GEOGRAPHY

The biodiversity of the Amazon rain forest is not entirely pristine. It was also shaped by an ancient hunger for fruits and nuts. (Nature)

Use our activity to learn more about biodiversity in the Amazon.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• A new study analyzes the distribution of domesticated trees in the Amazon rain forest. What are domesticated species? Take a look at our encyclopedic entry for some help.
  • Domestication is the process of adapting wild plants and animals for human use. Domestic species are raised for food, work, clothing, medicine, and many other uses.
  • The chief domesticated trees in the Amazon are mostly harvested for food and medicine: Brazil nuts, Inga ynga fruit (commonly known as “ice-cream beans”), Amazon tree grapes, abiu (another tropical fruit), and cacao fruits (whose seeds are known as cocoa beans). Domestication of these trees started about 8,000 years ago.

• How did researchers determine that ancient human activity may have influenced biodiversity in the Amazon rain forest?
  • First, researchers analyzed data from the Amazon Tree Diversity Network, a group of scientists who share information about trees in the Amazon. They discovered that 85 of the Amazon’s 16,000 tree species were partly or fully domesticated. About 20 domesticated tree species were over-represented (hyperdominant) meaning their population was five times higher than the number expected by chance.
  • After determining the species that were over-represented in the biodiversity survey, researchers considered the distribution pattern of the over-represented trees—where they were located. They discovered that the over-represented domesticated trees were much more likely to thrive where prehistoric people had established settlements.
    • Scientists identify long-abandoned settlements by the tell-tale soil composition, rock art, and earthen mounds.

• Besides prehistoric human activity, what other factors may have influenced the distribution of domesticated trees in the Amazon rain forest?
  • environmental conditions. In most regions of the rain forest, factors such as soil quality, access to sunlight, and water availability have a greater influence on distribution of trees (both domesticated and wild).
  • animal interactions. Many trees rely on animals for seed dispersal, and are therefore influenced by the abundance and types of animals in a specific area. “For example, effective seed dispersal of large-seeded tree species decreases in heavily hunted forests because of the depletion of large vertebrates.”
  • unintentional human activity. Human activity may have contributed to environmental conditions that favor domesticated species long after the human settlement has vanished. For example, “When people abandoned Mayan sites in Central America,” Nature says, “Brosimum trees re-colonized the area. But for years, researchers thought the Mayans had planted them deliberately. [The Amazon team] could be observing a similar phenomenon.”
  • modern human activity. Human settlements can overlap for thousands of years—just ask the residents of Athens, Varanasi, or Beijing. In addition, 17th-century European colonists encouraged cocoa plantations in the Amazon, which may have increased the abundance of cocoa trees long after the plantations were abandoned. “So it’s possible that more modern groups influenced the ecosystems we see today as much as ancient ones.”

• “Domestication shapes Amazonian forests.” How is this conclusion important to ecologists and conservationists?
  • “Detecting the widespread effect of ancient societies in modern forests … strengthens efforts to conserve domesticated and useful wild-plant populations, which is of critical importance for modern food security.”

• Domesticated trees may be “relics of a vibrant past” in the Amazon rain forest. Why might archaeologists, anthropologists, and historians be interested in this study on the distribution of domesticated trees?
  • Forests close to archaeological sites often have a higher abundance of domesticated species, and examining similar “patterns could help other scientists to discover as yet unknown ancient settlements in the Amazon.”

TEACHERS TOOLKIT

Nature: Amazon rainforest was shaped by an ancient hunger for fruits and nuts

Nat Geo: Protecting Biodiversity in the Amazon Rain Forest

Amazon Tree Diversity Network

(extra credit—good read!) Science: Persistent effects of pre-Columbian plant domestication on Amazonian forest composition