Subscribe for updates and more.

BIO 121

Study guide.




What is included in the term “environment”? → Our environment consists of all the living and nonliving things around us.

What is “environmental science”? How might “environmental biology,” our course’s title differ? → Environmental science is the scientific study of how the natural world works, how our environment affects us, and how we affect our environment. Environmental biology focuses on studying specific organisms.

Natural resources are divided between renewable and nonrenewable natural resources. How do they differ and what are examples of each?

  • Inexhaustible renewables: Solar energy, wind energy, wave energy, geothermal energy
  • Exhaustible renewables: Fresh water, Forest products, Biodiversity, Soils
  • Nonrenewables: Crude oil, natural gas, coal, minerals

Perpetually renewable, or inexhaustible, resources such as sunlight and wind energy (a) will always be there for us.

Renewable resources such as timber, soils, and fresh water (b) are replenished on intermediate time scales, if we are careful not to deplete them.

Nonrenewable resources such as minerals and fossil fuels (c) exist in limited amounts that could one day be gone.

What are “ecosystem services” and what are some examples of them?

Ecosystem services are our planet’s ecological systems purify air and water, cycle nutrients, regulate climate, pollinate plants, and recycle our waste.

For example, forested hillsides help people living below by purifying water and air, cycling nutrients, regulating water flow, preventing flooding, and reducing erosion, as well as by providing game, wildlife, timber, recreation, and aesthetic beauty.

Approximately how many humans are found on planet Earth? What factors is associated with the dramatic increase in human population?

Today our population has grown beyond 7 billion people.

Industrial revolution

  • Fossil fuels
  • Cities and factories
  • Industrialized agriculture
  • Better medicine
  • Better sanitation

What does an ecological footprint represent and what does it mean that we have overshot the Earth’s capacity by current calculations (and by how much)?

An ecological footprint expresses 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 the person or population produces.

An ecological footprint shows the total area of biologically productive land and water used by a given person or population.

It measures the total area of Earth’s biologically productive surface that a given person or population “uses” once all direct and indirect impacts are totaled up.

Analyses by one research group indicate that we have overshot Earth’s biocapacity—its capacity to sup- port us—by 50%. We are using renewable natural resources 50% faster than they are being replenished.

How has environmental condition impacted historical societies?

Civilizations have crumbled when pressures from population and consumption overwhelm resource availability.

  • the fall of the Greek and Roman empires;
  • the Angkor civilization of Southeast Asia;
  • and the Maya, Anasazi, and other civilizations of the Americas.

In Iraq, Syria, and elsewhere in the Middle East, areas that today are barren desert had earlier been lush enough to support the origin of agriculture and thriving ancient societies. Easter Island has long been held up as a society that self-destructed after depleting its resources, although new research paints a more complex picture.

How are “ethics” defined as a field of study? What is environmental ethics?

Ethics is a branch of philosophy that involves the study of good and bad, of right and wrong. The term ethics can also refer to the set of moral principles or values held by a person or a society.

Environmental ethics is the application of ethical standards to relationships between people and nonhuman entities.

Distinguish between the three ethical perspectives/worldviews: Anthropocentrism, biocentrism, and ecocentrism.

  • Anthropocentrism describes a human-centered view of our relations with the environment. Anthropocentrism denies, overlooks, or devalues the notion that nonhuman entities have rights and inherent value. Anthropocentrism evaluates the costs and benefits of actions solely according to their impact on people.
  • Biocentrism ascribes inherent value to certain living things or to the biotic realm in general. In this perspective, human life and nonhuman life both have ethical standing. A biocentrist might oppose clearing a forest if this would destroy a great number of plants and animals, even if it would increase food production and generate economic growth for people.
  • Ecocentrism judges actions in terms of their effects on whole ecological systems, which consist of living and nonliving elements and the relationships among them. An ecocentrist values the well-being of entire species, communities, or ecosystems over the welfare of a given individual. Implicit in this view is that preserving systems generally protects their components, whereas protecting components may not safeguard the entire system.

What are the preservation ethic, conservation ethic, and land ethic, and who is associated with each ethic? Be able to recognize a statement as belonging/representing these different ethics.

  • Preservation ethic holds that we should protect the natural environment in a pristine, unaltered state. Ralph Waldo Emerson, Henry David Thoreau, John Muir.

  • Conservation ethic holds that people should put natural resources to use but that we have a responsibility to manage them wisely. Gifford Pinchot

  • Land ethic holds that people should view themselves and “the land” as members of the same community and that we are obligated to treat the land in an ethical manner. Aldo Leopold

What inequities are of concern to the environmental justice movement? Removal of lead from gasoline (p 19) is touted as a success story—do you expect that this resolved an environmental justice issue?

Environmental justice involves the fair and equitable treatment of all people with respect to environmental policy and practice, regardless of their income, race, or ethnicity.


How does population size, consumption drive, and energy choices influence sustainability?

Our consumption of resources has risen even faster than our population. The modern rise in affluence has been a positive development for humanity, and our conversion of the planet’s natural capital has made life better for most of us so far. However, like rising population, rising per capita consumption magnifies the demands we make on our environment.

How does the US’s ecological footprint compare to other nations? (See Figure 1.16)

Shown are ecological footprints for average citizens of several nations, along with the world’s average per capita footprint of 2.7 hectares. One hectare (ha) = 2.47 acres.


What is the difference between “Descriptive Science” and “Hypothesis-driven Science”?

  • Descriptive science: gather basic information not yet well known—explore new frontiers of knowledge by observing and measuring phenomena to gain a better understanding of them.
  • Hypothesis-driven science: using experiments to test hypotheses within a framework traditionally known as the scientific method.

What is the difference between a hypothesis and a prediction?

  • Hypothesis: is a statement that attempts to explain a phenomenon or answer a scientific question.
  • Prediction: specific statements that can be directly and unequivocally tested.

How do you distinguish dependent and independent variables?

  • Independent variable: a variable the scientist manipulates
  • Dependent variable: a variable that depends on the independent input

What is a control and why are they valuable in an experiment? What is the role of replicates?

  • Control: an unmanipulated point of comparison for the manipulated treatment.
  • Replicates:

It is correct to say “A study supports the hypothesis…” rather than “The study proves the hypothesis….” Why?

If experiments fail to disprove a hypothesis, this lends support to the hypothesis but does not prove it is correct.

What is a strength of a manipulative experiment relative to a “natural” experiment/study? What is a strength of a natural experiment relative to a manipulative study?

  • Manipulative experiment: provides strong evidence because it can reveal causal relationships, showing that changes in an independent variable cause changes in a dependent variable
  • Natural experiments: compare how dependent variables are expressed in naturally different contexts, and to search for correlation, or statistical association among variables

What are four ways that data are commonly displayed in graphs?

  • Line graph
  • Bar chart
  • Scatter plot
  • Pie chart

Is the independent variable typically on the x- or y-axis in the graphs in Figure 1.9? → X-axis

What is the importance of peer review to the scientific process? → Peer review is a valuable guard against faulty research contaminating the literature from although personal biases and politics can sometimes creep in the review process.

Why is it worth noting the funding the source? How could funding source influence scientific outcomes? → A researcher obtains data showing their funding source in an unfavorable light may be reluctant to publish the results for fear of losing funding— or worse yet, could be tempted to doctor the results.

How is a scientific theory different from a hypothesis?

  • Theory: a widely accepted, well-tested explanation of one or more cause-and-effect relationships that have been extensively validated by a great amount of research.
  • Hypothesis: a simple explanatory statement that may be disproved by a single experiment

A theory consolidates many related hypotheses that have been supported by a large body of data.

What is a paradigm shift? → When a dominant view, is abandoned for another.

What are the reasons that Oreskes believes we should trust scientists? → Trust based on evidence under scrutiny. “Show me the evidence.”


What “ecosystem service” do oysters provide? Why are oyster populations reduced to 1% of their former abundance in the Chesapeake Bay?

Hundreds of millions of oysters kept the bay’s water clear by filtering nutrients and phytoplankton (microscopic photosynthetic algae, protists, and cyanobacteria that drift near the surface) from the water column.

Perpetual overharvesting, habitat destruction, virulent oyster diseases, and water pollution had nearly eradicated this economically and ecologically important organism from bay waters.

How has loss of oysters impacted the Chesapeake Bay ecosystem? How does hypoxia occur?

with so few oysters in the bay, elevated nutrient levels have caused phytoplankton populations to increase. When phytoplankton die, settle to the bay bottom, and are decomposed by bacteria, oxygen in the water is depleted—a condition called hypoxia—which creates “dead zones” in the bay.

What is a “systems approach”?

Assessing questions holistically.

No matter how we attempt to isolate or define a system, we soon see that it has connections to systems larger and smaller than itself. Systems may exchange energy, matter, and information with other systems, and they may contain or be contained within other systems. Thus, where we draw boundaries may depend on the spatial (space) or temporal (time) scale on which we choose to focus.

What happens in a negative and positive feedback loop? What are examples of each?

Negative feedback loop → output that results from a system moving in one direction acts as input that moves the system in the other direction. Input and output essentially neutralize one another’s effects, stabilizing the system. (body temperature in humans)

Positive feedback loop → increased output from a system leads to increased input, leading to further increased output, and so on. Drives the system further toward an extreme. (population growth)

Dave Schulte designed an experiment to test a restoration approach in the Chesapeake Bay. What was the experiment and what did it show?

to construct artificial reefs like those that once existed, to get oysters off the bottom—away from smothering sediments and hypoxic waters—and up into the plankton-rich upper waters.

it proposed a combination of native oyster restoration, a temporary moratorium on oyster harvests (accompanied by a compensation program for the oyster industry), and enhanced support for oyster aquaculture in the bay region.

Eutrophication: nutrient over-enrichment, increased production of organic matter, and subsequent ecosystem degradation.

What is the major source for both nitrogen and phosphorus entering the Chesapeake Bay?

Runoff from agriculture was a major source of these nutrients, contributing 43% of the nitrogen and 55% of the phosphorus entering the bay.

How many marine hypoxic dead zones are there around the world? (See Fig. 2.5)

More than 500

Ecosystem ecology focuses on the movement of energy and nutrients through an ecosystem. What is an ecosystem?

An ecosystem consists of all organisms and nonliving entities that occur and interact in a particular area at the same time. Animals, plants, water, soil, nutrients—all these and more help compose ecosystems.

How does the movement of nutrients differ from energy (which flows through ecosystems requiring a constant input into the system)?

Nutrients move through ecosystems in nutrient cycles (or biogeochemical cycles) that circulate elements or molecules through the lithosphere, atmosphere, hydrosphere, and biosphere.

How is water involved in nearly all other nutrient cycles?

Water carries nutrients, sediments, and pollutants from the continents to the oceans via surface runoff, streams, and rivers. These materials can then be carried thousands of miles on ocean currents. Water also carries atmospheric pollutants to Earth’s surface when they dissolve in falling rain or snow.

The oceans are the largest reservoir in the hydrologic cycle, holding more than ____% of all water on Earth. In what form is most of the freshwater?

The oceans are the largest reservoir in the hydrologic cycle, holding more than 97% of all water on Earth. Less than 1% of the planet’s water is in a form that we can readily use—groundwater, surface fresh water, and rain from atmospheric water vapor.

What are some ways that human activity affects the water cycle?

  • By damming rivers, we slow the movement of water from the land to the sea, and we increase evaporation by holding water in reservoirs.
  • We remove natural vegetation by clear-cutting and developing land, which increases surface runoff, decreases infiltration and transpiration, and promotes evaporation.
  • Our withdrawals of surface water and groundwater for agriculture, industry, and domestic uses deplete rivers, lakes, and streams and lower water tables.

The largest reservoir of carbon is in what and found where? Second largest?

The largest reservoir of carbon, sedimentary rock, is formed in oceans and freshwater wetlands. Ocean waters are the second-largest reservoir of carbon on Earth.

How do humans affect the carbon cycle?

Human activity affects the carbon cycles through our uses of coal, oil, and natural gas.

Level of carbon in the atmosphere, in the form of carbon dioxide, is the largest atmospheric reservoir in … how many years?

Today’s atmospheric carbon dioxide reservoir is the largest that Earth has experienced in the past 1 million years, and likely in the past 20 million years.

Note that the nitrogen cycle moves through the earth, water, and atmosphere, while the phosphorous cycle does not have an atmospheric component.

What are some of the methods to reduce nutrient pollution? Fig. 2.24 notes the differences in cost of different strategies—given that some approaches will have additional costs or benefits, are there some approaches that seem better than others?

planting forested buffers

The extinction of species on the Hawaiian island mirrors the biodiversity crisis in areas around the world. What were some of the causes listed for extinction of some of the bird species found nowhere else in the world?

Polynesian settlers colonized the islands, cutting down trees and introducing non-native animals.

Natural selection: inherited characteristics that enhance survival and reproduction are passed on more frequently to future generations than characteristics that do not, thereby altering the genetic makeup of populations through time.

In what ways is understanding evolution useful for society?

we depend on a working knowledge of evolution for the food we eat and the clothes we wear, each and every day, as these have been made possible by the selective breeding of crops and livestock. Applying an understanding of evolution to agriculture can also help us avoid antibiotic resistance in feedlots and pesticide resistance in crop-eating insects

What are some sources of genetic variation upon which natural selection can act?

Accidental changes in DNA, called mutations, give rise to genetic variation among individuals.

Genetic variation also results as organisms mix their genetic material through sexual reproduction.

What are some examples of evolution by means of natural selection?

Through artificial selection we’ve chosen animals possessing traits we like and bred them together, while culling out individuals with traits we do not like. Through such selective breeding, we have been able to augment particular traits we prefer.

How many species have been described? What is the estimated number of species on earth?

Scientists have described about 1.8 million species, but many more remain undiscovered or unnamed. Estimates vary for the actual number of species in the world, but they range from 3 million up to 100 million.

How does allopatric speciation occur?

Speciation: the process by which new species are generated is termed.

Allopatric speciation: Where species form from populations that become physically separated over some geographic distance. Populations must remain isolated for a very long time, generally thousands of generations

What does a phylogenic tree demonstrate?

Phylogenetic trees can show relationships among species, groups of species, populations, or genes. Once a phylogenetic tree is created, traits can be mapped onto the tree according to which organisms possess them, and we can thereby trace how the traits have evolved.

What does the fossil record reveal about the evolutionary history of life on Earth?

The fossil record shows that the number of species existing at any one time has generally increased, but that the species alive on Earth today are just a small fraction of all species that have ever existed. During life’s 3.5 billion years on Earth, complex structures have evolved from simple ones, and large sizes from small ones. However, simplicity and small size have also evolved when favored by natural selection; it is easy to argue that Earth still belongs to the bacteria and other microbes, some of them little changed over eons.

When does extinction usually occur? What conditions lead to extinction?

Extinction occurs when environmental conditions change rapidly or drastically enough that a species cannot adapt genetically to the change; the slow process of natural selection simply does not have enough time to work.

Small populations are vulnerable to extinction because fluctuations in their size could, by chance, bring the population size to zero.

Endemic species face elevated risks of extinction because when some event influences their region, it may affect all members of the species.

How many mass extinction vents have occurred and how do they differ from the background extinction rate?

Fossil record reveals that Earth has seen at least five events of staggering proportions that killed off massive numbers of species at once. These episodes, called mass extinction events, have occurred at widely spaced intervals in our planet’s history and have wiped out 50–95% of Earth’s species each time.

Hypotheses as to what caused the end-Permian extinction event include massive volcanism, an asteroid impact, methane releases and global warming, or some combination of these factors.

What is the Sixth Extinction and what is the cause?

Changes to our planet’s natural systems set in motion by human population growth, development, and resource depletion have driven many species to extinction and are threatening countless more. As we alter and destroy natural habitats; overhunt and overharvest populations; pollute air, water, and soil; introduce invasive non-native species; and alter climate, we set in motion processes that combine to threaten Earth’s biodiversity. Because we depend on organisms for life’s necessities—food, fiber, medicine, and vital ecosystem services—biodiversity loss and extinction ultimately threaten our own survival.


How have the Great Lakes been connected by humans to the eastern Atlantic coast and the Gulf of Mexico? How has this contributed to the threat and spread of invasive exotic species in the Great Lakes?

When Chicago (inset) built canals and reversed the flow of the Chicago River to flow into the Illinois River, this connected the watersheds of the Great Lakes and the Mississippi River, enabling species to move between them, affecting aquatic communities in each watershed. Today an electric barrier (see inset) is in place to try to stop Asian carp from reaching the Great Lakes.

Meanwhile, hundreds of miles away at their eastern end, the Great Lakes were connected to the Atlantic Ocean when engineers completed the Saint Lawrence Seaway in 1959. This 600-km (370-mi) system of locks and canals along the Saint Lawrence River allowed ocean-going ships to travel into the lakes. It also allowed access for non-native species, including the sea lamprey, an eel-like creature that began attacking and parasitizing the lakes’ freshwater fish. All told, the Great Lakes today host 180 non-native species that are considered to be invasive.

Competition is defined as a negative-negative interaction among two species (interspecific competition) or among individuals within the same species (Intraspecific competition). In what way(s) is it negative for both players in the interaction?

In competitive interactions, each participant exerts a negative effect on other participants by taking resources the others could have used.

Resource Partitioning is one outcome of competition—how could it contribute to species coexistence? What effect should resource partitioning have on the strength of competition (i.e., should it make it stronger or weaker)?

For example, if two bird species eat the same type of seeds, natural selection might drive one species to specialize on larger seeds and the other to specialize on smaller seeds.

There are three types of species interactions that benefit one species, while negatively impacting another species—what are they? (Table 4.1 may help) Distinguish between each.

Predator-prey interactions can drive selection for traits for either predator or prey. What are some of the outcomes of selection that can result and how would they enhance/reduce the advantage of individuals with that trait? (Figure 4.4 may help)

Why would mutualistic interactions evolve? What are some examples?

Mutualism is a relationship in which two or more species benefit from interacting with one another. Generally, each partner provides some resource or service that the other needs.

What is a “keystone species” and which species in a community are more likely to be a keystone?

A species that has strong or wide-reaching impact far out of proportion to its abundance is often called a keystone species.

What is a trophic cascade? [Definition at the back of the book is clearer than definition in this section—but the text in this section offers some good examples.] What is an example of a trophic cascade?

A series of changes in the population sizes of organisms at different trophic levels in a food chain, occurring when predators at high trophic levels indirectly promote populations of organisms at low trophic levels by keeping species at intermediate trophic levels in check. Trophic cascades may become apparent when a top predator is eliminated from a system.

What are three ways communities may respond to disturbance?

  1. A community that resists change and remains stable despite disturbance is said to show resistance to the disturbance.
  2. A community may show resilience, meaning that it changes in response to disturbance but later returns to its original state.
  3. A community may be modified by disturbance permanently and never return to its original state.

Distinguish between primary and secondary succession.

Primary succession follows a disturbance so severe that no vegetation or soil life remains from the community that had occupied the site. In primary succession, a community is built essentially from scratch.

Secondary succession begins when a disturbance dramatically alters an existing community but does not destroy all life and organic matter. In secondary succession, vestiges of the previous community remain, and these building blocks help shape the process.

While traditional ecology suggested that succession would lead to predictable climax communities, today we understand that succession is less predictable than earlier believed. What can result in a “regime/phase” shift? How are novel communities part of this change?

A regime shift, or phase shift, in which the character of the community fundamentally changes. This can occur if some crucial climatic threshold is passed, a keystone species is lost, or a non-native species invades.

Today human disturbance and the introduction of non-native species are creating wholly new communities that 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. Given today’s fast-changing climate, habitat alteration, species extinctions, and species invasions, scientists predict that we will see more and more novel communities.

Distinguish introduced and invasive species. What factors increase the likelihood of an introduced species become invasive?

Plants and animals brought to a new area may leave behind the predators, parasites, herbivores, and competitors that had exploited them in their native land. If few organisms in a new environment eat, parasitize, or compete with an introduced species, then it may thrive and spread. As the species proliferates, it may exert diverse influences on other community members.

What does the ecological recovery of Mount Saint Helens suggest about the system’s resilience? Will it return to the same ecological community? Did humans aid or hinder its recovery?

The results also show life’s resilience. Even when the vast majority of organisms perish in a natural disaster, a few may survive, and their descendants may eventually build a new community.

Ecological change at Mount Saint Helens will continue for many decades more. All along, ecologists will continue to study and learn from this tremendous natural experiment.

Why is prevention often viewed as the best policy in invasive species management?

However, most of these are localized or short-term fixes. With one invasive species after another, managers find that control and eradication are so difficult and expensive that trying to prevent invasions in the first place represents a better investment.

What are the end goals of restoration ecology?

Restoration ecologists research the historical conditions of ecological communities as they existed before our industrialized civilization altered them. They then devise ways to restore altered areas to an earlier condition. In some cases, the intent is to restore the functionality of a system—to reestablish a wetland’s ability to filter pollutants and recharge groundwater, for example, or a forest’s ability to cleanse the air, build soil, and provide wildlife habitat. In other cases, the aim is to return a community to its natural “presettlement” condition.

What is the largest restoration project in the world and what is it attempting to restore?

The world’s largest restoration project is the ongoing effort to restore the Everglades, a vast ecosystem of marshes and seasonally flooded grasslands stretching across southern Florida.

What are zoonoses and how common are they?

Zoonoses are diseases transmissible from humans to animals. Sixty percent of emerging infectious diseases that affect humans are zoonotic — they originate in animals. And more than two-thirds of those originate in wildlife.

What are some examples of zoonoses? And what role can domesticated animals play?

AIDS, Ebola, West Nile, SARS, Lyme disease

influenza, the he Nipah virus,

Research Institute found that more than two million people a year are killed by diseases that spread to humans from wild and domestic animals.

What factors contribute to the increase in emerging infection diseases in recent decades?

Any emerging disease in the last 30 or 40 years has come about as a result of encroachment into wild lands and changes in demography.

What are some examples of how habitat change has increased disease risk—and what are the implications for diseases that have not yet jumped from wildlife to humans?

So we’re going to the edge of villages, we’re going to places where mines have just opened up, areas where new roads are being built. We are going to talk to people who live within these zones and saying, ‘what you are doing is potentially a risk.’

How to Stop the Next Pandemic NYT

  1. Habitat destruction
  2. The dilution effect–less biological diverse landscape
  3. The wildlife trade

Module 2 Part 3

Species richness = current number of species + new species - loss of existing species.

5 mass extinction events:

  • Ordovician
  • Late Devonian
  • Permiam
  • Triassic
  • Cretaceous-Tertiary boundary

Charles Darwin:

  1. Potential for exponential increase
  2. Populations tend to be stable
  3. Resources are limited
  4. Variation among organisms
  5. Much of variation is heritable

Natural selection happens on the individual level and evolution happens at a population level.

  • Competition
  • Predation
  • Mutualism
  • Commensalism
  • Parasitism
  • Herbivory

—End Exam 1—

—Start Exam 2—


Will China’s New “Two-Child Policy” Defuse Its Population Time Bomb?

How did China handle the population bomb amidst its industrial and agricultural development that began eroding the nation’s soils, depleting its water, and polluting its air? What are some of the consequences of their approach?

The rapid reduction in fertility that resulted from this policy drastically changed China’s age structure. Once consisting predominantly of young people, China’s population has shifted, such that the numbers of children and older people are now more even. This means there will be relatively fewer workers for China’s growing economy, which is driving up wages and encouraging companies with factories in China to seek out more inexpensive labor in other nations. The growing number of older Chinese individuals poses problems because the Chinese government lacks the resources to fully support them, putting a heavy economic burden on the millions of only children produced under the one-child policy as they help provide for their retired parents.

Faced with the prospect of continued population issues, the Chinese government announced in October 2015 that the former one-child policy would immediately become a two-child policy, and couples would be permitted to have two children without penalty.

Our World at Seven Billion

How long did it take human population size to reach 1 billion (i.e., what year)? How does exponential growth influence human population size?

It took until after 1800, virtually all of human history, for our population to reach 1 billion. Yet by 1930 we had reached 2 billion, and 3 billion in just 30 more years. Our population added its next billion in just 15 years, and it has taken only 12 years to add each of the next three installments of a billion people.

How do you determine the time at which the population will double? What is the global average growth rate of population? See Fig. 6.4 on how it varies across the globe.

At a 1.2% annual growth rate, a population doubles in size in only 58 years. We can roughly estimate doubling times with a handy rule of thumb. Just take the number 70 (which is 100 times 0.7, the natural logarithm of 2) and divide it by the annual percentage growth rate: 70/1.2 = 58.3.

What factors have decreased the death rate and allowed human population to soar?

Technological innovations, improved sanitation, better medical care, increased agricultural output, and other factors that have brought down death rates. Birth rates have not declined as much, so births have outpaced deaths for many years now, leading to population growth. But can the human population continue to grow indefinitely?

What is the estimated human carrying capacity on planet Earth and what makes it challenging to estimate?

The most rigorous estimates range from 1–2 billion people living prosperously in a healthy environment to 33 billion people living in extreme poverty in a degraded world of intensive cultivation without natural areas.

What is the IPAT model and how is it used?

A formula that represents how humans total Impact (I) on the environment results from the interaction among three factors: Population (P), Affluence (A), and Technology (T).

I = P * A * T

Impact = Population * Affluence * Technology

We can interpret impact in various ways, but can generally boil it down either to unsustainable resource consumption or to the degradation of ecosystems by pollution.

We could refine the IPAT equation further by adding terms for the influence of social factors such as education, laws, ethical standards, and social stability and cohesion. Such factors all affect how population, affluence, and technology translate into environmental impact.


What do demographers evaluate?

Demographers study population size, density, distribution, age structure, sex ratio, and rates of birth, death, immigration, and emigration of people, just as population ecologists study these characteristics in other organisms. Each is useful for predicting population dynamics and environmental impacts.

The distribution of organisms is called “dispersion” – how are humans distributed across space?

At the global scale, population density is highest in regions with temperate, subtropical, and tropical climates and lowest in regions with extreme-climate biomes, such as desert, rainforest, and tundra. Human population is dense along seacoasts and rivers, and less dense farther away from water. At more local scales, we cluster together in cities and towns.

This uneven distribution means that certain areas bear more environmental impact than others.

How can population age structure help indicate whether a population is growing or declining.

A population made up mostly of individuals past reproductive age will tend to decline over time. In contrast, a population with many individuals of reproductive age or pre-reproductive age is likely to increase. A population with an even age distribution will likely remain stable as births keep pace with deaths.

Is there a pattern between infant mortality rates in Fig. 6.10 and population growth rates in Fig. 6.6? Fig 6.6 The United Nations predicts world population growth.

Fig 6.10 Infant mortality rates are highest in poorer nations, such as those in sub-Saharan Africa, and lowest in wealthier nations.

The global growth rate has changed in what way since the 1950s? (See Fig. 6.11)

Growth rates of developed nations have fallen since 1950, whereas those of developing nations have fallen since the global peak in the late 1960s. For the world’s least developed nations, growth rates began to fall in the 1990s. Although growth rates are declining, global population size is still growing about the same amount each year, because smaller percentage increases of ever-larger numbers produce roughly equivalent additional amounts.

How does total fertility rates for major regions of the world compare to the replacement fertility rate? What reasons explain the trends in total fertility rate?

Total Fertility Rate (TFR) is the average number of children born per woman during her lifetime. Replacement fertility is the TFR that keeps the size of a population stable.

For humans, replacement fertility roughly equals a TFR of 2.1. (Two children replace the mother and father, and the extra 0.1 accounts for the risk of a child dying before reaching reproductive age.) If the TFR drops below 2.1, population size in a given country (in the absence of immigration) will shrink.

Factors such as industrialization, improved women’s rights (pp. 133–134), access to family planning, and quality health care have driven the TFR downward in many nations in recent years.

What is a demographic transition and how do birth and death rates change before, during, and after (from pre-industrial to post-industrial)?


The Demographic Transition is a model of economic and cultural change—first proposed in the 1940s and 1950s by demographer Frank Notestein—to explain the declining death rates and birth rates that have occurred in Western nations as they industrialized.

Notestein argued that nations move from a stable pre-industrial state of high birth and death rates to a stable post-industrial state of low birth and death rates (Figure 6.12). Industrialization, he proposed, causes these rates to fall by first decreasing mortality and then lessening the need for large families. Parents thereafter choose to invest in quality of life rather than quantity of children. Because death rates fall before birth rates fall, a period of net population growth results. Thus, under the demographic transition model, population growth is seen as a temporary phenomenon that occurs as societies move from one stage of development to another.

Is the demographic transition inevitable?

This pattern suggests that it may merely be a matter of time before all nations experience the transition. On the other hand, some developing nations may already be suffering too greatly from the impacts of large populations to replicate the developed world’s transition, a phenomenon called demographic fatigue. Demographically fatigued governments face overwhelming challenges related to population growth, including educating and employing swelling ranks of young people. When these stresses are coupled with large-scale environmental degradation or disease epidemics, the society may never complete the demographic transition.

Population and Society

What are some of the important societal factors that demographers have found influence fertility?

They include public health issues, such as people’s access to contraceptives and the rate of infant mortality. They also include cultural factors—such as the level of women’s rights, the relative acceptance of contraceptive use, and even cultural influences like television programs. There are also effects from economic factors, such as the society’s level of affluence, the importance of child labor, and the availability of governmental support for retirees.

In 2016, the worldwide use of modern contraceptives by women 15-49 was 56% with wide variation around that average. What are some of the issues the influence contraceptive use?

The ability of women and couples to engage in family planning, the effort to plan the number and spacing of one’s children. Family-planning programs and clinics offer information and counseling to potential parents on reproductive issues.

An important component of family planning is birth control, the effort to control the number of children one bears, particularly by reducing the frequency of pregnancy. Birth control relies on contraception.

What are some of the ways that government policies and societal influence have lowered population growth rates, whether industrialized or not? (including in “Success Story” Box and “Did Soap Operas”)

In the 1960s, the average woman in Brazil had six children. Today, Brazil’s total fertility rate is 1.8 children per woman, which is lower than that of the United States. Brazil accomplished this, in part, by providing women equal access to education and opportunities to pursue careers outside the home. Women now make up 40% of the workforce in Brazil and graduate from college in greater numbers than men. In 2010, Brazilians elected a woman, Dilma Rousseff, as their nation’s president.

The Brazilian government also provides family planning and contraception to its citizens free of charge.

People in Thailand were provided with family-planning counseling and modern contraceptives supported by an engaging public education campaign. Aided by a relatively high level of women’s rights in Thai society, this program—and the fertility reductions that accompanied the nation’s economic development over the past 45 years—reduced the growth rate to 0.4%, with a TFR of 1.6 children per woman in 2016.

What is the connection between women’s rights and fertility rates/population growth? What might explain this relationship? (Fig. 6.14 may be useful)

Expanding educational opportunities for women is an important component of equal rights. In many nations, girls are discouraged from pursuing an education or are kept out of school altogether. Worldwide, more than two-thirds of people who cannot read are women. And data clearly show that as women become educated, fertility rates decline. Education encourages women to delay childbirth as they pursue careers, and gives them more knowledge of reproductive options and greater say in reproductive decisions.

Why would fertility rate and poverty/wealth be a concern to conservation organizations?

As nations industrialize, they become wealthier and more urban. This depresses fertility, as children are no longer needed as farmhands and better healthcare reduces the need for parents to account for infant mortality when deciding on family size. Women move into the workforce and modern contraception becomes available and affordable. Moreover, if a government provides some form of social security to retirees, parents need fewer children to support them in their old age.

Where will most of the future population growth occur in the coming decades?

The vast majority of future population growth will occur in developing regions. Africa will experience the greatest population growth of any region in coming decades. The highly industrialized regions of Europe and North America are predicted to experience only minor population change.

Many conservation organizations have made poverty reduction a conservation priority, but what conservation concerns come with increasing wealth and how does affluence compare to population growth?

Just as population is rising, so is consumption. Researchers have found that humanity’s global ecological footprint surpassed Earth’s capacity to support us in 1971, and that our species is now living 50% beyond its means. We are running a global ecological deficit, gradually draining our planet of its natural capital and its long-term ability to support our civilization. The rising consumption that is accompanying the rapid industrialization of China, India, and other populous nations makes it all the more urgent for us to reverse this trend and find a path to global sustainability.


Costa Rica Values Its Ecosystem Services

How did Costa Rica create economic incentive to protect its natural resources?

Costa Rica had lost over three-quarters of its forest. Political leaders adopted a financial acccentive approach in Forest Law 7575, passed in 1996. Since then, the Costa Rican government has been paying farmers and ranchers to preserve forest on their land, replant cleared areas, allow forest to regenerate naturally, and establish sustainable forestry systems. Payments are designed to be competitive with potential profits from farming or cattle ranching, and in recent years these payments have averaged $78/hectare (ha)/yr ($32/acre/yr).

To fund the PSA program, Costa Rica’s government sought money from people and companies that benefit from these services.

Economics and the Environment

What do economics and ecology have in common?

An economy is a social system that converts resources into goods (material commodities made and bought by individuals and businesses) and services (work done for others as a form of business). Economics is the study of how people decide to use potentially scarce resources to provide goods and services that are in demand. The word economics and the word ecology come from the same Greek root, oikos, meaning “household.” Economists traditionally have studied the household of human society, whereas ecologists study the broader household of all life. Just as the environment influences our economy, the economic decisions we all make from day to day have implications for the environment. For these reasons, understanding economics helps us appreciate the complex interface between environmental science and society.

Fig. 5.2 highlights the role of nature’s goods and services to the economy. What are the consequences of including the environmental links to economies?

We can think of natural resources as “goods” produced by nature. The degradation of ecosystem services can weaken economies.

What is the difference in classical economics and neoclassical economics, according to the text?

As the field of economics developed in the 18th century, many people felt that individuals acting in their own self-interest harm society. However, Scottish philosopher Adam Smith (1723–1790) argued that self-interested economic behavior can benefit society, as long as the behavior is constrained by the rule of law and private property rights within a competitive marketplace.

A founder of classical economics, Smith felt that when people pursue economic self-interest under these conditions, the marketplace will behave as if guided by “an invisible hand” to benefit society as a whole.

Economists subsequently adopted more quantitative approaches. Neoclassical economics examines consumer choices and explains market prices in terms of preferences for units of particular commodities. In neoclassical economics, buyers desire a low price whereas sellers desire a high price, so a compromise price is reached. Marketplace dynamics are expressed in terms of supply, the amount of a product offered for sale at a given price, and demand, the amount of a product people will buy at a given price if free to do so.

Why are the environmental costs of actions often under appreciated in cost-benefit analyses?

This reasoning seems eminently logical, but problems arise when not all costs and benefits can be easily identified, defined, or quantified. It may be simple to quantify the dollar value of bananas grown or cattle raised on a tract of Costa Rican land cleared for agriculture, yet difficult to assign monetary value to the complex ecological costs of clearing the forest. Because monetary benefits are usually more easily quantified than environmental costs, benefits tend to be overrepresented in traditional cost-benefit analyses. As a result, environmental advocates often feel such analyses are biased toward economic development and against environmental protection.

How do the four assumptions of neoclassical economics contribute to environmental degradation?

  1. Replacing resources: Earth’s material resources are ultimately limited.
  2. External costs: A cost of a transaction that affects someone other than the buyer or seller is known as an external cost
  3. Discounting: meant to reflect how people tend to grant more importance to present conditions than to future conditions; encourages policymakers to play down the long-term consequences of decisions.
  4. Growth: growth cannot be sustained forever

What are some examples of external costs (also known as “externalities)? See Figure 5.1.

When a landowner fells a forest, people nearby suffer poorer water quality, dirtier air, and less wildlife. When a factory, power plant, or mining operation pollutes the air or water, it harms the health of those who live nearby.

  1. Health impacts
  2. Depletion of resources
  3. Aesthetic damage
  4. Financial loss

How would environmental economics help account for externalities that have been traditionally ignored in economics?

Economists in the field of environmental economics feel we can modify neoclassical economic principles to make resource use more efficient and thereby attain sustainability within our current economic system. Environmental economists were the first to develop methods to tackle the problems of external costs and discounting.

What is a stable-state economy?

A steady-state economy is intended to mirror natural systems. Many ecological economists advocate economies that neither grow nor shrink, but are stable.

What are the nonmarket values not included in the price of a good or service that Ecosystem Services have? (See Figure 5.3)

  1. Use value: the worth of something we use directly
  2. Existence value: the worth of knowing that something exists, even if not experienced
  3. Option value: the worth of something we might use later
  4. Aesthetic value: the worth of beauty
  5. Scientific value: the worth of something for research
  6. Educational value: the worth of something for learning
  7. Cultural value: the worth of something for culture

Costanza and colleagues estimated that nature’s services total how much and how does that compare to global annual monetary value of the goods and services created by people?

The 2014 study calculated that Earth’s biosphere in total provides more than $125 trillion worth of ecosystem services each year, in 2007 dollars. This is equal to $148 trillion in 2017 dollars, an amount that exceeds the global annual monetary value of goods and services created by people!

What does the Genuine Progress Indicator (GPI) do that the Gross Domestic Product (GDP) fails to do? Does the GPI have short-comings?

Environmental economists have developed indicators meant to distinguish desirable from undesirable economic activity and to better reflect our well-being.

Full cost accounting indicators such as the GPI aim to measure progress and well-being more effectively than the GDP–it aims to account fully for all costs and benefits.

GDP is the Genuine Progress Indicator (GPI).

Critics of full cost accounting argue that the approach is subjective and too easily driven by ideology. Proponents respond that making a subjective attempt to measure progress is better than misapplying an indicator such as the GDP to quantify well-being—something it was never meant to do.

To calculate GPI, we begin with conventional economic activity and add to it positive contributions not paid for with money, such as volunteer work and parenting. We then subtract negative impacts, such as crime and pollution.

Environmental Policy: An Overview

Why do governments intervene in the marketplace?

Governments typically intervene in the marketplace for several reasons:

  • To provide social services, such as national defense, health care, and education
  • To provide “safety nets” (for the elderly, the poor, victims of natural disasters, and so on)
  • To eliminate unfair advantages held by single buyers or sellers
  • To manage publicly held resources
  • To minimize pollution and other threats to health and quality of life.

What is the relationship between the idea of “tragedy of the commons” and environmental policy?

In a public pasture (or “common”) open to unregulated grazing, each person who grazes animals will be motivated by self-interest to increase the number of his or her animals in the pasture. Because no single person owns the pasture, no one has incentive to expend effort taking care of it. Instead, each person takes what he or she can until overgrazing causes grass growth to collapse, hurting everyone.

Tragedy of the commons, pertains to many types of resources held and used in common by the public: forests, fisheries, clean air, clean water—even global climate.

Guidelines might limit the number of animals each person can graze or might require pasture users to help restore and manage the resource. These two concepts—management and restriction of use—are central to environmental policy today.

Environmental policy can deal with tragedy of the commons, but also free riders, and external costs in what way?

Free-riders: Because of the free-rider problem, private voluntary efforts are often less effective than efforts mandated by public policy.

External costs: If the government forces the company running the factory to clean up its pollution, pay fees, or reimburse affected residents for damage, this helps to “internalize” costs. The costs would then be paid by the company, which would likely pass them on to consumers by raising the prices of its products. Higher market prices may reduce demand for the products, and consumers may instead favor less expensive products that impose fewer costs on society.

Why is environmental policy sometimes challenged or not in-acted, and why might science play less of a role than one might expect or hope?

Sometimes policymakers allow factors other than science to determine their decision making on scientific matters.

Politicians may ignore scientific consensus on well-established matters such as evolution, vaccination, or climate change if it suits their political needs or if they are motivated chiefly by political or religious ideology. Some may reject or distort scientific advice if this helps to please campaign contributors or powerful constituencies.

The perception that environmental protection requires economic sacrifice.

Businesses often view regulations as restrictive and costly.

Landowners may fear that zoning or protections for endangered species will restrict how they can use their land.

Developers complain of time and money lost in obtaining permits; reviews by government agencies; and required environmental controls, monitoring, and mitigation.

The news media focus coverage on new and sudden events. Politicians often act in their short-term interest because they depend on reelection. For all these reasons, environmental policy may be obstructed.

US Environmental Law and Policy

What were the three waves of environmental policy related to?

  1. Early U.S. environmental policy promoted settlement and natural resource extraction
  2. The Second Wave of U.S. Environmental Policy Encouraged Conservation
  3. The Third Wave Responded to Pollution

Major advances in environmental law happened in the 1960s and 70s for what reasons? (i.e., why then?)

  1. Environmental problems became readily apparent and were directly affecting people’s lives
  2. People could visualize policies to deal with the problems
  3. Citizens were politically active and leaders were willing to act.
  4. Photographs from NASA’s space program allowed humanity to see, for the first time ever, images of Earth from space.

A landmark event was the 1962 publication of Silent Spring, a best-selling book by American scientist and writer Rachel Carson. Silent Spring awakened the public to the ecological and health impacts of pesticides and industrial chemicals. The book’s title refers to Carson’s warning that pesticides might kill so many birds that few would be left to sing in springtime.

Legal scholar Joseph Sax in 1970 published a seminal paper developing the public trust doctrine, which holds that natural resources such as air, water, soil, and wildlife should be held in trust for the public and that government should protect them from exploitation by private parties. Wisconsin Senator Gaylord Nelson founded Earth Day in 1970, a now-annual event, which galvanized public support for action to address pollution problems.

What is the significance of NEPA?

The National Environmental Policy Act (NEPA) created an agency called the Council on Environmental Quality and required that an environmental impact statement (EIS) be prepared for any major federal action that might significantly affect environmental quality.

The EIS process forces government agencies and the businesses that contract with them to evaluate impacts using a cost-benefit approach before proceeding with a new dam, highway, or building project. The EIS process rarely halts development projects, but it serves as an incentive to lessen environmental damage.

Why has environmental policy become bipartisan to a large extent?

Despite the fact that some of the greatest early conservationists were Republicans, and even though the words conservative and conservation share the same root meaning, environmental issues have today become identified as a predominantly Democratic concern. As a result, significant bipartisan advances rarely occur, and most environmental policy is now being crafted at the state and local level.



Fracking the Marcellus Shale

What is significant about the Marcellus Shale?

The Marcellus Shale formation underlies large portions of Pennsylvania, New York, Ohio, and West Virginia.

What are the pros and cons of fracking the Marcellus Shale?


  • Money and jobs from the gas boom kept Dimock economically afloat, even as other towns in the region reeled from recession and cut funding for schools and basic services.


  • The community was now experiencing noise, nighttime light, and air pollution; heavy truck traffic; and toxic wastewater spills.
  • Drinking water began to turn brown, gray, or cloudy with sediment, and chemical smells began wafting from their wells.

How does hydraulic fracturing (aka fracking) work? (Also see Fig. 15.2)

Hydraulic fracturing (fracking) involves drilling deep into the earth and angling the drill horizontally once a shale formation is reached. An electrical charge sets off targeted explosions that perforate the drilling pipe and create fractures in the shale. Drillers pump a slurry of water, sand, and chemicals down the pipe under great pressure. The sand lodges in the fractures and holds them open, while some of the liquids return to the surface. Natural gas trapped in the shale migrates into the fractures and rises through the drilling pipe to the surface, where it is collected.

What is the basis for exempting fracking from seven major environmental laws that protect public health? What are some of the consequences?


  • Employed thousands of people
  • Driven down the price of natural gas.
  • Reduced reliance on coal for electricity.
  • Burning it in place of coal reduces the greenhouse gas emissions that drive climate change.


  • at least 10 chemicals high enough to threaten health in 27 of the wells tested, along with widespread methane contamination and other water quality issues.
  • In Dimock, 44 families brought lawsuits against Cabot. After years of legal struggles, all but two settled with the company and signed non-disclosure agreements binding them to silence.

Sources of Energy

Fossil fuels are the energy we use most of: 80% of our energy and 2/3 of our electricity come from the three main fossil fuels.

How many person hours of labor are contained in a gallon of oil?

A single gallon of oil contains as much energy as a person would expend in nearly 600 hours of human labor.

How many years does it take for the biosphere to generate the amount of organic matter that must be buried to produce a single day’s worth of fossil fuels for our society?

It takes a thousand years for the biosphere to generate the amount of organic matter that must be buried to produce a single day’s worth of fossil fuels for our society.

To replenish the fossil fuels we have used so far would take many millions of years.

Energy is unevenly distributed

Who has the world’s largest proven reserves of the three main type of fossil fuels? (See Table 15.2)

  • Oil: Venezuela
  • Natural gas: Iran
  • Coal: United States

It takes energy to make energy

What do “net energy” and “EROI” indicate? What causes changes to these values? Be able to interpret these values.

Net energy expresses the difference between energy returned and energy invested: Net energy = Energy returned − Energy invested

EROI (energy returned on investment). EROI ratios are calculated as follows:

Energy Returned On Investment (EROI). EROI ratios: EROI = Energy returned / Energy invested

Higher EROI ratios mean that we receive more energy from each unit of energy we invest. Fossil fuels are widely used because their EROI ratios have historically been high. However, EROI ratios can change over time. Ratios rise as technologies to extract and process fuels become more efficient, and they fall as resources are depleted and become harder to extract.

EROI ratios for both the discovery and the production of oil and gas have declined because we found and extracted the easiest deposits first and now must work harder and harder to find and extract the remaining amounts.

Fossil fuels have many uses

What are the main uses of coal, natural gas, and oil?

  • Coal: generate electricity
  • Natural gas: generate electricity in power plants
  • Oil: fuel for vehicles

Why is natural gas considered a “clean burning” fossil fuel?

Natural gas emits just half as much carbon dioxide per unit of energy released as coal and two-thirds as much as oil.

We are depleting fossil fuel reserves

How long are fossil fuel reserves expected to last?

To estimate how long this remaining oil will last, analysts calculate the reserves-to-production ratio, or R/P ratio, by dividing the amount of remaining reserves by the annual rate of “production” (extraction and processing).

At current levels of production (33.6 billion barrels globally per year), 1.7 trillion barrels would last about 51 more years.

Applying the R/P ratio to natural gas, we find that the world’s proven reserves of this resource would last 53 more years.

For coal, the latest R/P ratio estimate is 153 years.

What is “peak oil”?

Peak oil describes a peak in extraction.

Peak oil will pose challenges

When did the peak come in US oil extraction, and in global extraction? When is peak extraction for other types of fossil fuels expected?

U.S. extraction of crude oil peaked in 1970 (a), just as geologist M. King Hubbert had predicted.

What are the challenges of peak oil?

We have to seek out a variety of less-conventional petroleum sources to compensate for this decline.

Writer James Howard Kunstler has sketched a frightening scenario of our post-peak world during what he calls “the long emergency”: Lacking cheap oil with which to transport goods long distances, today’s globalized economy would collapse into isolated local economies. Large cities would need to run urban farms to feed their residents, and with less mechanized farming and fewer petroleum-based fertilizers and pesticides, we might feed only a fraction of the world’s people. The American suburbs would be hit particularly hard because of their dependence on the automobile.

We all pay external costs

What are some of the externalities of fossil fuel extraction?

Medical expenses, costs of environmental cleanup, and impacts on our quality of life.

The prices we pay at the gas pump or on our monthly utility bill have been kept inexpensive as a result of government subsidies to extraction companies. The profitable fossil fuel industries receive far more financial support from taxpayers than do the emerging renewable energy sources.

What are some of the consequences of fossil fuel extraction for local people?

They must weigh the environmental, health, and social drawbacks of extractive development against the financial benefits they may gain.

Economic booms often prove temporary, whereas residents may be left with a polluted environment for generations to come.

Dependence on foreign energy affects the economies of nations

What changes have followed when there have oil shortages?

Such reliance means that seller nations can control energy prices, forcing buyer nations to pay more as supplies dwindle.

Efficiency and conservation bring benefits

How much has the US been able to reduce its energy intensity and per capita energy consumption? How has this been achieved? How does the US compare to the rest of the world (See Fig. 15.23)

The United States also cut in half its energy intensity, or energy use per dollar of Gross Domestic Product (GDP).

The United States trails other developed nations in energy efficiency but has made much progress.

U.S. per-person energy use has fallen slightly since 1979 but remains greater than that of most other nations. U.S. energy intensity has fallen steeply and now approaches that of other developed nations.

Personal actions and efficient technologies are two routes to conservation

What proportion of fossil fuel energy is lost? How and where? And what are energy saving solutions?

Currently, more than two-thirds of the fossil fuel energy we use is simply lost, as waste heat, in automobiles and power plants.

In homes, offices, and public buildings, a significant amount of heat is needlessly lost in winter and gained in summer because of poor design and inadequate insulation.

Improvements in design can reduce the energy required to heat and cool buildings. Such improvements can involve passive solar design (p. 382), better insulation, a building’s location, the vegetation around it, and the color of its roof (lighter colors keep buildings cooler by reflecting sunlight).

Automobile fuel efficiency is a key to conservation

Why does fuel efficiency in transportation offer our best opportunity to conserve energy?

We can accomplish this with electric cars, electric/gasoline hybrids, plug-in hybrids, or vehicles that use hydrogen fuel cells.

Many fully electric vehicles now obtain fuel-economy ratings of over 100 mpg.

The rebound effect cuts into efficiency gains

What is the rebound effect?

When gains in efficiency from better technology may be partly offset if people engage in more energy-consuming behavior as a result.

PrepG_7 The Land

Saving the World’s Greatest Rainforest

What are the threats to the Amazon rain forest?

Massive forest loss. Deforestation.

Starting in the 1990s, rising global demand for soy, sugar, rice, corn, and palm oil fueled the destruction of Amazonian forest for industrial-scale farming.

Forest Ecosystems and Forest Resources

What ecosystem services to forest provide? (Text and Fig. 9.6)

A Forest Provides us with a Diversity of Ecosystem Services, as Well as Resources that we can Harvest.

  • Stores carbon
  • Supports biodiversity
  • Provides fuel wood, lumber, paper, medicines, dyes, foods, fibers
  • Promotes and provides heal, beauty, recreation
  • Returns organs matter to soil
  • Stabilizes soil, prevents erosion
  • Transports minerals to soil surface
  • Slows runoff, prevents flooding
  • Purifies water, filters pollution
  • Produces oxygen

What percentage (%) of the Earths land surface does forest cover?

Forests Cover 31% of Earth’s Land Surface.

How important is the ecosystem service of carbon storage of forests?

Carbon storage limits climate change. Scientists estimate that the world’s forests store about 296 billion metric tons of carbon in living tissue, which is more than the atmosphere contains.

Each year forests absorb about 2.4 billion metric tons of carbon from the air, with the Amazon rainforest taking care of one-quarter of that total.

The more forests we preserve or restore, the more carbon we keep out of the atmosphere, and the better we can address climate change.

What are some of the products that forests provide for us?

Plants for medicines, dyes, and fibers; and animals, fruits, and nuts for food.

Forest Loss

What impacts does deforestation have? What is the net loss in forests?

Deforestation leads to biodiversity loss, soil degradation, and desertification. It also releases carbon dioxide to the atmosphere, contributing to climate change.

The UN Food and Agriculture Organization (FAO) found we are eliminating 7.6 million hectares (ha; 18.8 million acres) of forest each year. Subtracting annual regrowth from this amount makes for an annual net loss of 3.3 million ha (8.2 million acres)—an area about the size of Maryland. This rate (for the period 2010–2015) is lower than deforestation rates for earlier years. In the 1990s, the world had been losing 1.8% of its forest each year; in 2010–2015 it lost just 0.8% each year.

Another team found calculated from 2000 to 2012 annual losses of 19.2 million ha and annual gains of 6.7 million ha, for a net loss per year of 12.5 million ha (30.9 million acres—an area larger than New York State).

How much primary forest remains in North America relative to secondary forest? (Fig. 9.7 may help. Where is forest loss greatest in the world?

Primary forest: natural forest uncut by people

Very little primary forest remains in the lower 48 U.S. states, and today even less is left. Nearly all the largest trees in North America today are second-growth trees: trees that sprouted after old-growth trees were cut.

Africa, Latin America, and Indonesia are losing the most forest, whereas Europe and North America are slowly gaining secondary forest. In Asia, tree plantations are increasing, but natural primary forests are still being lost.

What is one of the consequences of a country allowing their timber to be extracted by foreign multinational corporations which pay fees for a concession? (Flashback to “Love will save this place.”)

Once a concession is granted, the corporation has little or no incentive to manage resources sustainably. Local people may receive temporary employment from the corporation, but once the timber is gone they no longer have the forest and the ecosystem services it provided. As a result, most economic benefits are short term and are reaped not by local residents but by the foreign corporation. Much of the wood extracted in developing nations is exported to Europe and North America. In this way, our consumption of high-end furniture and other wood products can drive forest destruction in poorer nations.

What is the concern over oil palm plantations?

Oil palm fruit produces palm oil, which we use in snack foods, soaps, cosmetics, and as a biofuel. In Indonesia, the world’s largest palm oil producer, oil palm plantations have displaced over 8 million ha (20 million acres) of rainforest. Clearing for plantations encourages further development and eases access for people to enter the forest and conduct logging illegally, leading to extensive loss of biodiversity.

Oil Palm Plantations are Replacing Primary Forest Across Southeast Asia and Indonesia.

What are some of the solutions for reducing deforestation?

Community-based conservation projects that empower local people to act as stewards of their forest resources.

In other cases, conservation organizations, such as Conservation International, are buying concessions and using them to preserve forest rather than to cut it down.

Another approach is the debt-for-nature swap, in which a conservation organization or a government offers to pay off a portion of a developing nation’s international debt in exchange for a promise by the nation to conserve natural land.

At recent international climate conferences, negotiators have outlined a program called Reducing Emissions from Deforestation and Forest Degradation (REDD; changed to REDD+ as the program expanded in scope), whereby wealthy industrialized nations pay poorer developing nations to conserve forest.

What is the significance of Dr. Wangari Maathai and the Green Belt Movement?

In 1977 she founded a grass-roots organization, the Green Belt Movement, to teach people how forests help conserve water and to organize people to plant trees near where they live. Since then, farmers and villagers have planted 51 million trees at 6500 sites across southern Kenya. Rural women are paid for each tree they plant that survives—a valuable source of income in an impoverished region.

Today her institute, her foundation, her four books, and the ongoing work of the Green Belt Movement inspire countless individuals to carry on her work with trees, people, and communities.

Forest Management

Compare and contrast the management of Maximum Sustainable Yield, Ecosystem-based Management, and Adaptive Management.

Maximum sustainable yield: to achieve the maximum amount of resource extraction without depleting the resource from one harvest to the next.

Ecosystem-based management: to minimize impact on the ecological processes that provide the resource.

Adaptive management: testing different approaches and trying to improve methods through time.

What role does the US Forest Service and private land play in US timber and how do their strategies differ?

Today almost 90% of timber harvesting in the United States takes place on private land owned by the timber industry or by small landowners.

Timber companies generally pursue maximum sustainable yield on their land, as well as extracting timber from public forests.

In the national forests, U.S. Forest Service staff conduct timber sales and build roads to provide access for logging companies, which sell the timber they harvest for profit. In this way, taxpayers subsidize private harvesting on public land.

Distinguish the differences & similarities between clear-cutting, seed tree or shelterwood systems, and selection systems for harvesting forests.

Clear-cutting systems: cost-efficient, and to some extent it can mimic natural disturbance events, such as fires or windstorms. However, the ecological impacts are severe.

Seed-tree / shelterwood systems: a few large trees are left standing in clear-cuts to reseed the area or to provide shelter for seedlings.

Selection systems: a minority of trees is removed at any one time, while most are left standing. Preserve much of a forest’s structural diversity, but are less cost-efficient for the industry.

Why has the management strategy changed from fire suppression to prescribed burns?

Fuel buildup from decades of fire suppression has contributed to wildfires burning more acreage across the United States.

Prescribed burns clear away fuel loads, nourish the soil with ash, and encourage the vigorous growth of new vegetation.

Prescribed Fire Helps to Promote Forest Health and Prevent Larger Damaging Fires.

How can deforestation and climate change create a dangerous positive feedback loop?

Deforestation can worsen the impacts of climate change, because when forests are removed across a large region, humidity and transpiration are reduced and less precipitation falls, making the region drier.

Climate change also is promoting outbreaks of pest insects. Bark beetles feed within the bark of conifer trees. They attract one another to weakened trees and attack en masse, eating tissue, laying eggs, and bringing with them a small army of fungi, bacteria, and other pathogens. Since the 1990s, infestations of bark beetles have devastated tens of millions of acres of forest in western North America (Figure 9.17), killing tens of billions of conifer trees and leaving them as fodder for fires.

If you buy something that is Forest Stewardship Council-certified, what does that indicate?

FSC-certified timber-harvesting operations are required to protect rare species and sensitive habitats, safeguard water sources, control erosion, minimize pesticide use, and maintain the diversity of the forest and its ability to regenerate after harvesting.

Parks and Protected Areas

Distinguish between National Parks (first created by the US), National Wildlife Refuges, Wilderness Areas, and Land Trusts.

National Parks: public lands protected from resource extraction and development but open to nature appreciation and recreation

National Wildlife Refuges: serve as havens for wildlife and encourage hunting, fishing, wildlife observation, photography, environmental education, and other public uses.

Wilderness Areas: areas are off-limits to development but are open to hiking, nature study, and other low-impact public recreation.

Land Trusts: local or regional organizations that purchase ecologically important tracts of land in order to preserve them for future generations.

What percent of the planet’s land area and ocean area is protected?

Today thousands of protected areas cover almost 15% of the planet’s land area and 4% of its ocean area.

Distinguish between biosphere reserves and world heritage sites.

Biosphere reserves: areas with exceptional biodiversity that couple preservation with sustainable development

World heritage sites: designated for their natural or cultural value. One such site is a transboundary reserve for mountain gorillas shared by three nations in Africa. Protected areas that overlap national borders sometimes function as “peace parks,” acting as buffers between nations.

What ecological problems result from fragmentation?

When forests are fragmented, many species suffer.

Fragmentation results from clear-cutting and agriculture and residential development.

Fragmentation affects forest-dwelling species such as the wood thrush, whose nests are parasitized by cowbirds that thrive in surrounding open country.

How does climate change highlight the limitations of habitat protection?

In a landscape of fragmented habitat, some organisms may be unable to move from one fragment to another. Species we had hoped to protect in parks may, in a warming world, become trapped in them.

The Changing Face of Agriculture

How much of the land surface is dedicated to cropland and rangeland worldwide and how does this compare to the US?

Agriculture is currently practiced on 38% of Earth’s land surface, and uses more land area than any other human activity.

Of this land, 26% is rangeland and 12% is cropland.

The percentages are even greater in the United States, where nearly half the land is devoted to agriculture. Here, rangeland covers 27% and cropland covers 19% of our land area.

What are some of the differences between traditional and industrial agriculture?

Traditional agriculture: the work of cultivating, harvesting, storing, and distributing crops was performed by human and animal muscle power, along with hand tools and simple machines.

  • Traditional farmers typically plant polycultures (“many types”), mixtures of different crops in small plots of farmland, such as the Native American farming systems that mixed maize, beans, squash, and peppers.

Industrial agriculture: Farmers replaced horses and oxen with machinery that provided faster and more powerful means of cultivating, harvesting, transporting, and processing crops.

  • boosted yields by intensifying irrigation and introducing synthetic fertilizers, while the advent of chemical pesticides reduced herbivory by crop pests and competition from weeds. Today, industrial agriculture is practiced on over 25% of the world’s cropland and has been a major factor in reducing food prices worldwide due to its large-scale, intensive production model.

What are some of the problems with monocultures?

The use of machinery created a need for highly organized approaches to farming, and this led to the planting of vast areas with single crops in orderly, straight rows.

Such monocultures (“one type”) make farming more efficient, but they reduce biodiversity by eliminating habitats used by organisms in and around traditional farm fields.

Moreover, when all plants in a field are genetically similar, they are equally susceptible to bacterial and viral diseases, fungal pathogens, or insect pests that can spread quickly.

The Green Revolution increased yields without large increases in land use (which protected habitat), but it came at a cost to what?

the intensified use of fossil fuels, water, inorganic fertilizers, and synthetic pesticides has worsened pollution, topsoil erosion, and soil and water quality.

Sustainable agriculture is a response to industrial agriculture—what are the pros and cons of this approach?

Sustainable agriculture describes agriculture that maintains the healthy soil, clean water, pollinators, and genetic diversity essential to long-term crop and livestock production. The best approach for making an agricultural system sustainable is to mimic the way a natural ecosystem functions.

PROS: use lesser amounts of fossil fuel energy, water, pesticides, fertilizers, growth hormones, and antibiotics.


Industrial agriculture PROS: more productive varieties of crops and livestock.

CONS: degraded soils, polluted waters, and affected biodiversity.


Forming one inch of soil can take how long?

Forming just 1 inch of soil can require hundreds or thousands of years, we would be wise to conserve the soil we have.

Watering and Fertilizing Crops

How does irrigation damage soil and what are the sustainability challenges with irrigation?

70% of the fresh water withdrawn by people is applied to crops. In some cases, withdrawing water for irrigation has depleted aquifers and dried up rivers and lakes.

Waterlogging occurs when overirrigation causes the water table to rise to the point that water drowns plant roots, depriving them of access to gases and essentially suffocating them.

A more frequent problem is salinization, the buildup of salts in surface soil layers.

What is the difference between inorganic and organic fertilizers?

Inorganic fertilizers: are mined or synthetically manufactured nutrient supplements.

Organic fertilizers: consist of the remains or wastes of organisms and include animal manure, crop residues, fresh vegetation (green manure), and compost, a mixture produced when decomposers break down organic matter, including food and crop waste, in a controlled environment.

How can precision agriculture, planting buffer strips, and using organic fertilizers improve sustainability of agriculture?

Precision agriculture involves using technology to precisely monitor crop conditions, crop needs, and resource use, to maximize production while minimizing waste of resources.

In addition, by planting buffer strips of vegetation along field edges and watercourses, growers can help to capture nutrient runoff before it enters streams and rivers.

Organic fertilizers provide not only nutrients but also organic matter that improves soil structure, nutrient retention, and water-retaining capacity.

Conserving Agricultural Resources

How much productive cropland do we lose globally and why?

Each year, our planet gains around 80 million people yet loses 5–7 million ha (12–17 million acres, about the size of West Virginia) of productive cropland to degradation.

The common causes include soil erosion, nutrient depletion, water scarcity, salinization, waterlogging, chemical pollution, changes in soil structure and pH, and loss of organic matter from the soil.

How can overgrazing and erosion result in a positive feedback loop?

When livestock remove too much plant cover or churn up the soil with their hooves, soil is exposed and made vulnerable to erosion. In a positive feedback cycle, soil erosion makes it difficult for vegetation to regrow, a problem that perpetuates the lack of cover and gives rise to more erosion.

Moreover, non-native weedy plants that are unpalatable or poisonous to livestock may invade and outcompete native vegetation in the new, modified environment. Too many livestock trampling the ground can also compact soil and alter its structure. Soil compaction makes it more difficult for water to infiltrate, for soil to be aerated, and for plants’ roots to expand. All of these effects further decrease plant growth and survival.

The Soil Conservation Act of 1935 was born out of the events of The Dust Bowl. What did it do and how did it help make the Dust Bowl a thing of the past?

Soil Conservation Act of 1935, establishing the Soil Conservation Service (SCS). This new agency worked closely with farmers to develop conservation plans for individual farms. The SCS (now the Natural Resources Conservation Service) served as a model for other nations that established their own soil conservation agencies to aid farmers in fighting soil erosion.

What are the sustainable agriculture practices to protect soil?

These include:

  • rotating crops
  • contour farming (farming along contours)
  • terracing (level platforms on steep terrain)
  • intercropping (alternating bands of crops in a field)
  • planting shelterbelts (windbreaks)
  • and no-till agriculture (most intensive conservation tillage)

What are the pros and cons of government subsidies for farmers?

In the United States, roughly one-fifth of the income of the average farmer comes from subsidies.

CONS: encourage people to cultivate land that would otherwise not be farmed; to produce more food than is needed, driving down prices for other producers; and to practice unsustainable farming methods that further degrade the land.

What is the Conservation Reserve Program (CRP) and what are its benefits?

The Conservation Reserve Program (CRP), established in the 1985 U.S. Farm Bill, pays farmers to stop cultivating highly erodible cropland and instead place it in conservation reserves planted with grasses and trees.

Besides reducing erosion, the CRP generates income for farmers, improves water quality, and provides habitat for wildlife.