ECOLOGY/EVOLUTION

Smaller Harvests Than Expected

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Science  20 Jul 2007:
Vol. 317, Issue 5836, pp. 296
DOI: 10.1126/science.317.5836.296b

Leaf-cutting ants of the genus Atta are ubiquitous residents of neotropical forests. They construct large subterranean colonies and journey on trails across the forest floor and into the forest canopy, where they harvest leaf fragments that are carried back to the nest. The fragments nourish a mutualistic fungus that in turn provides protein and carbohydrate for the ant colony. Leaf-cutters have been widely assumed to be the dominant herbivores in the forests they inhabit, but supportive quantitative data for this assumption are sparse. Herz et al. first used a rapid and nondestructive method, involving the sampling of refuse deposited by ants outside their nests, as a proxy for measuring the daily harvest of leaves. Then they collected data from nearly 50 nests over 15 months in a Panamanian forest and calculated that the ants were actually responsible for only about 0.7% of total leaf consumption by all folivores (insects and vertebrates) in the forest. Even though these results indicate that the defoliation by leaf-cutters is more modest than previously thought, Urbas et al. found that herbivory by leaf-cutters in a Brazilian forest increased at the margins (versus the interiors) of forests that had been fragmented by human disturbance, thus amplifying environmental change at the forest edge. — AMS

Biotropica 39, 476; 482; 489 (2007).

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