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Sustainable Living Guide Contributions: Sustaining Biodiversity and Ecosystems

Week 1 Assignment Template

Sustainable Living Guide Contributions, Part One of Four:

Sustaining Biodiversity and Ecosystems

Instructions: Using the term that you have selected from the list provided in the classroom, please complete the following three-paragraph essay. Write a minimum of 5 to 7 well-crafted, original sentences per paragraph. In your response, you are expected to cite and reference, in APA format, at least two outside sources in addition to the class text. The sources must be credible (from experts in the field of study); at least one scholarly source (published in a peer-reviewed academic journal) is strongly encouraged. Delete all instructions before submitting your work to Waypoint.

Your Term: [type your term here]

[First Paragraph: Thoroughly define your term, using your own words to do so. In your definition, be sure explain why the term is important to know. Be as specific as possible and provide examples as necessary to support your ideas.]

[Second Paragraph: Discuss how the term affects living beings (including humans) and/or the physical environment. Provide examples as needed.]

[Third Paragraph: Suggest two clear, specific actions that you and the other students might take to promote environmental sustainability in relation to this term. Be creative and concrete with your suggestions. For example, you might recommend supporting a particular organization that is active in the field of your term. Explain exactly how those actions will aid in safeguarding our environment in relation to your chosen term.]

References: Following your essay, list all references you cited, in APA format.

After proofreading your assignment carefully, please submit your work to Waypoint for evaluation.

Sustainable Living Guide Contributions: Sustaining Biodiversity and Ecosystems

Week 1 Assignment Template

Sustainable Living Guide Contributions, Part One of Four:

Sustaining Biodiversity and Ecosystems

Instructions: Using the term that you have selected from the list provided in the classroom, please complete the following three-paragraph essay. Write a minimum of 5 to 7 well-crafted, original sentences per paragraph. In your response, you are expected to cite and reference, in APA format, at least two outside sources in addition to the class text. The sources must be credible (from experts in the field of study); at least one scholarly source (published in a peer-reviewed academic journal) is strongly encouraged. Delete all instructions before submitting your work to Waypoint.

Your Term: [type your term here]

[First Paragraph: Thoroughly define your term, using your own words to do so. In your definition, be sure explain why the term is important to know. Be as specific as possible and provide examples as necessary to support your ideas.]

[Second Paragraph: Discuss how the term affects living beings (including humans) and/or the physical environment. Provide examples as needed.]

[Third Paragraph: Suggest two clear, specific actions that you and the other students might take to promote environmental sustainability in relation to this term. Be creative and concrete with your suggestions. For example, you might recommend supporting a particular organization that is active in the field of your term. Explain exactly how those actions will aid in safeguarding our environment in relation to your chosen term.]

References: Following your essay, list all references you cited, in APA format.

After proofreading your assignment carefully, please submit your work to Waypoint for evaluation.

Sustainable Living Guide Contributions: Sustaining Biodiversity and Ecosystems

1 Understanding Environmental Science and Sustainability

Purestock/Thinkstock

Learning Outcomes

After reading this chapter, you should be able to

• Define environmental science.
• Describe the importance of critical thinking, information literacy, and the scientific method.
• Analyze the impact of palm oil plantations on biodiversity and the environment in Borneo.
• Define the core concepts of natural capital and sustainability.
• Define the core concepts of the environmental footprint and the Anthropocene.
• Define the core concepts of uncertainty, scale, risk, and cost–benefit analysis.

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Section 1.1 Why Study Environmental Science?

1.1 Why Study Environmental Science?

Whether we realize it or not, almost every aspect of our daily lives is dependent on and con-
nected to the natural world around us. We are a part of, and not separate from, that natural
world. The food we eat, the air we breathe, and the water we drink all originate from the natu-
ral world. Perhaps less obvious, the items we use every day—such as the fuel for our cars, the
clothes we wear, and our phones and electronic devices—all have their origins in the natural
world. At the same time, our everyday actions and use of these products—be it driving, eat-
ing, or throwing out the trash—all have an impact on this natural world on which we depend.

The study of environmental science encompasses all of these relationships. At its most basic,
environmental science is the study of how the natural world works, how we are affected by
the natural world, and how we in turn impact the natural world around us.

Our fundamental dependence on the natural world makes the study of environmental science
relevant to all of us. Environmental issues—including deforestation, ozone depletion, water
pollution, and climate change—affect us all. These issues are also in the news now more than
ever, and they are often at the center of heated political debates. Acquiring an understanding
of the basic science behind these debates is thus an important part of becoming an educated
citizen and forming your own opinion of the issues. And while you may not go on to make a
career in environmental science, you will likely find that this discipline intersects with your
major or field of study in some way.

The goal of this book is to help you understand the basics of environmental science so that
you can further explore and research environmental issues that interest and affect you
directly. Because environmental issues can be so complex, developing solutions requires a
solid understanding of policy and scientific concepts. In this book, we will apply natural sci-
ence and social science concepts to the study of environmental issues that are in the news
every day. The hope is that you—armed with the knowledge, perspectives, and up-to-date
information provided in this book—will begin to form your own, informed opinions on these
subjects. Ideally, you will also develop ideas about how you as an individual or society more
broadly can take action to address some of the most pressing environmental challenges fac-
ing the world today. Ultimately, this book aims to empower you as a student both to grasp the
environmental challenges facing the world and to do something about them.

Outline of the Book
Much of the rest of this chapter, and most of Chapter 2, focuses on introducing you to concepts
and ways of thinking that are essential to the study of environmental science and that will
appear repeatedly throughout the rest of the book. You can think of these chapters as laying a
foundation for your study of specific environmental issues in subsequent chapters. Just as you
would not expect to be able to cook or repair cars without the right tools and basic knowledge
of those activities, it would be difficult to study environmental issues without the information
provided in these first two chapters.

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Section 1.1 Why Study Environmental Science?

With a strong foundation in place, we’ll
move to the study of human population and
material consumption in Chapter 3. Vir-
tually all of the environmental challenges
we face are thanks to the growing number
of people on the planet and high rates of
material consumption among some of those
people. In this way, we could say that human
population growth and material consump-
tion are the fundamental drivers of environ-
mental change in the world today.

Chapters 4 through 9 focus on specific envi-
ronmental issues and challenges: manage-
ment of agricultural and forest resources,
freshwater resources, oceanic resources,
energy resources, atmosphere and climate,

and waste. These chapters involve a heavy emphasis on negative news and challenges, so
Chapter 10 aims to end the book on a more upbeat note. While it’s true that we face enormous
and complicated worldwide environmental problems, it’s also true that governments, non-
governmental organizations (NGOs), corporations, small companies, schools and universi-
ties, and individual citizens are taking steps to address and reverse those challenges. We will
examine their stories in hopes of inspiring positive change in our own lives.

Key Definitions in Environmental Science
While we may hear or use the words environment, environmentalism, and environmental sci-
ence quite often, we might not always appreciate what they mean and how they are used in
the study of environmental issues. At its most basic level, the environment is everything that
surrounds you. This includes all living things (such as animals, plants, and other people), as
well as all nonliving things (such as water, rocks, air, and sunlight). A more scientific definition
of the environment would be all physical, chemical, and biological factors and processes that
affect an organism.

Based on that definition, it should be clear that we are all a part of the environment rather
than apart from it. In fact, one major theme of this book is that, despite all the technological
gadgets and scientific advances that attract our attention, we are all fundamentally depen-
dent on the environment for our well-being and survival. The task of sustaining our agri-
cultural resources, forests, water sources, oceans, atmosphere, and climate is not just about
“caring” for this creature or “saving” that endangered animal. It’s also about saving ourselves
and ensuring that we and generations to come can breathe clean air, drink clean water, and
live under relatively stable and benign climate conditions.

Because the environment by definition is basically everything, environmental science is a
complex and interdisciplinary field of study. Environmental science draws together knowl-
edge and concepts from many disciplines—ecology, biology, chemistry, geology, atmospheric
science, physics, economics, political science, and other fields—to understand both how we
are impacting the environment and what can be done to lessen that impact.

danielvfung/iStock/Getty Images Plus
The biggest driver of environmental change in
today’s world is human population growth and
rates of consumption, which have increased
exponentially in the past 200 years.

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Section 1.2 Thinking Critically About Environmental Science

Note that there is a difference between environmental science and environmentalism. Envi-
ronmentalism is a social and political movement committed to protecting the natural world.
While many environmental scientists likely consider themselves environmentalists, as scien-
tists they adopt a more objective approach to the issues they study. This approach is based in
large part on the use of the scientific method, an approach to research based on observation,
data collection, hypothesis testing, and experimentation. As a student, you are not required
or expected to become an environmentalist, but as an educated citizen, you should learn to
recognize the critical role played by the scientific method in forming our understanding of the
environment and the environmental challenges we face. Such an understanding of the scien-
tific method will help you develop critical-thinking skills and enable you to weigh competing
claims and arguments about environmental issues.

1.2 Thinking Critically About Environmental Science

Many environmental scientists see their
work as largely nonpolitical and noncontro-
versial. They are attempting to understand
how a particular piece of the environment
or system—a stream, a wetland, a patch of
forest—functions and what might happen
to that system in the wake of pollution or
some other environmental disturbance.
However, because the findings of this envi-
ronmental research are often used in craft-
ing and implementing environmental pol-
icy, environmental science and debates over
environmental issues can become highly
contentious and political.

Take, for example, the topic of global cli-
mate change (which will be covered in more
detail in Chapter 8). Thousands of environmental scientists are engaged in research that is
in some way related to the subject of climate change. Some scientists study how combus-
tion of fossil fuels or other human activities add greenhouse gases to the atmosphere, others
how these gases change the Earth’s energy balance and climate systems, and still others how
changes to the climate are affecting trees, animals, and other living organisms.

The majority of these scientists would probably not see their work as contentious or political.
They are instead usually motivated by scientific curiosity and a desire to pursue knowledge.
However, because the sum of these thousands of research efforts points with overwhelming
confidence to the realities of global climate change, and because addressing climate change
will require changes to all sorts of economic and social behaviors, the efforts of these envi-
ronmental scientists can become politicized. Because of this politicization, it’s important to
understand the concepts of critical thinking, information literacy, and the scientific method.
Careful application of these approaches to your own study of the environment will help you

patriziomartorana/iStock/Getty Images Plus
Environmental scientists aim to understand
how different elements of the environment
function and how they change in response to
other factors, such as pollution.

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Section 1.2 Thinking Critically About Environmental Science

develop informed opinions on many issues and help you avoid falling for arguments that are
based on opinion and personal belief rather than grounded in facts and scientific evidence.

Critical Thinking and Information Literacy
Critical thinking is the objective analysis and evaluation of an issue to form a judgment.
In this case, the key term is objective analysis—in other words, analysis that is not based
on personal opinion or belief. For example, one of this book’s authors had a student who,
while hiking, saw a number of dead birds on the ground near the base of some wind turbines.
The student later expressed a conviction that wind power was bad for the environment and
should not be used. While there are legitimate reasons to be concerned about the effect of
wind turbines on bird (and bat) mortality, this student should also consider what the envi-
ronmental impact of other forms of electricity production are. In the authors’ region of the
country (Pennsylvania), much of the electricity is produced by burning coal. A better example
of objective analysis would be a comparison of the environmental impacts of coal mining and
coal burning (including the impact on birds and bats) to the impact of wind turbines.

As you engage with the material in this book, and as you do your own research and form your
own opinions about environmental issues, keep the following principles of critical thinking
in mind:

• Evaluate the basis for a particular conclusion. What evidence is being presented to
support a claim or an argument, and how was that evidence collected?

• Keep an open mind. Attempt to gather information from a variety of perspectives
before forming a final opinion.

• Be skeptical. While keeping an open mind, ask yourself where information is coming
from and how it was developed.

• Consider possible biases, including your own. Most scientists strive mightily to avoid
the introduction of bias into their work, and the scientific method (described in
more detail later) helps them do that.

• Distinguish between facts and values or opinions. For example, it is a fact that atmo-
spheric concentrations of the greenhouse gas carbon dioxide now exceed 400 parts
per million (ppm) compared to levels of roughly 280 ppm at the start of the Indus-
trial Revolution. However, it’s an opinion or value statement to say that the use of
all fossil fuels should be halted immediately to prevent further increases in carbon
dioxide concentrations.

A key part of establishing and utilizing critical-thinking skills is to develop what’s often
referred to as information literacy. Information literacy is the ability to know when informa-
tion is needed and the ability to identify, locate, evaluate, and effectively use that information
to address an issue. For our purposes, the most important of these abilities will be locating
and evaluating information. The past two decades have witnessed an explosion of informa-
tion and information sources, and our ability to access that information is becoming easier
every day. However, our ability to know where to look for reliable information and to evaluate
that information for reliability and usefulness has not kept pace. For example, there are thou-
sands of sources of information on the topic of climate change. Who should you believe? Who

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Section 1.2 Thinking Critically About Environmental Science

can you trust? We can see how critical-thinking skills are needed for information literacy and
how information literacy is required for critical thinking. As you read this book and explore
on your own the environmental topics and issues that interest you, ask yourself where infor-
mation is coming from, how it was gathered, and how reliable it might be. The Apply Your
Knowledge: Is This Information Reliable? feature box presents one quick opportunity to test
your critical-thinking skills.

A less appreciated but nevertheless important skill for environmental analysis and problem
solving is creative thinking. As scientists examine an environmental issue and ponder its
possible causes and consequences, it helps if they can think creatively and with an open mind,
as opposed to being locked into one way of looking at the world. Environmental scientists
also tap into creative thinking to design effective field experiments that help them better
understand the workings of nature. And as we’ll see throughout this book, it will take creative
thinking and even imagination to develop alternative approaches to meeting our food, water,
energy, and other resource needs in ways that do not destroy the environment.

Apply Your Knowledge: Is This Information Reliable?

Evaluating the quality and reliability of information can be a difficult task, especially when
we are considering resources found on the Internet. We live in a world in which opinions are
sometimes presented as the unbiased truth, and pretty much anyone with a computer can
create a convincing website that is accessible to the entire world.

To highlight some of these challenges, let us explore a website called Save the Pacific
Northwest Tree Octopus. At first, the prospect of a tree-dwelling octopus might seem
absurd, but nature often surprises us. There are birds that can swim and fish that can fly, so
why not an octopus that climbs trees? If you read the article, you might also notice that the
information presented is fairly detailed. The author provides a Latin name for this creature,
along with measurements that describe tree octopus physiology. There are even photographs
and links to additional resources, suggesting that others have documented these creatures in
the past.

Despite the website’s flashy appearance, it is a total hoax. There is no such thing as a tree
octopus, and if we take a closer look at the website, we can see some warning signs that call
its information into question. Take a moment to explore the Save the Pacific Northwest Tree
Octopus website on your own, and see if you can find any red flags indicating that the article
is unreliable.

(continued)

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Section 1.2 Thinking Critically About Environmental Science

Apply Your Knowledge: Is This Information Reliable?
(continued)

One characteristic of trustworthy information is that it comes from a reputable author
or organization. For example, information from a government agency, an institution of
higher education, or a peer-reviewed journal is often considered to be more reliable than
information from a personal blog. Reliable resources will also provide access to author
biographies so that you can tell if the author is an expert on the subject matter. If you look
at the author information at the bottom of the tree octopus website, you will notice that the
author description is downright silly. There is no indication that the person has any training
related to the subject matter.

Reliable resources also need to be fact-checked or backed up with supporting information
that is usually identified using links and citations. This website appears to have active links to
other resources, but if you follow these links, you will notice that they take you to other hoax
websites or to sites that have no mention of tree octopuses.

Finally, reliable sources will be clear about whether their goal is to inform you with factual
information or to convince you of a particular argument. A close reading of the material
can often tell you if an unreliable resource is trying to convince you of an opinion while
appearing to present objective facts. Consider the following sentence from the tree octopus
website:

Tree octopuses became prized by the fashion industry as ornamental decorations for
hats, leading greedy trappers to wipe out whole populations to feed the vanity of the
fashionable rich. (Zapato, n.d., para. 8)

Phrases like “greedy trappers” and “vanity of the fashionable rich” suggest that the author
is making judgments about certain actions and groups of people. This is not what we would
expect from a well-written article that is intended to present factual information.

Now, take a moment to explore another web resource titled “Discovery of the First
Endemic Tree-Climbing Crab.” Once again, the topic sounds bizarre, but if we look closely,
the information seems much more trustworthy. The article was produced by an academic
institution. The language used in the article appears to be unbiased, and the information can
be easily fact-checked using the peer-reviewed journal articles and academic websites that
are referenced at the end. This article appears to be a source of reliable information.

Save the Pacific Northwest Tree Octopus is a silly example of “bad” information, but the
critical-thinking skills we used to evaluate this source can be applied to everything that
we read, hear, and watch. If we approach media critically, we’ll be able to recognize the
trustworthy information that helps us make better policies and decisions. In your future
studies, look for information that is from a trusted source. Look for information that is
backed up by quality research and journalism. Finally, look for information that is attempting
to inform rather than persuade (unless you are researching opinions, of course).

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Section 1.2 Thinking Critically About Environmental Science

The Scientific Method
The use of the scientific method is one way that environmental scientists seek to improve the
reliability, usefulness, and relevance of their research. The scientific method is an approach
whereby scientists observe, test, and draw conclusions about the world around us in a sys-
tematic manner, rather than simply stating opinion. The scientific method consists of a series
of five steps, as illustrated in Figure 1.1.

Figure 1.1: The scientific method

The scientific method is a five-step model used to observe, test, and draw conclusions scientifically.

1. Make observations

2. Ask questions

3. Formulate hypothesis

4. Make predictions

5. Test predictions

Scenario A: Test supports
hypothesis. Additional predictions

can be made and tested.

Scenario B: Test does not
support hypothesis. Formulate

new hypothesis and retest.

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Section 1.2 Thinking Critically About Environmental Science

Scientists begin with simple observations of the world around us. They then form questions
based on those observations. For example, environmental scientists might observe the death
and decline of numerous trees alongside a major highway and naturally wonder what is caus-
ing this to happen. This leads to the third step, the formulation of a hypothesis or hypotheses
that might explain the trees’ death. Hypotheses can be thought of as a first guess or “hunch”
about something, and they help scientists formulate predictions, specific statements that can
be tested. In this case, the scientists might form a hypothesis that the trees are dying because
of road salt running off the highway in the winter or because of an herbicide sprayed to con-
trol weeds on the side of the highway. Based on these guesses, they can take the fourth step
in the scientific method and develop specific and testable predictions about how much road
salt or herbicide needs to be applied to bring about the same levels of tree death and decline
they have observed in nature.

All of these steps lead up to the final step of testing the predictions. To clearly determine what
might be killing the trees, scientists devise experiments that attempt to hold conditions con-
stant and then change one variable at a time. In this case, scientists might identify four similar
small groves of trees that show no sign of stress or tree death. They might then expose one
area to road salt, another to herbicide, and a third to both road salt and herbicide, while the
fourth area is left alone. (Apply Your Knowledge: How Does Road Salt Affect Trees? shows how
scientists might record their data.)

Note that regardless of the outcome of these experiments, scientists will typically still do two
additional things. First, if the road salt or herbicide appeared to have some impact on the
trees, the scientists might refine their predictions to gain a better understanding of why this
is happening. This might include adjusting the levels of road salt or herbicide to see if they can
better determine at what levels these applications become toxic. If the trees were not affected
by the road salt and herbicide, the scientists would be forced to revise their hypotheses or
form new ones. Second, scientists typically seek to share their results with others, usually
by presenting their research at scientific conferences and publishing articles in professional
journals. These presentations and papers are subject to analysis and scrutiny by other scien-
tists, a process known as peer review. Scientists also have to explain the methods used in their
research so that other scientists can run the same experiments, a process known as replica-
tion. These two aspects of scientific research, peer review and replication, help ensure the
accuracy and legitimacy of the work.

It’s important to recognize just how the scientific method can shield scientists from claims of
bias. Scientists don’t really set out to “prove” anything; instead, they observe, ask questions,
hypothesize, predict, test, and usually repeat. Politicians’ demands for scientific “proof ” are
therefore problematic. Environmental policy should be informed by the best science avail-
able, as well as other issues such as ethical concerns, economic impacts, and risks involved.

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Section 1.2 Thinking Critically About Environmental Science

Apply Your Knowledge: How Does Road Salt Affect Trees?

Environmental scientists make use of many different types of graphs to summarize and
present the data they gather in their research. Graphs help in taking enormous amounts of
data and information and presenting them in a way that tells a story or makes an argument.
Your ability to understand and interpret graphs will be an important part of reading this
book and learning environmental science.

Consider the following figures, which show possible results from the road salt/herbicide
example used in the discussion of the scientific method. Figures 1.2 and 1.3 report basically
the same information on tree death and decline from the experiment in different ways.
Figure 1.2 portrays the number of trees that died in the different plots of the experiment over
time. Figure 1.3 presents overall tree deaths by plot type at the end of the experiment.

Figure 1.2: Line graph showing tree damage

This graph shows tree damage over time.

Week 1

12

11

10

9

8

7

6

5

4

3

2

1

0

Week 2

N
u

m
b

e
r

o
f

tr
e
e
s
s

h
o

w
in

g
s

tr
e
s
s
o

r
d

a
m

a
g

e

Week 3 Week 4

No application

Road salt

Herbicide

Road salt and herbicide

(continued)

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Section 1.2 Thinking Critically About Environmental Science

Based on the data presented from this experiment, it appears that road salt might be the
biggest contributor to tree mortality. Imagine then that the scientists conducted a second
experiment with four plots of trees in which they applied different amounts of road salt and
measured tree mortality over a 4-week period. Table 1.1 gives information on the amount of
road salt applied to each of the four plots and the corresponding tree mortality. Try plotting
these numbers on a piece of paper. Draw a straight line that comes closest to connecting each
of the four points on the graph. What does the shape and direction of this line tell you about
the relationship between road salt application and tree mortality?

Table 1.1: Amount of road salt and tree damage

Road salt application (metric tons/hectare) Tree damage (dead trees per plot)

Plot 1 (1 metric ton/hectare) 2

Plot 2 (2 metric tons/hectare) 5

Plot 3 (3 metric tons/hectare) 8

Plot 4 (4 metric tons/hectare) 12

Figure 1.3: Bar graph showing tree damage

This graph shows tree damage by plot type.

No application

12

11

10

9

8

7

6

5

4

3

2

1

0
Road salt

N
um

be
r

of
tr

ee
s

sh
ow

in
g

st
re

ss
o

r
da

m
ag

e

HerbicideRoad salt
and herbicide

Apply Your Knowledge: How Does Road Salt Affect Trees?
(continued)

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Section 1.3 Case Study: Palm Oil Production and Deforestation in Borneo

1.3 Case Study: Palm Oil Production and Deforestation
in Borneo

Environmental scientists, as well as other natural and social scientists, frequently make use
of “case studies” to illustrate important points or concepts. In some ways, case studies are
simply formalized stories about a specific place, person, group, or other thing. The case study
presented here will help illustrate concepts and terms such as environment and environmen-
tal science and demonstrate how environmental scientists make use of critical-thinking skills
and the scientific method in their work. This case study will also be used to explain some of
the foundational concepts introduced later in this chapter and in Chapter 2.

About Borneo
The island of Borneo straddles the equator in Southeast Asia and is the third largest island in
the world and the largest island in Asia. The island is divided between Indonesia, Malaysia,
and Brunei, with Indonesia controlling roughly 73% of Borneo’s land area, Malaysia 26%, and
tiny Brunei just 1% (see Figure 1.4).

Figure 1.4: Borneo

Located in Southeast Asia, Borneo is known for its high rates of biodiversity, but its rain forests are in
decline due to deforestation

Adapted from PeterHermesFurian/iStock/Getty Images Plus

BORNEO

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Section 1.3 Case Study: Palm Oil Production and Deforestation in Borneo

Until very recently, Borneo was sparsely populated, and much of the island was covered in
dense tropical rain forests. Because of this, Borneo is known for its extremely high rates of
biological diversity, or biodiversity—the variety of life and organisms in a specific ecosys-
tem. That variety can be measured by considering the number of species found in a particu-
lar area. Species are groups of organisms that share certain characteristics, interbreed, and
produce fertile offspring. In addition to having an incredibly high number of species overall,
Borneo is also known for having a large number of endemic species—plants and animals
that exist in only one specific geographic region. There are dozens of endemic mammal spe-
cies (such as the proboscis monkey and pygmy elephant), hundreds of endemic birds, and
thousands of endemic plant species in Borneo. Rates of biodiversity are so high in Borneo that
scientists have identified over 20,000 types of insect species in one small national park alone
(Shoumatoff, 2017).

The Problem
Beginning roughly 50 years

Sustainable Living Guide Contributions: Sustaining Biodiversity and Ecosystems

Prior to beginning work on this assignment, read Chapters 1 and 2 in the course textbook. The purpose of this assignment is twofold: first, to enable you to explore a term (concept, technique, place, etc.) related to this week’s theme of sustaining Earth’s biodiversity and ecosystems; second, to provide your first contribution to a collective project, the Class Sustainable Living Guide. Your work this week, and in the weeks that follow, will be gathered (along with that of your peers) into a master document that you will receive a few days after the end of the course. The document will provide everyone with a variety of ideas for how we can all live more sustainably in our homes and communities.

To complete this assignment,

· Select a term from the list of choices in the Week 1 – Term Selection Table located in the course. Type your name in the table, next to the word that you would like to choose.

· Do not select a term that a classmate has already chosen; only one student per term. If you choose a term that is hyperlinked to a source, that term is one that is not mentioned in our textbook. Instead of being required to use the text as your third source for completing the assignment, you will be expected to use the hyperlinked source provided for you.

· Download the Template Template available in the course and replace the guiding text with your own words based upon your online research.

· Please do not include a cover page. All references, however, should be cited in your work and listed at the end, following APA Style expectations.

In the template, you will

· Define the term thoroughly, in your own words.

· Explain the importance of the term using evidence.

· Discuss how the term affects living things and the physical world.

· Suggest two specific actions that you and your peers might take to promote environmental sustainability in relation to the term.

· Explain exactly how those actions will aid in safeguarding our environment in relation to your chosen term.

· Provide detailed examples to support your ideas.

The Sustaining Living Guide Contributions: Sustaining Biodiversity and Ecosystems paper

· Must be a minimum of three paragraphs in length (not including title, any quoted text, or references) and formatted according to APA style as outlined in the University of Arizona Global Campus Writing Center’s APA Formatting for Word 2013 (Links to an external site.)

· Must utilize academic voice. See the Academic Voice (Links to an external site.) resource for additional guidance.

· Must use at least two scholarly sources in addition to the course text. To aid you in your research, and particularly in locating scholarly sources via the University of Arizona Global Campus Library or using Google Scholar, please review the following University of Arizona Global Campus videos and tutorials:

·
Scholarly and Popular Resources (Links to an external site.)

·
Database Search Tips (Links to an external site.)

·
University of Arizona Global Campus Library Quick ‘n’ Dirty (Links to an external site.)

· Accessing Full text and citation in Google Scholar: 
SCI207 – Google Scholar (Links to an external site.)

· Must document any information used from sources in APA Style as outlined in the University of Arizona Global Campus Writing Center’s APA: Citing Within Your Paper (Links to an external site.)

· Must include a separate references page that is formatted according to APA Style as outlined in the University of Arizona Global Campus Writing Center. See the APA: Formatting Your References List (Links to an external site.) resource in the University of Arizona Global Campus Writing Center for specifications.

Sustainable Living Guide Contributions: Sustaining Biodiversity and Ecosystems

1 Understanding Environmental Science and Sustainability

Purestock/Thinkstock

Learning Outcomes

After reading this chapter, you should be able to

• Define environmental science.
• Describe the importance of critical thinking, information literacy, and the scientific method.
• Analyze the impact of palm oil plantations on biodiversity and the environment in Borneo.
• Define the core concepts of natural capital and sustainability.
• Define the core concepts of the environmental footprint and the Anthropocene.
• Define the core concepts of uncertainty, scale, risk, and cost–benefit analysis.

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Section 1.1 Why Study Environmental Science?

1.1 Why Study Environmental Science?

Whether we realize it or not, almost every aspect of our daily lives is dependent on and con-
nected to the natural world around us. We are a part of, and not separate from, that natural
world. The food we eat, the air we breathe, and the water we drink all originate from the natu-
ral world. Perhaps less obvious, the items we use every day—such as the fuel for our cars, the
clothes we wear, and our phones and electronic devices—all have their origins in the natural
world. At the same time, our everyday actions and use of these products—be it driving, eat-
ing, or throwing out the trash—all have an impact on this natural world on which we depend.

The study of environmental science encompasses all of these relationships. At its most basic,
environmental science is the study of how the natural world works, how we are affected by
the natural world, and how we in turn impact the natural world around us.

Our fundamental dependence on the natural world makes the study of environmental science
relevant to all of us. Environmental issues—including deforestation, ozone depletion, water
pollution, and climate change—affect us all. These issues are also in the news now more than
ever, and they are often at the center of heated political debates. Acquiring an understanding
of the basic science behind these debates is thus an important part of becoming an educated
citizen and forming your own opinion of the issues. And while you may not go on to make a
career in environmental science, you will likely find that this discipline intersects with your
major or field of study in some way.

The goal of this book is to help you understand the basics of environmental science so that
you can further explore and research environmental issues that interest and affect you
directly. Because environmental issues can be so complex, developing solutions requires a
solid understanding of policy and scientific concepts. In this book, we will apply natural sci-
ence and social science concepts to the study of environmental issues that are in the news
every day. The hope is that you—armed with the knowledge, perspectives, and up-to-date
information provided in this book—will begin to form your own, informed opinions on these
subjects. Ideally, you will also develop ideas about how you as an individual or society more
broadly can take action to address some of the most pressing environmental challenges fac-
ing the world today. Ultimately, this book aims to empower you as a student both to grasp the
environmental challenges facing the world and to do something about them.

Outline of the Book
Much of the rest of this chapter, and most of Chapter 2, focuses on introducing you to concepts
and ways of thinking that are essential to the study of environmental science and that will
appear repeatedly throughout the rest of the book. You can think of these chapters as laying a
foundation for your study of specific environmental issues in subsequent chapters. Just as you
would not expect to be able to cook or repair cars without the right tools and basic knowledge
of those activities, it would be difficult to study environmental issues without the information
provided in these first two chapters.

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Section 1.1 Why Study Environmental Science?

With a strong foundation in place, we’ll
move to the study of human population and
material consumption in Chapter 3. Vir-
tually all of the environmental challenges
we face are thanks to the growing number
of people on the planet and high rates of
material consumption among some of those
people. In this way, we could say that human
population growth and material consump-
tion are the fundamental drivers of environ-
mental change in the world today.

Chapters 4 through 9 focus on specific envi-
ronmental issues and challenges: manage-
ment of agricultural and forest resources,
freshwater resources, oceanic resources,
energy resources, atmosphere and climate,

and waste. These chapters involve a heavy emphasis on negative news and challenges, so
Chapter 10 aims to end the book on a more upbeat note. While it’s true that we face enormous
and complicated worldwide environmental problems, it’s also true that governments, non-
governmental organizations (NGOs), corporations, small companies, schools and universi-
ties, and individual citizens are taking steps to address and reverse those challenges. We will
examine their stories in hopes of inspiring positive change in our own lives.

Key Definitions in Environmental Science
While we may hear or use the words environment, environmentalism, and environmental sci-
ence quite often, we might not always appreciate what they mean and how they are used in
the study of environmental issues. At its most basic level, the environment is everything that
surrounds you. This includes all living things (such as animals, plants, and other people), as
well as all nonliving things (such as water, rocks, air, and sunlight). A more scientific definition
of the environment would be all physical, chemical, and biological factors and processes that
affect an organism.

Based on that definition, it should be clear that we are all a part of the environment rather
than apart from it. In fact, one major theme of this book is that, despite all the technological
gadgets and scientific advances that attract our attention, we are all fundamentally depen-
dent on the environment for our well-being and survival. The task of sustaining our agri-
cultural resources, forests, water sources, oceans, atmosphere, and climate is not just about
“caring” for this creature or “saving” that endangered animal. It’s also about saving ourselves
and ensuring that we and generations to come can breathe clean air, drink clean water, and
live under relatively stable and benign climate conditions.

Because the environment by definition is basically everything, environmental science is a
complex and interdisciplinary field of study. Environmental science draws together knowl-
edge and concepts from many disciplines—ecology, biology, chemistry, geology, atmospheric
science, physics, economics, political science, and other fields—to understand both how we
are impacting the environment and what can be done to lessen that impact.

danielvfung/iStock/Getty Images Plus
The biggest driver of environmental change in
today’s world is human population growth and
rates of consumption, which have increased
exponentially in the past 200 years.

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Section 1.2 Thinking Critically About Environmental Science

Note that there is a difference between environmental science and environmentalism. Envi-
ronmentalism is a social and political movement committed to protecting the natural world.
While many environmental scientists likely consider themselves environmentalists, as scien-
tists they adopt a more objective approach to the issues they study. This approach is based in
large part on the use of the scientific method, an approach to research based on observation,
data collection, hypothesis testing, and experimentation. As a student, you are not required
or expected to become an environmentalist, but as an educated citizen, you should learn to
recognize the critical role played by the scientific method in forming our understanding of the
environment and the environmental challenges we face. Such an understanding of the scien-
tific method will help you develop critical-thinking skills and enable you to weigh competing
claims and arguments about environmental issues.

1.2 Thinking Critically About Environmental Science

Many environmental scientists see their
work as largely nonpolitical and noncontro-
versial. They are attempting to understand
how a particular piece of the environment
or system—a stream, a wetland, a patch of
forest—functions and what might happen
to that system in the wake of pollution or
some other environmental disturbance.
However, because the findings of this envi-
ronmental research are often used in craft-
ing and implementing environmental pol-
icy, environmental science and debates over
environmental issues can become highly
contentious and political.

Take, for example, the topic of global cli-
mate change (which will be covered in more
detail in Chapter 8). Thousands of environmental scientists are engaged in research that is
in some way related to the subject of climate change. Some scientists study how combus-
tion of fossil fuels or other human activities add greenhouse gases to the atmosphere, others
how these gases change the Earth’s energy balance and climate systems, and still others how
changes to the climate are affecting trees, animals, and other living organisms.

The majority of these scientists would probably not see their work as contentious or political.
They are instead usually motivated by scientific curiosity and a desire to pursue knowledge.
However, because the sum of these thousands of research efforts points with overwhelming
confidence to the realities of global climate change, and because addressing climate change
will require changes to all sorts of economic and social behaviors, the efforts of these envi-
ronmental scientists can become politicized. Because of this politicization, it’s important to
understand the concepts of critical thinking, information literacy, and the scientific method.
Careful application of these approaches to your own study of the environment will help you

patriziomartorana/iStock/Getty Images Plus
Environmental scientists aim to understand
how different elements of the environment
function and how they change in response to
other factors, such as pollution.

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Section 1.2 Thinking Critically About Environmental Science

develop informed opinions on many issues and help you avoid falling for arguments that are
based on opinion and personal belief rather than grounded in facts and scientific evidence.

Critical Thinking and Information Literacy
Critical thinking is the objective analysis and evaluation of an issue to form a judgment.
In this case, the key term is objective analysis—in other words, analysis that is not based
on personal opinion or belief. For example, one of this book’s authors had a student who,
while hiking, saw a number of dead birds on the ground near the base of some wind turbines.
The student later expressed a conviction that wind power was bad for the environment and
should not be used. While there are legitimate reasons to be concerned about the effect of
wind turbines on bird (and bat) mortality, this student should also consider what the envi-
ronmental impact of other forms of electricity production are. In the authors’ region of the
country (Pennsylvania), much of the electricity is produced by burning coal. A better example
of objective analysis would be a comparison of the environmental impacts of coal mining and
coal burning (including the impact on birds and bats) to the impact of wind turbines.

As you engage with the material in this book, and as you do your own research and form your
own opinions about environmental issues, keep the following principles of critical thinking
in mind:

• Evaluate the basis for a particular conclusion. What evidence is being presented to
support a claim or an argument, and how was that evidence collected?

• Keep an open mind. Attempt to gather information from a variety of perspectives
before forming a final opinion.

• Be skeptical. While keeping an open mind, ask yourself where information is coming
from and how it was developed.

• Consider possible biases, including your own. Most scientists strive mightily to avoid
the introduction of bias into their work, and the scientific method (described in
more detail later) helps them do that.

• Distinguish between facts and values or opinions. For example, it is a fact that atmo-
spheric concentrations of the greenhouse gas carbon dioxide now exceed 400 parts
per million (ppm) compared to levels of roughly 280 ppm at the start of the Indus-
trial Revolution. However, it’s an opinion or value statement to say that the use of
all fossil fuels should be halted immediately to prevent further increases in carbon
dioxide concentrations.

A key part of establishing and utilizing critical-thinking skills is to develop what’s often
referred to as information literacy. Information literacy is the ability to know when informa-
tion is needed and the ability to identify, locate, evaluate, and effectively use that information
to address an issue. For our purposes, the most important of these abilities will be locating
and evaluating information. The past two decades have witnessed an explosion of informa-
tion and information sources, and our ability to access that information is becoming easier
every day. However, our ability to know where to look for reliable information and to evaluate
that information for reliability and usefulness has not kept pace. For example, there are thou-
sands of sources of information on the topic of climate change. Who should you believe? Who

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Section 1.2 Thinking Critically About Environmental Science

can you trust? We can see how critical-thinking skills are needed for information literacy and
how information literacy is required for critical thinking. As you read this book and explore
on your own the environmental topics and issues that interest you, ask yourself where infor-
mation is coming from, how it was gathered, and how reliable it might be. The Apply Your
Knowledge: Is This Information Reliable? feature box presents one quick opportunity to test
your critical-thinking skills.

A less appreciated but nevertheless important skill for environmental analysis and problem
solving is creative thinking. As scientists examine an environmental issue and ponder its
possible causes and consequences, it helps if they can think creatively and with an open mind,
as opposed to being locked into one way of looking at the world. Environmental scientists
also tap into creative thinking to design effective field experiments that help them better
understand the workings of nature. And as we’ll see throughout this book, it will take creative
thinking and even imagination to develop alternative approaches to meeting our food, water,
energy, and other resource needs in ways that do not destroy the environment.

Apply Your Knowledge: Is This Information Reliable?

Evaluating the quality and reliability of information can be a difficult task, especially when
we are considering resources found on the Internet. We live in a world in which opinions are
sometimes presented as the unbiased truth, and pretty much anyone with a computer can
create a convincing website that is accessible to the entire world.

To highlight some of these challenges, let us explore a website called Save the Pacific
Northwest Tree Octopus. At first, the prospect of a tree-dwelling octopus might seem
absurd, but nature often surprises us. There are birds that can swim and fish that can fly, so
why not an octopus that climbs trees? If you read the article, you might also notice that the
information presented is fairly detailed. The author provides a Latin name for this creature,
along with measurements that describe tree octopus physiology. There are even photographs
and links to additional resources, suggesting that others have documented these creatures in
the past.

Despite the website’s flashy appearance, it is a total hoax. There is no such thing as a tree
octopus, and if we take a closer look at the website, we can see some warning signs that call
its information into question. Take a moment to explore the Save the Pacific Northwest Tree
Octopus website on your own, and see if you can find any red flags indicating that the article
is unreliable.

(continued)

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Section 1.2 Thinking Critically About Environmental Science

Apply Your Knowledge: Is This Information Reliable?
(continued)

One characteristic of trustworthy information is that it comes from a reputable author
or organization. For example, information from a government agency, an institution of
higher education, or a peer-reviewed journal is often considered to be more reliable than
information from a personal blog. Reliable resources will also provide access to author
biographies so that you can tell if the author is an expert on the subject matter. If you look
at the author information at the bottom of the tree octopus website, you will notice that the
author description is downright silly. There is no indication that the person has any training
related to the subject matter.

Reliable resources also need to be fact-checked or backed up with supporting information
that is usually identified using links and citations. This website appears to have active links to
other resources, but if you follow these links, you will notice that they take you to other hoax
websites or to sites that have no mention of tree octopuses.

Finally, reliable sources will be clear about whether their goal is to inform you with factual
information or to convince you of a particular argument. A close reading of the material
can often tell you if an unreliable resource is trying to convince you of an opinion while
appearing to present objective facts. Consider the following sentence from the tree octopus
website:

Tree octopuses became prized by the fashion industry as ornamental decorations for
hats, leading greedy trappers to wipe out whole populations to feed the vanity of the
fashionable rich. (Zapato, n.d., para. 8)

Phrases like “greedy trappers” and “vanity of the fashionable rich” suggest that the author
is making judgments about certain actions and groups of people. This is not what we would
expect from a well-written article that is intended to present factual information.

Now, take a moment to explore another web resource titled “Discovery of the First
Endemic Tree-Climbing Crab.” Once again, the topic sounds bizarre, but if we look closely,
the information seems much more trustworthy. The article was produced by an academic
institution. The language used in the article appears to be unbiased, and the information can
be easily fact-checked using the peer-reviewed journal articles and academic websites that
are referenced at the end. This article appears to be a source of reliable information.

Save the Pacific Northwest Tree Octopus is a silly example of “bad” information, but the
critical-thinking skills we used to evaluate this source can be applied to everything that
we read, hear, and watch. If we approach media critically, we’ll be able to recognize the
trustworthy information that helps us make better policies and decisions. In your future
studies, look for information that is from a trusted source. Look for information that is
backed up by quality research and journalism. Finally, look for information that is attempting
to inform rather than persuade (unless you are researching opinions, of course).

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Section 1.2 Thinking Critically About Environmental Science

The Scientific Method
The use of the scientific method is one way that environmental scientists seek to improve the
reliability, usefulness, and relevance of their research. The scientific method is an approach
whereby scientists observe, test, and draw conclusions about the world around us in a sys-
tematic manner, rather than simply stating opinion. The scientific method consists of a series
of five steps, as illustrated in Figure 1.1.

Figure 1.1: The scientific method

The scientific method is a five-step model used to observe, test, and draw conclusions scientifically.

1. Make observations

2. Ask questions

3. Formulate hypothesis

4. Make predictions

5. Test predictions

Scenario A: Test supports
hypothesis. Additional predictions

can be made and tested.

Scenario B: Test does not
support hypothesis. Formulate

new hypothesis and retest.

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Section 1.2 Thinking Critically About Environmental Science

Scientists begin with simple observations of the world around us. They then form questions
based on those observations. For example, environmental scientists might observe the death
and decline of numerous trees alongside a major highway and naturally wonder what is caus-
ing this to happen. This leads to the third step, the formulation of a hypothesis or hypotheses
that might explain the trees’ death. Hypotheses can be thought of as a first guess or “hunch”
about something, and they help scientists formulate predictions, specific statements that can
be tested. In this case, the scientists might form a hypothesis that the trees are dying because
of road salt running off the highway in the winter or because of an herbicide sprayed to con-
trol weeds on the side of the highway. Based on these guesses, they can take the fourth step
in the scientific method and develop specific and testable predictions about how much road
salt or herbicide needs to be applied to bring about the same levels of tree death and decline
they have observed in nature.

All of these steps lead up to the final step of testing the predictions. To clearly determine what
might be killing the trees, scientists devise experiments that attempt to hold conditions con-
stant and then change one variable at a time. In this case, scientists might identify four similar
small groves of trees that show no sign of stress or tree death. They might then expose one
area to road salt, another to herbicide, and a third to both road salt and herbicide, while the
fourth area is left alone. (Apply Your Knowledge: How Does Road Salt Affect Trees? shows how
scientists might record their data.)

Note that regardless of the outcome of these experiments, scientists will typically still do two
additional things. First, if the road salt or herbicide appeared to have some impact on the
trees, the scientists might refine their predictions to gain a better understanding of why this
is happening. This might include adjusting the levels of road salt or herbicide to see if they can
better determine at what levels these applications become toxic. If the trees were not affected
by the road salt and herbicide, the scientists would be forced to revise their hypotheses or
form new ones. Second, scientists typically seek to share their results with others, usually
by presenting their research at scientific conferences and publishing articles in professional
journals. These presentations and papers are subject to analysis and scrutiny by other scien-
tists, a process known as peer review. Scientists also have to explain the methods used in their
research so that other scientists can run the same experiments, a process known as replica-
tion. These two aspects of scientific research, peer review and replication, help ensure the
accuracy and legitimacy of the work.

It’s important to recognize just how the scientific method can shield scientists from claims of
bias. Scientists don’t really set out to “prove” anything; instead, they observe, ask questions,
hypothesize, predict, test, and usually repeat. Politicians’ demands for scientific “proof ” are
therefore problematic. Environmental policy should be informed by the best science avail-
able, as well as other issues such as ethical concerns, economic impacts, and risks involved.

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Section 1.2 Thinking Critically About Environmental Science

Apply Your Knowledge: How Does Road Salt Affect Trees?

Environmental scientists make use of many different types of graphs to summarize and
present the data they gather in their research. Graphs help in taking enormous amounts of
data and information and presenting them in a way that tells a story or makes an argument.
Your ability to understand and interpret graphs will be an important part of reading this
book and learning environmental science.

Consider the following figures, which show possible results from the road salt/herbicide
example used in the discussion of the scientific method. Figures 1.2 and 1.3 report basically
the same information on tree death and decline from the experiment in different ways.
Figure 1.2 portrays the number of trees that died in the different plots of the experiment over
time. Figure 1.3 presents overall tree deaths by plot type at the end of the experiment.

Figure 1.2: Line graph showing tree damage

This graph shows tree damage over time.

Week 1

12

11

10

9

8

7

6

5

4

3

2

1

0

Week 2

N
u

m
b

e
r

o
f

tr
e
e
s
s

h
o

w
in

g
s

tr
e
s
s
o

r
d

a
m

a
g

e

Week 3 Week 4

No application

Road salt

Herbicide

Road salt and herbicide

(continued)

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Section 1.2 Thinking Critically About Environmental Science

Based on the data presented from this experiment, it appears that road salt might be the
biggest contributor to tree mortality. Imagine then that the scientists conducted a second
experiment with four plots of trees in which they applied different amounts of road salt and
measured tree mortality over a 4-week period. Table 1.1 gives information on the amount of
road salt applied to each of the four plots and the corresponding tree mortality. Try plotting
these numbers on a piece of paper. Draw a straight line that comes closest to connecting each
of the four points on the graph. What does the shape and direction of this line tell you about
the relationship between road salt application and tree mortality?

Table 1.1: Amount of road salt and tree damage

Road salt application (metric tons/hectare) Tree damage (dead trees per plot)

Plot 1 (1 metric ton/hectare) 2

Plot 2 (2 metric tons/hectare) 5

Plot 3 (3 metric tons/hectare) 8

Plot 4 (4 metric tons/hectare) 12

Figure 1.3: Bar graph showing tree damage

This graph shows tree damage by plot type.

No application

12

11

10

9

8

7

6

5

4

3

2

1

0
Road salt

N
um

be
r

of
tr

ee
s

sh
ow

in
g

st
re

ss
o

r
da

m
ag

e

HerbicideRoad salt
and herbicide

Apply Your Knowledge: How Does Road Salt Affect Trees?
(continued)

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Section 1.3 Case Study: Palm Oil Production and Deforestation in Borneo

1.3 Case Study: Palm Oil Production and Deforestation
in Borneo

Environmental scientists, as well as other natural and social scientists, frequently make use
of “case studies” to illustrate important points or concepts. In some ways, case studies are
simply formalized stories about a specific place, person, group, or other thing. The case study
presented here will help illustrate concepts and terms such as environment and environmen-
tal science and demonstrate how environmental scientists make use of critical-thinking skills
and the scientific method in their work. This case study will also be used to explain some of
the foundational concepts introduced later in this chapter and in Chapter 2.

About Borneo
The island of Borneo straddles the equator in Southeast Asia and is the third largest island in
the world and the largest island in Asia. The island is divided between Indonesia, Malaysia,
and Brunei, with Indonesia controlling roughly 73% of Borneo’s land area, Malaysia 26%, and
tiny Brunei just 1% (see Figure 1.4).

Figure 1.4: Borneo

Located in Southeast Asia, Borneo is known for its high rates of biodiversity, but its rain forests are in
decline due to deforestation

Adapted from PeterHermesFurian/iStock/Getty Images Plus

BORNEO

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Section 1.3 Case Study: Palm Oil Production and Deforestation in Borneo

Until very recently, Borneo was sparsely populated, and much of the island was covered in
dense tropical rain forests. Because of this, Borneo is known for its extremely high rates of
biological diversity, or biodiversity—the variety of life and organisms in a specific ecosys-
tem. That variety can be measured by considering the number of species found in a particu-
lar area. Species are groups of organisms that share certain characteristics, interbreed, and
produce fertile offspring. In addition to having an incredibly high number of species overall,
Borneo is also known for having a large number of endemic species—plants and animals
that exist in only one specific geographic region. There are dozens of endemic mammal spe-
cies (such as the proboscis monkey and pygmy elephant), hundreds of endemic birds, and
thousands of endemic plant species in Borneo. Rates of biodiversity are so high in Borneo that
scientists have identified over 20,000 types of insect species in one small national park alone
(Shoumatoff, 2017).

The Problem
Beginning roughly 50 years

Sustainable Living Guide Contributions: Sustaining Biodiversity and Ecosystems

Prior to beginning work on this assignment, read Chapters 1 and 2 in the course textbook. The purpose of this assignment is twofold: first, to enable you to explore a term (concept, technique, place, etc.) related to this week’s theme of sustaining Earth’s biodiversity and ecosystems; second, to provide your first contribution to a collective project, the Class Sustainable Living Guide. Your work this week, and in the weeks that follow, will be gathered (along with that of your peers) into a master document that you will receive a few days after the end of the course. The document will provide everyone with a variety of ideas for how we can all live more sustainably in our homes and communities.

To complete this assignment,

· Select a term from the list of choices in the Week 1 – Term Selection Table located in the course. Type your name in the table, next to the word that you would like to choose.

· Do not select a term that a classmate has already chosen; only one student per term. If you choose a term that is hyperlinked to a source, that term is one that is not mentioned in our textbook. Instead of being required to use the text as your third source for completing the assignment, you will be expected to use the hyperlinked source provided for you.

· Download the Template Template available in the course and replace the guiding text with your own words based upon your online research.

· Please do not include a cover page. All references, however, should be cited in your work and listed at the end, following APA Style expectations.

In the template, you will

· Define the term thoroughly, in your own words.

· Explain the importance of the term using evidence.

· Discuss how the term affects living things and the physical world.

· Suggest two specific actions that you and your peers might take to promote environmental sustainability in relation to the term.

· Explain exactly how those actions will aid in safeguarding our environment in relation to your chosen term.

· Provide detailed examples to support your ideas.

The Sustaining Living Guide Contributions: Sustaining Biodiversity and Ecosystems paper

· Must be a minimum of three paragraphs in length (not including title, any quoted text, or references) and formatted according to APA style as outlined in the University of Arizona Global Campus Writing Center’s APA Formatting for Word 2013 (Links to an external site.)

· Must utilize academic voice. See the Academic Voice (Links to an external site.) resource for additional guidance.

· Must use at least two scholarly sources in addition to the course text. To aid you in your research, and particularly in locating scholarly sources via the University of Arizona Global Campus Library or using Google Scholar, please review the following University of Arizona Global Campus videos and tutorials:

·
Scholarly and Popular Resources (Links to an external site.)

·
Database Search Tips (Links to an external site.)

·
University of Arizona Global Campus Library Quick ‘n’ Dirty (Links to an external site.)

· Accessing Full text and citation in Google Scholar: 
SCI207 – Google Scholar (Links to an external site.)

· Must document any information used from sources in APA Style as outlined in the University of Arizona Global Campus Writing Center’s APA: Citing Within Your Paper (Links to an external site.)

· Must include a separate references page that is formatted according to APA Style as outlined in the University of Arizona Global Campus Writing Center. See the APA: Formatting Your References List (Links to an external site.) resource in the University of Arizona Global Campus Writing Center for specifications.

Sustainable Living Guide Contributions: Sustaining Biodiversity and Ecosystems

2 Understanding Ecology and Biodiversity

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Learning Outcomes

After reading this chapter, you should be able to

• Describe the components of the ecological hierarchy.
• Identify characteristics of all ecosystems.
• Explain how energy flows through ecosystems.
• Describe how matter cycles in ecosystems.
• Explain how and why eutrophication occurs.
• Describe the importance of biodiversity and the major threats to it.
• Discuss what is being done to address threats to biodiversity.
• Define the term planetary boundaries.

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Section 2.1 The Earth as a System

The environment and the study of the environment encompass everything that surrounds us,
including all living and nonliving things. Ecology is the study of the relationships and interac-
tions between living organisms and their surrounding environment. The term ecology derives
from the Greek word for “house” or “dwelling,” oikos, and “study,” or logy. In other words, ecol-
ogy is the “study of our house,” and it is at the core of what environmental science is about.

The goal of this chapter is to give you a foundation in some key ecological concepts that will
be important to studying environmental issues in subsequent chapters. The chapter starts
by introducing the idea of the Earth as a system and how ecologists and environmental sci-
entists use a “systems view” or “systems thinking” in the work they do. We will then focus on
the study of the environment at the ecosystem scale, considering what ecosystems are, how
they are defined, and what some of their key characteristics are. We will review two funda-
mental ecosystem processes—energy flow and matter cycling—that play a central role in
understanding environmental issues.

We then shift to the concept of biodiversity: what it means, why it matters, and what are the
major threats to it. The chapter concludes with a brief discussion of an interesting concept
known as planetary boundaries. These boundaries were developed as a way to help us think
of the planet’s overall health and to warn us when our actions might be jeopardizing the
environment we all depend on. If we think of ecology as the study of our “house,” planetary
boundaries are a way for us to monitor and stay aware of threats or dangers to the planet we
all call home.

2.1 The Earth as a System

Throughout this book, and in the study of environmental science, you will frequently hear
the environment described as a system or as being composed of numerous, interconnected
systems. What does this mean, and why does it help to think about the environment in terms
of systems?

A system can be defined as a set of connected or interdependent things that together form a
more complex whole. For example, the car you drive is made up of multiple, interacting sys-
tems that work together to provide you with mobility. These include the ignition, electrical,
braking, steering, cooling, and suspension systems. Likewise, a rain forest in Borneo, a wet-
land along the Gulf Coast, a mountain stream in the Rockies, or a grassland in the upper Mid-
west can all be thought of as systems (in this case, ecosystems). Forests, wetlands, streams,
grasslands, and other ecosystems all consist of organisms and elements that are interdepen-
dent and that together make up a more complex whole.

Given the sheer complexity of the Earth as a system, ecologists and environmental scien-
tists find it helpful to view and study the world at different scales. They do this through an
approach known as the ecological hierarchy theory. The ecological hierarchy illustrates the
relationships between different organisms and organizes those relationships into different
levels.

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Section 2.1 The Earth as a System

At the first level of the ecological hierarchy are individual organisms, such as a single elephant
or bird. Multiple individuals of the same species living in a particular location, such as a herd
of elephants or a flock of birds, are considered a population, the second level of the ecologi-
cal hierarchy. A group of populations of different species that interact and live in the same
place—such as a forest, stream, or wetland—is known as a community, the third level of the
ecological hierarchy. This community and its physical environment make up the next level, an
ecosystem. In other words, ecosystems include the living, or biotic, communities that occupy
them, as well as the nonliving, or abiotic, characteristics that often shape the abundance and
diversity of life in that location. Different ecosystems connect and interact with one another—
for example, a forest ecosystem connects with the stream ecosystem that runs through it—
and make up a landscape. At an even larger scale, or higher level, ecosystems and landscapes
that have similar climate and vegetation can be grouped into biomes (see Figure 2.1). Gener-
ally speaking, tropical regions characterized by warm temperatures, an abundance of mois-
ture, and relatively constant levels of daylight contain the biomes with the highest number
and diversity of organisms.

Figure 2.1: Biomes

Earth’s major biomes result primarily from differences in climate. Each biome contains many ecosystems
made up of species adapted for life in their specific biome.

Adapted from “Global Soil Regions Map,” by U.S. Department of Agriculture Natural Resources Conservation Service, 2005 (http://www
.nrcs.usda.gov/wps/portal/nrcs/detail/soils/use/worldsoils/?cid=nrcs142p2_054013).

Equator

Tropic of
Capricorn

Tropic
of Cancer

30° S

30° N

Tropical forest

Temperate
deciduous forest

Savanna

Temperate
grassland

Desert

Coniferous
forest

Chaparral

Tundra (arctic
and alpine)

Oceans

Polar and high-
mountain ice

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Section 2.1 The Earth as a System

Let’s use an example to illustrate the ecological hierarchy at work (see Figure 2.2). We’ll start
with a single bird common to our state of Pennsylvania, the wood thrush. A certain population
of wood thrushes breeds and reproduces in a specific forested region near the home of one
of the authors. That population of wood thrushes interacts with other populations of birds,
mammals, insects, and plants at the community or biotic community scale. The biotic com-
munity, combined with the abiotic or nonliving components, make up an ecosystem—in this
case a forested ecosystem that the wood thrush favors as habitat. That forest is embedded in
a larger landscape of rivers, streams, wetlands, and human-dominated land uses. The forests
of Pennsylvania are similar to temperate forests in other regions of the United States and the
world and make up part of the temperate forest biome.

Figure 2.2: The ecological hierarchy

The ecological hierarchy enables ecologists and environmental scientists to study the Earth at different
scales.

PredatorsPredators

Population

Community

Ecosystem

Landscape

Biome

Individual

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Section 2.1 The Earth as a System

At the highest scale, or level, the entire planet is made up of four separate but interact-
ing realms or spheres (see Figure 2.3). These four spheres include the lithosphere (or geo-
sphere), the hydrosphere, the atmosphere, and the biosphere. The lithosphere is the solid
Earth, specifically the upper crust (extending up to 100 kilometers, or 62 miles, below the
surface) and the uppermost mantle (extending as far as 2,500 kilometers, or 1,550 miles,
below the surface). The hydrosphere is the watery parts of our planet: the oceans, rivers,
lakes, clouds, groundwater reservoirs, and glaciers that cover three quarters of the Earth’s
surface. The atmosphere is a mixture of gases, mostly nitrogen and oxygen, with smaller
amounts of argon, carbon dioxide, and other trace gases. The atmosphere is held to the
Earth’s surface by gravity and thins rapidly with altitude. Ninety-nine percent of the Earth’s

Figure 2.3: The four spheres

The highest scale, or level, of the ecological hierarchy is made up of four spheres. Environmental
scientists study interactions among the atmosphere, lithosphere, and hydrosphere. The biosphere is the
zone of all three spheres that contains life.

Hydrosphere
(water)

Hydrosphere
(water)

Lithosphere
(earth)

Lithosphere
(earth)

Atmosphere
(air)

Biosphere

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Section 2.2 Ecosystems as a Concept

atmosphere is concentrated in the first 30 kilometers (19 miles), but a few traces of atmo-
spheric gases remain even in frigid, near-space conditions thousands of kilometers above the
Earth’s surface. The biosphere is the zone where life exists on Earth. Most life concentrates at
or near the surface of the land and ocean, but some bacteria thrive in rocks 4 kilometers (2.5
miles) beneath the surface, some organisms live in deep ocean trenches, and a few windblown
microorganisms drift in thin, cold, inhospitable air waves 10 kilometers (6 miles) above the
surface. Most of this book will focus on issues and conditions that occur in the biosphere, but
we will also examine the lithosphere (energy resources), the hydrosphere (freshwater and
ocean resources), and the atmosphere (climate change, air pollution, and ozone depletion).

The concepts of the ecological hierarchy and the four spheres allow us to take something as
vast and complex as the entire planet and view it at many different scales. A systems view or
systems thinking helps us see how the pieces within each level connect and interact. Systems
thinking is an approach to science that considers not just the individual parts of a system
but also how they interact and interrelate over time. When we think of the environment as a
system, we become more aware of how our actions in one place might have consequences in
another. The late ecologist Barry Commoner (1971) summed this up in his first law of ecol-
ogy: Everything is connected to everything else.

Section 2.2 will home in on one level of the ecological hierarchy—the ecosystem. Much of the
work done by ecologists and environmental scientists is at the ecosystem scale, and so it is
important to better define and understand what ecosystems are and how they operate.

2.2 Ecosystems as a Concept

Section 2.1 described ecosystems as a collection of living (biotic) and nonliving (abiotic) enti-
ties that exist and interact in a particular location and time. For example, the forest ecosystem
that is home to the wood thrush is made up of birds, insects, mammals, amphibians, fungi,
trees and plants, soils, rocks, and nutrients. Forests and other ecosystems are characterized
by a number of factors that are the focus of this section.

Ecosystems Are Open
Virtually all of the Earth’s ecosystems are open systems, meaning that they receive inputs from
surrounding systems and produce outputs. Some of ecosystems’ most important inputs and
outputs come in the form of energy and matter, which will be described in much greater detail
in Section 2.3. For now, it’s enough to visualize an ecosystem in much the same way you might
view your home, as an open system that relies on inputs of food, energy, and water while pro-
ducing outputs like solid waste, wastewater, and emissions of air pollutants. Ecologists refer
to the energy and matter that flow into, through, and out of an ecosystem as throughput.

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Section 2.2 Ecosystems as a Concept

Ecosystems Are Subject to Feedback Loops
As energy and matter flow into and out of
ecosystems, and as ecosystems are subject to
various kinds of disturbance and change, we
often see what are known as feedback loops.
A positive feedback loop causes the system
to keep changing further in the same direc-
tion. A negative feedback loop causes the
system to change in the opposite direction.

In nature, a positive feedback loop might
occur when a section of a forest is clear-cut,
creating light and temperature conditions
along the new forest edge that lead to even
further loss of trees and worsening defores-
tation. A negative feedback loop might occur
if there were a sudden increase in the popu-
lation of a certain insect species. This might
lead to an equivalent increase in the population of birds and other organisms that prey on
or eat that insect, returning the insect population to what it was originally. Positive feedback
loops tend to be destabilizing, resulting in continual change, while negative feedback loops
tend to be self-correcting or stabilizing.

In other words, don’t think of positive feedback loops as “good” or negative feedback loops
as “bad.” In fact, the opposite is generally the case. Most systems in nature are characterized
by negative feedback loops, which result in a dynamic equilibrium or homeostasis—the ten-
dency of a system to maintain relatively stable conditions over time.

When a system is experiencing a series of positive feedback loops, changing further and fur-
ther in the same direction, it’s possible that it could reach a threshold or tipping point. When
this happens, the system collapses or shifts to a new, different state. For example, when water
is boiled to a tipping point of 100 °C (212 °F), it turns to vapor. When water is cooled to 0 °C
(32 °F), it turns to ice.

A potential tipping point that worries many environmental and climate scientists involves a
positive feedback loop from melting permafrost areas in the Arctic. This will be explained in
more detail in Chapter 8, but basically, permafrost soils hold large quantities of methane and
carbon, which can become carbon dioxide as these soils thaw. Human activities like burning
fossil fuels are already raising methane and carbon dioxide levels in the atmosphere. Meth-
ane and carbon dioxide are greenhouse gases that trap heat in the atmosphere, and this is
increasing temperatures in the Arctic. As temperatures increase, permafrost soils begin to
thaw and release more methane and carbon dioxide into the atmosphere. This methane and
carbon dioxide leads to further warming and more thawing of permafrost soils, which results
in even greater releases of methane and carbon dioxide, and so on. Such a situation could
lead to rapid and runaway global warming and climate change, pushing our planet beyond a
threshold and over a tipping point.

luoman/E+/Getty Images
Clear-cutting forest can create conditions that
lead to further deforestation—an example of a
positive feedback loop.

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

Ecosystems Provide a Range of Conditions
For a wood thrush to survive in the forested ecosystem in Pennsylvania, it requires certain
resources and conditions such as food, water, and reasonable temperatures. When these envi-
ronmental factors and conditions are present in a way that is most favorable for the wood
thrush, they are said to be in the optimal range. The entire range over which the wood thrush
could survive, even if it did not thrive in an optimal sense, is known as the range of toler-
ance, with the extreme ends of that range known as the limits of tolerance. Conditions that fall
between the optimal range and the limits of tolerance are known as zones of stress because
organisms experience increasing stress the further they are from their optimal range.

All living organisms have an optimal range, zones of stress, and limits of tolerance for every
abiotic factor they depend on, and these are different for different species. Some species have
a very broad optimal range and can tolerate a wide variety of conditions, while other species
are more sensitive and have optimal ranges that are narrow. Ecologists refer to a factor that
limits growth as a limiting factor, meaning that even if other factors and conditions are pres-
ent in optimal amounts, the absence or shortage of a limiting factor will stress organisms that
depend on it. For example, you can give a plant all the water and nutrients you want, but if
there is not enough light, the plant will be limited in its growth. Lastly, we generally find that
certain species, like the wood thrush, are present in specific habitats, like a temperate forest.
Within that forest, the wood thrush occupies a specific ecological niche, the combination of
conditions and resources needed for it to live. Different species can occupy the same habitat
but have very different niches. Different bird species in the same forest habitat can nest in
different places, eat different foods, eat at different times of day, and have other differences in
their ecological niche that limits competition between them.

2.3 Fundamental Ecosystem Processes: Energy Flow
and Matter Cycling

Despite the range of conditions that characterize the ecosystems found in different biomes
around the world, all these ecosystems have something in common. With few exceptions,
Earth’s ecosystems are powered by solar energy, and the organisms within those ecosystems
depend on matter in the form of nutrients, water, oxygen, and other gases to survive. This sec-
tion reviews two fundamental ecosystem processes that will help you better understand life
on Earth: energy flow through ecosystems and matter cycling in ecosystems.

Energy Flow Through Ecosystems
The most basic definition of energy is the capacity or ability to do work. In ecology, the term
energy is usually used to define the ability of organisms to do biological work, such as moving,
growing, eating, or reproducing. Scientists further divide energy into two basic forms: kinetic
and potential. Kinetic energy is energy in motion, while potential energy is stored energy.
The image of a dam is often used to illustrate the difference between these two types of energy.

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

By holding moving water back, a dam is cre-
ating a reservoir, which represents accumu-
lated or potential energy. When the gates
of the dam are opened and the water starts
to move again, that potential energy is con-
verted to kinetic energy. Likewise, gasoline
represents a type of potential energy, stored
in the chemical bonds among the atoms that
compose it. When that gasoline is ignited in
the engine of a car, the potential energy held
in those chemical bonds is released and
converted to the kinetic energy of motion.

Laws of Thermodynamics
There are two fundamental laws or prin-
ciples that apply to energy. The first law of
thermodynamics (also known as the law

of conservation of energy) states that energy can change from one form to another but can-
not be created or destroyed. When we burn gasoline in a car engine, we are converting that
chemical energy to the energy of motion and heat, but we end up with the same amount of
energy. The second law of thermodynamics states that even though the overall amount of
energy is conserved, energy conversion will always change that energy from a more useful
to a less useful state. Gasoline is a highly useful form of energy because small quantities of it
contain great potential to do work, but once combusted it changes to mostly heat energy that
is too diffuse to be useful. This tendency for energy to move from a more useful state to a less
useful state is known as entropy. An important implication of the laws of thermodynamics
is that energy conversions tend to be inefficient. Only a small portion of the chemical energy
stored in gasoline (typically 15%–25%) is actually converted to mechanical energy.

If every energy conversion moves us from a more useful state to a less useful state, we would
appear to be doomed to a world of increasing disorder. Yet in the world around us, we see
many signs of increasing order—for example, humans, animals, plants, and other organisms
being born and growing. So how can this be? The answer lies in the fact that the Earth is an
open system subject to inputs of solar energy. That incoming solar (light) energy drives pro-
cesses that create new stores of potential energy that fuel virtually all the Earth’s ecosystems.

Fuel for Life
Most living systems and organisms on the planet are ultimately powered by energy from the
sun. The starting point is a group of organisms known as autotrophs or primary produc-
ers: mostly plants, algae, and some types of bacteria. Primary producers take the building
blocks of carbon dioxide and water and produce sugar (glucose) molecules with high poten-
tial energy content. Primary producers do this through a process known as photosynthesis.
Photosynthesis is driven by light energy from the sun, as illustrated in Figure 2.4.

Jupiterimages/Stockbyte/Thinkstock
A dam represents the difference between
kinetic and potential energy. Water held by the
dam in a reservoir is potential (stored) energy.
When the water is released by opening the
gates of the dam, it turns into kinetic energy.

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

The ability of plants and other primary producers to do photosynthesis is really the foun-
dation for life on Earth as we know it. Photosynthesis starts with chlorophyll, which gives
plants their green color. Chlorophyll absorbs light energy from the sun and uses it to remove
hydrogen atoms from water (H2O) molecules. The hydrogen is combined with carbon atoms
from carbon dioxide (CO2) to form long chains of glucose molecules, or sugar (C6H12O6). One
by-product of photosynthesis is oxygen (O2) released to the atmosphere, and this is another
way plants and other primary producers can be seen as essential to life as we know it: Plants
are sometimes referred to as “the lungs of the planet.” The process of photosynthesis can be
summarized in an equation:

6CO2 (carbon dioxide) + 6H2O (water) + light energy = C6H12O6 (glucose) + 6O2 (oxygen)

Glucose molecules produced through photosynthesis represent a form of high-quality poten-
tial energy. This energy can be used by primary producers for their own biological functions
as well as by other organisms that consume the primary producers. Plants use glucose to build
stems, roots, fruit, leaves, and other structural elements. Plants also store glucose for future

Figure 2.4: Photosynthesis

Producers use photosynthesis to convert the basic building blocks of sunlight, carbon dioxide, and water
into energy other organisms can use.

Sunlight

Carbon dioxide

Water

Minerals

Oxygen

Sugar

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

use and to power a process known as cellular respiration. Cellular respiration allows the
plant to utilize the potential energy stored in glucose to perform the biochemical processes it
needs to grow and survive. Cellular respiration is essentially photosynthesis in reverse:

C6H12O6 (glucose) + 6O2 (oxygen) = 6CO2 (carbon dioxide) + 6H2O (water) + energy

Some of the potential energy that is stored in plants as glucose is also available to other organ-
isms that eat either plants or the animals that eat plants. Just as with plants, these animals
use respiration to “burn” the energy stored in the glucose molecules, in the process releasing
low-quality heat energy. You can see why energy is described as flowing through ecosystems.
Energy enters the system as sunlight and is converted to high-quality potential energy in the
form of glucose, utilized by organisms in the environment through respiration, and released
as energy that dissipates back into space.

Chains of Energy
Ecologists use the concepts of producers, consumers, and decomposers to describe the flow of
energy through an ecosystem. As discussed earlier, autotrophs like plants and algae are pro-
ducers because they are able to manufacture glucose through the process of photosynthesis.
The entire amount of potential energy produced by plants in a given ecosystem is referred to
as gross primary production. Because plants use much of this energy for their own biochemi-
cal needs, the energy that is “left over” for other organisms is called net primary production.

The organisms that rely on plants for some of that “leftover” energy are known as consum-
ers. A rabbit that eats grass in an open meadow would be considered a primary consumer,
whereas a snake that eats the rabbit would be considered a secondary consumer. A hawk that
eats the snake would be considered a tertiary consumer. All of these consumers are known as
heterotrophs. Recall that primary producers are referred to as autotrophs, meaning they can
produce their own food (auto = “self ”; troph = “nourish”). In contrast, heterotrophs refers to
organisms that rely on other organisms for their food (hetero = “other”; troph = “nourish”).
While primary consumers are herbivores (plant eaters), secondary and tertiary consumers
can be either carnivores (which eat other animals) or omnivores (which eat both plants and
other animals).

Last but not least are what are known as decomposers. Decomposers break down dead
organic material, whether plants or animals, to obtain the energy and nutrients they need.
Also known as saprotrophs (sapro = “rotten”; troph = “nourish”), decomposers include bacte-
ria and fungi like mushrooms, as well as scavenging animals like vultures and hyenas. Decom-
posers play a critical but often overlooked role in breaking down dead organic material and
releasing important nutrients that can be reused by producers for a new round of growth.

Energy flows in an ecosystem through food chains—for example, the hawk that ate the snake
that ate the rabbit that ate the grass. In other words, food chains describe simple, linear
feeding relationships among organisms. Ecosystems are characterized by many different food
chains that combined make up a food web, which describes the many feeding relationships
in a community (see Figure 2.5).

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

One important characteristic of food chains and food webs is that primary producers are far
more abundant than primary consumers, and primary consumers are more abundant than
secondary consumers, and so on. Ecologists use the concept of trophic levels to explain this.
Each link in a food chain is considered a trophic level, and as we move from one trophic level
to the next, we lose energy because of the second law of thermodynamics. As a result, tro-
phic levels in ecosystems tend to be characterized by a pyramid shape, with large numbers
of organisms at lower trophic levels and few at the top (see Figure 2.6). On average, ecolo-
gists estimate that only about 10% of the energy consumed at one trophic level is available

Figure 2.5: Food web

Energy flows in an ecosystem through the food web.

Bald eagles
Salmon

Birds

Rabbits
Snakes

Mice

Insects Grasses and plant material

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

to the next level. In other words, 10,000 pounds of grass in a meadow might only support
1,000 pounds of rabbits, which could support 100 pounds of snakes, which could support 10
pounds of hawks. As a result, most food chains are typically characterized by only three or
four trophic levels.

Figure 2.6: Trophic levels

Energy enters an ecosystem through an external source (the sun) and flows through the progressive
trophic levels of a food chain. On average, about 10% of the net energy produced at one trophic level is
passed on to the next level; the rest is lost as heat energy.

Solar energy

Tertiary consumers

Secondary consumers
(animals that feed on herbivores)

Primary consumers
(animals that feed on plants)

Heat
lost

Primary producers
(plants, algae, and some bacteria)

Decomposers

Matter Cycling in Ecosystems
The previous section described how energy tends to flow through ecosystems, entering as
sunlight and leaving as heat. In contrast, water and chemical elements such as carbon, nitro-
gen, and phosphorous tend to cycle in ecosystems. Scientists who study such cycles, known
as biogeochemical cycles, know that the same atom of carbon used by a tree outside your
window for photosynthesis may have been exhaled by a human or animal thousands of years

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

ago. This is because of the law of conservation of matter, which holds that matter can nei-
ther be created nor destroyed. If you look back at the chemical reactions for photosynthesis
and respiration, you will see that the carbon, oxygen, and hydrogen take different forms but
are always present in the same quantities on both sides of the equation.

This principle of conservation of matter was summed up by the late ecologist Barry Com-
moner (1971) as “everything must go somewhere,” or “there is no away” (p. 39). When we
burn fossil fuels like oil and coal, which contain mostly carbon, we are moving that carbon
from one place (the deep Earth), where it had been buried for millions of years, and put-
ting it another place (in this case the atmosphere as carbon dioxide). When we mine phos-
phate deposits to make fertilizer and some of that fertilizer runs into streams and rivers, we
are moving phosphorous from one place to another, but it does not go away. The rest of this
section will review three critical biogeochemical cycles: carbon, phosphorous, and nitrogen.
(The water cycle will be explained in Chapter 5).

The Carbon Cycle
Carbon is a basic building block of organic
compounds required for life. Carbon circu-
lates through the biosphere, atmosphere,
and hydrosphere and is stored in under-
ground deposits in the lithosphere. Figure
2.7 is a basic illustration of the carbon cycle,
showing carbon flows from one reservoir
of carbon to another. Recall that carbon in
the atmosphere—in the form of carbon
dioxide—is utilized by plants for photosyn-
thesis. Some of that carbon is used to build
plant tissue, and some of the plant tissue is
eaten by animals and converted into their
own tissue. Both plants and animals respire,
ret

Sustainable Living Guide Contributions: Sustaining Biodiversity and Ecosystems

2 Understanding Ecology and Biodiversity

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Learning Outcomes

After reading this chapter, you should be able to

• Describe the components of the ecological hierarchy.
• Identify characteristics of all ecosystems.
• Explain how energy flows through ecosystems.
• Describe how matter cycles in ecosystems.
• Explain how and why eutrophication occurs.
• Describe the importance of biodiversity and the major threats to it.
• Discuss what is being done to address threats to biodiversity.
• Define the term planetary boundaries.

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Section 2.1 The Earth as a System

The environment and the study of the environment encompass everything that surrounds us,
including all living and nonliving things. Ecology is the study of the relationships and interac-
tions between living organisms and their surrounding environment. The term ecology derives
from the Greek word for “house” or “dwelling,” oikos, and “study,” or logy. In other words, ecol-
ogy is the “study of our house,” and it is at the core of what environmental science is about.

The goal of this chapter is to give you a foundation in some key ecological concepts that will
be important to studying environmental issues in subsequent chapters. The chapter starts
by introducing the idea of the Earth as a system and how ecologists and environmental sci-
entists use a “systems view” or “systems thinking” in the work they do. We will then focus on
the study of the environment at the ecosystem scale, considering what ecosystems are, how
they are defined, and what some of their key characteristics are. We will review two funda-
mental ecosystem processes—energy flow and matter cycling—that play a central role in
understanding environmental issues.

We then shift to the concept of biodiversity: what it means, why it matters, and what are the
major threats to it. The chapter concludes with a brief discussion of an interesting concept
known as planetary boundaries. These boundaries were developed as a way to help us think
of the planet’s overall health and to warn us when our actions might be jeopardizing the
environment we all depend on. If we think of ecology as the study of our “house,” planetary
boundaries are a way for us to monitor and stay aware of threats or dangers to the planet we
all call home.

2.1 The Earth as a System

Throughout this book, and in the study of environmental science, you will frequently hear
the environment described as a system or as being composed of numerous, interconnected
systems. What does this mean, and why does it help to think about the environment in terms
of systems?

A system can be defined as a set of connected or interdependent things that together form a
more complex whole. For example, the car you drive is made up of multiple, interacting sys-
tems that work together to provide you with mobility. These include the ignition, electrical,
braking, steering, cooling, and suspension systems. Likewise, a rain forest in Borneo, a wet-
land along the Gulf Coast, a mountain stream in the Rockies, or a grassland in the upper Mid-
west can all be thought of as systems (in this case, ecosystems). Forests, wetlands, streams,
grasslands, and other ecosystems all consist of organisms and elements that are interdepen-
dent and that together make up a more complex whole.

Given the sheer complexity of the Earth as a system, ecologists and environmental scien-
tists find it helpful to view and study the world at different scales. They do this through an
approach known as the ecological hierarchy theory. The ecological hierarchy illustrates the
relationships between different organisms and organizes those relationships into different
levels.

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Section 2.1 The Earth as a System

At the first level of the ecological hierarchy are individual organisms, such as a single elephant
or bird. Multiple individuals of the same species living in a particular location, such as a herd
of elephants or a flock of birds, are considered a population, the second level of the ecologi-
cal hierarchy. A group of populations of different species that interact and live in the same
place—such as a forest, stream, or wetland—is known as a community, the third level of the
ecological hierarchy. This community and its physical environment make up the next level, an
ecosystem. In other words, ecosystems include the living, or biotic, communities that occupy
them, as well as the nonliving, or abiotic, characteristics that often shape the abundance and
diversity of life in that location. Different ecosystems connect and interact with one another—
for example, a forest ecosystem connects with the stream ecosystem that runs through it—
and make up a landscape. At an even larger scale, or higher level, ecosystems and landscapes
that have similar climate and vegetation can be grouped into biomes (see Figure 2.1). Gener-
ally speaking, tropical regions characterized by warm temperatures, an abundance of mois-
ture, and relatively constant levels of daylight contain the biomes with the highest number
and diversity of organisms.

Figure 2.1: Biomes

Earth’s major biomes result primarily from differences in climate. Each biome contains many ecosystems
made up of species adapted for life in their specific biome.

Adapted from “Global Soil Regions Map,” by U.S. Department of Agriculture Natural Resources Conservation Service, 2005 (http://www
.nrcs.usda.gov/wps/portal/nrcs/detail/soils/use/worldsoils/?cid=nrcs142p2_054013).

Equator

Tropic of
Capricorn

Tropic
of Cancer

30° S

30° N

Tropical forest

Temperate
deciduous forest

Savanna

Temperate
grassland

Desert

Coniferous
forest

Chaparral

Tundra (arctic
and alpine)

Oceans

Polar and high-
mountain ice

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Section 2.1 The Earth as a System

Let’s use an example to illustrate the ecological hierarchy at work (see Figure 2.2). We’ll start
with a single bird common to our state of Pennsylvania, the wood thrush. A certain population
of wood thrushes breeds and reproduces in a specific forested region near the home of one
of the authors. That population of wood thrushes interacts with other populations of birds,
mammals, insects, and plants at the community or biotic community scale. The biotic com-
munity, combined with the abiotic or nonliving components, make up an ecosystem—in this
case a forested ecosystem that the wood thrush favors as habitat. That forest is embedded in
a larger landscape of rivers, streams, wetlands, and human-dominated land uses. The forests
of Pennsylvania are similar to temperate forests in other regions of the United States and the
world and make up part of the temperate forest biome.

Figure 2.2: The ecological hierarchy

The ecological hierarchy enables ecologists and environmental scientists to study the Earth at different
scales.

PredatorsPredators

Population

Community

Ecosystem

Landscape

Biome

Individual

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Section 2.1 The Earth as a System

At the highest scale, or level, the entire planet is made up of four separate but interact-
ing realms or spheres (see Figure 2.3). These four spheres include the lithosphere (or geo-
sphere), the hydrosphere, the atmosphere, and the biosphere. The lithosphere is the solid
Earth, specifically the upper crust (extending up to 100 kilometers, or 62 miles, below the
surface) and the uppermost mantle (extending as far as 2,500 kilometers, or 1,550 miles,
below the surface). The hydrosphere is the watery parts of our planet: the oceans, rivers,
lakes, clouds, groundwater reservoirs, and glaciers that cover three quarters of the Earth’s
surface. The atmosphere is a mixture of gases, mostly nitrogen and oxygen, with smaller
amounts of argon, carbon dioxide, and other trace gases. The atmosphere is held to the
Earth’s surface by gravity and thins rapidly with altitude. Ninety-nine percent of the Earth’s

Figure 2.3: The four spheres

The highest scale, or level, of the ecological hierarchy is made up of four spheres. Environmental
scientists study interactions among the atmosphere, lithosphere, and hydrosphere. The biosphere is the
zone of all three spheres that contains life.

Hydrosphere
(water)

Hydrosphere
(water)

Lithosphere
(earth)

Lithosphere
(earth)

Atmosphere
(air)

Biosphere

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Section 2.2 Ecosystems as a Concept

atmosphere is concentrated in the first 30 kilometers (19 miles), but a few traces of atmo-
spheric gases remain even in frigid, near-space conditions thousands of kilometers above the
Earth’s surface. The biosphere is the zone where life exists on Earth. Most life concentrates at
or near the surface of the land and ocean, but some bacteria thrive in rocks 4 kilometers (2.5
miles) beneath the surface, some organisms live in deep ocean trenches, and a few windblown
microorganisms drift in thin, cold, inhospitable air waves 10 kilometers (6 miles) above the
surface. Most of this book will focus on issues and conditions that occur in the biosphere, but
we will also examine the lithosphere (energy resources), the hydrosphere (freshwater and
ocean resources), and the atmosphere (climate change, air pollution, and ozone depletion).

The concepts of the ecological hierarchy and the four spheres allow us to take something as
vast and complex as the entire planet and view it at many different scales. A systems view or
systems thinking helps us see how the pieces within each level connect and interact. Systems
thinking is an approach to science that considers not just the individual parts of a system
but also how they interact and interrelate over time. When we think of the environment as a
system, we become more aware of how our actions in one place might have consequences in
another. The late ecologist Barry Commoner (1971) summed this up in his first law of ecol-
ogy: Everything is connected to everything else.

Section 2.2 will home in on one level of the ecological hierarchy—the ecosystem. Much of the
work done by ecologists and environmental scientists is at the ecosystem scale, and so it is
important to better define and understand what ecosystems are and how they operate.

2.2 Ecosystems as a Concept

Section 2.1 described ecosystems as a collection of living (biotic) and nonliving (abiotic) enti-
ties that exist and interact in a particular location and time. For example, the forest ecosystem
that is home to the wood thrush is made up of birds, insects, mammals, amphibians, fungi,
trees and plants, soils, rocks, and nutrients. Forests and other ecosystems are characterized
by a number of factors that are the focus of this section.

Ecosystems Are Open
Virtually all of the Earth’s ecosystems are open systems, meaning that they receive inputs from
surrounding systems and produce outputs. Some of ecosystems’ most important inputs and
outputs come in the form of energy and matter, which will be described in much greater detail
in Section 2.3. For now, it’s enough to visualize an ecosystem in much the same way you might
view your home, as an open system that relies on inputs of food, energy, and water while pro-
ducing outputs like solid waste, wastewater, and emissions of air pollutants. Ecologists refer
to the energy and matter that flow into, through, and out of an ecosystem as throughput.

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Section 2.2 Ecosystems as a Concept

Ecosystems Are Subject to Feedback Loops
As energy and matter flow into and out of
ecosystems, and as ecosystems are subject to
various kinds of disturbance and change, we
often see what are known as feedback loops.
A positive feedback loop causes the system
to keep changing further in the same direc-
tion. A negative feedback loop causes the
system to change in the opposite direction.

In nature, a positive feedback loop might
occur when a section of a forest is clear-cut,
creating light and temperature conditions
along the new forest edge that lead to even
further loss of trees and worsening defores-
tation. A negative feedback loop might occur
if there were a sudden increase in the popu-
lation of a certain insect species. This might
lead to an equivalent increase in the population of birds and other organisms that prey on
or eat that insect, returning the insect population to what it was originally. Positive feedback
loops tend to be destabilizing, resulting in continual change, while negative feedback loops
tend to be self-correcting or stabilizing.

In other words, don’t think of positive feedback loops as “good” or negative feedback loops
as “bad.” In fact, the opposite is generally the case. Most systems in nature are characterized
by negative feedback loops, which result in a dynamic equilibrium or homeostasis—the ten-
dency of a system to maintain relatively stable conditions over time.

When a system is experiencing a series of positive feedback loops, changing further and fur-
ther in the same direction, it’s possible that it could reach a threshold or tipping point. When
this happens, the system collapses or shifts to a new, different state. For example, when water
is boiled to a tipping point of 100 °C (212 °F), it turns to vapor. When water is cooled to 0 °C
(32 °F), it turns to ice.

A potential tipping point that worries many environmental and climate scientists involves a
positive feedback loop from melting permafrost areas in the Arctic. This will be explained in
more detail in Chapter 8, but basically, permafrost soils hold large quantities of methane and
carbon, which can become carbon dioxide as these soils thaw. Human activities like burning
fossil fuels are already raising methane and carbon dioxide levels in the atmosphere. Meth-
ane and carbon dioxide are greenhouse gases that trap heat in the atmosphere, and this is
increasing temperatures in the Arctic. As temperatures increase, permafrost soils begin to
thaw and release more methane and carbon dioxide into the atmosphere. This methane and
carbon dioxide leads to further warming and more thawing of permafrost soils, which results
in even greater releases of methane and carbon dioxide, and so on. Such a situation could
lead to rapid and runaway global warming and climate change, pushing our planet beyond a
threshold and over a tipping point.

luoman/E+/Getty Images
Clear-cutting forest can create conditions that
lead to further deforestation—an example of a
positive feedback loop.

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

Ecosystems Provide a Range of Conditions
For a wood thrush to survive in the forested ecosystem in Pennsylvania, it requires certain
resources and conditions such as food, water, and reasonable temperatures. When these envi-
ronmental factors and conditions are present in a way that is most favorable for the wood
thrush, they are said to be in the optimal range. The entire range over which the wood thrush
could survive, even if it did not thrive in an optimal sense, is known as the range of toler-
ance, with the extreme ends of that range known as the limits of tolerance. Conditions that fall
between the optimal range and the limits of tolerance are known as zones of stress because
organisms experience increasing stress the further they are from their optimal range.

All living organisms have an optimal range, zones of stress, and limits of tolerance for every
abiotic factor they depend on, and these are different for different species. Some species have
a very broad optimal range and can tolerate a wide variety of conditions, while other species
are more sensitive and have optimal ranges that are narrow. Ecologists refer to a factor that
limits growth as a limiting factor, meaning that even if other factors and conditions are pres-
ent in optimal amounts, the absence or shortage of a limiting factor will stress organisms that
depend on it. For example, you can give a plant all the water and nutrients you want, but if
there is not enough light, the plant will be limited in its growth. Lastly, we generally find that
certain species, like the wood thrush, are present in specific habitats, like a temperate forest.
Within that forest, the wood thrush occupies a specific ecological niche, the combination of
conditions and resources needed for it to live. Different species can occupy the same habitat
but have very different niches. Different bird species in the same forest habitat can nest in
different places, eat different foods, eat at different times of day, and have other differences in
their ecological niche that limits competition between them.

2.3 Fundamental Ecosystem Processes: Energy Flow
and Matter Cycling

Despite the range of conditions that characterize the ecosystems found in different biomes
around the world, all these ecosystems have something in common. With few exceptions,
Earth’s ecosystems are powered by solar energy, and the organisms within those ecosystems
depend on matter in the form of nutrients, water, oxygen, and other gases to survive. This sec-
tion reviews two fundamental ecosystem processes that will help you better understand life
on Earth: energy flow through ecosystems and matter cycling in ecosystems.

Energy Flow Through Ecosystems
The most basic definition of energy is the capacity or ability to do work. In ecology, the term
energy is usually used to define the ability of organisms to do biological work, such as moving,
growing, eating, or reproducing. Scientists further divide energy into two basic forms: kinetic
and potential. Kinetic energy is energy in motion, while potential energy is stored energy.
The image of a dam is often used to illustrate the difference between these two types of energy.

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

By holding moving water back, a dam is cre-
ating a reservoir, which represents accumu-
lated or potential energy. When the gates
of the dam are opened and the water starts
to move again, that potential energy is con-
verted to kinetic energy. Likewise, gasoline
represents a type of potential energy, stored
in the chemical bonds among the atoms that
compose it. When that gasoline is ignited in
the engine of a car, the potential energy held
in those chemical bonds is released and
converted to the kinetic energy of motion.

Laws of Thermodynamics
There are two fundamental laws or prin-
ciples that apply to energy. The first law of
thermodynamics (also known as the law

of conservation of energy) states that energy can change from one form to another but can-
not be created or destroyed. When we burn gasoline in a car engine, we are converting that
chemical energy to the energy of motion and heat, but we end up with the same amount of
energy. The second law of thermodynamics states that even though the overall amount of
energy is conserved, energy conversion will always change that energy from a more useful
to a less useful state. Gasoline is a highly useful form of energy because small quantities of it
contain great potential to do work, but once combusted it changes to mostly heat energy that
is too diffuse to be useful. This tendency for energy to move from a more useful state to a less
useful state is known as entropy. An important implication of the laws of thermodynamics
is that energy conversions tend to be inefficient. Only a small portion of the chemical energy
stored in gasoline (typically 15%–25%) is actually converted to mechanical energy.

If every energy conversion moves us from a more useful state to a less useful state, we would
appear to be doomed to a world of increasing disorder. Yet in the world around us, we see
many signs of increasing order—for example, humans, animals, plants, and other organisms
being born and growing. So how can this be? The answer lies in the fact that the Earth is an
open system subject to inputs of solar energy. That incoming solar (light) energy drives pro-
cesses that create new stores of potential energy that fuel virtually all the Earth’s ecosystems.

Fuel for Life
Most living systems and organisms on the planet are ultimately powered by energy from the
sun. The starting point is a group of organisms known as autotrophs or primary produc-
ers: mostly plants, algae, and some types of bacteria. Primary producers take the building
blocks of carbon dioxide and water and produce sugar (glucose) molecules with high poten-
tial energy content. Primary producers do this through a process known as photosynthesis.
Photosynthesis is driven by light energy from the sun, as illustrated in Figure 2.4.

Jupiterimages/Stockbyte/Thinkstock
A dam represents the difference between
kinetic and potential energy. Water held by the
dam in a reservoir is potential (stored) energy.
When the water is released by opening the
gates of the dam, it turns into kinetic energy.

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

The ability of plants and other primary producers to do photosynthesis is really the foun-
dation for life on Earth as we know it. Photosynthesis starts with chlorophyll, which gives
plants their green color. Chlorophyll absorbs light energy from the sun and uses it to remove
hydrogen atoms from water (H2O) molecules. The hydrogen is combined with carbon atoms
from carbon dioxide (CO2) to form long chains of glucose molecules, or sugar (C6H12O6). One
by-product of photosynthesis is oxygen (O2) released to the atmosphere, and this is another
way plants and other primary producers can be seen as essential to life as we know it: Plants
are sometimes referred to as “the lungs of the planet.” The process of photosynthesis can be
summarized in an equation:

6CO2 (carbon dioxide) + 6H2O (water) + light energy = C6H12O6 (glucose) + 6O2 (oxygen)

Glucose molecules produced through photosynthesis represent a form of high-quality poten-
tial energy. This energy can be used by primary producers for their own biological functions
as well as by other organisms that consume the primary producers. Plants use glucose to build
stems, roots, fruit, leaves, and other structural elements. Plants also store glucose for future

Figure 2.4: Photosynthesis

Producers use photosynthesis to convert the basic building blocks of sunlight, carbon dioxide, and water
into energy other organisms can use.

Sunlight

Carbon dioxide

Water

Minerals

Oxygen

Sugar

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

use and to power a process known as cellular respiration. Cellular respiration allows the
plant to utilize the potential energy stored in glucose to perform the biochemical processes it
needs to grow and survive. Cellular respiration is essentially photosynthesis in reverse:

C6H12O6 (glucose) + 6O2 (oxygen) = 6CO2 (carbon dioxide) + 6H2O (water) + energy

Some of the potential energy that is stored in plants as glucose is also available to other organ-
isms that eat either plants or the animals that eat plants. Just as with plants, these animals
use respiration to “burn” the energy stored in the glucose molecules, in the process releasing
low-quality heat energy. You can see why energy is described as flowing through ecosystems.
Energy enters the system as sunlight and is converted to high-quality potential energy in the
form of glucose, utilized by organisms in the environment through respiration, and released
as energy that dissipates back into space.

Chains of Energy
Ecologists use the concepts of producers, consumers, and decomposers to describe the flow of
energy through an ecosystem. As discussed earlier, autotrophs like plants and algae are pro-
ducers because they are able to manufacture glucose through the process of photosynthesis.
The entire amount of potential energy produced by plants in a given ecosystem is referred to
as gross primary production. Because plants use much of this energy for their own biochemi-
cal needs, the energy that is “left over” for other organisms is called net primary production.

The organisms that rely on plants for some of that “leftover” energy are known as consum-
ers. A rabbit that eats grass in an open meadow would be considered a primary consumer,
whereas a snake that eats the rabbit would be considered a secondary consumer. A hawk that
eats the snake would be considered a tertiary consumer. All of these consumers are known as
heterotrophs. Recall that primary producers are referred to as autotrophs, meaning they can
produce their own food (auto = “self ”; troph = “nourish”). In contrast, heterotrophs refers to
organisms that rely on other organisms for their food (hetero = “other”; troph = “nourish”).
While primary consumers are herbivores (plant eaters), secondary and tertiary consumers
can be either carnivores (which eat other animals) or omnivores (which eat both plants and
other animals).

Last but not least are what are known as decomposers. Decomposers break down dead
organic material, whether plants or animals, to obtain the energy and nutrients they need.
Also known as saprotrophs (sapro = “rotten”; troph = “nourish”), decomposers include bacte-
ria and fungi like mushrooms, as well as scavenging animals like vultures and hyenas. Decom-
posers play a critical but often overlooked role in breaking down dead organic material and
releasing important nutrients that can be reused by producers for a new round of growth.

Energy flows in an ecosystem through food chains—for example, the hawk that ate the snake
that ate the rabbit that ate the grass. In other words, food chains describe simple, linear
feeding relationships among organisms. Ecosystems are characterized by many different food
chains that combined make up a food web, which describes the many feeding relationships
in a community (see Figure 2.5).

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

One important characteristic of food chains and food webs is that primary producers are far
more abundant than primary consumers, and primary consumers are more abundant than
secondary consumers, and so on. Ecologists use the concept of trophic levels to explain this.
Each link in a food chain is considered a trophic level, and as we move from one trophic level
to the next, we lose energy because of the second law of thermodynamics. As a result, tro-
phic levels in ecosystems tend to be characterized by a pyramid shape, with large numbers
of organisms at lower trophic levels and few at the top (see Figure 2.6). On average, ecolo-
gists estimate that only about 10% of the energy consumed at one trophic level is available

Figure 2.5: Food web

Energy flows in an ecosystem through the food web.

Bald eagles
Salmon

Birds

Rabbits
Snakes

Mice

Insects Grasses and plant material

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

to the next level. In other words, 10,000 pounds of grass in a meadow might only support
1,000 pounds of rabbits, which could support 100 pounds of snakes, which could support 10
pounds of hawks. As a result, most food chains are typically characterized by only three or
four trophic levels.

Figure 2.6: Trophic levels

Energy enters an ecosystem through an external source (the sun) and flows through the progressive
trophic levels of a food chain. On average, about 10% of the net energy produced at one trophic level is
passed on to the next level; the rest is lost as heat energy.

Solar energy

Tertiary consumers

Secondary consumers
(animals that feed on herbivores)

Primary consumers
(animals that feed on plants)

Heat
lost

Primary producers
(plants, algae, and some bacteria)

Decomposers

Matter Cycling in Ecosystems
The previous section described how energy tends to flow through ecosystems, entering as
sunlight and leaving as heat. In contrast, water and chemical elements such as carbon, nitro-
gen, and phosphorous tend to cycle in ecosystems. Scientists who study such cycles, known
as biogeochemical cycles, know that the same atom of carbon used by a tree outside your
window for photosynthesis may have been exhaled by a human or animal thousands of years

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Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

ago. This is because of the law of conservation of matter, which holds that matter can nei-
ther be created nor destroyed. If you look back at the chemical reactions for photosynthesis
and respiration, you will see that the carbon, oxygen, and hydrogen take different forms but
are always present in the same quantities on both sides of the equation.

This principle of conservation of matter was summed up by the late ecologist Barry Com-
moner (1971) as “everything must go somewhere,” or “there is no away” (p. 39). When we
burn fossil fuels like oil and coal, which contain mostly carbon, we are moving that carbon
from one place (the deep Earth), where it had been buried for millions of years, and put-
ting it another place (in this case the atmosphere as carbon dioxide). When we mine phos-
phate deposits to make fertilizer and some of that fertilizer runs into streams and rivers, we
are moving phosphorous from one place to another, but it does not go away. The rest of this
section will review three critical biogeochemical cycles: carbon, phosphorous, and nitrogen.
(The water cycle will be explained in Chapter 5).

The Carbon Cycle
Carbon is a basic building block of organic
compounds required for life. Carbon circu-
lates through the biosphere, atmosphere,
and hydrosphere and is stored in under-
ground deposits in the lithosphere. Figure
2.7 is a basic illustration of the carbon cycle,
showing carbon flows from one reservoir
of carbon to another. Recall that carbon in
the atmosphere—in the form of carbon
dioxide—is utilized by plants for photosyn-
thesis. Some of that carbon is used to build
plant tissue, and some of the plant tissue is
eaten by animals and converted into their
own tissue. Both plants and animals respire,
ret