More Predators, Healthier Prey
Courtesy of Jon Eisenback, NemaPix

A new mathematical model is turning the conventional notion of predator-prey
relationships on its head. David Brown and colleagues at the University of
California, Davis, have shown that prey populations can benefit from a high
predator density.1

Ecologists previously have shown that predators can have indirect positive
effects on their prey through nutrient cycling and mineralization. Brown's
group, however, modeled predators' direct positive effects on the prey
population--a nematode eats soil-dwelling bacteria, moves to another
location, and then deposits live bacteria in new soil, where it can thrive.
Belying the paradox of the enrichment theory, which states that increasing
resources at a food web base will eventually cause populations to oscillate
to the point of extinction, Brown's model shows that positive feedback has a
stabilizing effect. Using a simple food chain involving a resource, its
consumer, and the consumer's predator, researchers demonstrated that the
consumer's feeding rate is proportional to predator density, or to the
number of predator-prey encounters.

While this model is based on the nematode-bacteria relationship, it
eventually could serve as a framework for modeling higher organisms, Brown
suspects. At some level, "all models are wrong," but his is
designed as "a
simple framework to serve as a reference point for more system-specific
models."

Bill Longland, of the US Department of Agriculture's Research Service in
Reno, Nev., acknowledges that the model is directed toward microbial
systems, but hopes it "will add new emphasis to the importance of predator
conservation in general."

--Maria W. Anderson

1. D.H. Brown et al., "Modeling direct positive feedback between predators
and prey," Theor Popul Biol, 65:143-52, March 2004.

>From The Scientist.com
http://www.the-scientist.com/yr2004/mar/upfront1_040301.html

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