Herbivore

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This article is about anatomically and physiologically adapted diets to plants. Herbivore_sentence_0

For the Japanese social phenomenon, see Herbivore men. Herbivore_sentence_1

A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. Herbivore_sentence_2

As a result of their plant diet, herbivorous animals typically have mouthparts adapted to rasping or grinding. Herbivore_sentence_3

Horses and other herbivores have wide flat teeth that are adapted to grinding grass, tree bark, and other tough plant material. Herbivore_sentence_4

A large percentage of herbivores have mutualistic gut flora that help them digest plant matter, which is more difficult to digest than animal prey. Herbivore_sentence_5

This flora is made up of cellulose-digesting protozoans or bacteria. Herbivore_sentence_6

Etymology Herbivore_section_0

Herbivore is the anglicized form of a modern Latin coinage, herbivora, cited in Charles Lyell's 1830 Principles of Geology. Herbivore_sentence_7

Richard Owen employed the anglicized term in an 1854 work on fossil teeth and skeletons. Herbivore_sentence_8

Herbivora is derived from the Latin herba meaning a small plant or herb, and vora, from vorare, to eat or devour. Herbivore_sentence_9

Definition and related terms Herbivore_section_1

Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. Herbivore_sentence_10

More generally, organisms that feed on autotrophs in general are known as primary consumers. Herbivore_sentence_11

Herbivory is usually limited to animals that eat plants. Herbivore_sentence_12

Fungi, bacteria, and protists that feed on living plants are usually termed plant pathogens (plant diseases), while fungi and microbes that feed on dead plants are described as saprotrophs. Herbivore_sentence_13

Flowering plants that obtain nutrition from other living plants are usually termed parasitic plants. Herbivore_sentence_14

There is, however, no single exclusive and definitive ecological classification of consumption patterns; each textbook has its own variations on the theme. Herbivore_sentence_15

Evolution of herbivory Herbivore_section_2

The understanding of herbivory in geological time comes from three sources: fossilized plants, which may preserve evidence of defence (such as spines), or herbivory-related damage; the observation of plant debris in fossilised animal faeces; and the construction of herbivore mouthparts. Herbivore_sentence_16

Although herbivory was long thought to be a Mesozoic phenomenon, fossils have shown that within less than 20 million years after the first land plants evolved, plants were being consumed by arthropods. Herbivore_sentence_17

Insects 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. Herbivore_sentence_18

During the next 75 million years, plants evolved a range of more complex organs, such as roots and seeds. Herbivore_sentence_19

There is no evidence of any organism being fed upon until the middle-late Mississippian,  million years ago. Herbivore_sentence_20

There was a gap of 50 to 100 million years between the time each organ evolved and the time organisms evolved to feed upon them; this may be due to the low levels of oxygen during this period, which may have suppressed evolution. Herbivore_sentence_21

Further than their arthropod status, the identity of these early herbivores is uncertain. Herbivore_sentence_22

Hole feeding and skeletonization are recorded in the early Permian, with surface fluid feeding evolving by the end of that period. Herbivore_sentence_23

Herbivory among four-limbed terrestrial vertebrates, the tetrapods developed in the Late Carboniferous (307 – 299 million years ago). Herbivore_sentence_24

Early tetrapods were large amphibious piscivores. Herbivore_sentence_25

While amphibians continued to feed on fish and insects, some reptiles began exploring two new food types, tetrapods (carnivory) and plants (herbivory). Herbivore_sentence_26

The entire dinosaur order ornithischia was composed with herbivores dinosaurs. Herbivore_sentence_27

Carnivory was a natural transition from insectivory for medium and large tetrapods, requiring minimal adaptation. Herbivore_sentence_28

In contrast, a complex set of adaptations was necessary for feeding on highly fibrous plant materials. Herbivore_sentence_29

Arthropods evolved herbivory in four phases, changing their approach to it in response to changing plant communities. Herbivore_sentence_30

Tetrapod herbivores made their first appearance in the fossil record of their jaws near the Permio-Carboniferous boundary, approximately 300 million years ago. Herbivore_sentence_31

The earliest evidence of their herbivory has been attributed to dental occlusion, the process in which teeth from the upper jaw come in contact with teeth in the lower jaw is present. Herbivore_sentence_32

The evolution of dental occlusion led to a drastic increase in plant food processing and provides evidence about feeding strategies based on tooth wear patterns. Herbivore_sentence_33

Examination of phylogenetic frameworks of tooth and jaw morphologes has revealed that dental occlusion developed independently in several lineages tetrapod herbivores. Herbivore_sentence_34

This suggests that evolution and spread occurred simultaneously within various lineages. Herbivore_sentence_35

Food chain Herbivore_section_3

Herbivores form an important link in the food chain because they consume plants to digest the carbohydrates photosynthetically produced by a plant. Herbivore_sentence_36

Carnivores in turn consume herbivores for the same reason, while omnivores can obtain their nutrients from either plants or animals. Herbivore_sentence_37

Due to a herbivore's ability to survive solely on tough and fibrous plant matter, they are termed the primary consumers in the food cycle (chain). Herbivore_sentence_38

Herbivory, carnivory, and omnivory can be regarded as special cases of consumer–resource interactions. Herbivore_sentence_39

Feeding strategies Herbivore_section_4

Two herbivore feeding strategies are grazing (e.g. cows) and browsing (e.g. moose). Herbivore_sentence_40

For a terrestrial mammal to be called a grazer, at least 90% of the forage has to be grass, and for a browser at least 90% tree leaves and/or twigs. Herbivore_sentence_41

An intermediate feeding strategy is called "mixed-feeding". Herbivore_sentence_42

In their daily need to take up energy from forage, herbivores of different body mass may be selective in choosing their food. Herbivore_sentence_43

"Selective" means that herbivores may choose their forage source depending on, e.g., season or food availability, but also that they may choose high quality (and consequently highly nutritious) forage before lower quality. Herbivore_sentence_44

The latter especially is determined by the body mass of the herbivore, with small herbivores selecting for high-quality forage, and with increasing body mass animals are less selective. Herbivore_sentence_45

Several theories attempt to explain and quantify the relationship between animals and their food, such as Kleiber's law, Holling's disk equation and the marginal value theorem (see below). Herbivore_sentence_46

Kleiber's law describes the relationship between an animal's size and its feeding strategy, saying that larger animals need to eat less food per unit weight than smaller animals. Herbivore_sentence_47

Kleiber's law states that the metabolic rate (q0) of an animal is the mass of the animal (M) raised to the 3/4 power: q0=M Therefore, the mass of the animal increases at a faster rate than the metabolic rate. Herbivore_sentence_48

Herbivores employ numerous types of feeding strategies. Herbivore_sentence_49

Many herbivores do not fall into one specific feeding strategy, but employ several strategies and eat a variety of plant parts. Herbivore_sentence_50

Herbivore_table_general_0

Types of feeding strategiesHerbivore_table_caption_0
Feeding StrategyHerbivore_header_cell_0_0_0 DietHerbivore_header_cell_0_0_1 ExampleHerbivore_header_cell_0_0_2
AlgivoresHerbivore_cell_0_1_0 AlgaeHerbivore_cell_0_1_1 krill, crabs, sea snail, sea urchin, parrotfish, surgeonfish, flamingoHerbivore_cell_0_1_2
FrugivoresHerbivore_cell_0_2_0 FruitHerbivore_cell_0_2_1 Ruffed lemurs, chimpanzees, orangutans, humansHerbivore_cell_0_2_2
FolivoresHerbivore_cell_0_3_0 LeavesHerbivore_cell_0_3_1 Koalas, gorillas, red colobusesHerbivore_cell_0_3_2
NectarivoresHerbivore_cell_0_4_0 NectarHerbivore_cell_0_4_1 Honey possum, hummingbirdsHerbivore_cell_0_4_2
GranivoresHerbivore_cell_0_5_0 SeedsHerbivore_cell_0_5_1 Hawaiian honeycreepersHerbivore_cell_0_5_2
PalynivoresHerbivore_cell_0_6_0 PollenHerbivore_cell_0_6_1 BeesHerbivore_cell_0_6_2
MucivoresHerbivore_cell_0_7_0 Plant fluids, i.e. sapHerbivore_cell_0_7_1 AphidsHerbivore_cell_0_7_2
XylophagesHerbivore_cell_0_8_0 WoodHerbivore_cell_0_8_1 TermitesHerbivore_cell_0_8_2

Optimal Foraging Theory is a model for predicting animal behavior while looking for food or other resources, such as shelter or water. Herbivore_sentence_51

This model assesses both individual movement, such as animal behavior while looking for food, and distribution within a habitat, such as dynamics at the population and community level. Herbivore_sentence_52

For example, the model would be used to look at the browsing behavior of a deer while looking for food, as well as that deer's specific location and movement within the forested habitat and its interaction with other deer while in that habitat. Herbivore_sentence_53

This model has been criticized as circular and untestable. Herbivore_sentence_54

Critics have pointed out that its proponents use examples that fit the theory, but do not use the model when it does not fit the reality. Herbivore_sentence_55

Other critics point out that animals do not have the ability to assess and maximize their potential gains, therefore the optimal foraging theory is irrelevant and derived to explain trends that do not exist in nature. Herbivore_sentence_56

The marginal value theorem describes the balance between eating all the food in a patch for immediate energy, or moving to a new patch and leaving the plants in the first patch to regenerate for future use. Herbivore_sentence_57

The theory predicts that absent complicating factors, an animal should leave a resource patch when the rate of payoff (amount of food) falls below the average rate of payoff for the entire area. Herbivore_sentence_58

According to this theory, locus should move to a new patch of food when the patch they are currently feeding on requires more energy to obtain food than an average patch. Herbivore_sentence_59

Within this theory, two subsequent parameters emerge, the Giving Up Density (GUD) and the Giving Up Time (GUT). Herbivore_sentence_60

The Giving Up Density (GUD) quantifies the amount of food that remains in a patch when a forager moves to a new patch. Herbivore_sentence_61

The Giving Up Time (GUT) is used when an animal continuously assesses the patch quality. Herbivore_sentence_62

Attacks and counter-attacks Herbivore_section_5

Herbivore offense Herbivore_section_6

Main article: Herbivore adaptations to plant defense Herbivore_sentence_63

The myriad defenses displayed by plants means that their herbivores need a variety of skills to overcome these defenses and obtain food. Herbivore_sentence_64

These allow herbivores to increase their feeding and use of a host plant. Herbivore_sentence_65

Herbivores have three primary strategies for dealing with plant defenses: choice, herbivore modification, and plant modification. Herbivore_sentence_66

Feeding choice involves which plants a herbivore chooses to consume. Herbivore_sentence_67

It has been suggested that many herbivores feed on a variety of plants to balance their nutrient uptake and to avoid consuming too much of any one type of defensive chemical. Herbivore_sentence_68

This involves a tradeoff however, between foraging on many plant species to avoid toxins or specializing on one type of plant that can be detoxified. Herbivore_sentence_69

Herbivore modification is when various adaptations to body or digestive systems of the herbivore allow them to overcome plant defenses. Herbivore_sentence_70

This might include detoxifying secondary metabolites, sequestering toxins unaltered, or avoiding toxins, such as through the production of large amounts of saliva to reduce effectiveness of defenses. Herbivore_sentence_71

Herbivores may also utilize symbionts to evade plant defences. Herbivore_sentence_72

For example, some aphids use bacteria in their gut to provide essential amino acids lacking in their sap diet. Herbivore_sentence_73

Plant modification occurs when herbivores manipulate their plant prey to increase feeding. Herbivore_sentence_74

For example, some caterpillars roll leaves to reduce the effectiveness of plant defenses activated by sunlight. Herbivore_sentence_75

Plant defense Herbivore_section_7

Main article: Plant defense against herbivory Herbivore_sentence_76

See also: Plant tolerance to herbivory Herbivore_sentence_77

A plant defense is a trait that increases plant fitness when faced with herbivory. Herbivore_sentence_78

This is measured relative to another plant that lacks the defensive trait. Herbivore_sentence_79

Plant defenses increase survival and/or reproduction (fitness) of plants under pressure of predation from herbivores. Herbivore_sentence_80

Defense can be divided into two main categories, tolerance and resistance. Herbivore_sentence_81

Tolerance is the ability of a plant to withstand damage without a reduction in fitness. Herbivore_sentence_82

This can occur by diverting herbivory to non-essential plant parts, resource allocation, compensatory growth, or by rapid regrowth and recovery from herbivory. Herbivore_sentence_83

Resistance refers to the ability of a plant to reduce the amount of damage it receives from herbivores. Herbivore_sentence_84

This can occur via avoidance in space or time, physical defenses, or chemical defenses. Herbivore_sentence_85

Defenses can either be constitutive, always present in the plant, or induced, produced or translocated by the plant following damage or stress. Herbivore_sentence_86

Physical, or mechanical, defenses are barriers or structures designed to deter herbivores or reduce intake rates, lowering overall herbivory. Herbivore_sentence_87

Thorns such as those found on roses or acacia trees are one example, as are the spines on a cactus. Herbivore_sentence_88

Smaller hairs known as trichomes may cover leaves or stems and are especially effective against invertebrate herbivores. Herbivore_sentence_89

In addition, some plants have waxes or resins that alter their texture, making them difficult to eat. Herbivore_sentence_90

Also the incorporation of silica into cell walls is analogous to that of the role of lignin in that it is a compression-resistant structural component of cell walls; so that plants with their cell walls impregnated with silica are thereby afforded a measure of protection against herbivory. Herbivore_sentence_91

Chemical defenses are secondary metabolites produced by the plant that deter herbivory. Herbivore_sentence_92

There are a wide variety of these in nature and a single plant can have hundreds of different chemical defenses. Herbivore_sentence_93

Chemical defenses can be divided into two main groups, carbon-based defenses and nitrogen-based defenses. Herbivore_sentence_94

Herbivore_ordered_list_0

  1. Carbon-based defenses include terpenes and phenolics. Terpenes are derived from 5-carbon isoprene units and comprise essential oils, carotenoids, resins, and latex. They can have several functions that disrupt herbivores such as inhibiting adenosine triphosphate (ATP) formation, molting hormones, or the nervous system. Phenolics combine an aromatic carbon ring with a hydroxyl group. There are several different phenolics such as lignins, which are found in cell walls and are very indigestible except for specialized microorganisms; tannins, which have a bitter taste and bind to proteins making them indigestible; and furanocumerins, which produce free radicals disrupting DNA, protein, and lipids, and can cause skin irritation.Herbivore_item_0_0
  2. Nitrogen-based defenses are synthesized from amino acids and primarily come in the form of alkaloids and cyanogens. Alkaloids include commonly recognized substances such as caffeine, nicotine, and morphine. These compounds are often bitter and can inhibit DNA or RNA synthesis or block nervous system signal transmission. Cyanogens get their name from the cyanide stored within their tissues. This is released when the plant is damaged and inhibits cellular respiration and electron transport.Herbivore_item_0_1

Plants have also changed features that enhance the probability of attracting natural enemies to herbivores. Herbivore_sentence_95

Some emit semiochemicals, odors that attract natural enemies, while others provide food and housing to maintain the natural enemies' presence, e.g. ants that reduce herbivory. Herbivore_sentence_96

A given plant species often has many types of defensive mechanisms, mechanical or chemical, constitutive or induced, which allow it to escape from herbivores. Herbivore_sentence_97

Herbivore–plant interactions per predator–prey theory Herbivore_section_8

According to the theory of predator–prey interactions, the relationship between herbivores and plants is cyclic. Herbivore_sentence_98

When prey (plants) are numerous their predators (herbivores) increase in numbers, reducing the prey population, which in turn causes predator number to decline. Herbivore_sentence_99

The prey population eventually recovers, starting a new cycle. Herbivore_sentence_100

This suggests that the population of the herbivore fluctuates around the carrying capacity of the food source, in this case, the plant. Herbivore_sentence_101

Several factors play into these fluctuating populations and help stabilize predator-prey dynamics. Herbivore_sentence_102

For example, spatial heterogeneity is maintained, which means there will always be pockets of plants not found by herbivores. Herbivore_sentence_103

This stabilizing dynamic plays an especially important role for specialist herbivores that feed on one species of plant and prevents these specialists from wiping out their food source. Herbivore_sentence_104

Prey defenses also help stabilize predator-prey dynamics, and for more information on these relationships see the section on Plant Defenses. Herbivore_sentence_105

Eating a second prey type helps herbivores' populations stabilize. Herbivore_sentence_106

Alternating between two or more plant types provides population stability for the herbivore, while the populations of the plants oscillate. Herbivore_sentence_107

This plays an important role for generalist herbivores that eat a variety of plants. Herbivore_sentence_108

Keystone herbivores keep vegetation populations in check and allow for a greater diversity of both herbivores and plants. Herbivore_sentence_109

When an invasive herbivore or plant enters the system, the balance is thrown off and the diversity can collapse to a monotaxon system. Herbivore_sentence_110

The back and forth relationship of plant defense and herbivore offense drives coevolution between plants and herbivores, resulting in a "coevolutionary arms race". Herbivore_sentence_111

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. Herbivore_sentence_112

While much of the interaction of herbivory and plant defense is negative, with one individual reducing the fitness of the other, some is beneficial. Herbivore_sentence_113

This beneficial herbivory takes the form of mutualisms in which both partners benefit in some way from the interaction. Herbivore_sentence_114

Seed dispersal by herbivores and pollination are two forms of mutualistic herbivory in which the herbivore receives a food resource and the plant is aided in reproduction. Herbivore_sentence_115

Impacts Herbivore_section_9

Herbivorous fish and marine animals are indispensable parts of the coral reef ecosystem. Herbivore_sentence_116

Since algae and seaweeds grow much faster than corals, they can occupy spaces where corals could have settled. Herbivore_sentence_117

They can outgrow and thus outcompete corals on bare surfaces. Herbivore_sentence_118

In the absence of plant-eating fish, seaweeds deprive corals of sunlight. Herbivore_sentence_119

Herbivory can have impacts on both economics and ecology. Herbivore_sentence_120

For example, environmental degradation from white-tailed deer (Odocoileus virginianus) in the US alone has the potential to both change vegetative communities through over-browsing and cost forest restoration projects upwards of $750 million annually. Herbivore_sentence_121

Agricultural crop damage by the same species totals approximately $100 million every year. Herbivore_sentence_122

Insect crop damages also contribute largely to annual crop losses in the U.S. Herbivores affect economics through the revenue generated by hunting and ecotourism. Herbivore_sentence_123

For example, the hunting of herbivorous game species such as white-tailed deer, cottontail rabbits, antelope, and elk in the U.S. contributes greatly to the billion-dollar annually, hunting industry. Herbivore_sentence_124

Ecotourism is a major source of revenue, particularly in Africa, where many large mammalian herbivores such as elephants, zebras, and giraffes help to bring in the equivalent of millions of US dollars to various nations annually. Herbivore_sentence_125

See also Herbivore_section_10

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Herbivore.