Editing Herbivore (section)

==Feeding strategies==

Two herbivore feeding strategies are [[grazing]] (e.g. cows) and [[browsing (herbivory)|browsing]] (e.g. moose). 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 twigs. An intermediate feeding strategy is called "mixed-feeding".<ref name="Janis (1990)">{{Cite book |author=Janis |first=Christine M. |title=Body Size in Mammalian Paleobiology: Estimation and Biological Implications |publisher=Cambridge University Press |year=1990 |isbn=0-521-36099-4 |editor1-last=Damuth |editor-first=John |pages=255–299 |chapter=Chapter 13: Correlation of cranial and dental variables with body size in ungulates and macropodoids |editor2-last=MacFadden |editor-first2=Bruce J.}}</ref> In their daily need to take up energy from forage, herbivores of different body mass may be selective in choosing their food.<ref name="Belovsky (1997)">{{Cite journal | author=Belovsky, G.E. | date=November 1997 | title=Optimal foraging and community structure: The allometry of herbivore food selection and competition | journal=Evolutionary Ecology | volume=11 | issue=6 | pages=641–672 | doi= 10.1023/A:1018430201230| bibcode=1997EvEco..11..641B | s2cid=23873922 }}</ref> "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. 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.<ref name="Belovsky (1997)" /> 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).

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.<ref name=":6">{{cite journal |last1=Nugent |first1=G. |last2=Challies |first2=C. N. |date=1988 |title=Diet and Food Preferences of White-Tailed Deer in Northeastern Stewart-Island |url=https://newzealandecology.org/nzje/1765 |journal=New Zealand Journal of Ecology |volume=11 |pages=61–73}}</ref> Kleiber's law states that the metabolic rate (q<sub>0</sub>) of an animal is the mass of the animal (M) raised to the 3/4 power: q<sub>0</sub>=M<sup>3/4</sup>

Therefore, the mass of the animal increases at a faster rate than the metabolic rate.<ref name=":6" />

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

{| class="wikitable" style="margin:auto;"
|+ Types of feeding strategies
|-
! Feeding Strategy
! Diet
! Examples
|-
| [[Algivore]]s
| [[Algae]]
| [[Krill]], [[crabs]], [[sea snail]], [[sea urchin]], [[parrotfish]], [[surgeonfish]], [[flamingo]]
|-
| [[Frugivore]]s
| [[Fruit]]
| [[Ruffed lemur]]s, [[orangutan]]s
|-
| [[Folivore]]s
| [[Leaf|Leaves]]
| [[Koala]]s, [[gorilla]]s, [[red colobus]]es, many [[leaf beetle]]s
|-
| [[Nectarivore]]s
| [[Nectar]]
| [[Honey possum]]s, [[hummingbird]]s
|-
| [[Granivore]]s
| [[Seed]]s
| [[Hawaiian honeycreeper]]s, [[bean weevil]]s
|-
| [[Graminivore]]s
| [[Poaceae|Grass]]
| [[Horse]]s
|-
| [[Palynivore]]s
| [[Pollen]]
| [[Bee]]s
|-
| [[Mucivore]]s
| Plant fluids, i.e. [[sap]]
| [[Aphid]]s
|-
| [[Xylophage]]s
| [[Wood]]
| [[Termite]]s, [[Longhorn beetle|longicorn beetles]], [[ambrosia beetle]]s
|}

[[Optimal foraging theory]] is a model for predicting animal behavior while looking for food or other resources, such as shelter or water. 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. 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.<ref>{{cite journal|last1=Kie|first1=John G.|title=Optimal Foraging & Risk of Predation: Effects on Behavior & Social Structure in Ungulates|date=1999|journal=Journal of Mammalogy|doi=10.2307/1383163|volume=80|issue=4|pages=1114–1129|jstor=1383163|doi-access=free}}</ref>

This model has been criticized as circular and untestable. 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.<ref>{{cite journal | last1=Pierce | first1=G. J. | last2=Ollason | first2=J. G. | date=May 1987 | title=Eight reasons why optimal foraging theory is a complete waste of time | journal=Oikos | volume=49 | issue=1| pages=111–118 | doi=10.2307/3565560| jstor=3565560 | bibcode=1987Oikos..49..111P | s2cid=87270733 }}</ref><ref>{{cite journal | last1=Stearns | first1=S. C. | last2=Schmid-Hempel | first2=P. | date=May 1987 | title=Evolutionary insights should not be wasted | journal=Oikos | volume=49 | issue=1| pages=118–125 | doi=10.2307/3565561| jstor=3565561 | bibcode=1987Oikos..49..118S }}</ref> 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.<ref>{{cite journal | last1=Lewis | first1=A. C. | date=16 May 1986 | title=Memory constraints and flower choice in Pieris rapae | journal=Science | volume=232 | issue=4752| pages=863–865 | doi=10.1126/science.232.4752.863 | pmid=17755969 | bibcode=1986Sci...232..863L | s2cid=20010229 }}</ref><ref>{{cite journal | last1=Janetos | first1=A. C. | last2=Cole | first2=B. J. | date=October 1981 | title=Imperfectly optimal animals | journal=Behav. Ecol. Sociobiol. | volume=9 | issue=3| pages=203–209 | doi=10.1007/bf00302939| bibcode=1981BEcoS...9..203J | s2cid=23501715 }}</ref>

Holling's disk equation models the efficiency at which predators consume prey. The model predicts that as the number of prey increases, the amount of time predators spend handling prey also increases, and therefore the efficiency of the predator decreases.<ref>{{Cite book |last=Stephens |first=David W. |url=https://www.worldcat.org/oclc/13902831 |title=Foraging theory |date=1986 |others=J. R. Krebs |isbn=0-691-08441-6 |location=Princeton, New Jersey |oclc=13902831}}</ref>{{page needed|date=August 2015}} In 1959, S. Holling proposed an equation to model the rate of return for an optimal diet: Rate (R )=Energy gained in foraging (Ef)/(time searching (Ts) + time handling (Th))<br /><math>R=Ef/(Ts + Th) </math>

Where s=cost of search per unit time f=rate of encounter with items, h=handling time, e=energy gained per encounter.

In effect, this would indicate that a herbivore in a dense forest would spend more time handling (eating) the vegetation because there was so much vegetation around than a herbivore in a sparse forest, who could easily browse through the forest vegetation. According to the Holling's disk equation, a herbivore in the sparse forest would be more efficient at eating than the herbivore in the dense forest.

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. 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.<ref>{{Cite journal |last=Charnov |first=Eric L. |date=1976-04-01 |title=Optimal foraging, the marginal value theorem |url=https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1008&context=biol_fsp |journal=Theoretical Population Biology |language=en |volume=9 |issue=2 |pages=129–136 |doi=10.1016/0040-5809(76)90040-X |pmid=1273796 |bibcode=1976TPBio...9..129C |issn=0040-5809}}</ref> According to this theory, an animal 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. Within this theory, two subsequent parameters emerge, the Giving Up Density (GUD) and the Giving Up Time (GUT). The Giving Up Density (GUD) quantifies the amount of food that remains in a patch when a forager moves to a new patch.<ref>{{Cite journal |last1=Brown |first1=Joel S. |last2=Kotler |first2=Burt P. |last3=Mitchell |first3=William A. |date=1997-11-01 |title=Competition between birds and mammals: A comparison of giving-up densities between crested larks and gerbils |url=https://doi.org/10.1023/A:1018442503955 |journal=Evolutionary Ecology |language=en |volume=11 |issue=6 |pages=757–771 |doi=10.1023/A:1018442503955 |bibcode=1997EvEco..11..757B |s2cid=25400875 |issn=1573-8477}}</ref> The Giving Up Time (GUT) is used when an animal continuously assesses the patch quality.<ref>{{Cite journal |last1=Breed |first1=Michael D. |last2=Bowden |first2=Rachel M. |last3=Garry |first3=Melissa F. |last4=Weicker |first4=Aric L. |date=1996-09-01 |title=Giving-up time variation in response to differences in nectar volume and concentration in the giant tropical ant,Paraponera clavata (Hymenoptera: Formicidae) |url=https://doi.org/10.1007/BF02213547 |journal=Journal of Insect Behavior |language=en |volume=9 |issue=5 |pages=659–672 |doi=10.1007/BF02213547 |bibcode=1996JIBeh...9..659B |s2cid=42555491 |issn=1572-8889}}</ref>