Dispersal vector

A dispersal vector is an agent of biological dispersal that moves a dispersal unit, or organism, away from its birth population to another location or population in which the individual will reproduce. These dispersal units can range from pollen to seeds to fungi to entire organisms.

There are two types of dispersal vector, those that are active and those that are passive. Active dispersal involves pollen, seeds and fungal spores that are capable of movement under their own energy. Passive dispersal involves those that rely on the kinetic energy of the environment to move. In plants, some dispersal units have tissue that assists with dispersal and are called diaspores. Some types of dispersal are self-driven (autochory), such as using gravity (barochory), and does not rely on external agents. Other types of dispersal are due to external agents, which can be other organisms, such as animals (zoochory), or non-living vectors, such as the wind (anemochory) or water (hydrochory).

In many cases, a dispersal unit will be dispersed by more than one vector before reaching its final destination. It is often a combination of two or more modes of dispersal that act together to maximize dispersal distance, such as wind blowing a seed into a nearby river, that will carry it farther down stream.

Autochory is the dispersal of diaspores, which are dispersal units consisting of seeds or spores, using only the energy provided by the diaspore or the parent plant. The plant of origin is the dispersal agent itself, instead of an external agent. There are five main types of autochory that act on such seeds or spores: ballochory, or violent ejection by the parent organism; blastochory, or crawling with horizontal runners; barochory, or relying on gravity for dispersal; herpochory, or crawling with fine hair-like structures called trichomes; or being pushed or twisted into the ground by hygromorphic awns in response to humidity changes, e.g. Erodium cicutarium.

In some cases, ballochory can be more effective when combined with a secondary dispersal vector: ejecting the seeds or spores in order for them to use wind or water for longer distance dispersal.

Dispersal by animals is called zoochory. Zoochory can be specified by which animal is acting as a dispersal vector. Animals are an important dispersal vector because they provide the ability to transfer dispersal units longer distances than their parent organism can. The main groups include dispersal by birds (ornithochory), dispersal by ants (myrmecochory), dispersal by mammals (mammaliochory), dispersal by amphibians or reptiles, and dispersal by insects, such as bees.

Animals are also a large contributor to pollination via zoophily. Flowering plants are mainly pollinated by animals, and while invertebrates are involved in the majority of that pollination, birds and mammals also play a role.

Birds contribute to seed dispersal in several ways that are unique from general vectors. Birds often cache, or store, the seeds of trees and shrubs to consume later. Only some of these seeds are later recovered and eaten, so many of the seeds are able to use the behavior of seed storage to allow them to germinate away from the mother tree.