An ecologist at Washington University in St. Louis has discovered that after ponds dry up through drought in a region, when they revive, the community of species in each pond tends to be very similar to one another, like so many suburban houses made of ticky tacky.
Jonathan M. Chase, WUSTL associate professor of biology in Arts & Sciences, and director of the universitys Tyson Research Center, created 20 artificial ponds out of tanks that hold 300 gallons of water. He made each pond community exactly the same in their environmental conditions, but varied the timing in which he added many species to the community lots of species, especially dragonflies, water-bugs, frogs, and even algae, happily colonized the ponds on their own accord.
As the communities thrived, most of the ponds diverged from each other some had only between 10 and 20 percent of species in common with other ponds. This factor was due to stochasticity, or randomness a plant introduced by a seed dropped from a duck, a frog having a lucky day, for instance.
But then Chase, having played beneficent god, played pernicious god, adding drought, normally random in nature, to one-half of the pond environments.
After the drought, the communities converged, and every community looked similar to each other, said Chase, who studies community assembly, among other areas of ecology. Its understandable that only certain kinds of species can stand the drought. When it comes to drought, there are wimpy species and hardy species. Several types of zooplankton, many water-bugs, and some frogs are the hardy ones. A wimpy species, perhaps surprisingly, is the bullfrog. Their tadpoles require two years to grow, so they often dont rebound very well from drought.
Some of the zooplankton have resting eggs that are deposited in mud. They rebound well when the ponds refill. Some frogs leave the pond when it dries up. Lots of different types of algae and one
|Contact: Tony Fitzpatrick|
Washington University in St. Louis