Simple rules predict the outcome of predator-prey...( ITHACA N.Y. -- Whether the battle...)

ITHACA, N.Y. -- Whether the battlefield was pond water filled with algae-eating zooplankton or London during a measles epidemic, life's struggles for survival once seemed so complex that only a highly sophisticated model running on a supercomputer could predict the outcome.

Not necessarily so, say ecologists at Cornell University and North Carolina State University who have developed a new mathematical model: If just a few factors are sufficient to capture the essentials of predator-prey battles, many seemingly complex problems in population dynamics can be understood using only a desktop computer.

"Ever since ecologists in the 1920s began to model interacting populations, they have been struggling with the observation that very simple theoretical models predict very complicated dynamics like population cycles," said Gregor F. Fussmann, a postdoctoral associate in ecology and evolutionary biology at Cornell and lead author of an article in the Nov. 17 issue of the journal Science (Vol. 290, No. 5495, pp. 1358-60).

But do these predictions hold when real, live organisms are the players?

"It is a problem of counting trees and missing the forest," said Nelson G. Hairston Jr., another article author and the Rhodes Professor of Environmental Science at Cornell whose laboratory performed a key test of the new model. "It has become popular recently to model populations using an equation for each individual as a way to try to understand complicated patterns of increases and decreases in numbers. It turns out for our system that a few simple and general equations can explain the complex switch from constant population sizes to extreme cycles." The test was simple enough: Day after day for more than 14 weeks, single-celled green algae (Chlorella vulgaris ) and the microscopic animals that eat them (planktonic rotifers, Brachinus calyciflorus ) faced off in vessels called chemostats. Chemostats are glass tubes that
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Contact: Roger Segelken
hrs2@cornell.edu
607-255-9736
Cornell University News Service
5-Dec-2000