Seeds by Carolyn Fry

Author:Carolyn Fry [Fry, Carolyn]
Language: eng
Format: azw3
Publisher: University of Chicago Press
Published: 2016-04-04T16:00:00+00:00

HOW SEED SIZE MATTERS

Seeds have masses spanning more than 11 orders of magnitude, from the tiny specks of orchid seeds to the 44 lb (20 kg) seed of the coco de mer (Lodoicea maldivica) palm. Scientists who analyzed seeds from around 11,500 species, along with the locations in which they grew, found that seeds are, on average, larger closer to the tropics and smaller farther from the equator. They recorded a 320-fold decline in seed mass between the equator and 60° latitude (see diagram). At the edge of the tropics, they detected a sevenfold drop in mean seed mass. The changes were most closely related to changes in plant growth form and type of vegetation (trees, shrubs, and so on).

While it might seem likely that seeds with a smaller mass would be dispersed farther than larger ones, the height of a plant is, in fact, a more important determinant of how far its seeds will travel. Scientists reviewing 148 studies from around the world studied 200 plant species with varied seed-dispersal methods, and concluded that seed dispersal distance is more closely correlated with plant height than with seed mass. This refuted a widely held perception that small-seeded species should disperse better than large-seeded species, trading off seed mass (a greater seed mass equating to a larger number of nutrients provided by the parent plant) against dispersal capacity.

SEED MASS REDUCES WITH DISTANCE FROM THE EQUATOR

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