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Adaptation and Inertia in the Australian Tropical Lowland Rain-Forest Flora: Contradictory Trends in Intergeneric and Intrageneric Comparisons of Seed Size in Relation to Light Demand

P. J. Grubb and D. J. Metcalfe
Functional Ecology
Vol. 10, No. 4 (Aug., 1996), pp. 512-520
DOI: 10.2307/2389944
Stable URL: http://www.jstor.org/stable/2389944
Page Count: 9
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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.
Adaptation and Inertia in the Australian Tropical Lowland Rain-Forest Flora: Contradictory Trends in Intergeneric and Intrageneric Comparisons of Seed Size in Relation to Light Demand
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Abstract

1. In 13 of 14 contrasts between light-demanding and shade-tolerant genera within the same subfamily or family, the shade-tolerators have seeds of greater mean dry mass, but in eight out of nine contrasts between light-demanding and shade-tolerant species within genera the shade-tolerators have seeds of about the same or slightly lesser mass. 2. We use the results to emphasize the low position of seed size in the hierarchy of characteristics enabling plants to become established in the shade. 3. Within genera and among confamilial genera of shade-tolerant plants there can be differences of one to three orders of magnitude in seed dry mass. By hypothesis, species whose seedlings have a given degree of tolerance of shade, as such, may make many `risky' seeds or few `safe' seeds, the larger-seeded species being buffered against drought and the effects of herbivores or falling branches. Extremes of seed size represent particular adaptations; very small-seeded species (<1 mg) establish on steep micro-slopes free of litter, while very large seeds (>2000 mg) attract especially large animals as dispersers. Seed size is seen as adaptive in contexts other than survival of shade as such.

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