Data and Graphs in Ecology
Learn
Scientists collect and organize data to understand patterns in ecosystems. Graphs help us visualize relationships between variables and communicate findings clearly. In this lesson, you will learn to interpret common types of graphs used in ecology.
Types of Graphs in Ecology
Line Graphs
Line graphs show how a variable changes over time or in response to another continuous variable. They are ideal for showing trends, such as population changes over years or temperature fluctuations across seasons.
- X-axis (horizontal): Usually shows time or the independent variable
- Y-axis (vertical): Shows the measured or dependent variable
- Trends: Look for increases, decreases, or stable patterns
Bar Graphs
Bar graphs compare quantities across different categories. They work well for comparing populations of different species or resource use across different ecosystems.
Pie Charts
Pie charts show parts of a whole as percentages. They can display the composition of an ecosystem, such as the percentage of different species in a community.
Scatter Plots
Scatter plots show the relationship between two variables. Each point represents one observation. They help identify correlations (positive, negative, or none).
Reading Graphs Effectively
- Read the title: What is the graph about?
- Check the axes: What variables are being compared? What are the units?
- Look for patterns: Is there a trend? Are there outliers?
- Draw conclusions: What does the data tell us about the ecosystem?
Examples
Example 1: Interpreting a Population Graph
The following data shows a deer population in a forest over 10 years:
| Year | Deer Population |
|---|---|
| 2015 | 120 |
| 2016 | 145 |
| 2017 | 180 |
| 2018 | 210 |
| 2019 | 195 |
| 2020 | 160 |
Analysis: The population increased from 2015-2018, then decreased. Possible causes: predators increased, food became scarce, disease outbreak, or hunting pressure.
Example 2: Predator-Prey Relationship
Classic predator-prey graphs show cyclical patterns. When prey population increases, predator population follows (more food). As predators increase, prey decreases (more hunting). Then predators decrease (less food), and prey recovers. This cycle repeats.
Example 3: Comparing Biodiversity
| Ecosystem | Number of Species |
|---|---|
| Tropical Rainforest | 1,500 |
| Temperate Forest | 800 |
| Grassland | 450 |
| Desert | 200 |
| Tundra | 100 |
Conclusion: Tropical rainforests have the highest biodiversity. This data would be best shown as a bar graph to compare categories.
Practice
Use the data and concepts from this lesson to answer the following questions.
1. A line graph shows wolf population on the y-axis and years on the x-axis. The line goes up from 2010 to 2015, then levels off. What does this indicate?
A) Wolves went extinct
B) Wolf population grew, then stabilized
C) Wolf population constantly decreased
D) The data is unreliable
2. Which type of graph would best show the percentage of each species in a pond ecosystem?
A) Line graph
B) Scatter plot
C) Pie chart
D) Bar graph
3. In a predator-prey graph, the rabbit population peaks at 1,000 in March. When would you expect the fox population to peak?
A) January (before rabbits)
B) March (same time as rabbits)
C) May (after rabbits peak)
D) Never
4. A scatter plot shows a positive correlation between rainfall and plant growth. What does this mean?
A) More rain leads to less plant growth
B) More rain leads to more plant growth
C) Rain has no effect on plant growth
D) Plants cause rainfall
5. Data shows: Year 1: 50 birds, Year 2: 75 birds, Year 3: 110 birds, Year 4: 160 birds. What is the trend?
A) Decreasing population
B) Stable population
C) Increasing population
D) No pattern
6. Why is it important to label axes on a graph?
A) To make the graph look pretty
B) So others can understand what is being measured
C) Graphs do not need labels
D) Only the title matters
7. A bar graph compares tree species in three forests. Forest A has 200 oaks, Forest B has 150 oaks, Forest C has 300 oaks. Which forest has the most oaks?
A) Forest A
B) Forest B
C) Forest C
D) They are all equal
8. An ecologist records temperature and number of active insects. Higher temperatures correlate with more active insects. This relationship is:
A) Negative correlation
B) No correlation
C) Positive correlation
D) Impossible to determine
9. What does an outlier on a graph represent?
A) The most common data point
B) A data point that differs significantly from others
C) The average of all data
D) The title of the graph
10. A graph shows grasshopper population declining as pesticide use increases. This suggests:
A) Pesticides have no effect on grasshoppers
B) Pesticides may be reducing grasshopper populations
C) Grasshoppers like pesticides
D) The variables are unrelated
Check Your Understanding
1. Explain why line graphs are better than bar graphs for showing population changes over time.
2. Describe what a predator-prey cycle looks like on a graph and explain why the predator population peak comes after the prey population peak.
3. You collect data on temperature and turtle activity. Create a simple data table with at least 4 data points that would show a positive correlation.
Next Steps
- Practice creating your own graphs from ecological data
- Look for graphs in news articles about environmental topics
- Continue to the next lesson on CER (Claim-Evidence-Reasoning) scientific writing