic structure of a community is
    determined by the feeding relationships between
  • The transfer of food energy from its source in
    photosynthetic organisms through herbivores and
    carnivores is called the food chain.
  • Charles Elton first pointed out that the length
    of a food chain is usually four or five links,
    called trophic levels.
  • He also recognized that food chains are not
    isolated units but are hooked together into food
  • Food webs describe
  • Who eats whom in a community?
  • Trophic relationships can be diagrammed in a
  • What transforms food chains into food webs?
  • A given species may weave into the web at more
    than one trophic level.

Food Chains
  • All food chains start with producers, an
    autotroph who can make food using inorganic
  • All other trophic levels contain consumers or
    heterotrophs who must eat or consume other

Food Webs
  • Multiple food chains can be combined to form a
  • Some organisms can be in more than one trophic
    level (ex. Leopard seal)

What limits the length of a food chain?
  • The energetic hypothesis suggests that the length
    of a food chain is limited by the inefficiency of
    energy transfer along the chain.
  • Only 10 of the energy from one trophic level is
    transferred into the next
  • The dynamic stability hypothesis states that long
    food chains are less stable than short chains.
  • Fluctuations at lower trophic levels are
    magnified in higher levels, potentially causing
    extinction of top predators

Dominant and Keystone Species
  • Certain species may have a large impact on the
    entire community because of either their
    abundance or their role.
  • Dominant species are those in a community that
    have the highest abundance or highest biomass
    (the sum weight of all individuals in a
  • If we remove a dominant species from a community,
    it can change the entire community structure,
    both biotic and abiotic.
  • Keystone species exert an important regulating
    effect on other species in a community.
  • If they are removed, community structure is
    greatly affected.
  • Example Sea Star

Keystone Species Example
  • Pisaster ochraceous eats mussels from tidal
  • If sea stars are removed, mussels take over and
    outcompete all other species.
  • Predation by the sea star limits the number of
    mussels and decreases their competitive edge
    and allows other species to use the space

Community Control
  • Simplified models based on relationships between
    adjacent trophic levels are useful for discussing
    how communities might be organized.
  • Consider three possible relationships between
    plants (V for vegetation) and herbivores (H).
  • V ? H V ? H V ? H
  • Arrows indicate that a change in biomass of one
    trophic level causes a change in the other
    trophic level.
  • The bottom-up model postulates V ? H linkages,
    where nutrients and vegetation control community
  • An increase in vegetation will impact the biomass
    of herbivores, herbivores are limited by
    vegetation. Usually involves nutrients or abiotic
  • The top-down model postulates that it is mainly
    predation that controls community organization V
    ? H.
  • Increases predators will decrease herbiovers,
    which in turn control plants
  • Other models go between the bottom-up and
    top-down extreme models.
  • All interactions between trophic levels could be

Disturbance and Community Structure
  • Disturbances affect community structure and
  • Stability is the ability of a community to
    persist in the face of disturbance.
  • Most communities are in a state of nonequilibrium
    owing to disturbances
  • Disturbances are events like fire, weather, or
    human activities that can alter communities.
  • Disturbances do not always have a negative impact
    on communities, but in many cases they are
    necessary for community development and survival.
  • Humans are the most widespread agents of
  • Human activities cause more disturbances than
    natural events and usually reduce species
    diversity in communities.

  • Ecological succession is the sequence of
    community changes after a disturbance or the
    transition in species composition over ecological
  • Primary succession begins in a lifeless area
    where soil has not yet formed.
  • Mosses and lichens colonize first and cause the
    development of soil, called pioneer species.
  • Examples after a glacier has retreated, new
    volcanic island
  • Secondary succession occurs where an existing
    community has been cleared by some event, but
    the soil is left intact.
  • Grasses grow first, then trees and other
  • Soil concentrations of nutrients show changes
    over time.
  • Examples range from an old tree falling to a
    widespread forest fire or natural disaster

  • Two key factors correlated with a communitys
    biodiversity (species diversity) are its size and
  • Community biodiversity measures the number of
    species and their relative abundance
  • The variety of different kinds of organisms that
    make up a community has two components.
  • Species richness, the total number of species in
    the community.
  • Relative abundance of the different species.
  • Heterogeneity is the combination of richness and
    diversity and is used to measure biodiversity

Which is more diverse?
  • Imagine two small forest communities with 100
    individuals distributed among four different tree
  • Species richness may be equal, but relative
    abundance may be different.
  • Counting species in a community to determine
    their abundance is difficult, especially for
    insects and smaller organisms

Species Richness vs. Equatorial-Polar Gradient
  • Species richness generally declines along an
    equatorial-polar gradient
  • Tropical habitats support much larger numbers of
    species of organisms than do temperate and polar
  • The two key factors causing these gradients are
    probably evolutionary history and climate.
  • Organisms have a history in an area where they
    are adapted to the climate.
  • Energy and water may factor into this phenomenon.

Species Richness Community Size
  • Species richness is related to a communitys
    geographic size
  • The species-area curve quantifies what may seem
    obvious the larger the geographic area, the
    greater the number of species.

Biodiversity on Islands
  • Because of their size and isolation, islands
    provide great opportunities for studying some of
    the biogeographic factors that affect the species
    diversity of communities.
  • Imagine a newly formed island some distance from
    the mainland.
  • Robert MacArthur and E. O. Wilson developed a
    hypothesis of island biogeography to identify the
    determinants of species diversity on an island.
  • Two factors will determine the number of species
    that eventually inhabit the island.
  • The rate at which new species immigrate to the
  • The rate at which species become extinct.
  • Studies of plants on many island chains confirm
    their hypothesis.

Hypothesis of Island Biogeography
  • The equilibrium number of species on an island
    represents a balance between the immigration of
    new species to the island and the extinction of
    species already there
  • Large islands may have a larger equilibrium
    because immigration rates tend to be higher and
    extinction rates lower
  • Near islands tend to have larger immigration

Evidence of Island Biogeography Hypothesis
  • Galapagos islands show an increase of the number
    of plant species as the area of the island

AP Biology
  • Chapter 54Ecosystems

  • An ecosystem consists of all the organisms living
    in a community as well as all the abiotic factors
    with which they interact.
  • The dynamics of an ecosystem involve two
  • energy flow
  • chemical cycling
  • Ecosystem ecologists view ecosystems as energy
    machines and matter processors.
  • We can follow the transformation of energy by
    grouping the species in a community into trophic
    levels of feeding relationships.

Trophic Relationships
  • Autotrophs are the primary producers, and are
    usually photosynthetic (plants or algae).
  • They use light energy to synthesize sugars and
    other organic compounds.
  • Heterotrophs are at trophic levels above the
    primary producers and depend on their
    photosynthetic output.
  • Herbivores that eat primary producers are called
    primary consumers.
  • Carnivores that eat herbivores are called
    secondary consumers.
  • Carnivores that eat secondary consumers are
    called tertiary consumers.
  • Another important group of heterotrophs is the
    detritivores, or decomposers.
  • They get energy from detritus, nonliving organic
    material, and play an important role in material

Ecosystem Dynamics
Decomposition Connects Trophic Levels
  • The organisms that feed as detritivores often
    form a major link between the primary producers
    and the consumers in an ecosystem.
  • The organic material that makes up the living
    organisms in an ecosystem gets recycled.
  • An ecosystems main decomposers are fungi and
    prokaryotes, which secrete enzymes that digest
    organic material and then absorb the breakdown

  • The law of conservation of energy applies to
    ecosystems. (Energy can be neither created nor
    destroyed, only transformed)
  • We can potentially trace all the energy from its
    solar input to its release as heat by organisms.
  • The second law of thermodynamics (When converting
    energy, some is lost as heat) allows us to
    measure the efficiency of the energy conversions.
  • Energy moves in a straight line through an
    ecosystem. Sun?Producers?Consumers

Primary Production
  • The amount of light energy converted to chemical
    energy by an ecosystems autotrophs in a given
    time period is called primary production.
  • An ecosystems energy budget depends on primary
  • Most primary producers use light energy to
    synthesize organic molecules, which can be broken
    down to produce ATP
  • Every day, Earth is bombarded by large amounts of
    solar radiation. Most of this radiation lands on
    water and land that either reflect or absorb it.
  • Of the visible light that reaches photosynthetic
    organisms, only about 1 is converted to chemical
  • Although this is a small amount, primary
    producers are capable of producing about 170
    billion tons of organic material per year.
  • Total primary production is known as gross
    primary production (GPP).
  • Amount of light energy that is converted into
    chemical energy.
  • The net primary production (NPP) is equal to
    gross primary production minus the energy used by
    the primary producers for respiration (R)
  • Primary production can be expressed in terms of
    energy per unit area per unit time, or as biomass
    of vegetation added to the ecosystem per unit
    area per unit time.
  • The total biomass of photosynthetic autotrophs
    present in a given time, called the standing
    cropnot the same thing

Primary Production in Aquatic Ecosystems
  • Production in Marine Ecosystems.
  • Light is the first variable to control primary
    production in oceans, since solar radiation can
    only penetrate to a certain depth (photic zone).
  • Nitrogen is the one nutrient that limits
    phytoplankton growth in many parts of the ocean.
  • In the open ocean, nitrogen and phosphorous
    levels are very low in the photic zone, but high
    in deeper water where light does not penetrate.
  • Production in Freshwater Ecosystems.
  • Solar radiation and temperature are closely
    linked to primary production in freshwater lakes.
  • During the 1970s, sewage and fertilizer pollution
    added nutrients to lakes, which shifted many
    lakes from having phytoplankton communities to
    those dominated by diatoms and green algae.
  • This process is called eutrophication and has
    undesirable impacts from a human perspective.
  • Controlling pollution may help control

Primary Production in Terrestrial Ecosystems
  • On a large geographic scale, temperature and
    moisture/water availability are the key factors
    controlling primary production in ecosystems.
  • On a more local scale, mineral nutrients in the
    soil can play key roles in limiting primary
  • Scientific studies relating nutrients to
    production have practical applications in
  • (i.e. fertilizers)

Primary Production in Different Ecosystems
Secondary Production
  • The amount of chemical energy in consumers food
    that is converted to their own new biomass during
    a given time period is called secondary
  • The efficiency of energy transfer between trophic
    levels is usually less than 20
  • If we view animals as energy transformers, we can
    ask questions about their relative efficiencies.
  • Production efficiency Net secondary
    production/Assimilation of primary production
  • Net secondary production is the energy stored in
    biomass represented by growth and reproduction.
  • Assimilation consists of the total energy taken
    in and used for growth, reproduction, and
  • In other words production efficiency is the
    fraction of food energy that is not used for
  • Trophic efficiency is the percentage of
    production transferred from one trophic level to
    the next.

Energy Partitioning
  • Less than 17 of the caterpillars food is
    actually converted to caterpillar biomass

Ecological Pyramids
  • Pyramids of production represent the
    multiplicative loss of energy from a food chain.
  • Biomass Pyramids represent the ecological
    consequence of low trophic efficiencies.
  • Most biomass pyramids narrow sharply from primary
    producers to top-level carnivores because energy
    transfers are inefficient.
  • In some aquatic ecosystems, the pyramid is
  • For example, phytoplankta grow, reproduce, and
    are consumed rapidly.
  • They have a short turnover time, which is a
    comparison of standing crop mass compared to
  • Pyramids of numbers show how the levels in the
    pyramids of biomass are proportional to the
    number of individuals present in each trophic

  • Idealized pyramid of net production
  • Trophic efficiency is 10
  • Pyramids of biomass (standing crop)
  • Aquatic are often inverted because of the rapid
    turnover of photoplankton
  • Pyramid of Numbers shows actual of organisms at
    each trophic level

Green World Hypothesis
  • With so many consumers, how can we explain why
    most terrestrial ecosystems have large standing
  • According to the green world hypothesis,
    herbivores consume relatively little plant
    biomass because they are held in check by a
    variety of factors.
  • Plants have defenses against herbivores.
  • Nutrients, not energy supply, usually limit
  • Abiotic factors limit herbivores.
  • Intraspecific competition can limit herbivore
  • Interspecific interactions check herbivore

Biogeochemical Cycles
  • Nutrient circuits involve both biotic and abiotic
    components of ecosystems and are called
    biogeochemical cycles.
  • Biological and geologic processes move nutrients
    between organic and inorganic compartments
  • There are four main reservoirs of elements and
    processes transfer elements between reservoirs.
  • A reservoir is defined by two characteristics
    whether it contains organic or inorganic
    materials, and whether or not the materials are
    directly usable by organisms.
  • Describing biogeochemical cycles in general
    terms is much simpler than trying to trace
    elements through these cycles.

Water Cycle
Carbon Cycle
Nitrogen Cycle
  • Nitrogen enters ecosystems through two natural
  • Atmospheric deposition, where usable nitrogen is
    added to the soil by rain or dust.
  • Nitrogen fixation, where certain prokaryotes
    convert N2 to minerals that can be used to
    synthesize nitrogenous organic compounds like
    amino acids.
  • In addition to the natural ways, industrial
    production of nitrogen-containing fertilizer
    contributes to nitrogenous materials in
  • The direct product of nitrogen fixation is
    ammonia, which picks up H and becomes ammonium
    in the soil (ammonification), which plants can
  • Certain aerobic bacteria oxidize ammonium into
    nitrate, a process called nitrification.
  • Nitrate can also be used by plants.
  • Some bacteria get oxygen from the nitrate and
    release N2 back into the atmosphere

Nitrogen Cycle
Phosphorous Cycle
  • This cycle is simpler than the others because
    phosphorous does not come from the atmosphere.
  • Phosphorus occurs only in phosphate, which plants
    absorb and use for organic synthesis.
  • Humus and soil particles bind ph
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