Visualizing Environmental Science

1. What is the difference between continuous and
   discrete data?

Interpreting and Using Graphs

LEARNING OBJECTIVES

1. Explain how graphs can be used to answer
   questions and test hypotheses.


2. Use graphs to generate your own questions and
   hypotheses.

M

uch of the study and practice of environmen-

tal science involves asking questions and

testing hypotheses related to these ques-

tions. As we have seen, graphs are a

particularly effective tool for visualizing and interpreting

the kinds of data scientists collect to investigate their

questions and test their hypotheses. In fact, some of the

Critical and Creative Thinking Questions at the end of each

chapter in this book can only be answered by interpret-

ing one or more of the graphs included in these sections.

For example, consider the question below and its accom-

panying bar graph (Figure A.9), from the end of Chapter

5 (How Ecosystems Work).

Answering this question requires us to first correctly

interpret what this graph is showing us. In this case, we

can conclude that the number of individuals of Species A

declined after the ecologists removed Species B because

the height of the bar over the “Species B removed” label

is lower than the height over the “Species B present” label.

Thus this graph is showing us that the presence of Species

B appears to have a positive effect on the abundance of

Species A. However, this graph does not tell us whether the

relationship between these two species is an example of a

mutualism (both species benefit from their interaction) or

a commensalism (Species A benefits from its interaction

with Species B but Species B is neither helped nor harmed

by this interaction), as explained earlier in the chapter, or

even if Species A is a predator of Species B.

These ecologists might therefore ask this follow-up

question: “Do Species A and Species B have a mutualis-

tic relationship in this study system?” If they had initially

observed that there appeared to be more individuals of

Species B in areas where there were also more individu-

als of Species A, they might hypothesize that the relation-

ship between these two species is in fact mutualistic. They

could investigate this question and test their hypothesis

by recording the number of individuals of Species B in

this study site before and after removing Species A. They

could then answer their question and support or reject

their hypothesis by using these data to produce another

bar graph similar to their original one, except this time

the y-axis would represent the number of individuals of

Species B, and the x-axis would show Species A present

and Species A removed.

Figure A.10 depicts another question and its ac-

companying graphs from the end of Chapter 7 (Human

Population Change and the Environment).

We can tell just by glancing at these pie charts that

France is the most urbanized of these three countries

and Ethiopia is the most rural. Yet we can also use the

patterns revealed by these simple charts to generate

more complex and interesting questions and hypotheses

2. What are line graphs, bar graphs, and pie charts?
   Under what circumstances would you use each of
   these different types of graphs?

Species B

present

Species B

removed

Number of individuals, Species A

Figure A.9

Ecologists investigating interactions

of two species at a study site first counted individuals of

Species A and then removed all Species B individuals. Six

months later, the ecologists again counted individuals of

Species A. Viewing their results as graphed below, what

is the likely ecological interaction between Species A and

Species B? Explain your answer.

Think Critically

470 Graphing Appendix