After plants have already fertilized and grown seeds, dispersal is the last important step before the new offspring finally establish independence on their own. There are a number of reasons why seed dispersal is integral to the survival of a plant species, but the methods of dispersal are varied.
Because plants lack any sort of mobility and remain in the same spot for their entire lives, they rely on seed dispersal to transport their offspring throughout the environment. This can be accomplished either collectively or individually. But because seeds ultimately abdicate their movement, they are at the mercy of environmental factors.
Another reason seed dispersal is important is to reduce competition. Plants that accrue all in one area will have to fight for resources, but seeds that are spread out are much more likely to find success in favorable environments without the danger of interbreeding in local habitats near the parent plant.
Seeds are somewhat analogous to the embryonic stage and grow after fertilization has already occurred. Plants increase the success rate in the somewhat stochastic (or random) process of dispersal by growing as many seeds as possible. Many of them do not take root because they are spread to unfavorable conditions.
In order to deal with the realities of dispersal, plants have evolved specific structures and strategies to carry their seeds throughout the environment. Some seeds have two lateral wings to help them glide. Dandelions and salsifies use umbrella-like parachutes instead. Other seeds are known as "helicopters" or "whirlybirds" because they have spinning wings.
The wind is not the only method for seed dispersal. Seeds also can hitch rides on animals, preferably winged animals such as insects, bats and birds, as they usually travel the greatest distances. Other methods include travel by water and "ballistics" that fling seeds away from the plant at great speeds.
- Photo Credit seed image by sasha from Fotolia.com
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