A
frugivore is a fruit eater. It can be any type of
herbivoreHerbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
or
omnivoreOmnivores are species that eat both plants and animals as their primary food source...
where
fruitIn broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
is a preferred food type. Because approximately 20% of all
mammalMammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian herbivores also eat fruit, frugivory is considered to be common among mammals. Since frugivores eat a lot of fruit they are highly dependent on the abundance and nutritional composition of fruits. Frugivores can either benefit fruit-producing plants by dispersing seeds, or they can negatively affect plants by digesting seeds along with the fruits. When both the fruit-producing plant and the frugivore species benefit by fruit-eating behavior their interaction is called a mutualism.
Frugivore seed dispersal
Seed 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...
is important for plants because it allows their progeny to move away from their parents in space and time. The advantages of seed dispersal may have led to the evolution of fleshy fruits, which entice animals to eat the fruits and move the plants seeds from place to place. While many fruit producing plant species would not disperse far without frugivores, they can usually germinate even if they fall to the ground directly below the parent plant.
Many types of animals are seed dispersers. Mammal and bird species represent the majority of seed dispersing species. However, frugivorous fish, tortoises, lizards, and even amphibians also disperse seeds. While frugivores and fruit-producing plant species are worldwide, there is some evidence that tropical forests have more frugivore seed dispersers than the temperate zone.
See the 5th International Symposium-Workshop on Frugivores and Seed Dispersal (Forthcoming meeting in 2010)
http://www.fsd2010.org
Plant adaptations to attract dispersers
There are a number of fruit characteristics that seem to be adaptive characteristics to attract frugivores. Many animal-dispersed fruits advertise their palatability to animals with bright colors and attractive smells (mimetic fruits). Fruit pulp is generally rich in water and carbohydrates and low in
proteinProteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
and lipids. However, the exact nutritional composition of fruits varies widely. The seeds of animal-dispersed fruits are often adapted to survive digestion by frugivores. For example, seeds can become more permeable to water after passage through an animal’s gut. This leads to higher germination rates. Some
mistletoeMistletoe is the common name for obligate hemi-parasitic plants in several families in the order Santalales. The plants in question grow attached to and within the branches of a tree or shrub.-Mistletoe in the genus Viscum:...
seeds even germinate inside the disperser’s intestine.
Frugivore adaptations for fruit consumption
In order for frugivores to be good
seed dispersersSeed 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...
they must digest fruits without consuming a high proportion of the seeds. Many seed-dispersing animals have specialized digestive systems to process fruits which leave seeds intact. Some bird species have shorter intestines to rapidly pass seeds from fruits, while some frugivorous bat species have longer intestines. Some seed-dispersing frugivores have short gut-retention times and others can alter intestinal enzyme composition when eating different types of fruits.
Plant mechanisms to delay or deter frugivory
Further information: Plant defense against herbivoryPlant defense against herbivory or host-plant resistance describes a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores. Plants use several strategies to defend against damage caused by herbivores...
Plants invest energy into the production of fruits. Plants have evolved to encourage mutualist frugivores to consume their fruit for seed dispersal but also evolved mechanisms to decrease consumption of fruits when unripe and from non-seed dispersing predators. Predators and parasites of fruit include seed predators, insects and microbial frugivores. Plants have chemical and physical adaptations.
Physical deterrents
- Cryptic
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
coloration (e.g. green fruits blend in with the plant leaves)
- Unpalatable textures (e.g. thick skins made of anti-nutritive substances)
- Resins and saps (e.g. prevent animals from swallowing)
- Repellent substances, hard outer coats, spines, thorns
Chemical deterrents
- Chemical deterrents in plants are called secondary metabolites. Secondary metabolites are compounds produced by the plant that are not essential for the primary processes such as growth and reproduction. Toxins might have evolved to prevent consumption by animals that disperse seeds into unsuitable habitats, to prevent too many fruits from being eaten per feeding bout by preventing too many seeds being deposited in one site, or to prevent digestion of the seeds in the gut of the animal. Secondary chemical defenses are divided into three categories: nitrogen based, carbon based terpenes, and carbon based phenolics
Polyphenols are a structural class of natural, synthetic, and semisynthetic organic chemicals characterized by the presence of large multiples of phenol structural units...
.
Examples of secondary chemical defenses in fruit:
- Capsaicin
Capsaicin 2CHCH=CH4CONHCH2C6H3-4--3- ) is the active component of chili peppers, which are plants belonging to the genus Capsicum. It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact...
is a carbon based phenolicPolyphenols are a structural class of natural, synthetic, and semisynthetic organic chemicals characterized by the presence of large multiples of phenol structural units...
compound only found in plant genus CapsicumCapsicum is a genus of flowering plants in the nightshade family, Solanaceae. Its species are native to the Americas where they have been cultivated for thousands of years, but they are now also cultivated worldwide, used as spices, vegetables, and medicines - and have become are a key element in...
(chili and bell peppers). CapsaicinCapsaicin 2CHCH=CH4CONHCH2C6H3-4--3- ) is the active component of chili peppers, which are plants belonging to the genus Capsicum. It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact...
is responsible for the pungent, “hot” flavor of peppers and inhibits growth of microbes and invertebrates.
- Cyanogenic glycosides are nitrogen based compounds and are found in 130 plant families but not necessarily in the fruit of all the plants. It is specifically found in the red berries of the genus Ilex (Holly, an evergreen woody plant). It can inhibit electron transport, cellular respiration
Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products. The reactions involved in respiration are catabolic reactions that involve...
, induce vomiting, diarrhea, and mild narcosisNarcosis may refer to:* Narcosis, the unconsciousness induced by a narcotic drug* Nitrogen narcosis, an effect of diving deep with nitrogen* Hydrogen narcosis, an effect of diving deep with hydrogenIn music:* Narcosis , an English metal band...
in animals.
- Emodin
Emodin is a purgative resin, 6-methyl-1,3,8-trihydroxyanthraquinone, from rhubarb, the buckthorn and Japanese Knotweed...
is a carbon based phenolicPolyphenols are a structural class of natural, synthetic, and semisynthetic organic chemicals characterized by the presence of large multiples of phenol structural units...
compound in plants like rhubarb. EmodinEmodin is a purgative resin, 6-methyl-1,3,8-trihydroxyanthraquinone, from rhubarb, the buckthorn and Japanese Knotweed...
can be catharticIn medicine, a cathartic is a substance that accelerates defecation. This is in contrast to a laxative, which is a substance which eases defecation, usually by softening feces. It is possible for a substance to be both a laxative and a cathartic...
or act as a laxative in humans, kills dipteran larvae, inhibits growth of bacteria and fungi and deters consumption by birds and mice.
Examples
Birds are a main focus of frugivory research. An article by B.A. Loisell and J.G. Blake, Potential Consequences of Extinction of Frugivorous Birds, discusses the important role frugivorous birds have on ecosystems. The conclusions of their research indicate how the extinction of seed dispersing species could negatively affect seed removal, seed viability, and plant establishment. This article highlights the importance that seed dispersing birds have on the deposition of plant species.
Examples of seed dispersing birds are the
hornbillHornbills 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-colored and sometimes has a casque on the upper mandible. Both the common English and the scientific name of the family...
, the
toucanToucans are members of the family Ramphastidae of near passerine birds from the Neotropics. The family is most closely related to the American barbets. They are brightly marked and have large, often colorful bills. The family includes five genera and about forty different species...
, the
aracariThe aracaris are medium-sized toucans in the genus Pteroglossus. As denoted by the presence of the cedilla on the C , the proper pronunciation is "ahr-uh-SAHR-ee" not "ahr-uh-KAR-ee"....
, the
cotingaThe cotingas are a large family of passerine bird species found in Central America and tropical South America. Cotingas are birds of forests or forest edges, which mostly eat fruit or insects and fruit. Comparatively little is known about this diverse group, although all have broad bills with...
, and some species of parrots. Frugivores are common in the temperate zone but mostly found in the
tropicsThe tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
. Many frugivorous birds feed mainly on fruits until nesting season when they incorporate protein rich insects into their diet.
Many types of animals are seed dispersers. Mammals and bird species represent the majority of seed dispersing species, however, frugivorous fish, tortoises, lizards, and even amphibians also disperse seeds.
Mammals are considered frugivorous if the seed is dispersed and able to establish. One example of a mammalian frugivore is the
maned wolfThe maned wolf is the largest canid of South America, resembling a large fox with reddish fur.This mammal is found in open and semi-open habitats, especially grasslands with scattered bushes and trees, in south, central-west and south-eastern Brazil The maned wolf (Chrysocyon brachyurus) is the...
, or Chrysocyon brachyurus, which is found in South America. A study by J.C. Motta-Junior and K. Martins found that the maned wolf is probably an important seed disperser. The researchers found that 22.5 to 54.3 percent of the diet was fruit.
Another example of mammalian frugivores is the
orangutanOrangutans are the only exclusively Asian genus of extant great ape. The largest living arboreal animals, they have proportionally longer arms than the other, more terrestrial, great apes. They are among the most intelligent primates and use a variety of sophisticated tools, also making sleeping...
, whose diet consists of 65 percent fruit. Orangutans primarily eat fruit, along with young leaves, bark, flowers, honey, insects, and vines. One of their preferred foods is the fruit of the
durianThe durian is the fruit of several tree species belonging to the genus Durio and the Malvaceae family . Widely known and revered in southeast Asia as the "king of fruits", the durian is distinctive for its large size, unique odour, and formidable thorn-covered husk...
tree, which tastes somewhat like sweet, cheesy, garlic custard. They discard the skin, eat the flesh, and spit out the seeds.
Another example of a mammalian frugivore is the
Gray-bellied Night MonkeyThe gray-bellied night monkey , also called the lemurine owl monkey, is a small New World monkey of the family Aotidae...
, also known as the owl monkey:
“Owl monkeys are frugivores and supplement their diet with flowers, insects, nectar, and leaves (Wright 1989; 1994). They prefer small, ripe fruit when available and in order to find these, they forage in large-crown trees (larger than ten meters [32.8 ft]) (Wright 1986). Seasonal availability of fruit varies across environments. Aotus species in tropical forests eat more fruit throughout the year because it is more readily available compared to the dry forests where fruit is limited in the dry season and owl monkeys are more dependent on leaves.”
Fruit batsFruit Bats is an American rock band formed in 1997 in Chicago. Noted as an early entrant into the folk-rock boom of the early 2000s, the group has had many personnel changes but revolves around singer/songwriter Eric D. Johnson.-History:In 2000, Eric D...
are another example of a mammalian frugivore. See the
MegabatMegabats constitute the suborder Megachiroptera, family Pteropodidae of the order Chiroptera . They are also called fruit bats, old world fruit bats, or flying foxes.-Description:...
article about Diet and Importance.
CassowariesThe cassowaries are ratites, very large flightless birds in the genus Casuarius native to the tropical forests of New Guinea, nearby islands and northeastern Australia. There are three extant species recognized today...
are a
keystone speciesA keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...
because they spread fruit through digestion, and many seeds will not grow unless they have been digested by a cassowary.
Ecological significance of frugivore seed dispersal
Frugivore seed dispersal is a common phenomenon in many ecosystems. However, it is not a highly specific type of plant-animal interaction. For example, a single species of frugivorous bird may disperse fruits from several species of plants, or a few species of bird may disperse seeds of one plant species. This lack of specialization could be because fruit availability varies by season and year, which tends to discourage frugivore animals from focusing on just one plant species. Furthermore, different seed dispersers tend to disperse seeds to different habitats, at different abundances, and distances depending on their behavior and numbers.
Conservation
Because
seed 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...
allows plant species to disperse to other areas the loss of frugivores could change plant communities and lead to the local loss of particular plant species. Since frugivore seed dispersal is so important in the tropics, many researchers have studied the loss of frugivores and related it to changed plant population dynamics. Several studies have noted that even the loss of only large frugivores (i.e. monkeys) could have a negative effect since monkeys are responsible for certain types of long-distance seed dispersal that is not seen with other frugivore types like birds. However, plant species whose seeds are dispersed by animals may be less vulnerable to fragmentation than other plant species. Frugivores can also benefit from the invasion of exotic fruit-producing species and can be vectors of exotic invasion by dispersing non-native seeds. In short, while anthropogenic habitat loss and change may negatively affect some frugivore species it may positively affect others.
Further reading
- Levey, D. J., W. R. Silva, and M. Galetti (editors) 2002. Seed dispersal and frugivory : ecology, evolution, and conservation New York : CABI Pub. 511 p. ISBN 085199525X