Seed dispersal is the term coined for the movement of the seed from one place to another. This movement generally occurs with the help of dispersal vectors. Dispersal vectors can be biotic or abiotic components. Biotic dispersal vectors include animals, bees, and other insects whereas abiotic factors are wind, and water.
The need for dispersion arises because plants need to transport their seed far from the parental plant, this is done to reduce the intraspecific competition between the parent and progeny. The pattern of seed dispersion is greatly dependent on the dispersal vector that is being used. The following are the main types of dispersion mode - gravity, wind, water, animal, and animals. The dispersal unit of the plant is known as the diaspora, it includes seeds and additional tissue that assists in the seed dispersion.
Seed dispersal can be broadly classified into autochory and allochory. Autochory refers to the dispersion of the diaspore without any help from the external environment, whereas allochory refers to the dispersion of seed with the help of dispersal vectors. Ballistic and dispersion through gravity comes under the autochory mode of dispersion. Ballistic dispersion refers to the condition when a seed is ejected by the dehiscence of the fruit.
Dispersal by Animals
Seed dispersal by animals comes under the category of the allochory. Dispersal by the animal is termed as zoochory, zoochory. It can be further classified into saurochory, ornithochory, and, myrmecochory, which means dispersion by reptiles, birds, and ants respectively. Based on the way of carrying the diaspore zoochory can be classified as endozoochory, epizoochory, and synzoochory.
It is the condition when seeds are carried within the dispersal vectors, which are animals in this case. It is an example of mutualism between plant and animal. In this type seed is generally inside the fruit, animals that perform dispersion eat the fruit surrounding the seed and discard the seed at a distant location, thus performing dispersion. The plant provides fruit to meet the nutritional requirements of the animal whereas the animal helps in plant survival by allowing it to grow in various locations, thus both the species mutually benefited from the seed dispersal by animals.
It is the condition when an animal carries the diaspore outside its body. This condition arises in the case of accidental dispersion of the seed by animals. When animals or birds pass by the seed some of the seed might get attached to the body of the animal and move along with it, diaspore than generally falls at a distant location from the parental plant.
It is a condition when the diaspore seed has not completely entered the alimentary canal of animals rather they carry the seed in their mouth. Synzoochory is often seen in seed dispersal by squirrels. It is also done by rodents and birds. Synzoochory has a characteristic feature, the seed is generally a nut that is used as a food source by the animals.
Diplochory is also considered as a type of synzoochory where it is indirect or two-step dispersion by an animal, this occurs when the nut is the food source of more than one species. It is a highly effective way of dispersion.
Example of Seed Dispersal by Animals
There are the following examples of seed dispersion by animals
Cucumis humifructus, South African melon is the food source of aardvarks, the bird which disperses its seed.
Seeds of Sonneratia are dispersed by catfish Arius maculatus.
Seeds of mango are commonly dispersed by monkeys and chipmunks.
Seeds of mango, guava, and other fruits are dispersed by bats. Dispersion by a bat is known as chiropterochory.
Rodents and squirrels perform the dispersal of nuts such as hazelnut, walnut, peanuts, etc.
Birds also help in the dispersal of seeds such as nuts and small berries.
Dispersal by Water
Hydrochory is termed used for water dispersal seeds, that is seeds are dispersed into water and moves along the direction of the flow of water. When the seeds reach a distant location where it can find all the necessary requirements for growth it anchors to the point and start germination. Hydrochory comes under the category of autochory. It is most preferable for the seeds that have some resistance to water-based rotting and can float on water. Mangrove trees are the best examples, they grow in water and their maturity seeds falls off into the water and is carried away with the tides as soon as it reaches the soil it germinates leading to the growth of population in a distant area.
Characteristics of Seed Dispersal by Water - There are some characteristic features of hydrochory they are as follows,
Diaspore must be lightweight and hollow
Diaspora can swim
They generally have long filaments
They generally do not produce nectar
They are not usually very colorful
They must have the property of hygrochasy, that is seed can germinate in moist weather.
Example of Seed Dispersal by Water
There are some of the following examples of water dispersal of seeds,
Mangrove plants are the best example of hydrochory.
Aster tripolium and Juncus species are some examples of hydrochory where seeds are transported to distant areas
Mesembryanthemum, Sedum, and other plants show characteristic feature of hygrochasy.
Sea dispersal of the coconut palm is the best-studied common example of hydrochory.
Some other examples of plants that use water for seed dispersal are water plantain, yellow flag, sea kale, sea rocket, sea beet.