From: David A Gabel, ENN
Published November 12, 2010 09:25 AM

Land and Sea Predators Create a Similar Ecological Effect on Their Environment

In ecology class, students are taught the effects of keystone species, the dominant species in the ecosystem. They are the top dogs, the big fish. The keystone species have a disproportionate effect on their environment and can determine the types and numbers of species in their ecosystem, not just their prey. A recent study published in the journal Frontiers in Ecology and the Environment shows that this keystone species effect is similar for both terrestrial and ocean-based predators.


The study was recently conducted by Aaron Wirsing of the University of Washington and William Ripple of Oregon State University (OSU). They analyzed the behavioral effects on prey from both the wolf and the shark, two keystone species from much different ecosystems. The wolves were observed at Yellowstone National Park, and the sharks at Australia’s Shark Bay. In both cases, the predators altered the behavior of the prey.

In Yellowstone, the wolf's main prey, the elk, shifted to new, less-sensitive grazing areas when wolves were present. This had a ripple down effect on the streamside shrubs and aspen trees which the elks normally eat. These species could then regrow and in turn support many other species. In Shark Bay, the tiger shark's main prey, the dugong altered its behavior similar to the elk. It would avoid shallow waters when the sharks were present. This allowed the sea-grass meadows to regrow and in turn support other marine species.

"For too long we've looked at ecosystem functions on land and in the oceans as if they were completely separate," said William Ripple, a professor in the Department of Forest Ecosystems at OSU. "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."

In both marine and terrestrial environments, the prey not only shifted to new areas when the predators were around, they also radically shifted their behavior. They displayed increased vigilance, always looking and listening for a silent stalker. They strove to leave room for escape if necessary, such as moving to areas where they would not feel boxed in, and keeping a safe distance from an approaching predator. The end result is less over-consumption of flora, leading to an overall healthier ecosystem.

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