When humans accelerate the typically slow evolutionary process by introducing new species in an ecosystem, the action encourages the disappearance of younger species, a new report revealed.

About 20 years ago, scientists had brought crayfish into Enos Lake on Vancouver Island. Three years later, two species of threespine stickleback fish - which had been in the lake for a long time but were endangered - went extinct.

The high contention for resources, which was triggered by the presence of crayfish, had prompted interbreeding. The two endangered species produced a hybrid of fish. This phenomenon is called reverse speciation.

Seth Rudman of University of British Columbia said when two similar species are in the same environment, they typically perform different ecological roles.

"When they go extinct, it has strong consequences for the ecosystem," said Rudman.

Changes In The Ecosystem

One of the two species of threespine stickleback that lived in Enos Lake used to reside in the middle of the lake and ate zooplankton. The other species lived nearer to the shore and ate insects that spent their larval stage in the water.

Between 1994 and 1997, scientists had documented how both species went extinct as a result of interbreeding. Hybrid species of the fish were left.

The new species of stickleback fish does not have all the functions that its parents had. It spends more time closer to the shore of the lake and feeds on large insects.

Because of this, the number of small insects growing on the lake increased. This shows how changes in the lake impacted the terrestrial ecosystem. Researchers also discovered that the leaves that drop into Enos Lake do not decompose as quickly.

Consider Conservation Efforts

Study authors said reverse speciation is becoming more common, especially in environments that have been impacted by humans. They said Canada is at high risk for the phenomenon because younger species are prone to reverse speciation.

For instance, much of the country's biodiversity, particularly fish in rivers and lakes, are classified as young species that formed only over the last 12,000 years, Rudman said.

Reverse speciation, as evidenced by what happened to the threespine stickleback, happens extraordinarily quickly, researchers said. At the same time, it causes changes to the ecology of an ecosystem.

"It means we need to consider evolution in our conservation efforts," added Rudman.

The paper, co-authored by Rudman and UBC Professor Dolph Schluter, was published in the journal Cell Biology.

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