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Sepal and nut size ratio of fruits of Asian Dipterocarpaceae and its implications for dispersal

Published online by Cambridge University Press:  10 July 2009

Eizi Suzuki
Affiliation:
Department of Biology, College of Liberal Arts, Kagoshima University, Kagoshima 890, Japan
Peter S. Ashton
Affiliation:
Arnold Arboretum, Harvard University, Cambridge, Massachusetts 02138, USA

Abstract

The relationship between sepal and nut size of fruits was studied in fruit of 394 species of Dipterocarpaceae in Malesia and Sri Lanka. The fruits of many dipterocarps have long twisted sepals which have a role as blades for dispersal by gyration. But long sepals decrease resource allocation to other parts, and increase the chance of fruit being trapped in the canopy. The frequency distribution of the ratio of sepal length to nut length was bimodal. The gyrationdispersed group with longer sepals comprised 74% of Dipterocarpaceae studied. The group with short sepal mainly comprised understorey trees, but there were a few emergents. In both groups, sepal areas were expressed as a power function of nut volumes'. Because fruit weight per sepal area increases with fruit size, larger fruits fall more quickly than smaller fruits, and sepals of the former can not serve so effectively as propeller blades. This is consistent with the fact that a few emergent trees with large nuts have short sepals and are not dispersed by gyration. Therefore, the re-evolution of short fruit sepals appears to have been mainly due to two reasons: reduction of tree height and enlargement of nut size.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1996

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