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The trophic level of an
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
is the position it occupies in a
food web
A food web is the natural interconnection of food chains and a graphical representation 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 ...
. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it is from the start of the chain. A food web starts at trophic level 1 with
primary producer
Primary or primaries may refer to:
Arts, entertainment, and media Music Groups and labels
* Primary (band), from Australia
* Primary (musician), hip hop musician and record producer from South Korea
* Primary Music, Israeli record label
Works
...
s such as plants, can move to
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 mouthpart ...
s at level 2,
carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
s at level 3 or higher, and typically finish with
apex predator
An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own.
Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...
s at level 4 or 5. The path along the chain can form either a one-way flow or a food "web". Ecological communities with higher
biodiversity
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
form more complex trophic paths.
The word ''trophic'' derives from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
τροφή (trophē) referring to food or nourishment.
History
The concept of trophic level was developed by
Raymond Lindeman
Raymond Laurel Lindeman (1915 – June 29, 1942) was an ecologist whose graduate research is credited with being a seminal study in the field of ecosystem ecology, specifically on the topic of trophic dynamics.
Graduate research work
Lindeman ...
(1942), based on the terminology of
August Thienemann
August Friedrich Thienemann (7 September 1882 in Gotha – 22 April 1960 in Plön) was a German limnologist, zoologist and ecologist. He studied zoology at the University of Greifswald.
He was an associate Professor of Hydrobiology at the Univer ...
(1926): "producers", "consumers" and "reducers" (modified to "decomposers" by Lindeman).
Overview
![ConsumerWikiPDiag](https://upload.wikimedia.org/wikipedia/commons/c/cb/ConsumerWikiPDiag.svg)
The three basic ways in which organisms get food are as producers, consumers, and decomposers.
* Producers (
autotroph
An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...
s) are typically
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
s 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 ...
. Plants and algae do not usually eat other organisms, but pull nutrients from the soil or the ocean and manufacture their own food using
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
. For this reason, they are called
primary producer
Primary or primaries may refer to:
Arts, entertainment, and media Music Groups and labels
* Primary (band), from Australia
* Primary (musician), hip hop musician and record producer from South Korea
* Primary Music, Israeli record label
Works
...
s. In this way, it is energy from the sun that usually powers the base of the food chain. An exception occurs in deep-sea
hydrothermal ecosystems, where there is no sunlight. Here primary producers manufacture food through a process called
chemosynthesis
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 ...
.
*
Consumers
A consumer is a person or a group who intends to order, or uses purchased goods, products, or services primarily for personal, social, family, household and similar needs, who is not directly related to entrepreneurial or business activities. T ...
(
heterotroph
A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
s) are
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
that cannot manufacture their own food and need to consume other organisms. Animals that eat primary producers (like plants) are called
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 mouthpart ...
s. Animals that eat other animals are called
carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
s, and animals that eat both plants and other animals are called
omnivore
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutr ...
s.
*
Decomposer
Decomposers are organisms that break down dead or decaying organisms; they carry out decomposition, a process possible by only certain kingdoms, such as fungi. Like herbivores and predators, decomposers are heterotrophic, meaning that they use o ...
s (
detritivores
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, ...
) break down dead plant and animal material and wastes and release it again as energy and nutrients into the ecosystem for recycling. Decomposers, such as
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
and
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
(mushrooms), feed on waste and dead matter, converting it into inorganic chemicals that can be recycled as mineral nutrients for plants to use again.
Trophic levels can be represented by numbers, starting at level 1 with plants. Further trophic levels are numbered subsequently according to how far the organism is along the food chain.
* Level 1: Plants and algae make their own food and are called producers.
* Level 2: Herbivores eat plants and are called primary consumers.
* Level 3: Carnivores that eat herbivores are called secondary consumers.
* Level 4: Carnivores that eat other carnivores are called tertiary consumers.
*
Apex predator
An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own.
Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...
s by definition have no predators and are at the top of their food web.
File:Sylvilagus floridanus.jpg,
File:Vulpes_vulpes_with_prey.jpg,
File:Aquila_chrysaetos_1_(Bohuš_Číčel).jpg,
File:Fungi in Borneo.jpg,
In real-world
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
s, there is more than one food chain for most organisms, since most organisms eat more than one kind of food or are eaten by more than one type of predator. A diagram that sets out the intricate network of intersecting and overlapping food chains for an ecosystem is called its
food web
A food web is the natural interconnection of food chains and a graphical representation 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 ...
.
[ Decomposers are often left off food webs, but if included, they mark the end of a food chain.] Thus food chains start with primary producers and end with decay and decomposers. Since decomposers recycle nutrients, leaving them so they can be reused by primary producers, they are sometimes regarded as occupying their own trophic level.
The trophic level of a species may vary if it has a choice of diet. Virtually all plants and phytoplankton are purely phototrophic and are at exactly level 1.0. Many worms are at around 2.1; insects 2.2; jellyfish 3.0; birds 3.6. A 2013 study estimates the average trophic level of human beings at 2.21, similar to pigs or anchovies.[
*
where is the catch of the species or group i in year y, and is the trophic level for species i as defined above.]
Fish at higher trophic levels usually have a higher economic value, which can result in overfishing
Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in th ...
at the higher trophic levels. Earlier reports found precipitous declines in mean trophic level of fisheries
Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place ( a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, both ...
catch, in a process known as fishing down the food web
Fishing down the food web is the process whereby fisheries in a given ecosystem, "having depleted the large predatory fish on top of the food web, turn to increasingly smaller species, finally ending up with previously spurned Forage fish, small f ...
.[ However, more recent work finds no relation between economic value and trophic level;][ and that mean trophic levels in catches, surveys and stock assessments have not in fact declined, suggesting that fishing down the food web is not a global phenomenon.][ However Pauly et al. note that trophic levels peaked at 3.4 in 1970 in the northwest and west-central Atlantic, followed by a subsequent decline to 2.9 in 1994. They report a shift away from long-lived, piscivorous, high-trophic-level bottom fishes, such as cod and haddock, to short-lived, planktivorous, low-trophic-level invertebrates (e.g., shrimps) and small, pelagic fish (e.g., herrings). This shift from high-trophic-level fishes to low-trophic-level invertebrates and fishes is a response to changes in the relative abundance of the preferred catch. They consider that this is part of the global fishery collapse,][ which finds an echo in the overfished Mediterranean Sea][Fishing Down the Mediterranean Food Webs? Executive Summary. (2000). Briand, F. and K.I. Stergio]
/ref>
Humans have a mean trophic level of about 2.21, about the same as a pig or an anchovy."Researchers calculate human trophic level for first time"
''Phys.org ''. 3 December 2013.[Bonhommeau, S., Dubroca, L., Le Pape, O., Barde, J., Kaplan, D.M., Chassot, E. and Nieblas, A.E. (2013) "Eating up the world's food web and the human trophic level". ''Proceedings of the National Academy of Sciences'', 110(51): 20617–20620. .]
FiB index
Since biomass Ecological efficiency, transfer efficiencies are only about 10%, it follows that the rate of biological production is much greater at lower trophic levels than it is at higher levels. Fisheries catch, at least, to begin with, will tend to increase as the trophic level declines. At this point the fisheries will target species lower in the food web.[ In 2000, this led Pauly and others to construct a "Fisheries in Balance" index, usually called the FiB index.][ The FiB index is defined, for any year ''y'', by]
::
where is the catch at year ''y'', is the mean trophic level of the catch at year ''y'', is the catch, the mean trophic level of the catch at the start of the series being analyzed, and is the transfer efficiency of biomass or energy between trophic levels.
The FiB index is stable (zero) over periods of time when changes in trophic levels are matched by appropriate changes in the catch in the opposite direction. The index increases if catches increase for any reason, e.g. higher fish biomass, or geographic expansion. Such decreases explain the "backward-bending" plots of trophic level versus catch originally observed by Pauly and others in 1998.
Tritrophic and other interactions
One aspect of trophic levels is called tritrophic interaction. Ecologists often restrict their research to two trophic levels as a way of simplifying the analysis; however, this can be misleading if tritrophic interactions (such as plant–herbivore–predator) are not easily understood by simply adding pairwise interactions (plant-herbivore plus herbivore–predator, for example). Significant interactions can occur between the first trophic level (plant) and the third trophic level (a predator) in determining herbivore population growth, for example. Simple genetic changes may yield morphological variants in plants that then differ in their resistance to herbivores because of the effects of the plant architecture on enemies of the herbivore.[ Plants can also develop defenses against herbivores such as chemical defenses.]
See also
* Cascade effect
A cascade effect is an inevitable and sometimes unforeseen chain of events due to an act affecting a system. If there is a possibility that the cascade effect will have a negative impact on the system, it is possible to analyze the effects with a ...
* Energy flow (ecology)
Energy flow is the flow of energy through living things within an ecosystem. All living organisms can be organized into producers and consumers, and those producers and consumers can further be organized into a food chain. Each of the levels wi ...
* Marine trophic level
* 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 ...
* Trophic cascade Trophic cascades are powerful indirect interactions that can control entire ecosystems, occurring when a trophic level in a food web is suppressed. For example, a top-down cascade will occur if predators are effective enough in predation to reduce t ...
* Trophic state index
The Trophic State Index (TSI) is a classification system designed to rate water bodies based on the amount of biological productivity they sustain. Although the term "trophic index" is commonly applied to lakes, any surface water body may be ind ...
– applied to lakes
* Trophic dynamics
A food web is the natural interconnection of food chains and a graphical representation 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 ...
– ''Food web''
References
External links
Trophic levels
BBC. Last updated March 2004.
{{DEFAULTSORT:Trophic Level
Fisheries science
Ecology