In
Spermatophyte
A spermatophyte (; ), also known as phanerogam (taxon Phanerogamae) or phaenogam (taxon Phaenogamae), is any plant that produces seeds, hence the alternative name seed plant. Spermatophytes are a subset of the embryophytes or land plants. They inc ...
plants, seed dispersal is the movement, spread or transport of
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
s away from the parent plant.
[
] Plants have limited mobility and rely upon a variety of
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 t ...
s to transport their seeds, including both
abiotic
In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them under ...
vectors, such as the wind, and living (
biotic) vectors such as birds. Seeds can be dispersed away from the parent plant individually or collectively, as well as dispersed in both space and time. The patterns of seed dispersal are determined in large part by the dispersal mechanism and this has important implications for the demographic and genetic structure of plant populations, as well as
migration
Migration, migratory, or migrate may refer to: Human migration
* Human migration, physical movement by humans from one region to another
** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
patterns and species interactions. There are five main modes of seed dispersal:
gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
, wind, ballistic, water, and by animals. Some plants are
serotinous
Serotiny in botany simply means 'following' or 'later'.
In the case of serotinous flowers, it means flowers which grow following the growth of leaves, or even more simply, flowering later in the season than is customary with allied species. Havi ...
and only disperse their seeds in response to an environmental stimulus. These modes are typically inferred based on adaptations, such as wings or fleshy fruit.
However, this simplified view may ignore complexity in dispersal. Plants can disperse via modes without possessing the typical associated adaptations and plant traits may be multifunctional.
Benefits
Seed dispersal is likely to have several benefits for different plant species. Seed survival is often higher away from the parent plant. This higher survival may result from the actions of density-dependent
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
and seedling predators and
pathogens
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
, which often target the high concentrations of seeds beneath adults.
Competition
Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indivi ...
with adult plants may also be lower when seeds are transported away from their parent.
Seed dispersal also allows plants to reach specific habitats that are favorable for survival, a hypothesis known as
directed dispersal
Director may refer to:
Literature
* ''Director'' (magazine), a British magazine
* ''The Director'' (novel), a 1971 novel by Henry Denker
* ''The Director'' (play), a 2000 play by Nancy Hasty
Music
* Director (band), an Irish rock band
* ''Di ...
. For example, ''Ocotea endresiana'' (Lauraceae) is a tree species from Latin America which is dispersed by several species of birds, including the
three-wattled bellbird
The three-wattled bellbird (''Procnias tricarunculatus'') is a Central American migratory bird of the cotinga family. The sexes are very dissimilar in appearance. The male has a white head and throat and the remaining plumage is chestnut brown. F ...
. Male bellbirds perch on dead trees in order to attract mates, and often defecate seeds beneath these perches where the seeds have a high chance of survival because of high light conditions and escape from fungal pathogens.
In the case of fleshy-fruited plants, seed-dispersal in animal guts (endozoochory) often enhances the amount, the speed, and the asynchrony of germination, which can have important plant benefits.
Seeds dispersed by ants (
myrmecochory
Myrmecochory ( (sometimes myrmechory); from grc, μύρμηξ, mýrmēks ("ant") and ''khoreíā'' ("circular dance") is seed dispersal by ants, an ecologically significant ant–plant interaction with worldwide distribution. Most myrmeco ...
) are not only dispersed short distances but are also buried underground by the ants. These seeds can thus avoid adverse environmental effects such as fire or drought, reach nutrient-rich microsites and survive longer than other seeds.
These features are peculiar to myrmecochory, which may thus provide additional benefits not present in other dispersal modes.
Seed dispersal may also allow plants to colonize vacant habitats and even new geographic regions.
Dispersal distances and deposition sites depend on the movement range of the disperser, and longer dispersal distances are sometimes accomplished through
diplochory Diplochory, also known as “secondary dispersal”, “indirect dispersal” or "two-phase dispersal", is a seed dispersal mechanism in which a plant's seed is moved sequentially by more than one dispersal mechanism or vector.
The significance of ...
, the sequential dispersal by two or more different dispersal mechanisms. In fact, recent evidence suggests that the majority of seed dispersal events involves more than one dispersal phase.
Types
Seed dispersal is sometimes split into ''autochory'' (when dispersal is attained using the plant's own means) and ''allochory'' (when obtained through external means).
Long distance
Long-distance seed dispersal (LDD) is a type of spatial dispersal that is currently defined by two forms, proportional and actual distance. A plant's fitness and survival may heavily depend on this method of seed dispersal depending on certain environmental factors. The first form of LDD, proportional distance, measures the percentage of seeds (1% out of total number of seeds produced) that travel the farthest distance out of a 99% probability distribution.
The proportional definition of LDD is in actuality a descriptor for more extreme dispersal events. An example of LDD would be that of a plant developing a specific dispersal vector or morphology in order to allow for the dispersal of its seeds over a great distance. The actual or absolute method identifies LDD as a literal distance. It classifies 1 km as the threshold distance for seed dispersal. Here, threshold means the minimum distance a plant can disperse its seeds and have it still count as LDD.
There is a second, unmeasurable, form of LDD besides proportional and actual. This is known as the non-standard form. Non-standard LDD is when seed dispersal occurs in an unusual and difficult-to-predict manner. An example would be a rare or unique incident in which a normally-lemur-dependent deciduous tree of Madagascar was to have seeds transported to the coastline of South Africa via attachment to a mermaid purse (egg case) laid by a shark or skate.
A driving factor for the evolutionary significance of LDD is that it increases plant fitness by decreasing neighboring plant competition for offspring. However, it is still unclear today as to how specific traits, conditions and trade-offs (particularly within short seed dispersal) affect LDD evolution.
Autochory
![Geranium sanguineum02](https://upload.wikimedia.org/wikipedia/commons/a/af/Geranium_sanguineum02.jpg)
Autochorous plants disperse their seed without any help from an external vector, as a result this limits plants considerably as to the distance they can disperse their seed.
Two other types of autochory not described in detail here are blastochory, where the stem of the plant crawls along the ground to deposit its seed far from the base of the plant, and herpochory (the seed crawls by means of
trichome
Trichomes (); ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a pla ...
s and changes in humidity).
Gravity
''
Barochory'' or the plant use of gravity for dispersal is a simple means of achieving seed dispersal. The effect of
gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
on heavier fruits causes them to fall from the plant when ripe. Fruits exhibiting this type of dispersal include
apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
s,
coconut
The coconut tree (''Cocos nucifera'') is a member of the palm tree family ( Arecaceae) and the only living species of the genus ''Cocos''. The term "coconut" (or the archaic "cocoanut") can refer to the whole coconut palm, the seed, or the ...
s and
passionfruit
''Passiflora edulis,'' commonly known as passion fruit, is a vine species of passion flower native to southern Brazil through Paraguay and northern Argentina. It is cultivated commercially in tropical and subtropical areas for its sweet, seedy f ...
and those with harder shells (which often roll away from the plant to gain more distance). Gravity dispersal also allows for later transmission by water or animal.
Ballistic dispersal
''Ballochory'' is a type of dispersal where the seed is forcefully ejected by
explosive dehiscence
Dehiscence is the splitting of a mature plant structure along a built-in line of weakness to release its contents. This is common among fruits, anthers and sporangia. Sometimes this involves the complete detachment of a part; structures that op ...
of the fruit. Often the force that generates the explosion results from
turgor pressure
Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall.
It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilibri ...
within the fruit or due to internal tensions within the fruit.
Some examples of plants which disperse their seeds autochorously include: ''
Arceuthobium spp.'', ''
Cardamine hirsuta
''Cardamine hirsuta'', commonly called hairy bittercress, is an annual or biennial species of plant in the family Brassicaceae, and is edible as a salad green. It is common in moist areas around the world.
Description
Depending on the climate ...
'', ''
Ecballium spp.'', ''
Euphorbia heterophylla
''Euphorbia heterophylla'', also known under the common names of Mexican fireplant, painted euphorbia, Japanese poinsettia, paintedleaf, painted spurge and milkweed, is a plant belonging to the Euphorbiaceae or spurge family.
Distribution
''Euph ...
'', ''
Geranium spp.'', ''
Impatiens spp.'', ''
Sucrea spp'', ''
Raddia spp.''
and others. An exceptional example of ballochory is ''
Hura crepitans
''Hura crepitans'', the sandbox tree, also known as possumwood and jabillo, is an evergreen tree of the spurge family (Euphorbiaceae), native to tropical regions of North and South America including the Amazon rainforest. It is also present in p ...
''—this plant is commonly called the dynamite tree due to the sound of the fruit exploding. The explosions are powerful enough to throw the seed up to 100 meters.
Witch hazel
Witch-hazels or witch hazels (''Hamamelis'') are a genus of flowering plants in the family Hamamelidaceae, with three species in North America ('' H. ovalis'', '' H. virginiana'', and '' H. vernalis''), and one each in Japan ('' H.&nb ...
uses ballistic dispersal without explosive mechanisms by simply squeezing the seeds out at approx. 45 km/h (28 mph).
Allochory
Allochory refers to any of many types of seed dispersal where a vector or secondary agent is used to disperse seeds. These vectors may include wind, water, animals or others.
Wind
![Entada phaseoloides MHNT graines](https://upload.wikimedia.org/wikipedia/commons/4/43/Entada_phaseoloides_MHNT_graines.jpg)
Wind dispersal (''anemochory'') is one of the more primitive means of dispersal. Wind dispersal can take on one of two primary forms: seeds or fruits can float on the breeze or, alternatively, they can flutter to the ground. The classic examples of these dispersal mechanisms, in the temperate northern hemisphere, include
dandelions
''Taraxacum'' () is a large genus of flowering plants in the family Asteraceae, which consists of species commonly known as dandelions. The scientific and hobby study of the genus is known as taraxacology. The genus is native to Eurasia and Nor ...
, which have a feathery
pappus attached to their fruits (
achenes
An achene (; ), also sometimes called akene and occasionally achenium or achenocarp, is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and indehiscent (they do not ope ...
) and can be dispersed long distances, and
maple
''Acer'' () is a genus of trees and shrubs commonly known as maples. The genus is placed in the family Sapindaceae.Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 nd more or less continuously updated since http ...
s, which have winged fruits (
samaras) that flutter to the ground.
An important constraint on wind dispersal is the need for abundant seed production to maximize the likelihood of a seed landing in a site suitable for
germination
Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...
. Some wind-dispersed plants, such as the dandelion, can adjust their morphology in order to increase or decrease the rate of germination. There are also strong evolutionary constraints on this dispersal mechanism. For instance, Cody and Overton (1996) found that species in the Asteraceae on islands tended to have reduced dispersal capabilities (i.e., larger
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
and smaller pappus) relative to the same species on the mainland. Also, ''
Helonias bullata
''Helonias bullata'' (swamp pink) is a rare perennial rhizomatous herb native to the eastern United States, the only known species in the genus ''Helonias''. The root system is extensive in comparison to the apparent size of the plant on the surf ...
'', a species of perennial herb native to the United States, evolved to utilize wind dispersal as the primary seed dispersal mechanism; however, limited wind in its habitat prevents the seeds to successfully disperse away from its parents, resulting in clusters of population. Reliance on wind dispersal is common among many
weed
A weed is a plant considered undesirable in a particular situation, "a plant in the wrong place", or a plant growing where it is not wanted.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. ...
y or
ruderal
A ruderal species is a plant species that is first to colonize disturbed lands. The disturbance may be natural for example, wildfires or avalanchesor the consequences of human activities, such as construction ( of roads, of buildings, mining, et ...
species. Unusual mechanisms of wind dispersal include
tumbleweed
A tumbleweed is a structural part of the above-ground anatomy of a number of species of plants. It is a diaspore that, once mature and dry, detaches from its root or stem and rolls due to the force of the wind. In most such species, the tumble ...
s, where the entire plant (except for the roots) is blown by the wind. ''
Physalis
''Physalis'' (, , , , from φυσαλλίς ''phusallís'' "bladder") is a genus of approximately 75 to 90 flowering plants in the Solanum, nightshade family (biology), family (Solanaceae), which are native to the Americas and Australasia. At l ...
'' fruits, when not fully ripe, may sometimes be dispersed by wind due to the space between the fruit and the covering
calyx which acts as an air bladder.
Water
Many
aquatic (water dwelling) and some
terrestrial
Terrestrial refers to things related to land or the planet Earth.
Terrestrial may also refer to:
* Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...
(land dwelling) species use ''hydrochory'', or seed dispersal through water. Seeds can travel for extremely long distances, depending on the specific mode of
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
dispersal; this especially applies to fruits which are waterproof and float on water.
The
water lily is an example of such a plant. Water lilies' flowers make a
fruit
In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.
Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
that floats in the water for a while and then drops down to the bottom to take
root
In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...
on the floor of the
pond
A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Defining them to be less than in area, less than deep, and with less than 30% emergent vegetation helps in distinguishing their ecology from th ...
.
The seeds of
palm tree
The Arecaceae is a family of perennial flowering plants in the monocot order Arecales. Their growth form can be climbers, shrubs, tree-like and stemless plants, all commonly known as palms. Those having a tree-like form are called palm trees ...
s can also be dispersed by water. If they grow near
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
s, the seeds can be transported by
ocean current
An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, s ...
s over long distances, allowing the seeds to be dispersed as far as other
continent
A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...
s.
Mangrove
A mangrove is a shrub or tree that grows in coastal saline water, saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evoluti ...
trees grow directly out of the water; when their seeds are ripe they fall from the
tree
In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
and grow
root
In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...
s as soon as they touch any kind of soil. During low tide, they might fall in soil instead of water and start growing right where they fell. If the water level is high, however, they can be carried far away from where they fell. Mangrove trees often make little
island
An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island ...
s as dirt and detritus collect in their roots, making little bodies of land.
Animals: epi- and endozoochory
![Epizoochory - black Labrador with hooked Geum fruits in his fur](https://upload.wikimedia.org/wikipedia/commons/6/61/Epizoochory_-_black_Labrador_with_hooked_Geum_fruits_in_his_fur.jpg)
Animals can disperse plant seeds in several ways, all named ''zoochory''. Seeds can be transported on the outside of vertebrate animals (mostly mammals), a process known as ''epizoochory''. Plant species transported externally by animals can have a variety of adaptations for dispersal, including adhesive mucus, and a variety of hooks, spines and barbs.
A typical example of an epizoochorous plant is ''Trifolium angustifolium'', a species of
Old World
The "Old World" is a term for Afro-Eurasia that originated in Europe , after Europeans became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia, which were previously thought of by the ...
clover
Clover or trefoil are common names for plants of the genus ''Trifolium'' (from Latin ''tres'' 'three' + ''folium'' 'leaf'), consisting of about 300 species of flowering plants in the legume or pea family Fabaceae originating in Europe. The genus ...
which adheres to animal fur by means of stiff
hair
Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals.
The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and f ...
s covering the
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
.
Epizoochorous plants tend to be herbaceous plants, with many representative species in the families
Apiaceae
Apiaceae or Umbelliferae is a family of mostly aromatic flowering plants named after the type genus ''Apium'' and commonly known as the celery, carrot or parsley family, or simply as umbellifers. It is the 16th-largest family of flowering plants ...
and
Asteraceae
The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...
.
However, epizoochory is a relatively rare dispersal syndrome for plants as a whole; the percentage of plant species with seeds adapted for transport on the outside of animals is estimated to be below 5%.
Nevertheless, epizoochorous transport can be highly effective if seeds attach to wide-ranging animals. This form of seed dispersal has been implicated in rapid plant migration and the spread of invasive species.
Seed dispersal via ingestion and
defecation
Defecation (or defaecation) follows digestion, and is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. The act has a variety of names ranging f ...
by vertebrate animals (mostly birds and mammals), or ''endozoochory'', is the dispersal mechanism for most tree species.
Endozoochory is generally a coevolved mutualistic relationship in which a plant surrounds seeds with an edible, nutritious
fruit
In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.
Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
as a good food resource for animals that consume it. Such plants may advertise the presence of food resource by using colour. Birds and mammals are the most important seed dispersers, but a wide variety of other animals, including turtles, fish, and insects (e.g.
tree wētā
Tree wētā are wētā in the genus ''Hemideina'' of the family Anostostomatidae. The genus is endemic to New Zealand. There are seven species within the genus ''Hemideina'', found throughout the country except lowland Otago and Southland. Beca ...
and
scree wētā), can transport viable seeds. The exact percentage of tree species dispersed by endozoochory varies between
habitats
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
, but can range to over 90% in some tropical rainforests.
Seed dispersal by animals in tropical rainforests has received much attention, and this interaction is considered an important force shaping the ecology and evolution of vertebrate and tree populations. In the tropics, large animal seed dispersers (such as
tapirs
Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a pig, with a short, prehensile nose trunk. Tapirs inhabit jungle and forest regions of South and Central America, with one species inhabit ...
,
chimpanzees
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative the ...
,
black-and-white colobus
Black-and-white colobuses (or colobi) are Old World monkeys of the genus ''Colobus'', native to Africa. They are closely related to the red colobus monkeys of genus '' Piliocolobus''. There are five species of this monkey, and at least eight subs ...
,
toucans
Toucans (, ) are members of the Neotropical near passerine bird family Ramphastidae. The Ramphastidae are most closely related to the American barbets. They are brightly marked and have large, often colorful bills. The family includes five gen ...
and
hornbills
Hornbills (Bucerotidae) are a family of bird found in tropical and subtropical Africa, Asia and Melanesia. They are characterized by a long, down-curved bill which is frequently brightly coloured and sometimes has a casque on the upper mandibl ...
) may disperse large seeds with few other seed dispersal agents. The extinction of these large
frugivore
A frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds. Approximately 20% of mammalian herbivores eat fruit. Frugivores are highly dependent on the abundance an ...
s from poaching and habitat loss may have negative effects on the tree populations that depend on them for seed dispersal and reduce genetic diversity. A variation of endozoochory is regurgitation of seeds rather than their passage in
faeces
Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...
after passing through the entire digestive tract. The seed dispersal by birds and other mammals are able to attach themselves to the feathers and hairs of these vertebrates, which is their main method of dispersal.
Seed dispersal by ants (''
myrmecochory
Myrmecochory ( (sometimes myrmechory); from grc, μύρμηξ, mýrmēks ("ant") and ''khoreíā'' ("circular dance") is seed dispersal by ants, an ecologically significant ant–plant interaction with worldwide distribution. Most myrmeco ...
'') is a dispersal mechanism of many shrubs of the southern hemisphere or understorey herbs of the northern hemisphere.
[ Seeds of myrmecochorous plants have a lipid-rich attachment called the ]elaiosome
Elaiosomes ( grc, ἔλαιον ''élaion'' "oil" + ''sóma'' "body") are fleshy structures that are attached to the seeds of many plant species. The elaiosome is rich in lipids and proteins, and may be variously shaped. Many plants have elaio ...
, which attracts ants. Ants carry such seeds into their colonies, feed the elaiosome to their larvae and discard the otherwise intact seed in an underground chamber. Myrmecochory is thus a coevolved mutualistic relationship between plants and seed-disperser ants. Myrmecochory has independently evolved at least 100 times in flowering plants and is estimated to be present in at least 11 000 species, but likely up to 23 000 or 9% of all species of flowering plants.[ Myrmecochorous plants are most frequent in the fynbos vegetation of the Cape Floristic Region of South Africa, the kwongan vegetation and other dry habitat types of Australia, dry forests and grasslands of the Mediterranean region and northern temperate forests of western Eurasia and eastern North America, where up to 30–40% of understorey herbs are myrmecochorous.][ Seed dispersal by ants is a mutualistic relationship and benefits both the ant and the plant.]
Seed predators, which include many rodents (such as squirrels) and some birds (such as jays) may also disperse seeds by hoarding the seeds in hidden caches. The seeds in caches are usually well-protected from other seed predators and if left uneaten will grow into new plants. In addition, rodents may also disperse seeds via seed spitting due to the presence of secondary metabolites
Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, fungi, animals, or plants, which are not directly involved in the nor ...
in ripe fruits. Finally, seeds may be secondarily dispersed from seeds deposited by primary animal dispersers, a process known as diplochory Diplochory, also known as “secondary dispersal”, “indirect dispersal” or "two-phase dispersal", is a seed dispersal mechanism in which a plant's seed is moved sequentially by more than one dispersal mechanism or vector.
The significance of ...
. For example, dung beetles are known to disperse seeds from clumps of feces in the process of collecting dung to feed their larvae.
Other types of zoochory are ''chiropterochory'' (by bats), ''malacochory'' (by molluscs, mainly terrestrial snails), ''ornithochory'' (by birds) and ''saurochory'' (by non-bird sauropsids). Zoochory can occur in more than one phase, for example through ''diploendozoochory'', where a primary disperser (an animal that ate a seed) along with the seeds it is carrying is eaten by a predator that then carries the seed further before depositing it.
Humans
Dispersal by humans ('' anthropochory'') used to be seen as a form of dispersal by animals. Its most widespread and intense cases account for the planting of much of the land area on the planet, through agriculture. In this case, human societies form a long-term relationship with plant species, and create conditions for their growth.
Recent research points out that human dispersers differ from animal dispersers by having a much higher mobility, based on the technical means of human transport. On the one hand, dispersal by humans also acts on smaller, regional scales and drives the dynamics of existing biological population
Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...
s. On the other hand, dispersal by humans may act on large geographical scales and lead to the spread of invasive species
An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
.
Humans may disperse seeds by many various means and some surprisingly high distances have been repeatedly measured. Examples are: dispersal on human clothes (up to 250 m), on shoes (up to 5 km), or by cars (regularly ~ 250 m, singles cases > 100 km). Seed dispersal by cars can be a form of unintentional transport of seeds by humans, which can reach far distances, greater than other conventional methods of dispersal. Cars that carry soil are able to contain viable seeds, a study by Dunmail J. Hodkinson and Ken Thompson found that the most common seeds that were carried by vehicle were broadleaf plantain
''Plantago major'', the broadleaf plantain, white man's footprint, waybread, or greater plantain, is a species of flowering plant in the plantain family Plantaginaceae. The plant is native to Eurasia.
The young, tender leaves can be eaten raw, ...
(''Plantago major''), Annual meadow grass (''Poa annua''), rough meadow grass (''Poa trivialis''), stinging nettle
''Urtica dioica'', often known as common nettle, burn nettle, stinging nettle (although not all plants of this species sting) or nettle leaf, or just a nettle or stinger, is a herbaceous perennial flowering plant in the family Urticaceae. Or ...
(''Urtica dioica'') and wild chamomile (''Matricaria discoidea'').
Deliberate seed dispersal also occurs as seed bombing. This has risks, as unsuitable provenance may introduce genetically unsuitable plants to new environments.
Consequences
Seed dispersal has many consequences for the ecology and evolution of plants. Dispersal is necessary for species migrations, and in recent times dispersal ability is an important factor in whether or not a species transported to a new habitat by humans will become an invasive species. Dispersal is also predicted to play a major role in the origin and maintenance of species diversity. For example, myrmecochory increased the rate of diversification more than twofold in plant groups in which it has evolved because myrmecochorous lineages contain more than twice as many species as their non-myrmecochorous sister groups. Dispersal of seeds away from the parent organism has a central role in two major theories for how biodiversity is maintained in natural ecosystems, the Janzen-Connell hypothesis and recruitment limitation. Seed dispersal is essential in allowing forest migration Forest migration or assisted migration is the movement of large seed plant dominated communities in geographical space over time.
The emphasis of forest migration is placed on the movement of the populations that make up the forest community. Thou ...
of flowering plants. It can be influenced by the production of different fruit morphs in plants, a phenomenon known as heterocarpy. These fruit morphs are different in size and shape and have different dispersal ranges, which allows seeds to be dispersed for varying distances and adapt to different environments.
In addition, the speed and direction of wind are highly influential in the dispersal process and in turn the deposition patterns of floating seeds in the stagnant water bodies. The transportation of seeds is led by the wind direction. This effects colonization situated on the banks of a river or to wetlands adjacent to streams relative to the distinct wind directions. The wind dispersal process can also affect connections between water bodies. Essentially, wind plays a larger role in the dispersal of waterborne seeds in a short period of time, days and seasons, but the ecological process allows the process to become balanced throughout a time period of several years. The time period of which the dispersal occurs is essential when considering the consequences of wind on the ecological process.
See also
*Biological dispersal
Biological dispersal refers to both the movement of individuals (animals, plants, fungi, bacteria, etc.) from their birth site to their breeding site ('natal dispersal'), as well as the movement from one breeding site to another ('breeding dis ...
* Biantitropical distribution
*Disturbance (ecology)
In ecology, a disturbance is a temporary change in environmental conditions that causes a pronounced change in an ecosystem. Disturbances often act quickly and with great effect, to alter the physical structure or arrangement of biotic and abiotic ...
*Dormancy
Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be clo ...
– "dispersal in time"
*Gene flow
In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent a ...
*Habitat fragmentation
Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes ...
*Landscape ecology
Landscape ecology is the science of studying and improving relationships between ecological processes in the environment and particular ecosystems. This is done within a variety of landscape scales, development spatial patterns, and organizati ...
*Metapopulation
A metapopulation consists of a group of spatially separated populations of the same species which interact at some level. The term metapopulation was coined by Richard Levins in 1969 to describe a model of population dynamics of insect pests in ...
*Oceanic dispersal
Oceanic dispersal is a type of biological dispersal that occurs when terrestrial organisms transfer from one land mass to another by way of a sea crossing. Island hopping is the crossing of an ocean by a series of shorter journeys between island ...
*Population ecology
Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment, such as birth and death rates, and by immigration and emigration.
The discipline is importa ...
*Seed dispersal syndrome Seed dispersal syndromes are morphological characters of seeds correlated to particular seed dispersal agents.Clobert, J., Le Galliard, J.F., Cote, J., Meylan, S. & Massot, M. (2009). Informed dispersal, heterogeneity in animal dispersal syndromes a ...
References
Further reading
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External links
Fruit and seed dispersal images at bioimages.vanderbilt.edu
* ttps://www.youtube.com/watch?v=BaTFV0Jo26Y Secondary metabolites promote seed dispersal
{{Authority control
Seeds
Ecology
Articles containing video clips