A food chain is a linear network of links in a
food web starting from producer organisms (such as
grass or
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
which produce their own food via
photosynthesis) and ending at an
apex predator species (like
grizzly bear
The grizzly bear (''Ursus arctos horribilis''), also known as the North American brown bear or simply grizzly, is a population or subspecies of the brown bear inhabiting North America.
In addition to the mainland grizzly (''Ursus arctos horri ...
s or
killer whales),
detritivore
Detritivores (also known as detrivores, detritophages, detritus feeders, or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...
s (like
earthworms or
woodlice), or
decomposer species (such as
fungi or
bacteria). A food chain also shows how organisms are related to each other by the food they eat. Each level of a food chain represents a different
trophic level. A food chain differs from a food web because the complex network of
different animals' feeding relations are aggregated and the chain only follows a direct, linear pathway of
one animal at a time. Natural interconnections between food chains make it a food web.
Food chains were first introduced by the Arab scientist and philosopher
Al-Jahiz in the 10th century and later popularized in a book published in 1927 by
Charles Elton Charles Elton may refer to:
*Charles Elton (Born, 1993) Professional Rugby Player for Otago Rugby
* Charles Isaac Elton (1839–1900), English lawyer, politician, writer and antiquarian
* Charles Sutherland Elton (1900–1991), English biologist
...
, which also introduced the food web concept.
A common metric used to quantify food web trophic structure is food chain length. In its simplest form, the length of a chain is the number of links between a trophic consumer and the base of the web. The mean chain length of an entire web is the arithmetic average of the lengths of all chains in the food web.
The food chain is an energy source diagram. The food chain begins with a producer, which is eaten by a primary consumer. The primary consumer may be eaten by a secondary consumer, which in turn may be consumed by a tertiary consumer. The tertiary consumers may sometimes become prey to the top predators known as the quaternary consumers. For example, a food chain might start with a green plant as the producer, which is eaten by a snail, the primary consumer. The snail might then be the prey of a secondary consumer such as a frog, which itself may be eaten by a tertiary consumer such as a snake which in turn may be consumed by an eagle.
Food chains are very important for the survival of most species. When only one element is removed from the food chain it can result in extinction of a species in some cases. The foundation of the food chain consists of
primary producers. Primary producers, or
autotrophs, utilize energy derived from either sunlight or inorganic chemical compounds to create complex organic compounds, whereas species at higher
trophic levels cannot and so must consume producers or other life that itself consumes producers. Because the sun's light is necessary for photosynthesis, most life could not exist if the sun disappeared. Even so, it has recently been discovered that there are some forms of life,
chemotrophs, that appear to gain all their metabolic energy from chemosynthesis driven by hydrothermal vents, thus showing that some life may not require solar energy to thrive.
Decomposers, which feed on dead animals, break down the organic compounds into simple nutrients that are returned to the soil. These are the simple nutrients that plants require to create organic compounds. It is estimated that there are more than 100,000 different decomposers in existence.
Many food webs have a
keystone species
A keystone species is a species which has a disproportionately large effect on its natural environment relative to its abundance, a concept introduced in 1969 by the zoologist Robert T. Paine. Keystone species play a critical role in maintaini ...
. A keystone species is a species that has a large impact on the surrounding environment and can directly affect the food chain. If this keystone species dies off it can set the entire food chain off balance. Keystone species keep herbivores from depleting all of the foliage in their environment and preventing mass extinction.
Length
The length of a food chain is a
continuous variable
In mathematics and statistics, a quantitative variable may be continuous or discrete if they are typically obtained by ''measuring'' or ''counting'', respectively. If it can take on two particular real values such that it can also take on all re ...
providing a measure of the passage of energy and an index of
ecological structure that increases through the linkages from the lowest to the highest trophic (feeding) levels.
Food chains are often used in
ecological modeling (such as a three-species food chain). They are simplified abstractions of real food webs, but complex in their dynamics and mathematical implications.
Ecologists have formulated and tested hypotheses regarding the nature of ecological patterns associated with food chain length, such as length increasing with
ecosystem volume,
limited by the reduction of energy at each successive level,
or reflecting habitat type.
Producers, such as plants, are organisms that utilize
solar
Solar may refer to:
Astronomy
* Of or relating to the Sun
** Solar telescope, a special purpose telescope used to observe the Sun
** A device that utilizes solar energy (e.g. "solar panels")
** Solar calendar, a calendar whose dates indicate t ...
or
chemical energy
Chemical energy is the energy of chemical substances that is released when they undergo a chemical reaction and transform into other substances. Some examples of storage media of chemical energy include batteries, Schmidt-Rohr, K. (2018). "How ...
to synthesize starch. All food chains must start with a producer. In the
deep sea, food chains centered on
hydrothermal vent
A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...
s and
cold seeps exist in the absence of sunlight.
Chemosynthetic
In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g., hydrogen gas, hydro ...
bacteria and
archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
use
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
and
methane from hydrothermal vents and cold seeps as an energy source (just as plants use sunlight) to produce carbohydrates; they form the base of the food chain.
Consumers are organisms that eat other organisms. All organisms in a food chain, except the first organism, are consumers.
Food chain length is important because the amount of energy transferred decreases as trophic level increases; generally only ten percent of the total energy at one trophic level is passed to the next, as the remainder is used in the
metabolic process
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
. There are usually no more than five tropic levels in a food chain.
Humans are able to receive more energy by going back a level in the chain and consuming the food before, for example getting more energy per pound from consuming a salad than an animal which ate lettuce.
The efficiency of a food chain depends on the energy first consumed by the primary producers.
The primary consumer gets its energy from the producer and passes it to the secondary and tertiary consumers.
Food chain studies play an important role in
ecotoxicology studies, which trace the pathways and
biomagnification of
environmental contaminant
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...
s.
See also
*
Heterotroph
*
Lithotroph
*
Ecological pyramid
*
Predator-prey interaction
References
{{Authority control
Systems ecology