Types of Seed Dispersal


Seed dispersal is an adaptive mechanism in all seed-bearing plants, participating in the movement, spread or transport of seeds away from their parent plant through different biotic (living) and abiotic (non-living) vectors to ensure the survival of the species. Seeds can be dispersed in an individual or collective manner, with their method of dispersal having important implications for the demographic and genetic structure of plant populations, as well as migration patterns and species interactions.

We distinguish six main types of seed dispersal, that can be classified into two main categories based on the type of vector used (external agent or plant’s own dispersal mechanism): autochorous plants, that disperse their seeds through explosive dehiscence (ballochory) or gravity (barochory); and allochorous plants, that disperse their seeds through animals (zoochory), wind (anemochory), water (hydrochory), and humans (anthropochory/hemerochory). Two other types of autochory, less common, are blastochory (where the stem of the plant crawls along the ground to deposit its seeds far from the base of the plant) and herpochory (where the seed crawls by means of trichomes and changes in humidity). Some plants are serotinous, only dispersing their seeds in response to an environmental stimulus such as fire (pyriscence)–a mechanism found in pines, cypresses, or sequoias.

Depending on the seed dispersal technique used by the plant, the seeds will feature specific characteristics and evolutionary traits aiming to facilitate their dispersal. Plants bearing seeds intended to be dispersed by wind are, for instance, much lighter and display wind-like apparatuses that allow them to be carried away from the parent plant. Longer dispersal distances can sometimes be accomplished through diplochory, a sequential dispersal using two or more vectors. Humans (anthropochory/hemerochory) are also known to disperse seeds over great distances through the use of various means such as clothes, shoes, or cars.

On the other hand, zoochorous plants usually use two dispersal mechanisms known as epizoochory, where seeds are carried on the fur of vertebrate animals through the use of stiff hairs, adhesive mucus, hooks, spines or barbs; and endozoochory, with the seeds being dispersed via ingestion and defecation by those animals (mostly birds and mammals) while providing a natural fertilizer that will help the seed to germinate. The latter is generally a coevolved mutualistic relationship in which the seeds are encased inside an edible, nutritious–and often colorful–fruit that will serve as a food resource for the animals. Numerous trees and shrubs disperse their seeds this way. Most seed-bearing fruits indeed produce a hormone that suppresses germination until the seeds pass through an animal’s digestive tract. At this stage, the hormone’s effect will dissipate and germination will occur once conditions are suitable. Some species lack this suppressant hormone as a central part of their reproductive strategy, in particular fruits that develop in climates without large seasonal variations.

Myrmecochory (seed dispersal by ants), another type of zoochory, also results from a coevolved mutualistic relationship. Seeds from those plants come with a lipid-rich fleshy structure, the elaiosome, which attracts ants. The ants will then carry the seeds into their colonies, feed the elaiosome to the larvae, and take the otherwise intact seed to their waste disposal area. Being rich in nutrients, this favorable environment will be particularly conductive to the germination of the seeds.