The Thorny Circle of Life

SCIENCE

The presence of carnivores helps some plants thrive, a new study of life on the savanna reveals. (BBC)

Use this activity to better understand the plants and animals of the African savanna.

Teachers: Scroll all the way down for a short list of key resources in our “Teachers’ Toolkit.”

Use this lovely illustration to see some members of the savanna ecosystem—and use this handout to identify them. Illustration by Tim Gunther, National Geographic

Use this lovely illustration to see some members of the savanna ecosystem—and use this handout to identify them.
Illustration by Tim Gunther, National Geographic

Discussion Ideas

  • Read the terrific BBC article on the African savanna food web. Then, look at our African savanna illustration above, and take a look at the illustration key here. Which savanna producers were studied by the researchers in the BBC article? Which primary consumers? Which secondary consumers?
    • producers: Researchers studied two species of acacia tree (#3 in the illustration)—one with thorns and one without.
    • primary consumers: Researchers tagged impala (#7 in the illustration) to monitor which species of acacia were being consumed in different situations (in areas frequented by predators, and in areas where predators were more scarce).
    • secondary consumers: Researchers tagged leopards (#11 in the illustration) and wild dogs. Both animals are predators of impala.
    • Can you spot acacia, impala, and leopards in this African food web?
      • Yep, and well-done, too! The primary producer, the acacia tree, is the very first living thing we see in the film, its dramatic silhouette against the sunrise becoming basis of everything to come at about 0:03. The primary consumers come next, with impala keeping their heads up at about 0:14. We see a leopard, an apex predator, at about 0:17. (Fun fact: I think this is the only leopard in the entire movie. Another species of big cat—#12 in our illustration—has the lion’s share of screen time!)

 

  • Researchers kept track of two species of acacia tree, one with thorns and one without. Which species benefitted the most from the presence of carnivores? Why?
    • The non-thorny variety (Acacia brevispica) thrived in areas favored by carnivores, because impala “deemed it too risky to graze at these sites.” (The enemy of my enemy is my friend, A. brevispica might think.)

 

  • How can human activity impact this delicate ecological balance—between thorny and not-thorny, predator and prey?
    • The researchers in the BBC articles says “As human activities continue to reduce populations of predators, herbivores like impala become willing to feed in areas that used to be risky, consuming more preferred vegetation and—ironically—allowing less-preferred thorny plant species to take over.”

 

TEACHERS’ TOOLKIT

BBC: Carnivores help trees thrive without thorns, study says

Science: Large carnivores make savanna tree communities less thorny

NG activity: African Savanna Community Web

NG illustration: African Savanna

(media extra credit!) Disney: The Lion King—”The Circle of Life”

(biology extra credit!) Nothing in Biology Makes Sense: Why grow thorns if they don’t work? . . . And here’s a ridiculously beautiful example of thorns not working (be sure to click and enlarge)!

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