The Enemy of My Enemy Is My…?

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Science  04 Nov 2011:
Vol. 334, Issue 6056, pp. 569
DOI: 10.1126/science.334.6056.569-a

The factors permitting the coexistence of large numbers of plant species in tropical forests remain a key focus of ecologists. An established mechanism for limiting the abundance of individual tree species is density-dependent predation, whereby specialist natural enemies—especially insect herbivores—congregate where concentrations of their preferred seeds or seedlings are high, typically close to adult reproductive trees. This process, however, which confers an advantage on rarer tree species, can be complicated by the activities of the enemies' enemies. Visser et al. studied a tri-trophic interaction in a Panamanian rainforest, between a palm, its predator beetles (right, emerging from a palm seed), and the rodent predators of the beetle. As expected, infestation of palm seeds by beetle larvae increased close to adult plants, but the density-dependent effects were negated by preferential predation by squirrels on beetle-infested seeds. Such topdown control of seed predators, if repeated across other large-seeded tropical tree species, would add new layers of complexity to the conundrum of multiple species' coexistence in tropical forests

Ecol. Lett. 14, 1093 (2011).

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