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Measuring nature's productivity. (Environment).

As animal species become extinct and ecosystems less diverse, the environment for remaining species will become less healthy, according to a University of Maryland study. Biology professor Margaret Palmer and doctoral student Bradley Cardinale found that several different species of caddis fly larvae living together in a given stream means greater food productivity than when only one species is present.

This new study builds on earlier research showing that a decrease in species diversity means a less-productive ecosystem. "What's really exciting about our work is that we were able to show why this happens," says Palmer. "We found that species sometimes help each other capture food. When you lose a species, the others may eat less and become less productive."

Caddis flies are found in many different freshwater environments. They can occur in very large numbers and serve as food for fish, water birds, and other aquatic vertebrates. Fishers often gather them for bait for trout and other game fish.

The researchers built streams and placed caddis fly larvae gathered from natural streams in this manufactured world. The lab-created environment enabled the team to exercise greater control over their research. In some lab streams, the researchers combined several species of larvae, while in others they placed only a single species.

Caddis fly larvae, which live in streams around the world, construct little cases to dwell in and attach themselves to rocks in riverbeds. The larvae build silk nets to capture and filter food from water. Researchers saw an increase in the speed of water flow in the streams containing different species. This increased speed meant that more food was being delivered to the capture nets.

"The pattern of water flow around the caddis flies totally changed when we mixed the species," says Palmer. "Water flow was faster, and more food particles were delivered to the larval capture nets than in the single species streams."

According to Cardinale, "It appears that placing species together, each with a different size filtration net, created a form of physical complexity that altered the flow of water near the stream bed and allowed the whole community to capture more food."

The study sheds significant light on what happens when a species becomes extinct. "Our study shows that ecosystems with more species are more efficient and that, as species vanish, the ecosystems we rely on so heavily will become less productive," Palmer concludes.

Source: Office of University Communications, University of Maryland, 2101 Turner Building, College Park, Maryland 20742. Telephone 1-301-405-4621.

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Publication:The Futurist
Date:Jul 1, 2002
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