AP Environmental Science Study Guide
Chapters 1-4
Key Terms
Ecological footprint
ecosystem services
environmentalism
natural capital
Peer review
sustainability
autotrophs
continental collision
Convergent plate boundary divergent plate boundary
1st Law of Thermodynamics half-life
Heterotrophs
hydrocarbon
law of conservation of matter igneous rock
Macromolecules
mineral
organic compounds
ozone
Plate tectonics
radioactive
adaptive trait
age distribution
Artificial selection
biodiversity
community
convergent evolution
Demographers
density dependent factor
density independent factors ecosystem
Emigration
endemic
generalists
habitat
Immigration
K-selected
limiting factors
natural selection
Polygenetic trees
population density
population distribution
rate of natural increase
r-selected
specialist
speciation
species
Survivorship curves
biome
character displacement
climate diagrams
Climax communities
coevolution
competitive exclusion
detritivores
Ecological restoration
fundamental niche
herbivory
host
Interspecific competition
intraspecific competition
introduces species
invasive species
Keystone species
mutualism
no-analog communities
novel communities
Omnivore’s
pathogens
parasite
parasitism
Parasitoid
permafrost
phase shift
pioneer species
Predation
prey
primary consumers
primary succession
Rain shadow
realized niche
resource partitioning
secondary consumers
secondary succession
species coexistence
succession
symbiosis
Tertiary consumers
trophic cascade
niche
Key Ideas: Chapter 1
Our Island, Earth: its systems are finite and limited: Increases in population, technological power, and resource
consumption alter our surroundings and damage the systems that keep us alive.
A. Our environment surrounds us.
1. Our environment consists of all the living and nonliving things around us.
2. We are part of the “natural” world, and our interactions with it matter a great deal.
B. Environmental science explores our interactions with the world.
1. We modify our environment.
2. Environmental science is the study of how the natural world works, how our environment affects
us, and how we affect our environment.
3. Environmental scientists study issues of central importance to our world and its future. Rapidly
changing global conditions demand that we act now to solve problems.
C. We rely on natural resources.
1. Natural resources are the substances and energy sources we need to survive. Our island, Earth, is
finite and bounded, and it places limitations on the availability of these resources.
2. Renewable natural resources, such as sunlight, wind, and wave energy, are essentially
inexhaustible, while other nonrenewable natural resources, such as minerals and crude oil, are in
finite supply, and formed much more slowly than we use them.
3. Renewability is a continuum. Some resources renew themselves over months, years, or decades,
and can be depleted if we use them faster than they are replenished.
D. We rely on ecosystem services.
1. Earth’s natural systems provide ecosystem services such as air and water purification, climate
regulation, and plant pollination. We could not survive without these processes.
2. We have degraded nature’s ability to provide these services by depleting resources, destroying
habitats, and generating pollution.
E. Population growth amplifies our impact.
1. Today, our population has grown beyond 7 billion people.
2. Two phenomena triggered remarkable increases in the Earth’s population. The agricultural
revolution occurred around 10,000 years ago as humans transitioned from a hunter-gatherer lifestyle
to an agricultural way of life.
3. The industrial revolution began in the mid-1700s. It was a shift from rural, agricultural life to an
urban society provisioned by mass-produced manufactured goods and powered by fossil fuels.
4. The population size is putting unprecedented stress on natural systems and the availability of
resources.
F. Resource consumption exerts social and environmental pressures.
1. Industrialization increased the amount of resources each one of us consumes.
2. One way to quantify resource consumption is to use the concept of the ecological footprint, which
expresses the environmental impact in terms of the cumulative area of biologically productive land
and water required to provide the resources a person or population consumes and to dispose of or
recycle the waste they produce.
3. Wackernagel and his colleagues calculate that our species is now using 50% more of the planet’s
resources than are available on a sustainable basis. This excess use has been termed overshoot.
4. People from wealthy nations have much larger ecological footprints than do people from poorer
nations.
G. Environmental science can help us avoid past mistakes.
1. Most great civilizations have fallen after degrading their environments, leaving devastated
landscapes behind.
2. Author Jared Diamond argues that success and persistence depend largely on the interaction
between the society and the environment, and response to problems.
3. The stakes are higher than ever today. If we cannot forge sustainable solutions, there will be global
societal collapse.
Sustainability and Our Future
A. Achieving sustainable solutions is vital.
1. The primary challenge in our increasingly populated world is how to live within our planet’s means.
This is the challenge of sustainability, a guiding principle of modern environmental science.
2. We are drawing down Earth’s natural capital, its accumulated wealth of resources, 50% faster than
it is being replenished. This cannot be sustained.
B. Population and consumption drive environmental impact.
1. The ways we modify the environment have been influenced by the steep and sudden rise in
human population.
2. Our consumption of resources has risen even faster than our population.
3. Discrepancies in income lead to large differences in the ecological footprint of citizens from
different nations.
4. Our dramatic growth in population and consumption is intensifying many environmental impacts.
5. The most comprehensive scientific assessment of the condition of the world’s ecological systems
and their capacity to continue supporting our civilization was completed in 2005, called the
Millennium Ecosystem Assessment.
C. Our energy choices will influence our future enormously.
1. Our reliance on fossil fuels, while bringing us material affluence, has intensified virtually every
impact that we have on the environment.
2. In addition to the environmental problems caused, we will soon have to deal with the depletion of
these fuels and the energy crisis that this could precipitate.
D. Sustainable solutions abound.
1. Many workable solutions are at hand.
a. Renewable energy and efficiency efforts are gaining ground.
b. Scientists have developed and promoted soil conservation, high-efficiency irrigation, and
organic agriculture.
c. Laws and new technologies have reduced emitted air pollution.
d. Conservation biologists are helping protect habitat and endangered species.
e. Recycling is helping conserve resources and alleviate waste disposal problems.
f. Steps are being taken to reduce greenhouse gas emissions that drive climate change.
2. These are a few of many efforts.
E. Students are promoting solutions on campus.
1. Proponents of campus sustainability seek ways to help colleges and universities reduce their
ecological footprints.
2. College and universities are centers of lavish resource consumption.
3. Reducing the size of this footprint is challenging.
4. Students are often the ones who initiate change, although support from faculty, staff, and
administrators is crucial for success.
F. Campus sustainability efforts are diverse.
1. Students are advancing sustainability efforts on their campuses in a variety of ways.
2. Seven hundred university presidents have signed onto the American College and Presidents’
Climate Commitment.
3. Students who take the initiative to promote sustainable practices on their campuses accomplish
several things at once:
a. Students can make a difference by reducing the ecological footprint of a campus.
b. Students who advance campus sustainability can serve as models for their peers.
c. Students can learn and grow as a result.
Key Ideas: Chapter 4
Evolution: The Source of Earth’s Biodiversity
1. A species is a particular type of organism or, more precisely, a population or group of populations whose members
share characteristics and can freely breed with one another and produce fertile offspring.
2. A population is a group of individuals of a particular species that live in a particular area.
3. Evolution in the broad sense means change over time, and biological evolution consists of change in populations of
organisms across generations.
4. Natural selection is the process by which inherited characteristics that enhance survival and reproduction are
passed on more frequently to future generations than those that do not, altering the genetic makeup of populations
through time.
A. Natural selection shapes organisms and diversity.
1. The idea of natural selection follows logically from a few straightforward premises that are readily apparent to
anyone who observes the life around us.
a. Organisms face a constant struggle to survive and reproduce.
b. Organisms tend to produce more offspring than can survive.
c. Individuals of a species vary in their characteristics.
2. Variation is due to differences in genes, the environments in which genes are expressed, and the interactions between
genes and environment. As a result of this variation, some individuals of a species will be better suited to their
environment than others and will be better able to reproduce.
3. From one generation to another through time, characteristics, or traits, that lead to better and better reproductive
success in a given environment will evolve in the population. This is termed adaptation, and a trait that promotes success
is also called an adaptation or an adaptive trait.
B. Selection acts on genetic variation.
1. Accidental changes in DNA, called mutations, give rise to genetic variation among individuals.
2. Genetic variation is also generated as organisms mix their genetic material through recombination during sexual
reproduction.
3. Because evolutionary change generally requires a great deal of time, a species cannot always adapt to
environmental conditions that change quickly.
4. However, genetic variation can sometimes help protect a population against novel challenges.
C. Selective pressures from the environment influence adaptation.
1. Closely related species living in different environments may evolve differently as a result of different selective
pressures. Conversely, sometimes very unrelated species may acquire similar traits as they adapt to selective
pressures from similar environments; this is called convergent evolution.
2. Environments change over time and traits that produce success at one time or location may not do so at another.
D. Evidence of selection is all around us.
1. Scientists have demonstrated the rapid evolution of traits by selection in countless lab experiments, mostly with fast
reproducing organisms such as bacteria, yeast, and fruit flies.
2. Through selective breeding, we have been able to augment particular traits we prefer.
3. This process of selection conducted under human direction is termed artificial selection.
4. Many of our domestic pets and food crops are a result of this process.
E. Evolution generates biological diversity.
1. Biological diversity, or biodiversity, refers to the variety of life across all levels of biological organization, including
the diversity of species, genes, populations, and communities.
2. Scientists have described about 1.8 million species but estimate that 100 million may exist.
F. Speciation produces new types of organisms.
1. The process by which new species are generated is termed speciation. The main mode is generally thought to be
allopatric speciation, whereby species form from populations that become physically separated over some geographic
distance.
2. When a mutation arises in the DNA of an organism in one of these newly isolated populations, it cannot spread to
the other populations.
G. Populations can be separated in many ways.
1. Populations can undergo long-term geographic isolation in various ways.
2. Alternatively, sometimes new areas are created and organisms colonize them, establishing isolated populations.
3. For speciation to occur, populations must remain isolated for a very long time, generally thousands of generations.
H. We can infer the history of life’s diversification by comparing organisms.
1. Evolutionary biologists study patterns, examining how groups of organisms arose and how they evolved the
characteristics they show.
2. Scientists represent the history of divergence by using branching, tree-like diagrams called phylogenetic trees.
3. Once we have a phylogenetic tree, we can map traits onto the tree according to which organisms possess them, and
we can thereby trace how the traits have evolved.
4. Taxonomists use an organism’s physical appearance and genetic makeup to determine its species. Related species
are grouped together into genera (singular, genus), related genera are grouped into families, and so on.
5. Today biologists use evolutionary information from phylogenetic trees to help classify organisms under the
Linnaean system’s rules.
Levels of Ecological Organization
Ecology is the scientific study of the distribution and abundance of organisms, the interactions among organisms, and the
relationships between organisms and their environments.We study ecology at several levels.
1. Life exists in a hierarchy of levels, from atoms, molecules, and cells up through the biosphere, which is the
cumulative total of living things on Earth and the areas they inhabit.
2. At the level of the organism, ecology describes the relationships between the organism and its physical
environment. In contrast, population ecology examines the dynamics of population change and the factors that affect
the distribution and abundance of members of a population.
3. A community consists of an assemblage of populations of interacting species. Community ecology focuses on
patterns of species diversity and on interactions among species, ranging from one-to-one interactions to complex
interrelationships involving the entire community.
4. Ecosystems encompass communities and the abiotic (nonliving) material, and forces with which community
members interact. Ecosystem ecology reveals patterns, such as the flow of energy and nutrients, by studying living and
non-living components of systems in conjunction.
Each organism has habitat needs.
1. The specific environment in which an organism lives is its habitat.
2. Each organism thrives in certain habitats and not others, leading to non-random patterns of habitat use. Mobile
select habitats in which to live from among the range of options they encounter, a process called habitat selection.
3. Habitats are scale dependent.
4. The criteria by which organisms favor some habitats over others can vary greatly.
5. Habitat use is important in environmental science because the availability and quality of habitat are crucial to an
organism’s well-being.
Niche and specialization are key concepts in ecology.
1. A species’ niche reflects its use of resources and its functional role in a community.
2. Species with narrow breadth, and thus very specific requirements, are said to be specialists. Those with broad
tolerances, able to use a wide array of resources, are generalists.
3. Specialists succeed over evolutionary time by being extremely good at the things they do, but they are vulnerable
when conditions change and threaten the habitat or resource on which they have specialized. Generalists succeed by
being able to live in many different places and to withstand variable conditions, but they may not thrive in any one
situation as much as a specialist would.
Population Ecology
A. Populations show characteristics that help predict their dynamics.
1. Population size is expressed as the number of individual organisms present at a given time, and may increase,
decrease, undergo cyclical change, or remain stable.
2. Population density describes the number of individuals in a population per unit area.
3. Population distribution describes the spatial arrangement of organisms in an area.
a. In a random distribution, individuals are located haphazardly in no particular pattern.
b. A uniform distribution is one in which individuals are evenly spaced.
c. In a clumped distribution, the pattern most common in nature, organisms arrange themselves according to
the availability of resources they need to survive.
4. A population’s sex ratio is its proportion of males to females, and this can influence whether the population will
increase or decrease in size over time.
5. Age distribution, or age structure, describes the relative numbers of organisms of each age within a population.
6. To show how the likelihood of survival varies with age, ecologists use graphs called survivorship curves.
B. Populations may grow, shrink, or remain stable.
1. Demographers, scientists who study human populations, use mathematical concepts to study population changes.
2. Population growth or decline is determined by four factors: births (natality), deaths (mortality), immigration into an
area, and emigration away from an area.
3. Births and immigration add individuals to a population, whereas deaths and emigration remove individuals. A
convenient way to express rates of birth and death is to measure the number of births and deaths per 1,000
individuals per year. These rates are termed the crude birth rate and the crude death rate.
4. The rate of natural increase is determined by subtracting the crude death rate from the crude birth rate.
5. The population growth rate equals the crude birth rate plus the immigration rate, minus the crude death rate plus
the emigration rate.
C. Unregulated populations increase by exponential growth.
1. When a population increases by a fixed percentage each year, it is said to undergo exponential growth. A J-shaped
curve shows this type of growth.
2. Populations of organisms increase exponentially unless they meet constraints.
3. Normally, exponential growth occurs in nature only when a population is small, competition is minimal, and
environmental conditions are ideal for the organism in question.
D. Limiting factors restrain population growth.
1. Every population is eventually contained by limiting factors—physical, chemical, and biological attributes of the
environment that restrain physical growth. These limiting factors determine the carrying capacity, the maximum
population size of a species that a given environment can sustain.
2. The logistic growth curve, an S-shaped curve, shows a population that increases sharply at first and then levels off as
it is affected by limiting factors.
3. Many factors influence a population’s growth rate and carrying capacity.
E. The influence of some factors depends on population density.
1. The influence of density-dependent factors waxes and wanes according to population density.
2. Density-independent factors are limiting factors whose influence is not affected by population density.
3. The logistic curve is a simplified model, and real populations in nature can behave differently.
F. Carrying capacities can change.
G. Reproductive strategies vary among species.
1. Organisms differ in their biotic potential, or capacity to produce offspring.
2. Species that devote large amounts of energy and resources to caring for a few offspring are said to be K-selected,
because their populations tend to stabilize over time at or near their carrying capacity.
3. Species that are r-selected have high biotic potential and devote their energy and resources to producing as many
offspring as possible in a relatively short time.
4. It is important to note, however, that these are two extremes on a continuum and that most species fall somewhere
between the extremes of r-selected and K-selected species.
V. Conserving of Biodiversity
A. Introduced species pose challenges for native populations and communities.
B. Innovative solutions are working.
1. Wildlife and natural areas draw tourists from around the world, a phenomenon called ecotourism.
C. Climate change now poses an extra challenge.
Key Ideas: Chapter 4
Species Interactions: Competition can occur when resources are limited.
1. When multiple organisms seek the same limited resource, their relationship is said to be one of competition.
Competitive interactions can take place among members of the same species (intraspecific competition), or between
members of different species (interspecific competition).
2. If one species is a very effective competitor, it may exclude another species from resource use entirely, an outcome
called competitive exclusion.
3. If neither competitor fully excludes the other, the species may continue to live side by side, a result called species
coexistence.
4. Coexisting species that use the same resources tend to adjust to their competitors to minimize competition with
them.
5. The full niche of a species is called its fundamental niche. An individual that plays only part of its role or uses only
some of its resources because of competition or other species interactions is said to be displaying a realized niche.
6. Over time, competing species may evolve to use slightly different resources or to use their shared resources in
different ways; this is resource partitioning.
7. Because species limit their resource use, over time, character displacement may occur as they evolve physical
characteristics that reflect their reliance on a particular portion of the resource.
B. Several types of interactions are exploitative.
C. Predators kill and consume prey.
1. Predation is the process by which an individual of one species—the predator—hunts, captures, kills, and consumes
individuals of another species, the prey.
2. Predation can sometimes drive cyclical population dynamics.
3. Predation also has evolutionary ramifications.
D. Parasites exploit living hosts.
1. Parasitism is a relationship in which one organism, the parasite, depends on another, the host, for nourishment or
some other benefit while doing the host harm.
2. Many types of parasites live inside their hosts.
3. Many insects parasitize other insects, killing them in the process, and are called parasitoids.
4. Parasites that cause disease in their hosts are called pathogens.
5. Coevolution describes a long-term reciprocal process in which two (or more) types of organisms repeatedly respond
by natural selection to the other’s adaptations. Hosts and parasites often become locked in a duel of escalating
adaptations, known as an evolutionary arms race.
E. Herbivores exploit plants.
1. Herbivory occurs when animals feed on the tissues of plants.
2. Like animal prey, plants have evolved an impressive arsenal of defenses against the animals that feed on them.
3. Some plants recruit certain animals as allies to assist in their defense.
F. Mutualists help one another.
1. Mutualism is a relationship in which two or more species benefit from interacting with one another.
2. Physically close association is called symbiosis, and symbiosis can be either mutualistic or parasitic.
3. Free-living organisms such as bees and flowers also engage in mutualism in the process of pollination.
Ecological Communities: A community is an assemblage of populations of organisms living in the same area at the same time.
A. Energy passes among trophic levels.
1. As organisms feed on one another, matter and energy move through the community, from one rank in the feeding
hierarchy, or trophic level, to another.
a. Producers, or autotrophs (“self-feeders”), comprise the first trophic level.
b. Organisms that consume producers are known as primary consumers and comprise the second trophic
level. Most primary consumers are herbivores because they consume plants.
c. The third trophic level consists of secondary consumers, which prey on primary consumers.
d. Predators that feed at still higher trophic levels are known as tertiary consumers.
Secondary and tertiary consumers are carnivores because they eat animals.
Animals that eat both plant and animal food are referred to as omnivores.
e. Detritivores, such as millipedes and soil insects, scavenge the waste products or dead bodies of other
community members.
f. Decomposers, such as fungi and bacteria, break down leaf litter and other nonliving matter into simpler
constituents that can be taken up and used by plants.
B. Energy, biomass, and numbers decrease at higher trophic levels.
1. A general rule of thumb is that each trophic level contains just 10% of the energy of the trophic level below it.
2. This pyramid-like pattern also tends to hold for the numbers of organisms at each trophic level; in general, fewer
organisms exist at higher trophic levels than at lower ones.
3. The pyramid pattern illustrates why eating at lower trophic levels—being vegan or vegetarian, for instance—
decreases a person’s ecological footprint.
C. Food webs show feeding relationships and energy flow.
1. As energy is transferred from lower trophic levels to higher ones, it is said to pass up a food chain, a linear series of
feeding relationships.
2. A more accurate representation of the feeding relationships in a community is a food web—a visual map of energy
flow that uses arrows to show the many paths along which energy passes as organisms consume one another.
D. Some organisms play outsized roles in communities.
1. A species that has strong or wide-reaching impact far out of proportion to its abundance is often called a keystone
species.
2. Predators at high trophic levels can indirectly promote populations of organisms at low trophic levels by keeping
species at intermediate trophic levels in check—a phenomenon ecologists refer to as a trophic cascade.
3. Animals at high trophic levels—such as wolves, sea stars, sharks, and sea otters—are often viewed as keystone
species that can trigger trophic cascades. However, other types of organisms also exert strong community-wide
effects.
4. Less conspicuous organisms toward the bottoms of food chains may exert still more impact.
E. Communities respond to disturbance in various ways.
1. In ecological terms, a disturbance is an event that affects environmental conditions rapidly and drastically, resulting
in changes to the community and ecosystem.
2. A community that resists change and remains stable despite disturbance is said to show resistance to the
disturbance. Alternatively, a community may show resilience, meaning that it changes in response to disturbance but
later returns to its original state.
F. Succession follows severe disturbance.
1. If a disturbance is severe enough to eliminate all or most of the species in a community, the affected site may then
undergo a somewhat predictable series of changes that ecologists call succession.
a. Primary succession follows a disturbance so severe that no vegetation or soil life remains from the
community that previously occupied the site.
b. Secondary succession begins when a disturbance dramatically alters an existing community but does not
destroy all living things or all organic matter in the soil.
2. Species that arrive first and colonize the new substrate are referred to as pioneer species. Pioneer species are well
adapted for colonization, having traits such as spores or seeds that can travel long distances.
3. Processes of succession occur in a diversity of ecological systems.
4. In the traditional view of succession described here, the process leads to a climax community, which remains in
place until some disturbance restarts succession.
G. Communities may undergo shifts.
1. Today, ecologists recognize that community change is far more variable and less predictable than early models of
succession suggested. In addition, climax communities are not determined solely by climate, but vary with soil
conditions and other factors from one time or place to another.
2. Once a community is disturbed and changes are set in motion, there is no guarantee that the community will ever
return to its original state. Sometimes communities may undergo a phase shift, or regime shift, in which the character
of the community fundamentally changes.
3. Many ecologists now think that human disturbance is creating communities that are wholly new and have not
previously occurred on Earth. These novel communities, or no-analog communities, are composed of novel mixtures
of plants and animals and have no analog or precedent.
H. Invasive species pose new threats to community stability.
1. In our age of global mobility and trade, people have moved countless organisms from place to place, intentionally or
by accident, such that today most non-native arrivals in a community are introduced species—species introduced by
people.
2. Most introduced species fail to establish populations in the places they arrive, but some turn invasive, spreading
widely and coming to dominate communities. Such invasive species often thrive in disturbed communities, and in turn
disturb them further.
3. Introduced species may become invasive when limiting factors that regulate their population growth are absent.
4. Examples abound of invasive species that have had major ecological impacts.
5. Ecologists generally view the impacts of invasive species—and introduced species in general—as overwhelmingl
negative. Whatever view one takes, the impacts of invasive species on native species and ecological communities are
significant, and they grow year by year with the increasing mobility of people and the globalization of our society.
I. We can respond to invasive species through control, eradication, orprevention.
1. In 1990 the U.S. Congress passed legislation that led to the National Invasive Species Act of 1996.
2. Since then, funding has become available for the control and eradication of invasive species.
3. To prevent invasions, it helps to be able to predict where a given species might spread.
J. Altered communities can be restored.
1. Because ecological systems support our civilization and all of life, when degraded systems cease to function, our
health and wellbeing are threatened.
2. This realization has given rise to the science of restoration ecology, and the process of ecological restoration, or
efforts to restore ecosystems to historical conditions (before industrialized civilization altered them).
3. Many ecological restoration efforts are underway today.
4. As our population grows and development spreads, ecological restoration is becoming an increasingly vital
conservation strategy. However, restoration is difficult, time consuming, expensive, and it is not always successful. It is
therefore best, whenever possible, to protect natural systems from degradation in the first place.