Feeding is the process by which organisms, typically animals, obtain food. Terminology often uses either the suffixes -vore, -vory, -vorous from Latin vorare, meaning "to devour", or -phage, -phagy, -phagous from Greek φαγειν (phagein), meaning "to eat".
The evolution of feeding is varied with some feeding strategies evolving several times in independent lineages. In terrestrial vertebrates, the earliest forms were large amphibious piscivores 400 million years ago. While amphibians continued to feed on fish and later insects, reptiles began exploring two new food types, other tetrapods (carnivory), and later, plants (herbivory). Carnivory was a natural transition from insectivory for medium and large tetrapods, requiring minimal adaptation (in contrast, a complex set of adaptations was necessary for feeding on highly fibrous plant materials).
The specialization of organisms towards specific food sources is one of the major causes of evolution of form and function, such as:
There are many modes of feeding that animals exhibit, including:
Another classification refers to the specific food animals specialize in eating, such as:
The eating of non-living or decaying matter:
There are also several unusual feeding behaviours, either normal, opportunistic, or pathological, such as:
An opportunistic feeder sustains itself from a number of different food sources, because the species is behaviourally sufficiently flexible.
Anthropophagy is the custom and practice of eating human flesh. It may refer to:
Human cannibalism, when one human consumes the flesh of another
Anthropophagi, a mythical race of cannibals first described by Herodotus in his Histories as androphagi, and later by other authors, including the playwright William Shakespeare
Child cannibalism, the act of eating a child or fetus
Self-cannibalism, the act of eating one's own flesh
Man-eating, the consumption of human flesh by a non-human predatorAquatic feeding mechanisms
Aquatic feeding mechanisms face a special difficulty as compared to feeding on land, because the density of water is about the same as that of the prey, so the prey tends to be pushed away when the mouth is closed. This problem was first identified by Robert McNeill Alexander. As a result, underwater predators, especially bony fish, have evolved a number of specialized feeding mechanisms, such as filter feeding, ram feeding, suction feeding, protrusion, and pivot feeding.
Most underwater predators combine more than one of these basic principles. For example, a typical generalized predator, such as the cod, combines suction with some amount of protrusion and pivot feeding.Cascade effect (ecology)
An ecological cascade effect is a series of secondary extinctions that is triggered by the primary extinction of a key species in an ecosystem. Secondary extinctions are likely to occur when the threatened species are: dependent on a few specific food sources, mutualistic (dependent on the key species in some way), or forced to coexist with an invasive species that is introduced to the ecosystem. Species introductions to a foreign ecosystem can often devastate entire communities, and even entire ecosystems. These exotic species monopolize the ecosystem's resources, and since they have no natural predators to decrease their growth, they are able to increase indefinitely. Olsen et al. showed that exotic species have caused lake and estuary ecosystems to go through cascade effects due to loss of algae, crayfish, mollusks, fish, amphibians, and birds. However, the principal cause of cascade effects is the loss of top predators as the key species. As a result of this loss, a dramatic increase (ecological release) of prey species occurs. The prey is then able to overexploit its own food resources, until the population numbers decrease in abundance, which can lead to extinction. When the prey's food resources disappear, they starve and may go extinct as well. If the prey species is herbivorous, then their initial release and exploitation of the plants may result in a loss of plant biodiversity in the area. If other organisms in the ecosystem also depend upon these plants as food resources, then these species may go extinct as well. An example of the cascade effect caused by the loss of a top predator is apparent in tropical forests. When hunters cause local extinctions of top predators, the predators' prey's population numbers increase, causing an overexploitation of a food resource and a cascade effect of species loss. Recent studies have been performed on approaches to mitigate extinction cascades in food-web networks.Durophagy
Durophagy is the eating behavior of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including fossil turtles, placodonts and invertebrates, as well as "bone-crushing" mammalian carnivores such as hyenas. Durophagy requires special adaptions, such as blunt, strong teeth and a heavy jaw. Bite force is necessary to overcome the physical constraints of consuming more durable prey and gain a competitive advantage over other organisms by gaining access to more diverse or exclusive food resources earlier in life. Those with greater bite forces require less time to consume certain prey items as a greater bite force can increase the net rate of energy intake when foraging and enhance fitness in durophagous species. In the order Carnivora there are two dietary categories of durophagy; bonecrackers and bamboo eaters. Bonecrackers are exemplified by hyenas and saber-toothed cats, while bamboo eaters are primarily the giant panda and the red panda. Both have developed similar cranial morphology. However, the mandible morphology reveals more about their dietary resources. Both have a raised and dome-like anterior cranium, enlarged areas for the attachment of masticatory muscles, enlarged premolars, and reinforced tooth enamel. Bamboo eaters tend to have larger mandibles, while bonecrackers have more sophisticated premolars.Energy flow (ecology)
In ecology, energy flow, also called the calorific flow, refers to the flow of energy through a food chain, and is the focus of study in ecological energetics. In an ecosystem, ecologists seek to quantify the relative importance of different component species and feeding relationships.
A general energy flow scenario follows:
Solar energy is fixed by the photoautotrophs, called primary producers, like green plants. Primary consumers absorb most of the stored energy in the plant through digestion, and transform it into the form of energy they need, such as adenosine triphosphate (ATP), through respiration. A part of the energy received by primary consumers, herbivores, is converted to body heat (an effect of respiration), which is radiated away and lost from the system. The loss of energy through body heat is far greater in warm-blooded animals, which must eat much more frequently than those that are cold-blooded. Energy loss also occurs in the expulsion of undigested food (egesta) by excretion or regurgitation.
Secondary consumers, carnivores, then consume the primary consumers, although omnivores also consume primary producers. Energy that had been used by the primary consumers for growth and storage is thus absorbed into the secondary consumers through the process of digestion. As with primary consumers, secondary consumers convert this energy into a more suitable form (ATP) during respiration. Again, some energy is lost from the system, since energy which the primary consumers had used for respiration and regulation of body temperature cannot be utilized by the secondary consumers.
Tertiary consumers, which may or may not be apex predators, then consume the secondary consumers, with some energy passed on and some lost, as with the lower levels of the food chain.
A final link in the food chain are decomposers which break down the organic matter of the tertiary consumers (or whichever consumer is at the top of the chain) and release nutrients into the soil. They also break down plants, herbivores and carnivores that were not eaten by organisms higher on the food chain, as well as the undigested food that is excreted by herbivores and carnivores. Saprotrophic bacteria and fungi are decomposers, and play a pivotal role in the nitrogen and carbon cycles.The energy is passed on from trophic level to trophic level and each time about 90% of the energy is lost, with some being lost as heat into the environment (an effect of respiration) and some being lost as incompletely digested food (egesta). Therefore, primary consumers get about 10% of the energy produced by autotrophs, while secondary consumers get 1% and tertiary consumers get 0.1%. This means the top consumer of a food chain receives the least energy, as a lot of the food chain's energy has been lost between trophic levels. This loss of energy at each level limits typical food chains to only four to six links.Food web
A food web (or food cycle) is the natural interconnection of food chains and a graphical representation (usually an image) of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs. To maintain their bodies, grow, develop, and to reproduce, autotrophs produce organic matter from inorganic substances, including both minerals and gases such as carbon dioxide. These chemical reactions require energy, which mainly comes from the Sun and largely by photosynthesis, although a very small amount comes from hydrothermal vents and hot springs. A gradient exists between trophic levels running from complete autotrophs that obtain their sole source of carbon from the atmosphere, to mixotrophs (such as carnivorous plants) that are autotrophic organisms that partially obtain organic matter from sources other than the atmosphere, and complete heterotrophs that must feed to obtain organic matter. The linkages in a food web illustrate the feeding pathways, such as where heterotrophs obtain organic matter by feeding on autotrophs and other heterotrophs. The food web is a simplified illustration of the various methods of feeding that links an ecosystem into a unified system of exchange. There are different kinds of feeding relations that can be roughly divided into herbivory, carnivory, scavenging and parasitism. Some of the organic matter eaten by heterotrophs, such as sugars, provides energy. Autotrophs and heterotrophs come in all sizes, from microscopic to many tonnes - from cyanobacteria to giant redwoods, and from viruses and bdellovibrio to blue whales.
Charles Elton pioneered the concept of food cycles, food chains, and food size in his classical 1927 book "Animal Ecology"; Elton's 'food cycle' was replaced by 'food web' in a subsequent ecological text. Elton organized species into functional groups, which was the basis for Raymond Lindeman's classic and landmark paper in 1942 on trophic dynamics. Lindeman emphasized the important role of decomposer organisms in a trophic system of classification. The notion of a food web has a historical foothold in the writings of Charles Darwin and his terminology, including an "entangled bank", "web of life", "web of complex relations", and in reference to the decomposition actions of earthworms he talked about "the continued movement of the particles of earth". Even earlier, in 1768 John Bruckner described nature as "one continued web of life".
Food webs are limited representations of real ecosystems as they necessarily aggregate many species into trophic species, which are functional groups of species that have the same predators and prey in a food web. Ecologists use these simplifications in quantitative (or mathematical representation) models of trophic or consumer-resource systems dynamics. Using these models they can measure and test for generalized patterns in the structure of real food web networks. Ecologists have identified non-random properties in the topographic structure of food webs. Published examples that are used in meta analysis are of variable quality with omissions. However, the number of empirical studies on community webs is on the rise and the mathematical treatment of food webs using network theory had identified patterns that are common to all. Scaling laws, for example, predict a relationship between the topology of food web predator-prey linkages and levels of species richness.Generalist and specialist species
A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources (for example, a heterotroph with a varied diet). A specialist species can thrive only in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either group, however. Some species are highly specialized (the most extreme case being monophagy), others less so, and some can tolerate many different environments. In other words, there is a continuum from highly-specialized to broadly-generalist species.
Omnivores are usually generalists. Herbivores are often specialists, but those that eat a variety of plants may be considered generalists. A well-known example of a specialist animal is the Monophagous koala, which subsists almost entirely on eucalyptus leaves. The raccoon is a generalist because it has a natural range that includes most of North and Central America, and it is omnivorous, eating berries, insects, butterflies (Hackberry Emperor, for example), eggs and small animals.
The distinction between generalists and specialists is not limited to animals. For example, some plants require a narrow range of temperatures, soil conditions and precipitation to survive while others can tolerate a broader range of conditions. A cactus could be considered a specialist species. It will die during winters at high latitudes or if it receives too much water.
When body weight is controlled for, specialist feeders such as insectivores and frugivores have larger home ranges than generalists like some folivores (leaf eaters). Because their food source is less abundant, they need a bigger area for foraging. An example comes from the research of Tim Clutton-Brock, who found that the black and white colobus, a folivore generalist, needs a home range of only 15ha. On the other hand, the more specialized red colobus monkey has a home range of 70 ha, which it requires to find patchy shoots, flowers and fruit.When environmental conditions change, generalists are able to adapt, but specialists tend to fall victim to extinction much more easily. For example, if a species of fish were to go extinct, any specialist parasites would also face extinction. On the other hand, a species with a highly specialized ecological niche is more effective at competing with other organisms. For example, a fish and its parasites are in an evolutionary arms race, a form of co-evolution, in which the fish constantly develops defenses against the parasite, while the parasite in turn evolves adaptations to cope with the specific defenses of its host. This tends to drive the speciation of more specialized species provided conditions remain relatively stable. This involves niche partitioning as new species are formed, and biodiversity is increased.Herbivore
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. As a result of their plant diet, herbivorous animals typically have mouthparts adapted to rasping or grinding. Horses and other herbivores have wide flat teeth that are adapted to grinding grass, tree bark, and other tough plant material.
A large percentage of herbivores have mutualistic gut flora that help them digest plant matter, which is more difficult to digest than animal prey. This flora is made up of cellulose-digesting protozoans or bacteria.Hypercarnivore
A hypercarnivore is an animal which has a diet that is more than 70% meat, with the balance consisting of non-animal foods such as fungi, fruits or other plant material. Some extant examples include crocodilians, owls, shrikes, eagles, vultures, felids, most wild canids, dolphins, orcas, snakes, spiders, scorpions, mantises, marlins, groupers, and most sharks. Every species in the Felidae family, including the domesticated cat, is a hypercarnivore in its natural state. Additionally, this term is also used in paleobiology to describe taxa of animals which have an increased slicing component of their dentition relative to the grinding component. Hypercarnivores per definition need not be apex predators. For example, salmon are exclusively carnivorous, yet they are prey at all stages of life for a variety of organisms.
Many prehistoric mammals of the clade Carnivoramorpha (Carnivora and Miacoidea without Creodonta), along with the early order Creodonta, and some mammals of the even earlier order Cimolesta, were hypercarnivores. The earliest carnivorous mammal is considered to be Cimolestes, which existed during the Late Cretaceous and early Paleogene periods in North America about 66 million years ago. Theropod dinosaurs such as Tyrannosaurus rex that existed during the late Cretaceous, although not mammals, were obligate carnivores.
Large hypercarnivores evolved frequently in the fossil record, often in response to an ecological opportunity afforded by the decline or extinction of previously dominant hypercarnivorous taxa. While the evolution of large size and carnivory may be favored at the individual level, it can lead to a macroevolutionary decline, wherein such extreme dietary specialization results in reduced population densities and a greater vulnerability for extinction. As a result of these opposing forces, the fossil record of carnivores is dominated by successive clades of hypercarnivores that diversify and decline, only to be replaced by new hypercarnivorous clades.
As an example of related species with differing diets, even though they diverged only 150,000 years ago, the polar bear is the most highly carnivorous bear (more than 90% of its diet is meat) while the grizzly bear is one of the least carnivorous in many locales, with less than 10% of its diet being meat.Hypocarnivore
A hypocarnivore is an animal that consumes less than 30% meat for its diet, the majority of which consists of non-animal foods that may include fungi, fruits, and other plant material. Examples of living hypocarnivores are the grizzly bear (Ursus horribilis), black bear (Ursus americanus), binturong (Arctictis binturong), and kinkajou (Potos flavus).
The evolutionary division of carnivory into three groups, including hypercarnivore and mesocarnivore, appears to have occurred about 40 million years ago (mya). The term hypocarnivory is used with increasing frequency in describing early Canidae evolution, and reliance upon that survival strategy has a documented history in North American Borophaginae during the Miocene (23.03 to 5.33 mya). Twenty-five species of hypocarnivore co-occurred on the North American continent 30 mya. A shift from hyper- to hypo- occurred at least three times among Oligocene and Miocene canids Oxetocyon, Phlaocyon, and Cynarctus.
Large hypocarnivores (Ursus) were rare and developed in the mid-to-late Miocene-Pliocene as Borophaginae became extinct.Insectivore
An insectivore is a carnivorous plant or animal that eats insects. An alternative term is entomophage, which also refers to the human practice of eating insects.
The first insectivorous vertebrates were amphibians. When they evolved 400 million years ago, the first amphibians were piscivores, with numerous sharp conical teeth, much like a modern crocodile. The same tooth arrangement is however also suited for eating animals with exoskeletons, thus the ability to eat insects is an extension of piscivory.At one time, insectivorous mammals were scientifically classified in an order called Insectivora. This order is now abandoned, as not all insectivorous mammals are closely related. Most of the Insectivora taxa have been reclassified; those that have not yet been reclassified remain in the order Eulipotyphla.
Although individually small, insects exist in enormous numbers – they number over a million described species and some of those species occur in enormous numbers. Accordingly, insects make up a very large part of the animal biomass in almost all non-marine, non-polar environments. It has been estimated that the global insect biomass is in the region of 1012 kg with an estimated population of 1018 organisms. Many creatures depend on insects as their primary diet, and many that do not (and are thus not technically insectivores) nevertheless use insects as a protein supplement, particularly when they are breeding.Invasive species
An invasive species is a species that is not native to a specific location (an introduced species), and that has a tendency to spread to a degree believed to cause damage to the environment, human economy or human health.The term as most often used applies to introduced species that adversely affect the habitats and bioregions they invade economically, environmentally, or ecologically. Such species may be either plants or animals and may disrupt by dominating a region, wilderness areas, particular habitats, or wildland–urban interface land from loss of natural controls (such as predators or herbivores). This includes plant species labeled as exotic pest plants and invasive exotics growing in native plant communities. The European Union defines "Invasive Alien Species" as those that are, firstly, outside their natural distribution area, and secondly, threaten biological diversity. The term is also used by land managers, botanists, researchers, horticulturalists, conservationists, and the public for noxious weeds.The term "invasive" is often poorly defined or very subjective and some broaden the term to include indigenous or "native" species, that have colonized natural areas - for example deer considered by some to be overpopulating their native zones and adjacent suburban gardens in the Northeastern and Pacific Coast regions of the United States.The definition of "native" is also sometimes controversial. For example, the ancestors of Equus ferus (modern horses) evolved in North America and radiated to Eurasia before becoming locally extinct. Upon returning to North America in 1493 during their hominid-assisted migration, it is debatable as to whether they were native or exotic to the continent of their evolutionary ancestors.Notable examples of invasive plant species include The kudzu vine, Andean pampas grass, and yellow starthistle. Animal examples include the New Zealand mud snail, feral pigs, European rabbits, grey squirrels, domestic cats, carp and ferrets.Invasion of long-established ecosystems by organisms from distant bio-regions is a natural phenomenon, but has been accelerated massively by humans, from their earliest migrations though to the age of discovery, and now international trade.Mesocarnivore
A mesocarnivore is an animal whose diet consists of 30–70% meat with the balance consisting of non-animal foods which may include fungi, fruits, and other plant material. Mesocarnivores are seen today among the Canidae (coyotes, foxes), Viverridae (civets), Mustelidae (martens, tayra), Procyonidae (ringtail, raccoon), Mephitidae (skunks), and Herpestidae (some mongooses).Mesopredator release hypothesis
The mesopredator release hypothesis is an ecological theory used to describe the interrelated population dynamics between apex predators and mesopredators within an ecosystem, such that a collapsing population of the former results in dramatically-increased populations of the latter. This hypothesis describes the phenomenon of trophic cascade in specific terrestrial communities.
A mesopredator is a medium-sized, middle trophic level predator, which both preys and is preyed upon. Examples are raccoons, skunks, snakes, cownose rays, and small sharks.Mud ring feeding
Mud ring feeding (or mud plume fishing) is a cooperative feeding behavior seen in bottlenose dolphins on the lower Atlantic coast of Florida, United States. Dolphins use this hunting technique to forage and trap fish. A single dolphin will swim in a circle around a group of fish, swiftly moving his tail along the sand to create a plume. This creates a temporary net around the fish and they become disoriented. The fish begin jumping above the surface, so the dolphins can lunge through the plume and catch the fish.Planktivore
A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton.Productivity (ecology)
In ecology, productivity refers to the rate of generation of biomass in an ecosystem. It is usually expressed in units of mass per unit surface (or volume) per unit time, for instance grams per square metre per day (g m−2 d−1). The mass unit may relate to dry matter or to the mass of carbon generated. Productivity of autotrophs such as plants is called primary productivity, while that of heterotrophs such as animals is called secondary productivity.Sustainable gardening
Sustainable gardening includes the more specific sustainable landscapes, sustainable landscape design, sustainable landscaping, sustainable landscape architecture, resulting in sustainable sites. It comprises a disparate group of horticultural interests that can share the aims and objectives associated with the international post-1980s sustainable development and sustainability programs developed to address the fact that humans are now using natural biophysical resources faster than they can be replenished by nature.Included within this compass are those home gardeners, and members of the landscape and nursery industries, and municipal authorities, that integrate environmental, social, and economic factors to create a more sustainable future.
Organic gardening and the use of native plants are integral to sustainable gardening.Vermivore
Vermivore (from Latin vermi, meaning "worm" and vorare, "to devour") is a zoological term for animals that eat worms (including annelids, nematodes, and other worm-like animals). Animals with such a diet are known to be vermivorous. Some definitions are less exclusive with respect to the diet, but limit the definition to particular animals, e.g. "Feeding on worms or insect vermin. Used of a bird."An entire genus of New World warblers has been given the name Vermivora.
One vermivore that may feed exclusively on worms is Paucidentomys vermidax, a rodent species of a type commonly known as shrew rats which was discovered in 2011 in Indonesia. The name, which can be translated as "worm-eating, few-toothed mouse", refers to the fact that they have only four teeth and may live exclusively on a diet of earthworms. This reduced dentition in vermivorous mammals is said to be due to relaxed selectional pressure on dental occlusion.