Dispersal Mechanisms Displayed by Fruits

Dispersal of fruits and seeds can be effected by wind, water, or animals. Other mechanisms occur but are less common. Observe the demonstration material.

(1) Wind Dispersal

For wind dispersal to be effective, the seeds have to be lightweight. This involves a high surface/volume ratio of the diaspore. A high surface-to-volume ratio is accomplished by having one or more of the following: 1) extremely light and/or small seeds,  2) hairs on seeds or fruits, or 3) wings on seeds or fruits. What are the advantages and disadvantages to this system of dispersal? Is this an efficient dispersal system?

(2) Water Dispersal

Some plants disperse their fruits in the water of the habitat they live in or near. Consequently, water dispersal should be looked for among plants living in marshes, swamps, or along rivers. What is the important characteristic which links this group together? What are some advantages to water dispersal? Are there any disadvantages?

(3) Animal Dispersal

Dispersal by animals can occur by a number of ways. Edibility is one method used frequently by plants. Often the fruits remain a dull color until the seeds are ripe, then the fruits change to a bright color (a signal), are consumed by animals (a reward), and the seeds pass through the animals, unharmed due to a thick protective seed coat.

Another common adaptation is to have appendages on the fruit which enable it to stick to animals. Hooks, barbs, long awns, and hairs are all ways in which fruits can stick to animal fur or feathers. These kinds of structures led to the invention of velcro!

Some seeds and fruits have an outside coating, which upon wetting, swells and becomes sticky. This adherence is alternative way of having animals disperse fruit. Another version of this is to be small enough to stick to animals by mud.

  Lest you think these seem in some cases to be fairly ineffective methods, realize that the native flora of the Hawaiian Islands are 95% due to immigration via seabird dispersal, and of that 95% roughly equal proportions are made up of edible, hook or barb type sticking, and tiny mud or coating type of adhesive seeds and fruits.

What is the importance of dispersal? Compare these methods in terms of the usual distance traveled, is one more effective than another? In a changing environment, which might be the most effective, in a constant environment?