Frugivore

Frugivore

[froo-juh-vawr, -vohr]
A frugivore is an animal that feeds primarily or, in some cases, exclusively on fruit. This method of feeding can be more efficient than consuming the stem, roots, or other vegetative portions of a plant, due to higher concentrations of sugars, vitamins or proteins that many plants put into fruit.

Plant and frugivore interactions

By the botanical definition fruit is a means by which a plant reproduces, and is a very important energy investment for the plant. This energy investment may be understood as the stored nutrients which the plant seedling will use to grow before it has an established leaf and root system to grow with. As the reproductive means for the plant, the plant species may have evolved means to either prevent animals from consuming their fruits, or conversely the fruit may have evolved to entice frugivores to the plant.

Enticement of frugivores

Over periods of time evolutionary interactions between a plant species and animal species may change both the animal and the plant to work with each other. This works because animals that eat all of their preferred fruits in a destructive manner may have no plants in following years to eat from. Animals who find and eat fruit in such a manner that both species profit will likely find more of the plants later on. This positive interaction, known as mutualism, may involve the following methods;

  • The animal eats the whole fruit, and later defecates the seeds in another place. The parent plant does not have to compete with the young seedlings, and the animal and its young will have a greater number of fruit bearing plants to eat from. Some plant species such as buckthorn have fruit with a natural laxative, so birds which eat the berries quickly empty their bowels as they fly away or at a nearby perch.
  • The animal eats the fruit, but only the soft or sweet parts, spitting out the core with its seeds or hard pits. This is especially effective if the animal takes the fruit away to a safe and different location to eat, or to store for later use. Fruits like apples have a tough casing around their seeds, which takes more time to eat, than perhaps reaching for another apple. Mangos have very sweet and soft fruit when ripe, but before the seed is ready, the flesh of the fruit is bitter and hard. This prevents the fruit from being harvested before the seed is fully developed.

Some plant and animal interactions have evolved to the point where the plant seeds may not germinate unless passed through the acidic digestive system of their attendant animal species. In other cases, the animal has evolved with specialized physical attributes, such as beaks or teeth or nutritional needs so that without the plant they will starve, even surrounded by a forest or field filled with other plants and fruits. This specialization is one reason the extinction of a single species can be much more harmful than immediately understood.

Plants that deter frugivores

As mentioned before, plants may invest significant energy into their fruit, to ensure the best chances for future generations. If an animal makes a habit of choosing this fruit as their main food source, only those plants with random mutations which the animal avoids will be able to reproduce in great numbers. In this fashion, secondary characteristics evolve to protect the plant from consumption. These fall into two main classes, chemical and physical.

Chemical deterrents may include:

  • Poisonous or bad tasting juices
  • Sedatives or nervous system affecting chemicals

The alkaloid chemical family is often seen in plants as a secondary metabolic chemical defense means. Cocaine is found in the coca plant, Erythroxylon coca, as an example.

Physical deterrents are perhaps more common, and may include:

  • Thick skins or shell-like exteriors, particularly made of cellulose, or some other non-nutritive tissue
  • Spikes, burrs, or other means to prevent the fruit from easily being chewed
  • Gummy or adhesive sap, which keeps the animal from swallowing
  • A lack of nutritive concentrations, such as sugars. This may keep the fruit from being preferred by frugivores, but it also lessens the helpful boost a fully developed plant can gift a seed with. It is evolutionarily logical, however, if all the sweet seeds get eaten, than the bitter or bland ones prosper.

Just as plants who work with their attendant frugivores may effect change to the consumer and themselves over time, the deterrent plants can also get into an evolutionary arms race with animals. If the rind gets thicker, so might the stronger jawed animal prosper over their lighter jawed cousins. Chemicals which are meant to poison a consumer may be eaten by an animal and give the animal in turn protection from being eaten, by means of concentrating the poisons it otherwise could not make in its body (the caterpillar of the monarch butterfly makes use of this technique).

Finding specialized consumers to otherwise invulnerable harmful invasive species is one of the main techniques in biocontrol. If a species were brought in to an ecological problem situation with the tendency to just eat everything, it would be of no use as a control mechanism. If a plant has a species that consumes nearly or completely exclusively on it, this species may be a good candidate for further research as a possible means of biocontrol.

Examples of frugivores

Many birds eat both fruits, such as wild berries, and insects (examples include the American Robin or the Cedar Waxwing) or seeds (e.g. Pesquet's Parrot). Mammals may eat both fruits and animal prey, or live nearly exclusively on fruit or fruit juices, such as many Old World bats, known as the megabats. A number of the primates, for example the Gray-bellied Night Monkey, the Ring-tailed Lemur, and the White-headed Capuchin are frugivores.

Humans are also sometimes described as frugivores, for instance prelapsarian man fed mainly on the fruit of the Pyrus Malus, a view taken by Linnaeus:.

Man's structure, external and internal, compared with that of other animals shows that fruit and succulent vegetables constitute his natural food.
Many writers have advanced a position which disputes that humans are omnivorous, including Geoffrey Hodson in his article "Source of Perfect Nourishment: The Plant Kingdom" (1949).

People who consciously adopt a strictly frugivorous diet call themselves fructarians or fruitarians.

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

External links

View on diet and health at NHE Self-Health Care Systems: Biological Adaptations

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