Difference between revisions of "Herbivory" - New World Encyclopedia
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{{otheruses4|plant-based diets for organisms in general|human diets that exclude meat|Vegetarianism|human diets that exclude all animal sources|Veganism}} | {{otheruses4|plant-based diets for organisms in general|human diets that exclude meat|Vegetarianism|human diets that exclude all animal sources|Veganism}} | ||
[[Image:Deer.jpg|thumb|250px|A [[deer]] and two fawns feeding on some foliage]] | [[Image:Deer.jpg|thumb|250px|A [[deer]] and two fawns feeding on some foliage]] | ||
| − | '''Herbivory''' is a type of biological interaction whereby an [[organism]], known as a '''herbivore''', | + | '''Herbivory''' is a type of biological interaction whereby an [[organism]], known as a '''herbivore''', [[heterotroph|consume]]s principally [[autotroph]]s or their products, such as subsisting on [[plant]] tissues, plant products (fruit, pollen, nectar), [[algae]], and photosynthesizing [[bacteria]]. By that definition, many [[fungi]], some [[bacteria]], many [[animal]]s, some [[protist]]s, and a small number of [[parasitic plant]]s can be considered herbivores. However, herbivory is generally restricted to animals eating plants and plant material, such as insects, cows, or elephants consuming plants. Fungi, bacteria, and protists that feed on living plants are usually termed [[phytopathology|plant pathogens]]. Microbes that feed on dead plants are [[saprotroph]]s. Flowering plants that obtain nutrition from other living plants are usually termed [[parasitic plant]]s. |
| − | The term herbivore | + | The term herbivore, referring to animals with a diet wholly or mainly of plant matter, is in contrast to [[carnivore]], which refers to animals with a diet consisting wholly or mainly of animal matter, and [[omnivore]], which refers to animals that consume both animal and plant matter. Unlike predation, herbivory typically does not result in the killing of the plants, although there are exceptions. Unlike detritivory, herbivory involves the consumption of living plants and products of living plants rather than the consumption of dead organic material (detritus). |
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| + | Organisms that feed on autotrophs in general often are known as '''primary consumers'''. Herbivores form an important link in the [[food chain]] as they transform the sun's energy stored in the plants to food that can be consumable by [[carnivore]]s and [[omnivore]]s up the food chain. As such, they are termed the primary consumers in the food chain. | ||
== Herbivores == | == Herbivores == | ||
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A herbivore is an [[animal]] that is adapted to eat plants and no meat. Although such animals are sometimes referred to as being [[vegetarian]], this term is more properly reserved for [[human]]s who choose not to eat meat as opposed to animals that are unable to make such choices. | A herbivore is an [[animal]] that is adapted to eat plants and no meat. Although such animals are sometimes referred to as being [[vegetarian]], this term is more properly reserved for [[human]]s who choose not to eat meat as opposed to animals that are unable to make such choices. | ||
| − | There is a misperception that if an animal is herbivorous, it represents less danger to humans than a [[carnivore]] (or, sometimes, no danger at all). This is not logically sound; few animals, even carnivores, will seek humans as a food source, but any animal will attack a human if necessary to defend itself. For example, in [[national parks]] such as the [[United States]]' [[Yellowstone National Park|Yellowstone Park]], bison represent significantly more danger to humans than wolves, which are likely to avoid people. Of [[Africa]]'s [[Big Five game]] (a term coined by hunters in Africa to refer to the five most dangerous animals to hunt: [[ | + | There is a misperception that if an animal is herbivorous, it represents less danger to humans than a [[carnivore]] (or, sometimes, no danger at all). This is not logically sound; few animals, even carnivores, will seek humans as a food source, but any animal will attack a human if necessary to defend itself. For example, in [[national parks]] such as the [[United States]]' [[Yellowstone National Park|Yellowstone Park]], [[bison]] represent significantly more danger to humans than wolves, which are likely to avoid people. Of [[Africa]]'s [[Big Five game]] (a term coined by hunters in Africa to refer to the five most dangerous animals to hunt: [[rhinoceros]], [[leopard]], [[cape buffalo]], [[elephant]], and [[lion]]), three are herbivores. |
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==Feeding strategies== | ==Feeding strategies== | ||
| − | Herbivores differ in the extent, specificity and nature of their feeding. | + | Herbivores differ in the extent, specificity, and nature of their feeding. |
| − | + | Herbivores can be grouped according to which part of the plant they eat. [[Frugivore]]s eat mainly [[fruit]], [[folivore]]s specialize in eating [[leaf|leaves]], and [[nectarivore]]s feed on [[nectar]]. Among herbivorous [[insect]]s and other [[arthropod]]s, the level of feeding specialization can be far more fine-tuned, including seed-eaters ("[[granivore]]s"), pollen-eaters ("[[palynivore]]s"), plant fluid-feeders ("[[mucivore]]s"), and those specialized to feed on wood ("[[xylophagy|xylophages]]"), or roots ("[[rhizophagy|rhizophages]]"). In other animals, the degree of specialization is not so advanced, however, and many fruit- and leaf-eating animals also eat other parts of plants, notably [[root]]s and [[seed]]s. | |
| − | The techniques used to get at the foodstuff are wide and varied, and include the "pierce and suck" technique, surface fluid feeding, hole feeding, margin feeding and skeletonisation. | + | The techniques used to get at the foodstuff are wide and varied, and include the "pierce and suck" technique, surface fluid feeding, hole feeding, margin feeding and skeletonisation (Labandeira 1998). |
| − | + | ==Evolution of herbivory== | |
| − | + | Our understanding of herbivory in geological time comes from three sources: fossilized plants, which may preserve evidence of defense (such as spines) or herbivory-related damage; the observation of plant debris in fossilized [[coprolite|animal feces]]; and the construction of herbivore mouthparts (Labandeira 1998). | |
| − | ==Evolution of herbivory | ||
| − | Our understanding of herbivory in geological time comes from three sources: | ||
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Long thought to be a [[Mesozoic]] phenomenon, evidence for herbivory is found almost as soon as fossils which could show it. Within under 20 million years of the first fossils of sporangia and stems towards the close of the Silurian, around {{Ma|{{period start|devonian|-1}}}}, there is evidence that they were being consumed.<ref name=Labandeira2007>{{cite journal | Long thought to be a [[Mesozoic]] phenomenon, evidence for herbivory is found almost as soon as fossils which could show it. Within under 20 million years of the first fossils of sporangia and stems towards the close of the Silurian, around {{Ma|{{period start|devonian|-1}}}}, there is evidence that they were being consumed.<ref name=Labandeira2007>{{cite journal | ||
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Campbell, N. A. (1996) ''Biology'' (4th edition) Benjamin Cummings, New York ISBN 0-8053-1957-3 | Campbell, N. A. (1996) ''Biology'' (4th edition) Benjamin Cummings, New York ISBN 0-8053-1957-3 | ||
| + | |||
| + | <ref name=Labandeira1998>{{cite journal | ||
| + | | author = Labandeira, C.C. | ||
| + | | year = 1998 | ||
| + | | title = Early History Of Arthropod And Vascular Plant Associations 1 | ||
| + | | journal = Annual Reviews in Earth and Planetary Sciences | ||
| + | | volume = 26 | ||
| + | | issue = 1 | ||
| + | | pages = 329–377 | ||
| + | | doi = 10.1146/annurev.earth.26.1.329 | ||
| + | }}</ref> | ||
==Further reading== | ==Further reading== | ||
Revision as of 23:40, 16 August 2008
- This article is about plant-based diets for organisms in general. For human diets that exclude meat, see Vegetarianism.
Herbivory is a type of biological interaction whereby an organism, known as a herbivore, consumes principally autotrophs or their products, such as subsisting on plant tissues, plant products (fruit, pollen, nectar), algae, and photosynthesizing bacteria. By that definition, many fungi, some bacteria, many animals, some protists, and a small number of parasitic plants can be considered herbivores. However, herbivory is generally restricted to animals eating plants and plant material, such as insects, cows, or elephants consuming plants. Fungi, bacteria, and protists that feed on living plants are usually termed plant pathogens. Microbes that feed on dead plants are saprotrophs. Flowering plants that obtain nutrition from other living plants are usually termed parasitic plants.
The term herbivore, referring to animals with a diet wholly or mainly of plant matter, is in contrast to carnivore, which refers to animals with a diet consisting wholly or mainly of animal matter, and omnivore, which refers to animals that consume both animal and plant matter. Unlike predation, herbivory typically does not result in the killing of the plants, although there are exceptions. Unlike detritivory, herbivory involves the consumption of living plants and products of living plants rather than the consumption of dead organic material (detritus).
Organisms that feed on autotrophs in general often are known as primary consumers. Herbivores form an important link in the food chain as they transform the sun's energy stored in the plants to food that can be consumable by carnivores and omnivores up the food chain. As such, they are termed the primary consumers in the food chain.
Herbivores
A herbivore is an animal that is adapted to eat plants and no meat. Although such animals are sometimes referred to as being vegetarian, this term is more properly reserved for humans who choose not to eat meat as opposed to animals that are unable to make such choices.
There is a misperception that if an animal is herbivorous, it represents less danger to humans than a carnivore (or, sometimes, no danger at all). This is not logically sound; few animals, even carnivores, will seek humans as a food source, but any animal will attack a human if necessary to defend itself. For example, in national parks such as the United States' Yellowstone Park, bison represent significantly more danger to humans than wolves, which are likely to avoid people. Of Africa's Big Five game (a term coined by hunters in Africa to refer to the five most dangerous animals to hunt: rhinoceros, leopard, cape buffalo, elephant, and lion), three are herbivores.
Feeding strategies
Herbivores differ in the extent, specificity, and nature of their feeding.
Herbivores can be grouped according to which part of the plant they eat. Frugivores eat mainly fruit, folivores specialize in eating leaves, and nectarivores feed on nectar. Among herbivorous insects and other arthropods, the level of feeding specialization can be far more fine-tuned, including seed-eaters ("granivores"), pollen-eaters ("palynivores"), plant fluid-feeders ("mucivores"), and those specialized to feed on wood ("xylophages"), or roots ("rhizophages"). In other animals, the degree of specialization is not so advanced, however, and many fruit- and leaf-eating animals also eat other parts of plants, notably roots and seeds.
The techniques used to get at the foodstuff are wide and varied, and include the "pierce and suck" technique, surface fluid feeding, hole feeding, margin feeding and skeletonisation (Labandeira 1998).
Evolution of herbivory
Our understanding of herbivory in geological time comes from three sources: fossilized plants, which may preserve evidence of defense (such as spines) or herbivory-related damage; the observation of plant debris in fossilized animal feces; and the construction of herbivore mouthparts (Labandeira 1998).
Long thought to be a Mesozoic phenomenon, evidence for herbivory is found almost as soon as fossils which could show it. Within under 20 million years of the first fossils of sporangia and stems towards the close of the Silurian, around , there is evidence that they were being consumed.[1] Animals fed on the spores of early Devonian plants, and the Rhynie chert also provides evidence that organisms fed on plants using a "pierce and suck" technique.[2]
During the ensuing 75 million years[citation needed], plants evolved a range of more complex organs - from roots to seeds. There is no evidence for these being fed upon until the middle-late Mississippian, . There was a gap of 50 to 100 million years between each organ evolving, and it being fed upon; this may be due to the low levels of O2 during this period, which may have suppressed evolution.[1] Further than their arthropod status, the identity of these early herbivores is uncertain.[1] Hole feeding and skeletonisation are recorded in the early Permian, with surface fluid feeding evolving by the end of that period.[2]
Arthropods have evolved herbivory in four phases, changing their approach to herbivory in response to changing plant communities.[3] {{#invoke:Message box|ambox}}
Plant defences
Plant defence against herbivory include a range of adaptations evolved by plants to improve their survival and reproduction by reducing the impact of animals that eat them. Plants have evolved an enormous array of mechanical and chemical defences against herbivores.
These defences include mechanical protections on the surface of the plant, production of complex polymers that reduce plant digestibility to animals, and the production of toxins that kill or repel herbivores. Defenses can either be constitutive, always present in the plant, or induced, produced or translocated by the plant following damage or stress. The term host plant resistance is also used by plant breeders to refer to these mechanisms.
Plants have also evolved features that enhance the probability of attracting natural enemies to herbivores. Specifically, they emit semiochemicals, odors that attract natural enemies, and provide food and housing to maintain the natural enemies’ presence.
A given plant species often has many types of defensive mechanisms, mechanical or chemical, constitutive or induced, which additively serve to protect the plant, and allow it to escape from herbivores.
In some cases, herbivory is actually encouraged by plants to assist in reproduction. A notable example is the production of nectar to attract bees, which are necessary for pollination.
Herbivore adaptations to defences
Herbivores are dependent on plants for food, and have coevolved mechanisms to obtain this food despite the evolution of a diverse arsenal of plant defenses against herbivory. Herbivores adaptations to plant defense have been likened to “offensive traits” and consist of those traits that allow for increased feeding and use of a host.[4] Plants, on the other hand, protect their resources for use in growth and reproduction, by limiting the ability of herbivores to eat them. Relationships between herbivores and their host plants often results in reciprocal evolutionary change. When a herbivore eats a plant it selects for plants that can mount a defensive response, whether the response is incorporated biochemically or physically, or induced as a counterattack. In cases where this relationship demonstrates “specificity” (the evolution of each trait is due to the other), and “reciprocity” (both traits must evolve), the species are thought to have coevolved.[5] The escape and radiation mechanisms for coevolution, presents the idea that adaptations in herbivores and their host plants, has been the driving force behind speciation.[6][7]
See also
- List of food habits
- Grazing
- Browser
- Pollination
- Seed dispersal
- Seed predation
- Veganism
ReferencesISBN links support NWE through referral fees
- ↑ 1.0 1.1 1.2 Labandeira, C. (2007). The origin of herbivory on land: Initial patterns of plant tissue consumption by arthropods. Insect Science 14 (4): 259–275.
- ↑ 2.0 2.1 Cite error: Invalid
<ref>tag; no text was provided for refs namedLabandeira1998 - ↑ Labandeira, C.C. (2006). The four phases of plant-arthropod associations in deep time. Geologica Acta 4 (4): 409–438.
- ↑ Karban, R., and A. A. Agrawal. 2002. Herbivore offense. Annual Review of Ecology and Systematics 33:641 – 664.
- ↑ Futuyma, D. J. and M. Slatkin. 1983. Introduction. Pages 1−13 in D. J. Futuyma and M. Slatkin, editors. Coevolution. Sinauer Associates Inc., Sunderland, Massachusetts, USA.
- ↑ Ehrlich, P. R. and P. H. Raven. 1964. Butterflies and plants: a study of coevolution. Evolution 18:586-608.
- ↑ Thompson, J. 1999. What we know and do not know about coevolution: insect herbivores and plants as a test case. Pages 7–30 in H. Olff, V. K. Brown, R. H. Drent, and British Ecological Society Symposium 1997 (Corporate Author), editors. Herbivores: between plants and predators. Blackwell Science, London, UK.
Campbell, N. A. (1996) Biology (4th edition) Benjamin Cummings, New York ISBN 0-8053-1957-3
Further reading
- Danell, K., R. Bergström, P. Duncan, J. Pastor (Editors)(2006) Large herbivore ecology, ecosystem dynamics and conservation Cambridge, UK : Cambridge University Press. 506 p. ISBN 0521830052
- Crawley, M. J. (1983) Herbivory : the dynamics of animal-plant interactions Oxford : Blackwell Scientific. 437 p. ISBN 0632008083
- Olff, H., V.K. Brown, R.H. Drent (editors) (1999) Herbivores : between plants and predators Oxford ; Malden, Ma. : Blackwell Science. 639 p. ISBN 0632051558
External links
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Amensalism • Commensalism • Mutualism • Neutralism • Synnecrosis • Predation (Carnivory, Herbivory, Parasitism, Parasitoidism, Cheating) • Symbiosis • Competition
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- ↑ Labandeira, C.C. (1998). Early History Of Arthropod And Vascular Plant Associations 1. Annual Reviews in Earth and Planetary Sciences 26 (1): 329–377.
