Fruit and Seed Dispersal

Some fruits can disperse seeds on their own, while others require assistance from wind, water, or animals.

Learning Objective

Summarize the ways in which fruits and seeds may be dispersed

Key Points

The means by which seeds are dispersed depend on a seed's structure, composition, and size.
Seeds dispersed by water are found in light and buoyant fruits, while those dispersed by wind may have specialized wing-like appendages.
Animals can disperse seeds by excreting or burying them; other fruits have structures, such as hooks, that attach themselves to animals' fur.
Humans also play a role as dispersers by moving fruit to new places and discarding the inedible portions containing the seeds.
Some seeds have the ability to remain dormant and germinate when favorable conditions arise.

Terms

seed dormancy
a seed with the ability to delay germination and propagation of the species until suitable conditions are found
dispersal
the movement of a few members of a species to a new geographical area, resulting in differentiation of the original group into new varieties or species

Full Text

Fruit and Seed Dispersal

The fruit has a single purpose: seed dispersal. Seeds contained within fruits need to be dispersed far from the mother plant so that they may find favorable and less-competitive conditions in which to germinate and grow.

Some fruits have built-in mechanisms that allow them to disperse by themselves, whereas others require the help of agents such as wind, water, and animals. Modifications in seed structure, composition, and size aid in dispersal. Wind-dispersed fruit are lightweight and may have wing-like appendages that allow them to be carried by the wind. Some have a parachute-like structure to keep them afloat. Some fruits, such as the dandelion, have hairy, weightless structures that are suited to dispersal by wind .

Wind dispersal

Wind is used as a form of dispersal by lightweight seeds, such as those found on dandelions.

Seeds dispersed by water are contained in light and buoyant fruit, giving them the ability to float. Coconuts are well known for their ability to float on water to reach land where they can germinate. Similarly, willow and silver birches produce lightweight fruit that can float on water.

Animals and birds eat fruits; seeds that are not digested are excreted in their droppings some distance away. Some animals, such as squirrels, bury seed-containing fruits for later use; if the squirrel does not find its stash of fruit, and if conditions are favorable, the seeds germinate. Some fruits have hooks or sticky structures that stick to an animal's coat and are then transported to another place. Humans also play a major role in dispersing seeds when they carry fruits to new places, throwing away the inedible part that contains the seeds.

All of the above mechanisms allow for seeds to be dispersed through space, much as an animal's offspring can move to a new location. Seed dormancy allows plants to disperse their progeny through time: something animals cannot do. Dormant seeds can wait months, years, or even decades for the proper conditions for germination and propagation of the species.

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