They found that, just three years after the introduction of crayfish to Enos Lake on Vancouver Island — not even the wink of an eye on evolutionary timescales — two species of fish that had existed in the lake for millenia blinked out of existence.
But it’s not so much the demise of the two pisceans that fascinated researchers but what replaced them.
The new UBC research demonstrates that when human intervention effectively turbo-charges the normally languid pace of evolution then such intervention can cause a lasting impact on ecosystems. This process is described as reverse speciation.
In the specific case of Enos Lake, two similar species of threespine stickleback fish vanished within three years.
Seth Rudman, a PhD student in zoology at UBC, explained, “When two similar species are in one environment, they often perform different ecological roles. When they go extinct, it has strong consequences for the ecosystem.”
The two species of endangered sticklebacks inhabited Lake Enos but each had distinct habitats and diets. One species’ neighbourhood was the middle of the lake, consuming mostly zooplankton. But the other species swam nearer the lake-shore preying on water-borne insect larvae.
At some point during the mid-1990s, crayfish were introduced to Enos Lake. It wasn’t so much the omnivorous appetite of the crayfish that did for the two distinct stickleback species; rather the foreign invader had a more indirect impact on the two tribes of stickleback.
The UBC researchers documented how, between 1994 and 1997, both stickleback species disappeared leaving in their stead a hybrid species, the result of interbreeding.
According to their study, recently published in Current Biology, the emergence of the hybrid has had an impact on the lake’s ecosystem since the new hybrid fish doesn’t perform the same ecological functions as its evolutionary antecedents.
The hybrid tends to shun the middle of the lake, spending more time near the shoreline. The diet of the hybrid is also different, with a marked liking for large insects as opposed to insects in their larval form. As an incidental the researchers also found that leaves finding their way into the lake’s waters don’t decompose as quickly as they did when Enos Lake was hoe to two different stickleback species.
A consequence of the hybrid’s different dietary preference and liking for the lake’s shallower waters is that the number of small insects emerging from the lake has increased. That, say the researchers, demonstrates how what may appear at first glance to be minor changes in the lake’s zoology can also cause changes to the surrounding terrestrial ecosystem.
According to Rudman and co-author Dolph Schluter, a professor at UBC’s department of zoology, Enos Lake is but one example of reverse speciation, a phenomenon that’s becoming more common particularly in environments altered by humans. They go on to say Canada is at greater risk of experiencing such evolutionary events since “young species” are prone to reverse speciation.
“Much of Canada’s biodiversity, particularly fish in lakes and rivers, are considered to be ‘young’ species that formed in the last 12,000 years or so,” commented Rudman, adding “This type of evolution, known as reverse speciation, happens remarkably quickly and can cause alterations to the ecology of the ecosystem. It means we need to consider evolution in our conservation efforts.”
The full study, “Ecological Impacts of Reverse Speciation in Threespine Stickleback”, can be found on Current Biology.
