Sharks dwell in the ocean, wolves on land; sharks are a type of fish, wolves are a mammal; sharks go back some 400 million years, wolves only some 2 million years. So, these animals should have little in common, right? However, a new study in Frontiers in Ecology and the Environment points to surprising similarities among these disparate animals. As top predators, both wolves and sharks impact their prey and other species in similar ways.
By examining interactions between sharks and their prey, dugongs, in Australia, researchers found a number of commonalities between how wolves impacted elk when reintroduced to Yellowstone National Park in the US.
Top predators do not only keep prey populations in check, but, according to a number of studies, establish an ‘ecology of fear’ in their prey, whereby the prey’s day-to-day behavior is constantly affected by the predator’s presence, i.e. shark and wolf. These impacts go far beyond predator and prey: research has shown that the presence of such predators can significantly impact a whole trove of species from plants to other animals.
Top: a wolf in Yellowstone National Park. Photo courtesy of Yellowstone National Park. Bottom: a tiger shark. Photo by N. Hammerschlag, courtesy of Oregon State University.
“For too long we’ve looked at ecosystem functions on land and in the oceans as if they were completely separate,” said co-author William Ripple with the Department of Forest Ecosystems at Society at Ohio State University in a press release. “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.”
Past research has shown that the reintroduction of wolves in Yellowstone National Park reined in elk populations and kept elk wary and nervous, changing their feeding patterns. This change in the elk’s behavior lead to what is known by ecologists as a ‘trophic cascade’, whereby adding wolves to the environment spread ripples down throughout the entire food chain. Many local plants—long devastated by elk overgrazing—were suddenly returning.
“The removal of top predators from landscapes allows, via reduced predation and predation risk, unimpeded foraging by large herbivores such as elk and deer,” explained Dr. Robert Beschta, to mongabay.com for a previous story. “Heavy utilization of plants by these animals, over time, can greatly alter the composition of plant communities and thus impact other animals that are dependent upon these plants as part of their life cycles.”
With the wolves return, trees grew more abundantly, which heralded a population explosion of another mammal in Yellowstone National Park: the beaver.
Sharks, like wolves, have similar impacts according to Ripple’s study. Where sharks are abundant, dugongs—large mammalian herbivores—are forced by the ecology of fear to move their grazing areas just like elk. This allows seagrass meadows to recover, providing particular habitat for a host of marine biodiversity, both plant and animal.
The authors say their study should warrant more discussion between marine and terrestrial ecologists in the surprising similarities above and below water.
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