Plant version of checks and balances

UC SANTA BARBARA (US) — In the plant world, the strongest competitors are held back from total domination by predators that keep them in check.

“The species that are the best competitors are the most likely to be eaten, and this prevents them from winning outright,” says lead author David Viola, a doctoral student in the department of ecology, evolution, and marine biology at the University of California at Santa Barbara.

“Until now, no one has attempted to determine how widespread this competition-predator defense tradeoff is in nature.”

Details are published this week in the Proceedings of the National Academy of Sciences.

To measure the overall strength of the tradeoff, Viola, and professors Jonathan M. Levine and Bradley J. Cardinale, and five other doctoral students collected data from previously published studies of plant communities.

They found that in most plant communities, the best competitors were actually more resistant to herbivores, rather than less.

“We were quite surprised, because this particular tradeoff is such a common concept in ecology,” saysViola.

“We began with the simple goal of quantifying the strength of the competition-predator defense tradeoff,” Levine says. “The six doctoral students broadened the scope and took the analysis in a novel and interesting direction.”

For example, although the competition-defense tradeoff was uncommon, Viola notes “in the minority of cases, when the good competitors were more vulnerable to herbivores, diversity was maintained.”

The authors stress the practical implications of this last point. Both nutrient pollution and the loss of herbivore species can upset the equilibrium within plant communities and cause subsequent losses of diversity.

“We continue to learn how intricate the internal connections within natural systems are,” Viola says. “A change in one part will almost assuredly have consequences that propagate through to other levels.”

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