The tanks were stocked with six species of aquatic plants and three species of snails and inoculated with the smaller zooplankton and phytoplankton drawn from local ponds. The remainder of the aquatic community, such as frogs, dragonflies, flies, beetles and bugs, was allowed to assemble naturally.
Loosestrife plants in pots were placed in each of the four small pools. The pools were separated from the tanks so that only the flowers and not plant litter and pollen would play a role in the ecosystem of the central pool.
The eight "wetlands" thus created were divided into four treatment groups and the number of loosestrife flowers in each "wetland" was manipulated to mimic differences in loosestrife density.
The loosestrife in two wetlands were left alone but flowers at the other wetlands were picked to reduce their numbers to 75 percent, 50 percent or 25 percent of the flowers at the untouched wetlands.
During the course of the experiment, the small insects visiting the pools were regularly counted and categorized, as were the dragonflies and their behaviors.
At the end of the summer and the experiment, the zooplankton and phytoplankton in the eight central tanks were sampled and identified.
The scientists were able to track the effect of the loosestrife flowers across four trophic levels, or levels in the food web, and two ecosystems, the terrestrial and the aquatic ones.
The links worked as follows: Wetlands with abundant flowers attracted more pollinating insects; the insects in turn attracted more of the carnivorous dragonflies; the well-nourished dragonflies laid more eggs in the central ponds; the voracious dragonfly larvae that hatch
|Contact: Diana Lutz|
Washington University in St. Louis