SCIENCE

Even sharks—infamous predator of the sea—risk becoming prey to the American alligator. (Newsweek)

Use our activity to help students create an imaginary marine ecosystem—then throw an alligator in there.

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

American alligators like this one are indigenous to freshwater habitats of the southeastern U.S. This beauty is enjoying the sunny swamps of the Everglades in Florida. Photograph by Djngsf, courtesy Wikimedia. CC-BY-SA-4.0

Grey nurse sharks like this one are indigenous to subtropical and temperate coastal waters around the world, including the southeastern U.S. This one enjoying the warm waters of southern Australia. Photograph by VirtualWolf, courtesy Flickr. CC BY-SA 2.0

Discussion Ideas

• Why was it a surprise to find that American alligators are preying on sharks?
  • They’re usually not in the same neighborhood. Although they are both aquatic species, alligators and sharks have different habitats.
    • American alligators are found in freshwater habitats of the southeastern U.S. Freshwater habitats include swamps, rivers, lakes … and swimming pools! Watch our video for more information on that.
    • Sharks are generally saltwater fish, although a few species (such as bull sharks) can survive in both marine and freshwater habitats. Learn more about “river sharks” with our video here.

• So, are sharks venturing into alligator habitat, or are alligators invading shark habitat?
  • Both, although the study primarily considered marine-foraging alligators—alligators that swim into saltwater estuaries and coastal habitats.

• How do alligators adjust to saltwater environments?
  • According to James Nifong, who led the new study, “while alligators lack salt glands—a requirement if their body is to filter the saltwater they plan on surviving in—the species can suss out whenever saltwater becomes temporarily diluted, after heavy rainfall for example. ‘Alligators seek out fresh water in high-salinity environments. When it rains really hard, they can actually sip fresh water off the surface of the saltwater. That can prolong the time they can stay in a saltwater environment.’”

• Do alligators feed primarily on sharks in their offshore ecosystems?
  • No. When foraging in marine habitats, alligators “chiefly consume small-bodied prey such as crustaceans, fish and wading birds.” Alligators have also consumed sea turtles.

• So, do alligators always win? Are alligators always apex predators and sharks always secondary consumers?
  • No. Both American alligators and sharks are apex predators in their respective habitats. When those habitats overlap, scientists say alligators and sharks have a “reciprocal intraguild predation” relationship.
    • Reciprocal intraguild predation describes the killing and eating of potential competitors. Unlike traditional relationships in a food web, intraguild predation represents a combination of both competition and predation.
      • competition. Alligators and sharks compete for the same food sources, such as smaller fish or crustaceans.
      • predation. In the predator-prey relationship among alligators and sharks, scientists say size is usually the key aspect: “The frequency of one predator eating the other is really about size dynamic,” Nifong said “If a small shark swims by an alligator and the alligator feels like it can take the shark down, it will, but we also reviewed some old stories about larger sharks eating smaller alligators.”

• Can you think of other food webs that might include reciprocal intraguild predation among apex predators?
  • example: On land, Siberian tigers and polar bears can exhibit intraguild predation behavior. They compete for food sources such as small terrestrial mammals (rabbits, foxes). The big beasts can also prey on each other.
  • example: In the ocean, sharks and dolphins can exhibit intraguild predation behavior. They compete for food sources such as fish and marine mammals. They can also prey on each other.

TEACHERS TOOLKIT

Newsweek: Alligators Are Feasting on Sharks in America’s Rivers and Estuaries, Scientists Discover

Nat Geo: Create an Imaginary Marine Ecosystem

Nat Geo: River Shark Attacks

Nat Geo: ‘Gator Wild