Myrmecochory
Encyclopedia
Seed dispersal
Seed dispersal is the movement or transport of seeds away from the parent plant. Plants have limited mobility and consequently rely upon a variety of dispersal vectors to transport their propagules, including both abiotic and biotic vectors. Seeds can be dispersed away from the parent plant...
by ants
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
, an ecologically significant ant-plant
Myrmecophily
Myrmecophily is the term applied to positive interspecies associations between ants and a variety of other organisms such as plants, arthropods, and fungi...
interaction
Biological interaction
Biological interactions are the effects organisms in a community have on one another. In the natural world no organism exists in absolute isolation, and thus every organism must interact with the environment and other organisms...
with worldwide distribution. Myrmecochorous plants produce seeds with elaiosomes
Elaiosome
Elaiosomes 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 elaiosomes to attract ants, which take the seed to their nest and feed the elaiosome to their larvae...
, a term encompassing various external appendages or "food bodies" rich in lipids
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
, amino acid, or other nutrients
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
that are attractive to ants. The seed with its attached elaiosome is collectively known as a diaspore
Diaspore (botany)
In botany, a diaspore is a plant dispersal unit consisting of a seed or spore plus any additional tissues that assist dispersal. In some seed plants, the diaspore is a seed and fruit together, or a seed and elaiosome. In a few seed plants, the diaspore is most or all of the plant, known as a...
. Seed dispersal by ants is typically accomplished when foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
workers carry diaspores back to the ant colony
Ant colony
An ant colony is an underground lair where ants live, eat and mate. Colonies consist of a series of underground chambers, connected to each other and the surface of the earth by small tunnels. There are rooms for nurseries, food storage, and mating...
after which the elaiosome
Elaiosome
Elaiosomes 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 elaiosomes to attract ants, which take the seed to their nest and feed the elaiosome to their larvae...
is removed or fed directly to ant larvae
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
. Once the elaiosome is consumed the seed is usually discarded in underground middens
Midden
A midden, is an old dump for domestic waste which may consist of animal bone, human excrement, botanical material, vermin, shells, sherds, lithics , and other artifacts and ecofacts associated with past human occupation...
or ejected from the nest. Although diaspores are seldom distributed far from the parent plant, myrmecochores also benefit from this predominantly mutualistic interaction through dispersal to favourable locations for germination
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
as well as escape from seed predation
Seed predation
Seed predation, often referred to as granivory, is a type of plant-animal interaction in which granivores feed on the seeds of plants as a main or exclusive food source, in many cases leaving the seeds damaged and not viable...
.
Distribution and diversity
Myrmecochory is exhibited by more than 3,000 plant speciesSpecies
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
worldwide and is present in every major biome
Biome
Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a...
on all continents except Antarctica. Seed dispersal by ants is particularly common in the dry heath
Heath
-Habitats:* Heath or heathland, low-growing woody vegetation, mostly consisting of heathers and related species* Heaths in the British National Vegetation Classification system...
and sclerophyll
Sclerophyll
Sclerophyll is the term for a type of vegetation that has hard leaves and short internodes . The word comes from the Greek sclero and phyllon ....
woodlands of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
(1,500 species) and the South African fynbos
Fynbos
Fynbos is the natural shrubland or heathland vegetation occurring in a small belt of the Western Cape of South Africa, mainly in winter rainfall coastal and mountainous areas with a Mediterranean climate...
(1,000 species). Both regions have a Mediterranean climate
Mediterranean climate
A Mediterranean climate is the climate typical of most of the lands in the Mediterranean Basin, and is a particular variety of subtropical climate...
and largely infertile soils (characterized by low phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
availability), two factors that are often cited to explain the distribution of myrmecochory. Myrmecochory is also present in mesic
Mesic habitat
In ecology, a mesic habitat is a type of habitat with a moderate or well-balanced supply of moisture, e.g., a mesic forest, a temperate hardwood forest, or dry-mesic prairie. Compared to a dry habitat, a mesic habitat is moister....
forests in temperate regions of the northern hemisphere (i.e. in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and in eastern North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
) as well as in tropical forests
Tropical and subtropical moist broadleaf forests
Tropical and subtropical moist broadleaf forests , also known as tropical moist forests, are a tropical and subtropical forest biome....
and dry deserts
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
, though to a lesser degree. Estimates for the true biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
of myrmecochorous plants range from 11,000 to as high as 23,000 species worldwide, or approximately 5% of all flowering plant
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
species.
Evolutionary history
Myrmecochory has evolved independently many times in a large number of plant familiesFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
. A recent phylogenetic study
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
identified more than 100 separate origins of myrmecochory in 55 families of flowering plants
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
. With many independent evolutionary origins, elaiosomes have evolved from a wide variety of parent tissues. Strong selective pressure
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
or the relative ease with which elaiosomes
Elaiosome
Elaiosomes 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 elaiosomes to attract ants, which take the seed to their nest and feed the elaiosome to their larvae...
can develop from parent tissues may explain the multiple origins of myrmecochory. These findings identify myrmecochory as a prime example of convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
. In addition, phylogenetic comparison of myrmecochorous plant groups reveal that more than half of the lineages in which myrmecochory evolved are more species rich than their non-myrmecochorous sister groups. Not only is myrmecochory a convergent trait, but it also promotes diversification in multiple flowering plants lineages.
Ecology
Myrmecochory is usually classified as a mutualism but this is contingent on the degree to which participating species benefit from the interactionBiological interaction
Biological interactions are the effects organisms in a community have on one another. In the natural world no organism exists in absolute isolation, and thus every organism must interact with the environment and other organisms...
. It is likely that several different factors combine to create mutualistic conditions. Myrmecochorous plants may derive benefit from increased dispersal distance, directed dispersal to nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
-enriched or protected microsites
Microsite (ecology)
A microsite is a term used in ecology to describe a pocket within an environment with unique features, conditions or characteristics. Classifying different microsites may depend on temperature, humidity, sunlight, nutrient availability, soil physical characterictics, vegetation cover, etc....
, and/or seed predator
Seed predation
Seed predation, often referred to as granivory, is a type of plant-animal interaction in which granivores feed on the seeds of plants as a main or exclusive food source, in many cases leaving the seeds damaged and not viable...
avoidance. Costs incurred by myrmecochorous plants include the energy required to provision
Provisioning (disambiguation)
The term provisioning can refer to:* in telecommunications:**Provisioning, equipping a telecommunications network* in shipping:**Provisioning, stocking materials or supplies; especially food...
diaspores, particularly when there is a disproportionate investment of growth-limiting mineral nutrients. For instance, some Australian Acacias
Acacia
Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carl Linnaeus in 1773. Many non-Australian species tend to be thorny, whereas the majority of Australian acacias are not...
invest a significant portion of their yearly phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
uptake in producing diaspores. Diaspores must also be protected from outright predation by ants. This is typically accomplished by the production of a hard, smooth testa, or seed coat.
Few studies have examined the costs and benefits to ants participating in myrmecochory. Much remains to be understood about the selective advantages conferred upon myrmecochorous ants.
No single hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
explains the evolution and persistence of myrmecochory. Instead, it is likely that a combination of beneficial effects working at different spatio-temporal scales contribute to the viability of this predominantly mutualistic interaction. Three commonly cited advantages to myrmecochorous plants are increased dispersal distance, directed dispersal, and seed predator avoidance.
Dispersal distance
Increasing dispersal distance from the parent plant is likely to reduce seed mortality resulting from density-dependent effectsJanzen-Connell hypothesis
The Janzen-Connell hypothesis is a widely accepted explanation for the maintenance of tree species biodiversity in tropical rainforests. It was published independently in the early 1970s by Daniel Janzen and Joseph Connell...
. Ants can transport seeds as far as 180 m but the average is less than 2 m, and values between 0.5 to 1.5 m are most common. Perhaps due to the relatively limited distance that ants disperse seeds, many myrmecochores exhibit diplochory: a two-staged dispersal mechanism, often with ballistic projection as the secondary mechanism, that can increase dispersal distance by as much as 50%. In some cases, ballistic dispersal distance regularly exceeds that of transport by ants. The dispersal distance achieved through myrmecochory is likely to provide an advantage proportionate to the spatial scale of density-dependent effects
Janzen-Connell hypothesis
The Janzen-Connell hypothesis is a widely accepted explanation for the maintenance of tree species biodiversity in tropical rainforests. It was published independently in the early 1970s by Daniel Janzen and Joseph Connell...
acting on individual plants. As such, the relatively modest distances ants transport seeds are likely to be more advantageous for myrmecochorous shrubs
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
, forbs
Forb
A forb is a herbaceous flowering plant that is not a graminoid . The term is used in biology and in vegetation ecology, especially in relation to grasslands and understory.-Etymology:...
, and other plants of small stature.
Directed dispersal
Myrmecochorous plants may benefit when ants disperse seeds to nutrient-rich or protected micrositesMicrosite (ecology)
A microsite is a term used in ecology to describe a pocket within an environment with unique features, conditions or characteristics. Classifying different microsites may depend on temperature, humidity, sunlight, nutrient availability, soil physical characterictics, vegetation cover, etc....
that enhance germination
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
and establishment of seedlings
Seedling
thumb|Monocot and dicot seedlingsA seedling is a young plant sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle , the hypocotyl , and the cotyledons...
. Ants disperse seeds in fairly predictable ways, either by disposing of them in underground middens
Midden
A midden, is an old dump for domestic waste which may consist of animal bone, human excrement, botanical material, vermin, shells, sherds, lithics , and other artifacts and ecofacts associated with past human occupation...
or by ejecting them from the nest
Ant colony
An ant colony is an underground lair where ants live, eat and mate. Colonies consist of a series of underground chambers, connected to each other and the surface of the earth by small tunnels. There are rooms for nurseries, food storage, and mating...
. These patterns of ant dispersal are predictable enough to permit plants to manipulate animal behaviour
Ethology
Ethology is the scientific study of animal behavior, and a sub-topic of zoology....
and influence seed fate, effectively directing the dispersal of seeds to desirable sites. For example, myrmecochores can influence seed fate by producing rounder, smoother diaspores that inhibit ants from re-dispersing seeds after elaiosome
Elaiosome
Elaiosomes 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 elaiosomes to attract ants, which take the seed to their nest and feed the elaiosome to their larvae...
removal. This increases the likelihood that seeds will remain underground instead of being ejected from the nest.
Nest chemistry is ideally suited for seed germination given that ant colonies
Ant colony
An ant colony is an underground lair where ants live, eat and mate. Colonies consist of a series of underground chambers, connected to each other and the surface of the earth by small tunnels. There are rooms for nurseries, food storage, and mating...
are typically enriched with plant nutrients such as phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
and nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
. This is likely to be advantageous in areas with infertile soils and less important in areas with more favourable soil chemistry, as in fertile forests. In fire-prone areas
Fire ecology
Fire ecology is concerned with the processes linking the natural incidence of fire in an ecosystem and the ecological effects of this fire. Many ecosystems, such as the North American prairie and chaparral ecosystems, and the South African savanna, have evolved with fire as a natural and necessary...
, depth of burial is an important factor for successful post-burn germination. This, in turn, is influenced by the nesting habits of the myrmecochorous ants. As such, the value of directed dispersal is largely context dependent.
Seed predator avoidance
Myrmecochorous plants escape or avoid seed predationSeed predation
Seed predation, often referred to as granivory, is a type of plant-animal interaction in which granivores feed on the seeds of plants as a main or exclusive food source, in many cases leaving the seeds damaged and not viable...
by granivores when ants remove and sequester diaspores. This benefit is particularly pronounced in areas where myrmecochorous plants are subject to heavy seed predation, which may be common. In mesic forest habitats seed predators remove approximately 60% of all dispersed seeds within a few days and eventually remove all seeds not removed by ants. In addition to attracting ants, elaiosomes also appeal to granivores, and their presence can increase seed predation rates.
Nature of the interaction
Myrmecochory is traditionally thought to be a diffuse or facultativeFacultative
Facultative means "optional" or "discretionary" , used mainly in biology in phrases such as:* Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production...
mutualism with low specificity
Generalist and specialist species
A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources . A specialist species can only thrive in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either...
between myrmecochores and individual ant species. This assertion has been challenged in a study of Iberian
Iberia
The name Iberia refers to three historical regions of the old world:* Iberian Peninsula, in Southwest Europe, location of modern-day Portugal and Spain** Prehistoric Iberia...
myrmecochores demonstrating the disproportionate importance of specific ant species in dispersing seeds. Ant-plant interactions with a single species of myrmecochore were recorded for 37 species of ant but only 2 of these were found to disperse diaspores to any significant degree; the rest were seed predators or “cheaters” opportunistically feeding on elaiosomes in situ without dispersing seeds. Larger diaspores are hypothesized to increase the degree of specialization
Generalist and specialist species
A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources . A specialist species can only thrive in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either...
since ant mutualists need to be larger to successfully carry the diaspore back to the nest.
Ants, however, do not appear to form obligate relationships with myrmecochorous plants. Since no known ant species relies entirely on elaiosomes for their nutritional needs, ants remain generalist
Generalist and specialist species
A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources . A specialist species can only thrive in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either...
foragers even when entering into relationships with a more specialized myrmecochore.
As with many other facultative mutualisms, cheating is present on both sides of the interaction. Ants cheat by consuming elaiosomes without transporting seeds or through outright seed predation. Myrmecochorous plants can also cheat, either by producing diaspores with non-removable elaiosomes or by simulating the presence of a non-existent reward with chemical cues
Chemical mimicry
Chemical mimicry is mimicry mediated via chemoreception . Chemical mimicry may be used in combination with mimicry in other sensory modes or by itself. This sort of mimicry is less obvious to humans and thus has not received as much attention from researchers as other forms have...
. Ants are sometimes capable of discriminating between cheaters and mutualists as shown by studies demonstrating preference for the diaspores of non-cheating myrmecochores. Cheating is also inhibited by ecological interactions external to the myrmecochorous interaction; simple models suggest that predation exerts a stabilizing influence on a mutualism such as myrmecochory.
Myrmecochory and invasive species
Myrmecochores are threatened by invasive speciesInvasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
in some ecosystems. For instance, the Argentine ant
Argentine ant
The Argentine ant, Linepithema humile, is a dark ant native to northern Argentina, Uruguay, Paraguay, and southern Brazil...
is an aggressive invader capable of displacing native ant populations. Since Argentine ants do not disperse seeds, invasions may lead to a breakdown in the myrmecochory mutualism, inhibiting the dispersal ability of myrmecochores and causing long-term alterations in plant community dynamics. Invasive ant species can also maintain or even increase seed dispersal in their introduced range, as is the case with the red fire ant
Red imported fire ant
See main article Fire ant.The red imported fire ant , or simply RIFA, is one of over 280 species in the widespread genus Solenopsis...
in the southeastern United States.
Myrmecochorous plants are also capable of invading ecosystems. These invaders may gain an advantage in areas where native ants disperse invasive seeds. Similarly, the spread of myrmecochorous invaders may be inhibited by limitations in the ranges of native ant populations.
See also
- ElaiosomeElaiosomeElaiosomes 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 elaiosomes to attract ants, which take the seed to their nest and feed the elaiosome to their larvae...
- MyrmecophilyMyrmecophilyMyrmecophily is the term applied to positive interspecies associations between ants and a variety of other organisms such as plants, arthropods, and fungi...
- MyrmecophyteMyrmecophyteMyrmecophyte is a plant that lives in a mutualistic association with a colony of ants. There are over 100 different genera of myrmecophytes. These plants possess structural adaptations that provide ants with food and/or shelter. These specialized structures include domatia, food bodies, and...
- Seed dispersalSeed dispersalSeed dispersal is the movement or transport of seeds away from the parent plant. Plants have limited mobility and consequently rely upon a variety of dispersal vectors to transport their propagules, including both abiotic and biotic vectors. Seeds can be dispersed away from the parent plant...