While the debate over whether changes in climate are man-made, researchers have successfully proven that changes in river flow made by dams built just 300 years ago in the U.S. caused evolutionary changes in at least two species of fish.
A new study published in the journal Proceedings of the Royal Society B describes the work of a Yale University team led by David Post, professor of ecology and evolutionary biology. Prior to the 1700s, lakes in Connecticut were connected to the Atlantic Ocean by rivers and streams. Many fish species fattened up on lake fare, then swam to the sea where they themselves became ocean fare. When the lakes were dammed, the fish became landlocked.
The team reviewed previous studies on alewife, a spawning species of herring that fed on insects and large zooplankton in the lakes. After the dams were built, alewives caught behind them became smaller, ate all of the large zooplankton and then evolved smaller gills in order to be able to consume the remaining small zooplankton.
Post then looked at lake bluegills to see if the damming caused similar changes in that species. Bluegills living in lakes still open to the ocean did not eat the small zooplankton. However, those blocked by the dams also evolved the ability to survive on the smaller zooplankton. So the man-made dams changed the alewives and the bluegills, eliminated the large zooplankton in the lakes and forced ocean fish feeding on bluegills and alewives to find new food and feeding areas. And all of this happened in less than 300 years.
What does this simple yet damning dam study mean? While humans continue to alter the landscape to meet economic needs, most of the conservation efforts to protect the environment still get little attention or funding and much of it is after the fact. When landscape changes affect the food supply, as most do, the consequences can be drastic up and down the food chain and, with our global food trade, around the world.
David Post gives this warning:
Rapid evolution not only occurs, but runs across the food web in ways we are only now starting to understand.
Damn! Do you agree? What can we do?