Directions for teachers

This article details a clear example of an ecosystem disturbance and highlights several core ecology concepts including interspecific interactions, food webs and invasive species. If you’ve already covered these concepts in your classroom, this lesson plan could provide a great review. Follow the links below for other lesson plans on these ecology concepts:

• Interspecific interactions: Ecological relationship status
• Food webs: Web of changes
• Invasive species: Investigating invasive species
• Ecosystem disturbances: Do not disturb

Ask students to read the Science News article “How an invasive ant changed a lion’s dinner menu” and work with a partner to answer the following questions.

Directions for students

Read the Science News article “How an invasive ant changed a lion’s dinner menu” and answer the following questions as directed by your teacher.

How an ant shook up an ecosystem

1. What biome is highlighted in the article? Name one type of interspecific interaction between organism species that is found in the article.

The African savanna in the Ol Pejeta Conservancy in Kenya is highlighted in the article. The mutualistic relationship between the acacia ant and the whistling thorn tree is highlighted. The trees provide habitat while the ant provides protection against the elephants. 

2. Describe the ecosystem disturbance in the article. Fill in the table below to trace each cause and effect and include data, statistics or numbers mentioned in the article where possible. Highlight where data isn’t provided and name the species involved.

Species Involved	Cause and Effect	Data Provided
1.
2.
3.
4.

1. The big-headed ants invaded the ecosystem and killed acacia ants (data not provided).

2. The acacia ants protected the whistling thorn tree from elephants, and without them, elephants ate the trees (no data provided). Without the trees, the visibility in the area increased (areas with big-headed ants had 2.67 times higher visibility than areas without the ants).

3. With more visibility, lions were less able to kill zebras (with low visibility, probability of zebra kill was 62% and with high visibility, probability was 22%).

4. Since lions are less able to kill zebras, they kill buffalo instead (zebra kills by lions decreased from 67% to 42%, whereas buffalo kills by lions increased from 0% to 42%).

Graphing the data

1. Graph the change in the percentage of zebra and buffalo kills by lions between 2002 and 2005. Make sure you label your axes and place data points where they are appropriate. If this trend continued, what can you infer would happen to the population of zebras over time? What about the buffalo? What other species could you add to your graph if you had appropriate data?

Student graphs should show the four data points of zebra kills in 2002 and 2005 and buffalo kills in 2002 and 2005. The x-axis should be labeled with time in years and the y-axis should be labeled percent of kills by lions. If the trend continued, it is likely that the population of zebras would increase over time and the population of buffalo would decrease. You could add big-headed ant and acacia ant populations to the graph.

2. What was the duration of the study described in the article? How could you begin to predict the rate of change of the ecosystem’s food web resulting from this disturbance? What additional information and data might you need?

The study took place for three years. Based on the results of the study, you could write a system of equations to represent the rate of change of each species and how the rates of change related to each other. You might need to know additional factors such as how fast big-headed ants reproduce and spread across the ecosystem, how long it takes for the big-headed ants to kill the acacia ants, and how fast the elephants eat the trees.

3. What is the limitation of having only two data points spanning the duration of the study? Why would it be helpful to have more data points?

It’s hard to tell how quickly the number of zebra kills decreased. It could have been steady across the three years, or the shift could have happened quickly at the beginning or the end of the time frame. Knowing this information would make it easier to extrapolate how the trend may continue.

The mighty ant

1. Apart from the lions’ diet, list some other indirect effects of the invasive ant species.

The elephants’ diet, the population of buffalo, and the potential increase in the buffalos’ food source.

2. Pick one indirect effect that wasn’t mentioned in the article and trace what could happen to the ecosystem because of it.

The elephants are now able to eat the whistling thorn trees because the acacia ants are missing. If they’re eating the trees, they’re likely eating less of other vegetation types in the area, which could result in more food for another species that may increase its population due to greater prevalence of that food source.