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Escape of Juvenile Dioclea megacarpa (Leguminosae) Vines from Predators in a Deciduous Tropical Forest

Daniel H. Janzen
The American Naturalist
Vol. 105, No. 942 (Mar. - Apr., 1971), pp. 97-112
Stable URL: http://www.jstor.org/stable/2459059
Page Count: 16
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Escape of Juvenile Dioclea megacarpa (Leguminosae) Vines from Predators in a Deciduous Tropical Forest
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Abstract

Dioclea megacarpa (Leguminosae), a large woody vine in Costa Rican deciduous forest, loses most of its seeds and seedlings to predation by squirrels (Sciurus variegetoides), bruchid beetles (Caryedes brasiliensis), and moth larvae (Noctuidae, Erebinae). Squirrels take 0%-43% of the seeds in a crop while in the "milk stage," but leave a large absolute number of uneaten seeds; they are probably prevented from eating larger numbers by a toxic amino acid, canavanine, in the seeds. The bruchids kill from 13% to 100% of a given seed crop; the mortality percentage appears to be proportional to the number of females that find the crop. Caryedes brasiliensis may act as a density-dependent population regulator of D. megacarpa adults. Both squirrels and bruchids effectively lower the carrying capacity of the habitat for D. megacarpa by reducing the seed crop size. Noctuid larvae that normally feed on the crown of the adult vine are a severe threat to seedlings growing beneath the adult; these predators cause the death of nearly 100% of the seedlings before the rainy season has ended. New adult vines are more likely to appear far from the parent rather than very close because of these larvae. The significance of increased severity and unpredictability of the dry season is discussed for bruchid and vine populations.

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