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CHAPTER 4
Populations and
Communities
© 2011 Pearson Education, Inc.
An introduction to populations and
communities
• The golden frog is a national symbol of Panama
• Its black and yellow coloration warns of its poisonous
skin
• Populations are at very low levels, due to
• Habitat loss and overcollection for the pet trade
• Along with an introduced chytrid fungus
• To prevent extinction, conservationists collected all
amphibians from the wild in Panama
• Removing the last known population of golden frogs
in the world
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Dynamics of natural populations
• Population: a group of members of the same
species living in an area
• Community: populations of different species living
together in an area
• Populations grow with births and immigration
• They decline with deaths and emigration
(Births + Immigration) – (Deaths + Emigration)
= Change in population number
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Population growth
• Population growth: change in population
• Equilibrium: births + immigration are equal to
deaths + emigration
• Often, population growth is not zero
• Population growth rate: amount the population
has changed divided by the time it had to change
• Population growth curves: graph how
populations grow; used to find
• How fast a population could grow
• How many individuals there are now
• What the future population size could be
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Population growth curves
• Constant population growth rate: adding a
constant number of individuals over each time
period
• The simplest type of growth to model
• Is an unlikely pattern and is not generally found in
nature
• But it’s a good comparison to other growth patterns
• Starting with 2 individuals, and a constant growth
rate of 2, at the end of 24 weeks you would have
50 individuals
Population number at the start + (A constant * Time)
= Population number at the end
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Three models of population growth
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Exponential growth
• Each species can increase its population
• With favorable conditions
• Exponential increase: does not add a constant
number of individuals for each time period
• The doubling time remains constant
• For example, it takes 2 days to go from 8 to 16
individuals, as well as from 1,000 to 2,000 individuals
• Such growth is called an “explosion”
• J-curve: the curve of exponential growth
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The equation for exponential growth
• To calculate growth rate, you need to know
• The number in the current population
• The time period
• The number of offspring individuals can produce in
a given time if resources are unlimited (rmax or r)
• r = the number of times you multiply e by itself
• The potential to produce offspring
• Starting population * A constant (e) * itself a
certain number of times = Ending population
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Exponential growth of a population
• For example: for two worms
• r = 0.60, reproductive period = 1 week
• Over 4 weeks: 2 * e0.60*4 = 22 worms
• Over 24 weeks: 2 * e0.60*24 = over 3.5 million worms
• Under unlimited conditions, organisms with a high r
will have rapid population growth
• Carrying capacity (K): the maximum population of a
species that a given habitat can support without
being degraded
• This is the upper limit of population growth
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Outcomes of population increase
• The population continues to grow and then dies off
• Logistic growth: some process slows growth so it
levels off near carrying capacity
• Results in an S-shaped curve
• It levels off at K
• As the population approaches K, growth slows
• The population remains steady and growth = 0
• The maximum rate of population growth occurs
halfway to K
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Populations show logistic growth
• J-shaped explosions are often followed by crashes
• J-shaped growth results from unusual disturbances
• Introduction of a foreign species, a suddenly changed
habitat, the elimination of a predator, arrival in a new
habitat
• Other populations show an S-curve
• Followed by cycles of lower and higher numbers
around K
• Or shoot above K, eventually cycling around K
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Real-life growth
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Biotic potential vs. environmental
resistance
• Biotic potential: the number of offspring (live births,
eggs, or plant seeds and spores) produced under
ideal situations
• Measured by r (the rate at which organisms
reproduce)
• Varies tremendously from less than 1 birth/year (some
mammals) to millions/year (plants, invertebrates)
• Recruitment: survival through early growth stages
to become part of the breeding population
• Young must survive and reproduce to have any effect
on population size
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Environmental resistance
• Abiotic and biotic factors cause mortality (death)
• Prevents unlimited population growth
• Environmental resistance: the biotic and abiotic
factors that may limit a population’s increase
• Biotic: predators, parasites, competitors, lack of food
• Abiotic: unusual temperatures, moisture, light, salinity,
pH, lack of nutrients, fire
• Environmental resistance can also lower
reproduction
• Loss of suitable habitat, pollution
• Changed migratory habits of animals
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Biotic potential and environmental
resistance
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Reproductive strategies: r-strategists
• The interplay of environmental resistance and
biotic potential drives the success of two
reproductive strategies
• r-strategists (r-selected species): produce lots
of young, but leave their survival to nature
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Results in low recruitment
Rapid reproduction, rapid movement, short life span
Adapted to a rapidly changing environment
“Boom-and-bust” populations
“Weedy” or “opportunistic” species
For example, housefly
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Reproductive strategies: K-strategists
• K-strategists (K-selected species): lower biotic
potential
• Care for and protect young
• Live in a stable environment already populated by
the species
• Larger, longer lived, well-adapted to normal
environmental fluctuations
• Their populations fluctuate around carrying capacity
• Also called equilibrial species
• For example, elephant, California condor
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Life histories
• Life history: progression of changes in an
organism’s life
• Age at first reproduction, length of life, etc.
• Visualized in a survivorship graph
• Type I survivorship: low mortality in early life
• Most live the bulk of their life span (e.g., humans)
• Type III survivorship: many offspring that die young
• Few live to the end of their life (oysters, dandelions)
• Type II survivorship: intermediate survivorship
pattern (squirrels, coral)
• K-strategists have a Type I pattern; r-strategists
show Type III
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Survivorship curves
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Predictable pattern in species
• There is a predictable pattern to the way human
activities affect species
• r-strategists become pests when humans change an
area
• Houseflies, dandelions, cockroaches increase
• K-strategists become rarer or extinct with change
• Eagles, bears, and oaks decline
• An exception: rare opportunistic species (r-selected)
are separated from new habitat
• They cannot succeed, despite high biotic potential
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Why does a population grow?
• A population’s size depends on the interplay
between its biotic potential and environmental
resistance
• A population’s biotic potential remains constant
• Environmental resistance changes
• Population balance is a dynamic balance
• Additions (births, immigration) and subtractions
(death, emigration) occur continually
• The population may fluctuate widely or very little
• A population is at equilibrium when populations
restore their numbers and the ecosystem’s
capacity is not exceeded
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Limits on populations
• The carrying capacity may not explain what limits a
population
• Population density: number of individuals per unit
area
• The higher the density, the more likely a factor (e.g.,
crowding or disease) affects the population
• Some factors (e.g., a tornado) keep a population
from increasing, but have nothing to do with the
density of the organisms
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Density dependence and independence
• Density-dependent factor: increases with
increased population density
• Predation, disease, food shortage
• Logistic growth occurs when populations become
more crowded (approach carrying capacity)
• Density-independent factor: one whose effects are
independent of the density of the population
• Spring freeze, fire
• Is not involved in maintaining population equilibrium in
the logistic growth
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Regulating a population
• Only density-dependent factors can regulate a
population (keep it in equilibrium)
• Top-down regulation: control of a population (species)
by predation
• Bottom-up regulation: control of a population occurs
as a result of scarcity of a resource (food)
• Factors controlling a population determine the
effects on an ecosystem of adding or removing a
species
• Removal of a species can affect species that don’t
directly interact with it
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Top-down and bottom-up control
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Critical number
• Critical number: the minimum population base
allowing the survival and recovery of a population
• A pack of wolves, flock of birds, school of fish
• The group is necessary to provide protection and
support
• If a population falls below this number
• Surviving members become more vulnerable
• Breeding fails
• Extinction is almost inevitable
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Humans are responsible for
biodiversity loss
• Human activities are responsible for the decline and
extinction of species
• Humans change habitats, introduce alien species,
pollute, hunt, etc.
• Human activities are not density dependent
• They can even intensify as numbers decline
• The Endangered Species Act calls for recovery of
• Threatened species: populations are declining rapidly
• Endangered species: populations are near the critical
number
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Community interactions
• Relationships between species may be positive (helpful),
negative (harmful), or neutral for each species
• Predation: one member benefits, the other is harmed (+−)
• Includes parasitism, herbivory
• Competition: both species are harmed (−−)
• Interspecific competition: between different species
• Intraspecific competition: between the same species
• Mutualism: both species benefit (++)
• Commensalism: One species benefits, the other is not
affected (+0)
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Species interactions
• The most important relationships
• Predation, competition, mutualism, commensalism
• Amensalism: one species is unaffected, the other is
harmed (0−)
• For example, an elephant stepping on a flower
• It is theoretically possible to have a (00) relationship
• It has no name
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Major types of interactions between
species
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Predation
• Predator: the organism that does the feeding
• Prey: the organism that is fed upon
• Predator-prey interaction: carnivores (meat eaters)
eat herbivores (plant eaters)
• Herbivores feed on plants
• Parasites feed on hosts
• Parasite: an organism (plant or animal) that feeds on
its “prey,” usually without killing it
• Host: the organism that is being fed upon
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Parasitic organisms
• Include tapeworms, disease-causing bacteria,
viruses, fungi
• Parasites affect host populations in a densitydependent way
• Increased population density makes it easier for
parasites and their vectors (carriers of the parasite) to
find new hosts
• Pathogens: bacteria and viruses that cause
disease
• No real ecological difference from other parasites
• Highly specialized parasites
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Several types of parasites
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Regulation of prey
• Predators can regulate herbivore numbers (topdown control)
• Moose crossed to Isle Royale, in Lake Superior
• Several years later, wolves also reached the island
• Without wolves, the moose population grew rapidly
• Low environmental resistance for the moose
• The wolf population also increased and preyed on
moose
• Low environmental resistance for the wolves
• Fewer moose (high environmental resistance)
resulted in fewer wolves (high environmental
resistance)
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Predator-prey relationships
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Other factors affect populations
• Wolf predation is not the only factor affecting moose
• Deep snow limited access to food
• A tick infestation caused significant mortality
• A sharp decline in moose keeps wolf populations low
• Not enough calves to catch
• Wolves can’t catch a mature moose in good condition
• Predator-prey relationships involve top-down (on the
prey) and bottom-up (on the predator) regulation
• Parasites weaken hosts, making them more
vulnerable to predation
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Overgrazing
• If herbivores eat plants faster than they can grow,
plants are depleted and animals eventually suffer
• Reindeer were brought to St. Matthew Island
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At first, they were healthy and well-nourished
They ate up the lichens
A few years later, they were malnourished
With little food and harsh weather, almost the entire
herd starved
• No population can escape the ultimate limitations set
by environmental resistance
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Plant-herbivore interactions
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Predator removal
• Eliminating predators upsets plant-herbivore
relationships
• White-tailed deer in the U.S. were originally
controlled by wolves, mountain lion, bears
• But these were killed because they were thought to
threaten livestock and humans
• Deer populations can get so large they overgraze the
area
• Humans control numbers through hunting
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Keystone species
• Removal of one species can create a cascade of
effects
• Impacting far more than just the other species they
interact with
• Sea stars eat mussels in rocky intertidal zones
• Removing sea stars allows mussels to crowd out
all other species, reducing diversity
• Keystone species: play a crucial role in
maintaining ecosystem biotic structure
• Moderate other species that would take over
• Allow other, less-competitive species to flourish
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Sea stars: a keystone species
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Keystone species
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Competition
• Interactions where both species are harmed
• They compete for a scarce resource
• Species that compete have overlapping niches
• Over time, there is pressure to reduce the overlap
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Competition
• Intraspecific competition: competition between
members of the same species
• Occurs over resources
• Territory: an area defended by an individual or
group
• Is vigorously defended
• Most defense is intimidation—serious fights are rare
• Organisms fight to protect an area for nesting,
establishing a harem, or food resources
• Lack of territories: a density-dependent limitation on a
population
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Territoriality
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Competition
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Territoriality as an advantage
• It protects a population from the possibility of
everyone getting some resources, but nobody
getting enough to survive
• Without territoriality, when resources are scarce
• Every encounter could end in a potentially lethal fight
• All members would get only a part of what they need
and could die
• Competition lowers fitness and production of
offspring
• Territoriality lowers the direct effects of competition
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Not everyone gets a territory
• Individuals unable to claim a territory
• Are often young and may obtain a territory later
• May disperse, opening new habitats to the species
• May die
• Territoriality is most likely in K-strategists
• An adaptation that helps organisms disperse and
stabilizes populations
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Impact on the species
• Survival of the fittest: one of the forces in nature
leading to evolutionary changes in a species
• Those individuals in a competing group that can
survive and reproduce demonstrate superior fitness
to the environment
• Every factor of environmental resistance is a
selective pressure
• Individuals who survive and reproduce have the
genetic endowment to better cope with their
environment
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Intraspecific competition’s impact
• Short-term impact on a population: it leads to
density-dependent regulation of a population
• Through territoriality
• Through self-thinning: crowded organisms (e.g., trees)
become less numerous as they get bigger
• Long-term impact on a population: it leads to longterm changes as the species adapts to its
environment
• Those better able to compete, survive, and reproduce
• Their superior traits are passed on to successive
generations
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Interspecific competition
• Competitive exclusion principle: species cannot
survive competition if they compete directly in many
respects
• In simple habitats with species needing the same
resources
• But species do occupy the same area without
becoming extinct
• Abiotic conditions in an environment vary in space
and time
• Adaptations of species to specific conditions allows it
to thrive and overcome its competitors in one
location or time, but not in another
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Environments are heterogeneous
• Variable environments support species with different
niches
• Competitors in the same habitat have different
niches
• Woodpeckers eat insects; other birds eat seeds
• Space can also be a resource
• Resource partitioning: the division of a resource and
specialization in different parts of it
• With more intense competition, resources are even
further divided
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Resource partitioning in warblers
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Adaptations limit competition
• Adaptations, including behavior, limit competition
• Organisms can put energy into reproduction
• Competition changes some characteristics, so
organisms use only a part of their niche
• For example, two closely related finches on the same
island have different sized beaks to eat different
seeds
• Character displacement: a physical change that
decreases competition when two species co-occur
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Character displacement in finches
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Mutualism
• An arrangement between two species where both
benefit
• Examples of mutualism
• Pollinators (e.g., bees) receive nutrition while plants
receive pollination
• Fungi on roots: the fungus gets nutrition; the plant
gets easier intake of soil nutrients
• Lichens are made of a fungus and an alga
• The anemone fish protects the anemone from
predation by the butterfly fish, and the anemone
protects the fish
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Mutualistic relationships
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Commensalism and amensalism
• Commensalism: one species benefits; the other is
unaffected
• More rare
• Buffalo stir up insects that cattle egrets eat
• Orchids live on trees but do not harm or feed off of
them
• Amensalism: one species is harmed; the other is
unaffected
• Usually accomplished by natural chemical compounds
• Black walnut trees produce a chemical that kills other
plants
• Symbiosis: two species live close to each other
• Can be beneficial (mutualism) or harmful (parasitism)
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Commensalism
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Evolution as a force for change
• Predation and competition keep populations
under control
• Individuals with qualities that lower impacts of
negative interactions survive
• Predators and prey become adapted to each
other
• Intraspecific competition leads to improved
adaptations to the environment
• Interspecific competition promotes adaptations in
competitors
• They specialize in exploiting a resource
• Resource partitioning allows resource sharing
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Resource partitioning in plants
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Selective pressures
• Most young plants and animals do not survive
• Selective pressures: environmental resistance
factors affect which individuals survive and
reproduce
• Predators, parasites, drought, lack of food
• Animals with traits that protect them or allow them to
escape can survive and reproduce
• Predators function as a selective pressure: favoring
survival of traits that enable prey to escape predation
• Food is a selective pressure: predators with keen
eyesight or swift speed survive
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Cryptic coloration
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Natural selection and evolution
• Natural selection: the process of specific traits
favoring survival of certain individuals
• Charles Darwin’s On the Origin of Species by Means
of Natural Selection (1859)
• Biological evolution: modification of the gene pool
of a species by natural selection over generations
• Our understanding of DNA, mutations, and genetics
supports the theory of evolution by natural selection
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Adaptations to the environment
• Fitness: features (traits) that adapt an organism for
survival and reproduction
• A population’s gene pool is tested by selective
pressures exerted by environmental resistance
• All traits adapt an organism to survival and
reproduction
• Adaptations needed for coping with abiotic factors
• Obtaining nutrients, energy, defense against
predation
• Finding and attracting mates
• Migrating and dispersal
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Adaptation for survival and
reproduction
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The limits of change
• Does the trait increase survival and reproduction?
• If “yes,” the trait is maintained through natural
selection
• Various organisms have evolved different traits
• To accomplish the same function (e.g., avoid
predation)
• A species has three alternatives when faced with a
new selective pressure
• Adaptation: through natural selection
• Migration: move to an area with suitable conditions
• Extinction: inevitable if the first two options are not
possible
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Factors that determine whether a
species can adapt
• Some individuals have traits (alleles: variations or
new combinations of genes) that allow them to
survive and reproduce under the new conditions
• There must be enough survivors to maintain a viable
breeding population
• Natural selection should lead to increased
adaptations over successive generations
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The California condor
• By the early 1980s, only 20 birds remained
• Only nine lived in the wild
• Deaths due to poaching, lead poisoning, habitat
destruction
• Wildlife biologists captured all wild-living birds and
started a captive breeding program
• By 2008, 320 condors survived
• 180 in captivity
• This is still not a viable breeding population, but wild
condors are forming pairs and nesting
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Keys to survival
• Four variables affect whether a population survives
new conditions
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Geographical distribution
Specialization to a given habitat or food supply
Genetic variation within the population
The reproductive rate relative to the rate of
environmental change
• Less vulnerable species are r-strategists
• More vulnerable species are K-strategists
• Very rapidly reproducing species can be vulnerable
if the environment changes too rapidly or much
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Vulnerable and highly adaptive species
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Genetic change
• How fast can a population evolve adaptations to
cope with new or changing conditions?
• Over the lifetime of the individual: there is no genetic
change and no genetic adaptation
• Genetic variation occurs over generations through
hybridization, mutation, and crossover (sections of
chromosomes are swapped)
• Genetic variation is the norm in living things
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The evolution of species
• Biodiversity is decreasing because species are
going extinct faster than new species are appearing
• Mutations and natural selection adapt a species to
the biotic community and environment in which it
exists
• The process of speciation: the final result of
adaptation may be a population so different from the
original population it is considered a new species
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How two species may develop from one
• They must be reproductively isolated: the original
populations separate into nonbreeding populations
• Or else genes will continue to mix, keeping it one
species
• Separate populations must be exposed to different
selective pressures
• As they respond to these pressures, they become
different
• They can’t interbreed, even if they come together
again
• Arctic and gray foxes became separated by
glaciation
• Selective pressure on the northern population resulted
in heavier fur, shorter limbs, and white fur
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Evolution of new species
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Darwin’s finches
• Charles Darwin speculated that differences in beak
size and structure in finches on islands in the
Galápagos happened after subpopulations became
isolated on separate islands
• Birds blown west from South America landed on
islands
• Intraspecific competition caused birds to disperse
• Different selective pressures caused birds to become
specialized for feeding on different things
• When populations re-encountered each other, they
were so different, they could not interbreed
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Some of Darwin’s finches
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New species are arising right now
• Saltmarsh cordgrass developed as a hybrid of two
species that interbred in England’s mud flats
• It has a different niche and characteristics from the
parents
• New species are not formed from scratch
• They are formed only by modification of existing
species
• Selective pressures, isolation, and hybridization result
in new adaptations
• Closely related species are found in nature
• Overwhelming evidence tells us that species
developed through evolution over long periods of time
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Drifting continents
• Geographic isolation of populations is fundamental
to speciation
• Populations became isolated through the slow
movement of Earth’s continents
• Plate tectonics: continents were once connected
into a great land mass (Pangaea), which then
separated
• Tectonic plates: in the Earth’s crust, huge slabs of
rock that float on an elastic layer beneath them
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Drifting continents and plate tectonics
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Movement of tectonic plates
• Tectonic plates ride atop convection currents caused
by rising hot interior material and sinking cooler
material
• Adjacent tectonic plates move
• Separating (in mid-ocean ridges)
• Sliding past each other (at fault lines)
• Colliding (creating mountain ranges)
• The 2004 tsunami (tidal wave) in Indonesia
• The Indo-Australian plate slid under the Eurasian plate
• Displaced enormous quantities of water and caused
waves that killed 225,000 people
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Tectonic movement affects climate and
diversity
• As continents move, their climate changes
accordingly
• Continental movement changes the direction and
flow of ocean currents, which affects climate
• Uplifting of mountains changes movements of air
currents
• Changes in Earth’s crust have increased diversity
• Moving continents isolated populations into six
zoogeographic regions
• Australia is on the Indo-Australian tectonic plate
• Its ancient separation led to many unique species
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Unique species occur where tectonic
plates meet
• Indonesia is located on the junction of three tectonic
plates
• It has species that occur nowhere else in the world
• Papua New Guinea has species similar to Australia’s
• The island of Sulawesi lies between plates and was
formed by islands being pushed together
• Its plants and animals have relatives in far distant
parts of the world
• Australia and Indonesia show how long-term, largescale changes change the environment and increase
biodiversity
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Implications for human management
• Ecologists study populations and communities
• To increase our understanding of the world
• To better manage natural resources by protecting
declining species and controlling pest species
• To study our impacts on populations
• Keystone species are such an integral part of the
ecosystem
• Removing them can cause the ecosystem to collapse
• For example, removing beavers (by overhunting and
habitat destruction) hurt wetland meadow species
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Introduced species
• Humans have introduced species from foreign
ecosystems, changing community and population
relationships
• Thousands of species have been accidentally or
deliberately introduced
• Economic losses in the U.S. of $138 billion/year
• Rabbits were introduced into Australia for sport
shooting
• Without natural enemies, the population exploded,
devastating the environment
• After being eradicated on Philip Island, the island’s
vegetation was dramatically restored
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Rabbit eradication on Philip Island
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Plants
• Introduced plants can have a devastating effect on
plants and animals
• The chestnut blight fungus has killed almost every
American chestnut tree
• Kudzu, a vine introduced to control erosion and for
cattle fodder, has invaded and climbed over forests
• Spotted knapweed has ruined millions of acres of
rangelands
• Purple loosestrife has invaded wetlands and
replaced edible wildlife plants
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Introduced plant species
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Pests
• Most insect pests in croplands and forests are
introduced
• Japanese beetles, fire ants, gypsy moths
• Goats and pigs on islands
• Domestic cats diminish songbird populations
• The problem is increasing due to expanding world
trade and travel
• Zebra and quagga mussels, introduced into the
Great Lakes, are now found in California
• Jellyfishlike ctenophores cost Black Sea fishermen
$250 million
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Introduced species
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Two lessons from introducing
undesirable species
• Population regulation is a matter of complex
interactions among members of the biotic community
• Relationships are specific to organisms in each
ecosystem
• An introduced species is unlikely to fit into the
framework of relationships in the new community
• Severe environmental resistance may kill off the
species
• The species may join the native species and do no
harm (it has become naturalized: food crops)
• The species may become invasive: outcompeting
native species for food, space, predation, other
resources
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Remedies
• U.S. state and federal agencies work to slow and
stop invasive species
• Regulations and checkpoints
• Introduction of a natural enemy
• Control is due to many factors, including several
enemies and all abiotic factors
• Species have adapted to other species in their own
ecosystems
• They are not prepared to interact with other species
that developed in other ecosystems
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CHAPTER 4
Populations and
Communities
Active Lecture Questions
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Review Question-1
(Births plus ________) minus (________ plus
Emigration) = Change in population number
a. Emigration; Births
b. Immigration; Deaths
c. Immigration; Births
d. Emigration; Deaths
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Review Question-1 Answer
(Births plus ________) minus (________ plus
Emigration) = Change in population number
a. Emigration; Births
b. Immigration; Deaths
c. Immigration; Births
d. Emigration; Deaths
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Review Question-2
True or False: Natural selection results in a
modification of the gene pool toward traits that
enhance survival and reproduction of a
population.
a. True
b. False
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Review Question-2 Answer
True or False: Natural selection results in a
modification of the gene pool toward traits that
enhance survival and reproduction of a
population.
a. True
b. False
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Review Question-3
The rate at which members of a species
reproduce if there are no limiting factors is
referred to as
a. K-strategy.
b. r-strategy.
c. environmental resistance.
d. biotic potential.
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Review Question-3 Answer
The rate at which members of a species
reproduce if there are no limiting factors is
referred to as
a. K-strategy.
b. r-strategy.
c. environmental resistance.
d. biotic potential.
© 2011 Pearson Education, Inc.
Review Question-4
A species that has a critical role in maintaining
an ecosystem’s biotic structure is a
a. J-curve species.
b. K-strategist.
c. keystone species.
d. biotic potential.
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Review Question-4 Answer
A species that has a critical role in maintaining
an ecosystem’s biotic structure is a
a. J-curve species.
b. K-strategist.
c. keystone species.
d. biotic potential.
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Review Question-5
The theory that has helped us understand
earthquakes, volcanic activity, and the
geographic distribution of present-day biota is
a. the law of limiting factors.
b. the Laws of Thermodynamics.
c. the theory of evolution.
d. plate tectonics.
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Review Question-5 Answer
The theory that has helped us understand
earthquakes, volcanic activity, and the
geographic distribution of present-day biota is
a. the law of limiting factors.
b. the Laws of Thermodynamics.
c. the theory of evolution.
d. plate tectonics.
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Interpreting Graphs and Data-1
According to Fig. 4-2, the population growth
curve that represents logistic growth is
a. the J-curve.
b. the S-curve.
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Interpreting Graphs and Data-1 Answer
According to Fig. 4-2, the population growth
curve that represents logistic growth is
a. the J-curve.
b. the S-curve.
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Interpreting Graphs and Data-2
According to Fig. 4-8, the approximate date that
this population reached its greatest level of
environmental resistance was
a. 1944.
b. 1955.
c. 1963.
d. 1991.
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Interpreting Graphs and Data-2 Answer
According to Fig. 4-8, the approximate date that
this population reached its greatest level of
environmental resistance was
a. 1944.
b. 1955.
c. 1963.
d. 1991.
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Thinking Environmentally-1
A K-strategist’s population size typically
fluctuates around
a. the midpoint of the J-curve.
b. carrying capacity.
c. density-dependent factors.
d. density-independent factors.
© 2011 Pearson Education, Inc.
Thinking Environmentally-1 Answer
A K-strategist’s population size typically
fluctuates around
a. the midpoint of the J-curve.
b. carrying capacity.
c. density-dependent factors.
d. density-independent factors.
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Thinking Environmentally-2
A sudden hard freeze that kills members of an
ecosystem is an example of
a. a critical number.
b. a density-dependent factor.
c. a density-independent factor.
d. density-driven resistance.
© 2011 Pearson Education, Inc.
Thinking Environmentally-2 Answer
A sudden hard freeze that kills members of an
ecosystem is an example of
a. a critical number.
b. a density-dependent factor.
c. a density-independent factor.
d. density-driven resistance.
© 2011 Pearson Education, Inc.