Airdate: Jul 22, 2004
Scientist: Christopher Birkinshaw
Seed Dispersal - Animals
Why using animals to disperse their seeds is a good strategy for many plants.
ambience: Dawn chorus, Sierra
Most plants depend on seeds to reproduce. But just having seeds isn't enough to insure survival of a species. I'm Jim Metzner, and this is the Pulse of the Planet.
Christopher Birkinshaw is with the Missouri Botanic Garden.
"It’s been shown in very many experiments that if the seeds of a plant just fall below the parent tree, then they suffer very high mortality. Not only do the poor little seedlings have to compete against its mother for light and nutrients, but also the pests which feed on the mother plant often fall down, and while the mother plant can tolerate being eaten by a few caterpillars, a caterpillar can destroy the seedlings, if they’re underneath the mother plant. So it’s critical for the mother plant to get the seeds as far away from it as possible. For good regeneration, you need good seed dispersal. Generally, in temperate regions of the world, seed dispersal by wind is particularly important."
But for some species of plants, wind isn't an effective way to disperse their seed.
"If you’re going to be dispersed by the wind, you can’t have a very big seed, because the bigger the seed the heavier is the seed. So wind dispersal works fine, for small seeds, but not for big seeds. But the problem of having a small seed is that seed cannot contain many nutrients. And so that means that when the when it's germinating, you can’t get the young plant off to a good start. The good thing about animal seed dispersal is, animals are capable of dispersing much bigger seeds than the wind can disperse. That means that you can create a large seed and pack a lot of nutrients into that, so to get the young seedling off to a good start. And that’s why animal dispersal is really quite a good idea. It can give you an advantage over your other wind-dispersed species."
We'll hear more on seed dispersal in future programs. Pulse of the Planet is presented by the National Science Foundation. I'm Jim Metzner.