Sharks and Wolves: Separated at Birth?

Gray wolves and tiger sharks may seem like completely different animals, because—well—because they are. But aside from that, the two species are remarkably similar in how they function in their respective habitats, as revealed by studies of the interactions between U.S. wolves and elk on the one hand, and Australian sharks and dugongs on the other.

In both cases, the predators not only help control prey populations but also alter prey behavior through the “ecology of fear,” the term biologists are applying to the way predation affects how prey species use habitat.

Ecological Similarities

In a study published in Frontiers in Ecology and the Environment, scientists from Oregon State University (OSU) and the University of Washington tread new ground. And water. “For too long we’ve looked at ecosystem functions on land and in the oceans as if they were completely separate,” says William Ripple, a professor in the OSU Department of Forest Ecosystems and an international expert on large predators. “We’re now finding that there are many more similarities between marine and terrestrial ecosystems than we’ve realized. We need to better understand these commonalities and, from them, learn how interactions on land may be a predictor of what we will see in the oceans, and vice versa.”

Ripple and collaborator Aaron Wirsing, from the University of Washington’s School of Forest Resources, compared the interactions of wolves and elk in Yellowstone National Park with those of tiger sharks and dugongs in Shark Bay, Australia. Dugongs are large marine mammals, similar to manatees, that can weigh in excess of 1,500 pounds and that feed primarily on seagrasses. Research shows that the presence of wolves alters elk behavior, causing the elk to try to avoid encounters by remaining constantly vigilant and by staying in habitat that gives them room for escape. In Yellowstone, alterations in elk feeding areas is helping streamside shrubs and aspen trees to recover from decades of overbrowsing by the animals and also is producingpositive impacts on beaver dams and other wildlife.

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Similar effects take place between the Australian sharks and dugongs, the researchers found. When the sharks are abundant, dugongs graze less in shallow water, where seagrass grows thickest but dugongs are most vulnerable to sharks. This shift in feeding habitat—which causes the dugongs to give up food they might otherwise consume—allows seagrass meadows to thrive, along with a range of other plants and animals that depend on the vegetation.

Understanding the similarities between predator and prey relations in marine and terrestrial environments gives scientists a better grasp of the general behaviors that underlie the interplay of predator and prey. More frequent exchange of information between terrestrial and marine ecologists could provide additional insights into ecosystem functions, the researchers suggest.

Apex Consumers

Tiger sharks and gray wolves are apex predators—animals that, at maturity, prey on other species but are rarely preyed on themselves. The ecological importance of apex consumers is becoming increasingly clear as the body of research on these animals grows, showing that loss of or declines in these species can ripple throughout ecosystems. For more information, see the current issue of National Wildlife magazine.

 

The photographs in this blog were donated to NWF by entrants in the annual National Wildlife Photo Contest. Do you have photos you would like to put into competition? Here’s how you can do it.