How would a species' extinction impact the food web, our ecosystems?

Every living thing plays a role in the food chain and Earth’s ecosystems, and the extinction of certain species, whether predators or prey, can leave behind significant impacts.

“Since the origin of life on Earth, it’s fair to say that more species have gone extinct than are currently alive now,” said Dr. Anthony Giordano, president and chief conservation officer of the Society for the Preservation of Endangered Carnivores and their International Ecological Study (SPECIES). “Extinction itself is part of the normal course of evolution.”

The effect a species would have if it were to fade from existence depends largely on its role in the ecosystem. Predators, for example, are often the first to be threatened by hunting or competition with people and resources, said Clemson University conservation biologist Dr. Robert Baldwin.

“Think about large animals like the grizzly bear,” Baldwin said. “When a predator goes extinct, all of its prey are released from that predation pressure, and they may have big impacts on ecosystems.”

The loss of a predator can result in what is called a trophic cascade, which is an ecological phenomenon triggered by a predator's extinction that can also impact populations of prey, which can cause dramatic ecosystem and food web changes.

“If there are too many deer, for example, they can really change the ecosystem because they can destroy forests, and they also carry disease,” Baldwin said.

Scientists have noted the trophic cascade effect in parts of Africa where lion and leopard populations have dwindled, according to Smithsonian Magazine. It caused olive baboons to alter their behavior patterns and increase contact with nearby humans. The increased contact has led to a rise in intestinal parasites in both people and the baboons.

In the case of the northern white rhino, of which only two female rhinos now survive, the last male of the species was held in semi-captivity at the end of its life, and “the damage was already done in the ecosystem by that point,” Baldwin said.

However, in general, the loss of rhinos, which often face threats from humans, from the ecosystem can have wide-ranging effects, according to Baldwin, who noted that the rhino’s eating pattern helps with seed dispersal.

“They eat grasses and vegetation in one place, and they move and defecate in another place,” he said. “That helps those plants to disperse throughout the ecosystem, and it also helps populate the ecosystem with rhino food.”

The loss of abundant organisms that provide food for a wide variety of species would also interrupt the food web, according to Baldwin.

“For instance, if krill in the ocean goes extinct or becomes depressed in numbers, then that’s the bottom-up effect; predators that rely on krill will suffer,” he said.

While not at the top of the food chain, sea otters are keystone predators in the kelp forests in which they reside.

“The presence of sea otters in marine near-shore communities and coastal communities, particularly on the West Coast, have been shown to be essential and critical to healthy kelp forests underwater,” Giordano said.

These kelp forests provide habitat for many species. “One of the ways sea otters help to maintain those kelp forests is by preying upon other species that would slowly start to eat or consume the kelp, which, if they were left unchecked, would then rattle the entire kelp bed and turn it into a rocky or barren wasteland,” Giordano said.

Species like parrot fish, which graze on algae, are extremely important to coral reef ecosystems because they prevent algae growth from getting out of control and impacting those coral reefs, according to Giordano.

“As algae expands in those communities, it can lead to the expansion of coral dead zones,” he added.

The loss of certain species can impact the ecosystem in a number of ways, Giordano said, but the issue is that researchers don’t yet know about many of the species out there.

A 2011 study concluded that about 86 percent of the Earth’s species have yet to be discovered, according to National Geographic.

“We know more about some of the larger ones, but for many species, especially the ones that are disappearing, we don’t know the impact of their loss," he said.

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