ITHACA, N.Y. -- Surveying aquatic life from the Great Lakes to small ponds, ecologists at Cornell University and the Institute of Ecosystem Studies (IES) have found that food-chain length -- the number of mouths food passes through on the way to the top predators -- is determined by the size of an ecosystem, not by the amount of available food energy.
The finding, which is reported in the June 29 issue of the journal Nature, should help resolve one of the oldest questions in ecological science: How long are food chains and what determines their length?
But the systematic accounting of food-chain links and lengths also serves as a warning: The so-called top predators -- such as eagles, falcons and most of the fish that anglers catch to eat -- are more likely to accumulate high concentrations of mercury, PCBs and other contaminants when they live in large ecosystems. And that puts humans, the ultimate predators, at risk.
"If your neighbor comes home with two fish -- a 10-pound trout from Lake Erie and the same size fish from a smaller lake -- ask for the fish from the small lake. Your risk of consuming bioaccumulated contaminants is probably lower with the trout from the smaller lake," said David M. Post in a prepublication interview.
A graduate student of ecology at Cornell and IES, Post is one of three authors (together with Michael L. Pace, aquatic ecologist at IES in Millbrook, N.Y., and Nelson G. Hairston Jr., professor of ecology and evolutionary biology at Cornell) of the report titled "Ecosystem size determines food-chain length in lakes." Their results show that larger lakes have longer food chains than smaller lakes. The same principle may apply to food chains in terrestrial ecosystems, such as large forests and smaller forest fragments, Post observed.
"The standard, textbook explanation for 70 years has been that food-chain length is determined by energy availability," Post said. "Our results show that it is not energy availabil
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Contact: Roger Segelken
hrs2@cornell.edu
607-255-9736
Cornell University News Service
27-Jun-2000