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...

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