Adaptable Predators Survive Changes, But They Kill The Ecosystems

Humans, polar bears and killer whales have one thing in common - they are adaptable predators. When their most favored food is running low, they adapt to a new prey, which deteriorates the ecosystem, according to a recent study. 

Researchers found that predators change their prey after a species has been over exploited and its numbers run low, which can then lead to the extinction of species after species. Professor Bo Ebenman and Dr. Alva Curtsdotter, along with David Gilljam, a doctoral student in theoretical biology, have been working on the research study, according to a news release. 

"If the predator is efficient at killing its prey, such a change can lead to negative effects in the long term, for the entire food web, even if in the short term it benefits the predator's survival," Gilljam said. 

The killer whale was one of the main examples in the study. Its main prey was newborn whale calves. When the population declined, they hunted seals instead. After the seal population crumbled, they began hunting sea otters. Sea urchins were the sea otters' main diet, and when otter numbers dropped, the urchin population remained intact, and they grazed down the kelp beds, which served as nurseries for many fish species and small marine animals.

Ebenman compared this process to a rope with twisted fibers.

"Think of a rope that's made of a number of twisted fibers. When force is applied to the rope, the force is spread across all the fibers. If one fiber breaks, the remaining fibers take all the force, with more force on each individual fiber. If more break, eventually the whole rope will fail," Ebenman said in a news release. 

The researchers also used polar bears as a typical example of crashing ecosystems. Since the Arctic ice is melting, it has become difficult for polar bears to hunt seals. Instead, they are now hunting on land, feeding on eggs and young ground-nesting birds, which are already the prey of other types of predators, like arctic foxes. 

"The belief was that an extinction cascade would be avoided if the predator is adaptable and can shift to another prey. Our new results indicate that the opposite can occur, and the consequences can be even worse," Ebenman said.

"A change in prey is a double-edged sword, in the short term it can help a flexible predator survive, but long term it can negatively affect the entire existence of the food web."

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