He dosed the ponds with nutrients in the form of nitrogen- or phosphorus-containing chemicals. Each pond received low, medium or high levels of nutrients throughout the experiment.
Then he began adding species to the ponds. The species consisted of zooplankton; insects and small invertebrates such as snails; vascular aquatic plants; and filamentous green algae.
The first year, each pond had a randomly selected one-third of the species added. The following year, half the remaining species, again randomly selected, were added.
In the third year, the pond got a soup containing the remaining species.
Each pond received species in a different order but in the end, every pond got exactly the same species.
"Then we let nature take over," Chase says. "The plankton moved around in the wind and on frogs' backs, dragonflies flitted over and laid their eggs, beetles buzzed by, and it was a 'big happy wetland community.'"
Chase and a team of students sampled the ponds each summer to see how the communities were faring.
The low-productivity ponds all looked the same. But that was not the case for the high productivity ponds.
"The low productivity ponds were very predictable," he says. "The high productivity ponds were more stochastic [random]. Their history mattered more."
There were no big differences among the ponds when it came to number of species. The low productivity ones had roughly as many species as the high productivity ponds.
The biodiversity arose at a different scale, not within a pond but within a group of high-productivity ponds.
This kind of diversity is called beta diversity to distinguish it from local, or alpha diversity.
It directs our attention, Chase says, to ecosystem structure th
|Contact: Cheryl Dybas|
National Science Foundation