Hubbry Logo
Food webFood webMain
Open search
Food web
Community hub
Food web
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Contribute something
Food web
Food web
Food web
View on Wikipedia
from Wikipedia
A freshwater aquatic food web. The blue arrows show a complete food chain (algae → daphnia → gizzard shad → largemouth bass → great blue heron)

A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Position in the food web, or trophic level, is used in ecology to broadly classify organisms as autotrophs or heterotrophs. This is a non-binary classification; some organisms (such as carnivorous plants) occupy the role of mixotrophs, or autotrophs that additionally obtain organic matter from non-atmospheric sources.

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 link an ecosystem into a unified system of exchange. There are different kinds of consumer–resource interactions 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 topological 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.[1] Scaling laws, for example, predict a relationship between the topology of food web predator-prey linkages and levels of species richness.[2]

Taxonomy of a food web

[edit]
A simplified food web illustrating a three trophic food chain (producers-herbivores-carnivores) linked to decomposers. The movement of mineral nutrients is cyclic, whereas the movement of energy is unidirectional and noncyclic. Trophic species are encircled as nodes and arrows depict the links.[3][4]

Food webs are the road-maps through Darwin's famous 'entangled bank' and have a long history in ecology. Like maps of unfamiliar ground, food webs appear bewilderingly complex. They were often published to make just that point. Yet recent studies have shown that food webs from a wide range of terrestrial, freshwater, and marine communities share a remarkable list of patterns.[5]: 669 

Links in food webs map the feeding connections (who eats whom) in an ecological community. Food cycle is an obsolete term that is synonymous with food web. Ecologists can broadly group all life forms into one of two trophic layers, the autotrophs and the heterotrophs. Autotrophs produce more biomass energy, either chemically without the sun's energy or by capturing the sun's energy in photosynthesis, than they use during metabolic respiration. Heterotrophs consume rather than produce biomass energy as they metabolize, grow, and add to levels of secondary production. A food web depicts a collection of polyphagous heterotrophic consumers that network and cycle the flow of energy and nutrients from a productive base of self-feeding autotrophs.[5][6][7]

The base or basal species in a food web are those species without prey and can include autotrophs or saprophytic detritivores (i.e., the community of decomposers in soil, biofilms, and periphyton). Feeding connections in the web are called trophic links. The number of trophic links per consumer is a measure of food web connectance. Food chains are nested within the trophic links of food webs. Food chains are linear (noncyclic) feeding pathways that trace monophagous consumers from a base species up to the top consumer, which is usually a larger predatory carnivore.[8][9][10]

External videos
video icon "Why you should care about parasites", 12.14.2018, Knowable Magazine

Linkages connect to nodes in a food web, which are aggregates of biological taxa called trophic species. Trophic species are functional groups that have the same predators and prey in a food web. Common examples of an aggregated node in a food web might include parasites, microbes, decomposers, saprotrophs, consumers, or predators, each containing many species in a web that can otherwise be connected to other trophic species.[11][12]

Trophic levels

[edit]
Main article: Trophic level
A trophic pyramid (a) and a simplified community food web (b) illustrating ecological relations among creatures that are typical of a northern Boreal terrestrial ecosystem. The trophic pyramid roughly represents each level's biomass (usually measured as total dry weight). Plants generally have the greatest biomass. Names of trophic categories are shown to the right of the pyramid. Like many wetlands, some ecosystems do not organize as a strict pyramid because aquatic plants are less productive than long-lived terrestrial plants such as trees. Ecological trophic pyramids are typically one of three kinds: 1) pyramid of numbers, 2) pyramid of biomass, or 3) pyramid of energy.[6]

Food webs have trophic levels and positions. Basal species, such as plants, form the first level and are the resource-limited species that feed on no other living creature in the web. Basal species can be autotrophs or detritivores, including "decomposing organic material and its associated microorganisms which we defined as detritus, micro-inorganic material and associated microorganisms (MIP), and vascular plant material."[13]: 94  Most autotrophs capture the sun's energy in chlorophyll, but some autotrophs (the chemolithotrophs) obtain energy by the chemical oxidation of inorganic compounds and can grow in dark environments, such as the sulfur bacterium Thiobacillus, which lives in hot sulfur springs. The top level has top (or apex) predators that no other species kills directly for their food resource needs. The intermediate levels are filled with omnivores that feed on more than one trophic level and cause energy to flow through several food pathways starting from a basal species.[14]

In the simplest scheme, the first trophic level (level 1) is plants, then herbivores (level 2), and then carnivores (level 3). The trophic level equals one more than the chain length, which is the number of links connecting to the base. The base of the food chain (primary producers or detritivores) is set at zero.[5][15] Ecologists identify feeding relations and organize species into trophic species through extensive gut content analysis of different species. The technique has been improved through the use of stable isotopes to better trace energy flow through the web.[16] It was once thought that omnivory was rare, but recent evidence suggests otherwise. This realization has made trophic classifications more complex.[17]

Trophic dynamics and multitrophic interactions

[edit]

The trophic level concept was introduced in a historical landmark paper on trophic dynamics in 1942 by Raymond L. Lindeman. The basis of trophic dynamics is the transfer of energy from one part of the ecosystem to another.[15][18] The trophic dynamic concept has served as a useful quantitative heuristic, but it has several major limitations including the precision by which an organism can be allocated to a specific trophic level. Omnivores, for example, are not restricted to any single level. Nonetheless, recent research has found that discrete trophic levels do exist, but "above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores."[17]

A central question in the trophic dynamic literature is the nature of control and regulation over resources and production. Ecologists use simplified one trophic position food chain models (producer, carnivore, decomposer). Using these models, ecologists have tested various types of ecological control mechanisms. For example, herbivores generally have an abundance of vegetative resources, which meant that their populations were largely controlled or regulated by predators. This is known as the top-down hypothesis or 'green-world' hypothesis. Alternatively to the top-down hypothesis, not all plant material is edible and the nutritional quality or antiherbivore defenses of plants (structural and chemical) suggests a bottom-up form of regulation or control.[19][20][21] Recent studies have concluded that both "top-down" and "bottom-up" forces can influence community structure and the strength of the influence is environmentally context dependent.[22][23] These complex multitrophic interactions involve more than two trophic levels in a food web.[24] For example, such interactions have been discovered in the context of arbuscular mycorrhizal fungi and aphid herbivores that utilize the same plant species.[25]

caterpillar munching a leaf
Multitrophic interaction: Euphydryas editha taylori larvae sequester defensive compounds from specific types of plants they consume to protect themselves from bird predators

Another example of a multitrophic interaction is a trophic cascade, in which predators help to increase plant growth and prevent overgrazing by suppressing herbivores. Links in a food-web illustrate direct trophic relations among species, but there are also indirect effects that can alter the abundance, distribution, or biomass in the trophic levels. For example, predators eating herbivores indirectly influence the control and regulation of primary production in plants. Although the predators do not eat the plants directly, they regulate the population of herbivores that are directly linked to plant trophism. The net effect of direct and indirect relations is called trophic cascades. Trophic cascades are separated into species-level cascades, where only a subset of the food-web dynamic is impacted by a change in population numbers, and community-level cascades, where a change in population numbers has a dramatic effect on the entire food-web, such as the distribution of plant biomass.[26]

The field of chemical ecology has elucidated multitrophic interactions that entail the transfer of defensive compounds across multiple trophic levels.[27] For example, certain plant species in the Castilleja and Plantago genera have been found to produce defensive compounds called iridoid glycosides that are sequestered in the tissues of the Taylor's checkerspot butterfly larvae that have developed a tolerance for these compounds and are able to consume the foliage of these plants.[28][29] These sequestered iridoid glycosides then confer chemical protection against bird predators to the butterfly larvae.[28][29] Another example of this sort of multitrophic interaction in plants is the transfer of defensive alkaloids produced by endophytes living within a grass host to a hemiparasitic plant that is also using the grass as a host.[30]

Energy flow and biomass

[edit]
Energy flow diagram of a frog. The frog represents a node in an extended food web. The energy ingested is utilized for metabolic processes and transformed into biomass. The energy flow continues on its path if the frog is ingested by predators, parasites, or as a decaying carcass in soil. This energy flow diagram illustrates how energy is lost as it fuels the metabolic process that transform the energy and nutrients into biomass.
Main article: Energy flow (ecology)
See also: Ecological efficiency

The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction.[31]: 11 

An expanded three link energy food chain (1. plants, 2. herbivores, 3. carnivores) illustrating the relationship between food flow diagrams and energy transformity. The transformity of energy becomes degraded, dispersed, and diminished from higher quality to lesser quantity as the energy within a food chain flows from one trophic species into another. Abbreviations: I=input, A=assimilation, R=respiration, NU=not utilized, P=production, B=biomass.[32]

Food webs depict energy flow via trophic linkages. Energy flow is directional, which contrasts against the cyclic flows of material through the food web systems.[33] Energy flow "typically includes production, consumption, assimilation, non-assimilation losses (feces), and respiration (maintenance costs)."[7]: 5  In a very general sense, energy flow (E) can be defined as the sum of metabolic production (P) and respiration (R), such that E=P+R.

Biomass represents stored energy. However, concentration and quality of nutrients and energy is variable. Many plant fibers, for example, are indigestible to many herbivores leaving grazer community food webs more nutrient limited than detrital food webs where bacteria are able to access and release the nutrient and energy stores.[34][35] "Organisms usually extract energy in the form of carbohydrates, lipids, and proteins. These polymers have a dual role as supplies of energy as well as building blocks; the part that functions as energy supply results in the production of nutrients (and carbon dioxide, water, and heat). Excretion of nutrients is, therefore, basic to metabolism."[35]: 1230–1231  The units in energy flow webs are typically a measure mass or energy per m2 per unit time. Different consumers are going to have different metabolic assimilation efficiencies in their diets. Each trophic level transforms energy into biomass. Energy flow diagrams illustrate the rates and efficiency of transfer from one trophic level into another and up through the hierarchy.[36][37]

It is the case that the biomass of each trophic level decreases from the base of the chain to the top. This is because energy is lost to the environment with each transfer as entropy increases. About eighty to ninety percent of the energy is expended for the organism's life processes or is lost as heat or waste. Only about ten to twenty percent of the organism's energy is generally passed to the next organism.[38] The amount can be less than one percent in animals consuming less digestible plants, and it can be as high as forty percent in zooplankton consuming phytoplankton.[39] Graphic representations of the biomass or productivity at each tropic level are called ecological pyramids or trophic pyramids. The transfer of energy from primary producers to top consumers can also be characterized by energy flow diagrams.[40]

Food chain

[edit]
Main article: food chain

A common metric used to quantify food web trophic structure is food chain length. Food chain length is another way of describing food webs as a measure of the number of species encountered as energy or nutrients move from the plants to top predators.[41]: 269  There are different ways of calculating food chain length depending on what parameters of the food web dynamic are being considered: connectance, energy, or interaction.[41] 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 a food web.[42][14]

In a simple predator-prey example, a deer is one step removed from the plants it eats (chain length = 1) and a wolf that eats the deer is two steps removed from the plants (chain length = 2). The relative amount or strength of influence that these parameters have on the food web address questions about:

  • the identity or existence of a few dominant species (called strong interactors or keystone species)
  • the total number of species and food-chain length (including many weak interactors) and
  • how community structure, function and stability is determined.[43][44]

Ecological pyramids

[edit]
Illustration of a range of ecological pyramids, including top pyramid of numbers, middle pyramid of biomass, and bottom pyramid of energy. The terrestrial forest (summer) and the English Channel ecosystems exhibit inverted pyramids.Note: trophic levels are not drawn to scale and the pyramid of numbers excludes microorganisms and soil animals. Abbreviations: P=Producers, C1=Primary consumers, C2=Secondary consumers, C3=Tertiary consumers, S=Saprotrophs.[6]
A four level trophic pyramid sitting on a layer of soil and its community of decomposers.
A three layer trophic pyramid linked to the biomass and energy flow concepts.

In a pyramid of numbers, the number of consumers at each level decreases significantly, so that a single top consumer, (e.g., a polar bear or a human), will be supported by a much larger number of separate producers. There is usually a maximum of four or five links in a food chain, although food chains in aquatic ecosystems are more often longer than those on land. Eventually, all the energy in a food chain is dispersed as heat.[6]

Ecological pyramids place the primary producers at the base. They can depict different numerical properties of ecosystems, including numbers of individuals per unit of area, biomass (g/m2), and energy (k cal m−2 yr−1). The emergent pyramidal arrangement of trophic levels with amounts of energy transfer decreasing as species become further removed from the source of production is one of several patterns that is repeated amongst the planets ecosystems.[4][5][45] The size of each level in the pyramid generally represents biomass, which can be measured as the dry weight of an organism.[46] Autotrophs may have the highest global proportion of biomass, but they are closely rivaled or surpassed by microbes.[47][48]

Pyramid structure can vary across ecosystems and across time. In some instances biomass pyramids can be inverted. This pattern is often identified in aquatic and coral reef ecosystems. The pattern of biomass inversion is attributed to different sizes of producers. Aquatic communities are often dominated by producers that are smaller than the consumers that have high growth rates. Aquatic producers, such as planktonic algae or aquatic plants, lack the large accumulation of secondary growth as exists in the woody trees of terrestrial ecosystems. However, they are able to reproduce quickly enough to support a larger biomass of grazers. This inverts the pyramid. Primary consumers have longer lifespans and slower growth rates that accumulates more biomass than the producers they consume. Phytoplankton live just a few days, whereas the zooplankton eating the phytoplankton live for several weeks and the fish eating the zooplankton live for several consecutive years.[49] Aquatic predators also tend to have a lower death rate than the smaller consumers, which contributes to the inverted pyramidal pattern. Population structure, migration rates, and environmental refuge for prey are other possible causes for pyramids with biomass inverted. Energy pyramids, however, will always have an upright pyramid shape if all sources of food energy are included and this is dictated by the second law of thermodynamics.[6][50]

Material flux and recycling

[edit]
Main article: Nutrient cycle

Many of the Earth's elements and minerals (or mineral nutrients) are contained within the tissues and diets of organisms. Hence, mineral and nutrient cycles trace food web energy pathways. Ecologists employ stoichiometry to analyze the ratios of the main elements found in all organisms: carbon (C), nitrogen (N), phosphorus (P). There is a large transitional difference between many terrestrial and aquatic systems as C:P and C:N ratios are much higher in terrestrial systems while N:P ratios are equal between the two systems.[51][52][53] Mineral nutrients are the material resources that organisms need for growth, development, and vitality. Food webs depict the pathways of mineral nutrient cycling as they flow through organisms.[6][18] Most of the primary production in an ecosystem is not consumed, but is recycled by detritus back into useful nutrients.[54] Many of the Earth's microorganisms are involved in the formation of minerals in a process called biomineralization.[55][56][57] Bacteria that live in detrital sediments create and cycle nutrients and biominerals.[58] Food web models and nutrient cycles have traditionally been treated separately, but there is a strong functional connection between the two in terms of stability, flux, sources, sinks, and recycling of mineral nutrients.[59][60]

Kinds of food webs

[edit]

Food webs are necessarily aggregated and only illustrate a tiny portion of the complexity of real ecosystems. For example, the number of species on the planet are likely in the general order of 107, over 95% of these species consist of microbes and invertebrates, and relatively few have been named or classified by taxonomists.[61][62][63] It is explicitly understood that natural systems are 'sloppy' and that food web trophic positions simplify the complexity of real systems that sometimes overemphasize many rare interactions. Most studies focus on the larger influences where the bulk of energy transfer occurs.[19] "These omissions and problems are causes for concern, but on present evidence do not present insurmountable difficulties."[5]: 669 

Paleoecological studies can reconstruct fossil food-webs and trophic levels. Primary producers form the base (red spheres), predators at top (yellow spheres), the lines represent feeding links. Original food-webs (left) are simplified (right) by aggregating groups feeding on common prey into coarser grained trophic species.[64]

There are different kinds or categories of food webs:

  • Source web - one or more node(s), all of their predators, all the food these predators eat, and so on.
  • Sink web - one or more node(s), all of their prey, all the food that these prey eat, and so on.
  • Community (or connectedness) web - a group of nodes and all the connections of who eats whom.
  • Energy flow web - quantified fluxes of energy between nodes along links between a resource and a consumer.[5][46]
  • Paleoecological web - a web that reconstructs ecosystems from the fossil record.[64]
  • Functional web - emphasizes the functional significance of certain connections having strong interaction strength and greater bearing on community organization, more so than energy flow pathways. Functional webs have compartments, which are sub-groups in the larger network where there are different densities and strengths of interaction.[44][65] Functional webs emphasize that "the importance of each population in maintaining the integrity of a community is reflected in its influence on the growth rates of other populations."[46]: 511 

Within these categories, food webs can be further organized according to the different kinds of ecosystems being investigated. For example, human food webs, agricultural food webs, detrital food webs, marine food webs, aquatic food webs, soil food webs, Arctic (or polar) food webs, terrestrial food webs, and microbial food webs. These characterizations stem from the ecosystem concept, which assumes that the phenomena under investigation (interactions and feedback loops) are sufficient to explain patterns within boundaries, such as the edge of a forest, an island, a shoreline, or some other pronounced physical characteristic.[66][67][68]

An illustration of a soil food web.

Detrital web

[edit]

In a detrital web, plant and animal matter is broken down by decomposers, e.g., bacteria and fungi, and moves to detritivores and then carnivores.[69] There are often relationships between the detrital web and the grazing web. Mushrooms produced by decomposers in the detrital web become a food source for deer, squirrels, and mice in the grazing web. Earthworms eaten by robins are detritivores consuming decaying leaves.[70]

"Detritus can be broadly defined as any form of non-living organic matter, including different types of plant tissue (e.g. leaf litter, dead wood, aquatic macrophytes, algae), animal tissue (carrion), dead microbes, faeces (manure, dung, faecal pellets, guano, frass), as well as products secreted, excreted or exuded from organisms (e.g. extra-cellular polymers, nectar, root exudates and leachates, dissolved organic matter, extra-cellular matrix, mucilage). The relative importance of these forms of detritus, in terms of origin, size and chemical composition, varies across ecosystems."[54]: 585 

Quantitative food webs

[edit]

Ecologists collect data on trophic levels and food webs to statistically model and mathematically calculate parameters, such as those used in other kinds of network analysis (e.g., graph theory), to study emergent patterns and properties shared among ecosystems. There are different ecological dimensions that can be mapped to create more complicated food webs, including: species composition (type of species), richness (number of species), biomass (the dry weight of plants and animals), productivity (rates of conversion of energy and nutrients into growth), and stability (food webs over time). A food web diagram illustrating species composition shows how change in a single species can directly and indirectly influence many others. Microcosm studies are used to simplify food web research into semi-isolated units such as small springs, decaying logs, and laboratory experiments using organisms that reproduce quickly, such as daphnia feeding on algae grown under controlled environments in jars of water.[43][71]

While the complexity of real food webs connections are difficult to decipher, ecologists have found mathematical models on networks an invaluable tool for gaining insight into the structure, stability, and laws of food web behaviours relative to observable outcomes. "Food web theory centers around the idea of connectance."[72]: 1648  Quantitative formulas simplify the complexity of food web structure. The number of trophic links (tL), for example, is converted into a connectance value:

,

where, S(S-1)/2 is the maximum number of binary connections among S species.[72] "Connectance (C) is the fraction of all possible links that are realized (L/S2) and represents a standard measure of food web complexity..."[73]: 12913  The distance (d) between every species pair in a web is averaged to compute the mean distance between all nodes in a web (D)[73] and multiplied by the total number of links (L) to obtain link-density (LD), which is influenced by scale-dependent variables such as species richness. These formulas are the basis for comparing and investigating the nature of non-random patterns in the structure of food web networks among many different types of ecosystems.[73][74]

Scaling laws, complexity, chaos, and pattern correlates are common features attributed to food web structure.[75][76]

Complexity and stability

[edit]
A simplified version of a food web in the Gulf of Naples in eutrophic (green) and oligotrophic (blue) summer conditions. In the Green system state, both copepods and microzooplankton exert a strong grazing pressure on phytoplankton, while in the Blue state, copepods increase their predation over microzooplankton, which in turn shifts its predation from phytoplankton to bacterial plankton or picoplankton. These trophic mechanisms stabilize the delivery of organic matter from copepods to fish.

Food webs are extremely complex. Complexity is a term that conveys the mental intractability of understanding all possible higher-order effects in a food web. Sometimes in food web terminology, complexity is defined as product of the number of species and connectance.,[77][78][79] though there have been criticisms of this definition and other proposed methods for measuring network complexity.[80] Connectance is "the fraction of all possible links that are realized in a network".[81]: 12917  These concepts were derived and stimulated through the suggestion that complexity leads to stability in food webs, such as increasing the number of trophic levels in more species rich ecosystems. This hypothesis was challenged through mathematical models suggesting otherwise, but subsequent studies have shown that the premise holds in real systems.[77][74]

At different levels in the hierarchy of life, such as the stability of a food web, "the same overall structure is maintained in spite of an ongoing flow and change of components."[82]: 476  The farther a living system (e.g., ecosystem) sways from equilibrium, the greater its complexity.[82] Complexity has multiple meanings in the life sciences and in the public sphere that confuse its application as a precise term for analytical purposes in science.[79][83] Complexity in the life sciences (or biocomplexity) is defined by the "properties emerging from the interplay of behavioral, biological, physical, and social interactions that affect, sustain, or are modified by living organisms, including humans".[84]: 1018 

Several concepts have emerged from the study of complexity in food webs. Complexity explains many principals pertaining to self-organization, non-linearity, interaction, cybernetic feedback, discontinuity, emergence, and stability in food webs. Nestedness, for example, is defined as "a pattern of interaction in which specialists interact with species that form perfect subsets of the species with which generalists interact",[85]: 575  "—that is, the diet of the most specialized species is a subset of the diet of the next more generalized species, and its diet a subset of the next more generalized, and so on."[86] Until recently, it was thought that food webs had little nested structure, but empirical evidence shows that many published webs have nested subwebs in their assembly.[87]

Food webs are complex networks. As networks, they exhibit similar structural properties and mathematical laws that have been used to describe other complex systems, such as small world and scale free properties. The small world attribute refers to the many loosely connected nodes, non-random dense clustering of a few nodes (i.e., trophic or keystone species in ecology), and small path length compared to a regular lattice.[81][88] "Ecological networks, especially mutualistic networks, are generally very heterogeneous, consisting of areas with sparse links among species and distinct areas of tightly linked species. These regions of high link density are often referred to as cliques, hubs, compartments, cohesive sub-groups, or modules...Within food webs, especially in aquatic systems, nestedness appears to be related to body size because the diets of smaller predators tend to be nested subsets of those of larger predators (Woodward & Warren 2007; YvonDurocher et al. 2008), and phylogenetic constraints, whereby related taxa are nested based on their common evolutionary history, are also evident (Cattin et al. 2004)."[89]: 257  "Compartments in food webs are subgroups of taxa in which many strong interactions occur within the subgroups and few weak interactions occur between the subgroups. Theoretically, compartments increase the stability in networks, such as food webs."[65]

Food webs are also complex in the way that they change in scale, seasonally, and geographically. The components of food webs, including organisms and mineral nutrients, cross the thresholds of ecosystem boundaries. This has led to the concept or area of study known as cross-boundary subsidy.[66][67] "This leads to anomalies, such as food web calculations determining that an ecosystem can support one half of a top carnivore, without specifying which end."[68] Nonetheless, real differences in structure and function have been identified when comparing different kinds of ecological food webs, such as terrestrial vs. aquatic food webs.[90]

History of food webs

[edit]
Victor Summerhayes and Charles Elton's 1923 food web of Bear Island (Arrows point to an organism being consumed by another organism).

Food webs serve as a framework to help ecologists organize the complex network of interactions among species observed in nature and around the world. One of the earliest descriptions of a food chain was described by a medieval Afro-Arab scholar named Al-Jahiz: "All animals, in short, cannot exist without food, neither can the hunting animal escape being hunted in his turn."[91]: 143  The earliest graphical depiction of a food web was by Lorenzo Camerano in 1880, followed independently by those of Pierce and colleagues in 1912 and Victor Shelford in 1913.[92][93] Two food webs about herring were produced by Victor Summerhayes and Charles Elton[94] and Alister Hardy[95] in 1923 and 1924. Charles Elton subsequently 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.[96] After Charles Elton's use of food webs in his 1927 synthesis,[97] they became a central concept in the field of ecology. Elton[96] organized species into functional groups, which formed the basis for the trophic system of classification in Raymond Lindeman's classic and landmark paper in 1942 on trophic dynamics.[18][44][98] 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".[5][99][100][101]

Interest in food webs increased after Robert Paine's experimental and descriptive study of intertidal shores[102] suggesting that food web complexity was key to maintaining species diversity and ecological stability. Many theoretical ecologists, including Sir Robert May[103] and Stuart Pimm,[104] were prompted by this discovery and others to examine the mathematical properties of food webs.

See also

[edit]

References

[edit]

Further reading

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Food web

View on Grokipedia
from Grokipedia
A food web is a depicting the of feeding relationships among organisms in an , illustrating how and nutrients flow through interconnected from producers to consumers and decomposers. Unlike a linear , which traces a single pathway of energy transfer (such as grass to to ), a food web encompasses multiple overlapping chains to reflect the multifaceted interactions and dependencies within a community. The concept of the food web was first articulated by ecologist Charles Elton in his 1927 book Animal Ecology, where he described ecosystems as interconnected "food cycles" limited to about four or five trophic links, emphasizing the role of top predators in structuring communities. Organisms in a food web are organized into trophic levels: producers (autotrophs like plants and algae that convert solar energy into biomass via photosynthesis), primary consumers (herbivores such as zooplankton or rabbits), secondary and tertiary consumers (carnivores like forage fish or apex predators such as striped bass), and decomposers (bacteria, fungi, and detritivores that recycle nutrients from dead matter). Energy transfer between these levels is inefficient, with only about 10% passing to the next trophic level, the rest lost as heat or waste, resulting in a pyramid of biomass where producers vastly outnumber higher-level consumers. Food webs are essential for understanding ecosystem dynamics, including stability, resilience to disturbances, and the propagation of effects from —such as how the removal of top predators can cascade through the system, altering population sizes at lower levels. Examples abound across habitats: in a forest , decomposers break down fallen leaves to support soil nutrients, fueling grasses that sustain rabbits and foxes; in marine environments like the , form the base, supporting a chain to oysters, fish, and birds, with humans as top consumers influencing the web through fishing and . These models also highlight vulnerabilities, such as of toxins (e.g., mercury) that concentrate in apex predators, underscoring the interconnected health of ecosystems.

Fundamentals of Food Webs

Definition and Basic Concepts

A food web is a of feeding relationships among organisms in an , illustrating who consumes whom through interconnected pathways of energy and nutrient transfer. Unlike a , which represents a linear, sequential path of consumption from producers to top predators, a food web captures the branching and overlapping interactions that reflect the multifaceted nature of ecological communities. This network structure highlights how multiple food chains link together, allowing for alternative pathways that enhance resilience. The primary components of a food web include producers, consumers, and decomposers. Producers, or autotrophs such as plants and algae, form the base by converting into through . Consumers, which are heterotrophs, are categorized by their feeding habits: primary consumers (herbivores) feed directly on producers, secondary consumers (carnivores) prey on herbivores, and tertiary consumers occupy higher predatory roles. Decomposers, including and fungi, break down dead organic matter, recycling nutrients back into the system for reuse by producers. Food webs are organized around a trophic structure, where energy transfers from one level to the next, typically decreasing in at higher levels. Common complexities arise from omnivory, in which a single consumes organisms from multiple trophic levels, and , where predators both compete for and consume the same prey . These interactions deviate from simple linear models and contribute to the stability and dynamics of the web. Trophic levels serve as the foundational building blocks for this structure. A representative example of a simple terrestrial food web involves grasses and shrubs as producers, supporting herbivores like rabbits and deer (primary consumers), which are preyed upon by carnivores such as foxes and hawks (secondary and tertiary consumers), with decomposers like earthworms and processing waste and remains to sustain . This interconnected setup demonstrates how disruptions in one link, such as overpopulation, can ripple through the network, affecting predators and availability.

Role in Ecosystems

Food webs play a crucial role in maintaining stability by providing and alternative pathways that buffer against perturbations, such as loss, thereby preventing trophic cascades that could destabilize the entire system. structures in food webs enhance persistence and resistance to disturbances through diverse interaction pathways, allowing ecosystems to recover from events like predator removal or prey . For instance, in diverse aquatic systems, structural asymmetry in trophic interactions contributes to long-term stability by distributing risks across multiple levels. Food webs support by fostering coexistence through intricate linkages that reduce competitive exclusion and increase resilience to environmental disturbances. Higher trophic diversity within food webs promotes multifunctionality, enabling more to persist amid fluctuating conditions like . This diversity in connections, such as predator-prey and mutualistic ties, enhances overall resilience, as seen in terrestrial and marine habitats where varied food web topologies sustain higher . Food webs underpin key services, including nutrient retention by facilitating efficient cycling through trophic levels, via plant-pollinator interactions embedded in broader networks, and natural through predator-prey dynamics that regulate populations. In agricultural landscapes, intact food webs support agricultural by maintaining balanced populations of prey and predators, ensuring long-term . These services arise from the interconnected nature of food webs, which integrate multiple trophic processes to deliver benefits like and crop protection. Disruptions in food web structure serve as indicators of , signaling underlying environmental changes such as or shifts that alter interactions and abundances. For example, shifts in metrics, like changes in trophic indices, have been used to detect impacts and habitat degradation under frameworks like the Marine Strategy Framework Directive. Monitoring these disruptions allows early detection of stressors, guiding conservation efforts to restore balance. The integrity of food webs has direct implications for human activities, particularly in and , where maintaining web complexity supports by enhancing , pest regulation, and services essential for crop yields. In agroecosystems, disruptions from intensification can cascade through food webs, reducing and services that underpin sustainable production and global food supplies. Preserving food web structure is thus vital for resilient agricultural and practices that secure long-term human well-being.

Structural Components

Trophic Levels

Trophic levels represent the hierarchical positions of organisms within a food web based on their primary mode of acquisition, forming the foundational for understanding and transfer in ecosystems. The base level, 1, consists of primary producers such as , algae, and phytoplankton, which convert solar into biomass through or . 2 comprises primary consumers, primarily herbivores that feed directly on producers, while higher levels (3 and beyond) include secondary consumers (carnivores preying on herbivores), tertiary consumers, and apex predators that occupy the top positions. Decomposers, including and fungi, operate outside this strict numbering as they break down dead , recycling but not fitting neatly into the consumer hierarchy. This classification, originally conceptualized in the context of aquatic ecosystems, emphasizes the sequential flow from autotrophs to heterotrophs. In complex food webs, discrete integer trophic levels often prove insufficient due to the prevalence of omnivory and generalist feeding strategies, leading to the adoption of fractional trophic levels. For instance, an that consumes both producers and herbivores might occupy a fractional position such as 2.5, calculated as a weighted of the trophic levels of its prey. This approach accounts for dietary breadth, where the trophic level TLiTL_i for ii is determined by TLi=1+∑jpijTLjTL_i = 1 + \sum_j p_{ij} TL_j, with pijp_{ij} representing the fraction of prey jj's in the diet of ii. Such fractional assignments reveal that in real ecosystems, many —particularly at lower levels—exhibit mixed feeding, blurring strict boundaries. Despite their utility, trophic levels face limitations in capturing the full complexity of food webs, particularly from omnivory, detritivory, and feedback loops that create non-linear interactions. Analysis of diverse food webs shows that only about 54% of can be unambiguously assigned to integer levels, with omnivory predominantly affecting the lowest three levels and detritivores complicating producer-consumer distinctions through their reliance on decaying matter. Loop systems, where predators also consume lower-level resources, further erode the hierarchical model, highlighting that real-world feeding relations are reticulate rather than strictly vertical. These challenges underscore the need for nuanced representations beyond simple leveling. Empirical measurement of trophic levels relies heavily on stable isotope analysis, which provides a time-integrated assessment of dietary history. Nitrogen isotopes (δ15N\delta^{15}N) increase predictably by 3–4‰ per trophic step due to fractionation during assimilation, allowing estimation of an organism's position relative to basal resources, while carbon isotopes (δ13C\delta^{13}C) trace the origin of (e.g., pelagic vs. benthic sources) with minimal enrichment (0–1‰ per level). This method has been validated across aquatic and terrestrial systems, enabling precise assignment even for omnivores through mixing models. For example, in a temperate , occupy level 1 with low δ15N\delta^{15}N values, at level 2 show enrichment of approximately 3.5‰, and planktivorous at level 3 exhibit further increases, illustrating the gradient empirically.083[0703:USITET]2.0.CO;2)

Food Chains and Linkages

A food chain represents a linear sequence of organisms in an where each member consumes the preceding one, transferring nutrients and from producers to higher-level consumers. Typically, these sequences begin with producers such as or algae that capture solar energy through , followed by primary consumers like herbivores, secondary consumers such as carnivores, and sometimes tertiary consumers or apex predators. Food chains are classified into types including chains, which start with living material; detrital chains, involving decomposers processing dead ; and parasitic chains, where parasites derive sustenance from living hosts within the grazing or detrital pathways. These linear pathways form the foundational building blocks of more complex food webs, illustrating direct predator-prey relationships. In food webs, individual food chains interconnect through directed linkages, where energy flows unidirectionally from prey to predator, creating a . Connectance measures the proportion of realized feeding links relative to all possible links among , often ranging from 0.1 to 0.3 in empirical webs, indicating the density of interactions. Linkage density, defined as the average number of links per , quantifies the overall connectivity and typically increases with , reflecting how extensively organisms exploit resources. These metrics highlight the web's structure, where trophic levels—positions along chains from basal producers to top predators—emerge from the aggregation of these linkages. The complexity of food webs arises from branching and convergence in these linkages: branching occurs when a single predator consumes multiple prey , increasing out-degree in network terms, while convergence happens when multiple predators feed on the same prey, elevating in-degree. Such patterns, where predators exhibit generality through diverse diets and prey face from various consumers, prevent webs from remaining simple linear chains and instead foster intricate topologies that enhance stability and resilience. Food chain lengths vary across ecosystems, with shorter chains (often 2-3 links) prevalent in simple or resource-limited environments and longer ones (up to 5 or more) in diverse, productive systems that support more trophic levels. Empirical studies indicate an average chain length of approximately 3-5 trophic levels in most webs, limited by factors like dissipation and interactions. For instance, in marine ecosystems, a typical progresses from and (producers) to (primary consumers), small (secondary consumers), larger predatory , and ultimately apex predators like .

Ecological Pyramids

Ecological pyramids are graphical models that represent the trophic structure of an by quantifying the relative abundance of organisms, their , or the at successive trophic levels, typically with producers at the base and top predators at the apex. These diagrams, first conceptualized as pyramids of numbers by Charles Elton in his 1927 book Animal Ecology, provide a visual summary of how resources diminish as energy moves through the food web, emphasizing the decreasing availability from lower to higher trophic levels. The pyramid of numbers illustrates the count of individual organisms at each trophic level, showing a general decrease upward due to the larger populations required to support fewer consumers at higher levels; for instance, in a terrestrial ecosystem, thousands of insects may serve as prey for hundreds of birds, which in turn support a handful of predators. The pyramid of biomass depicts the total mass of living organisms per trophic level, measured in units like grams per square meter, which can reveal standing crop sizes but may vary in shape depending on ecosystem dynamics. The pyramid of energy, often expressed as the rate of energy flow (e.g., kilocalories per square meter per year), always forms an upright structure because energy diminishes progressively, with only a fraction transferred between levels. These pyramids are constructed using field data, such as direct counts for numbers, wet or dry weight measurements for biomass, and calorimetric or productivity estimates for energy, often collected through sampling methods like quadrats or net hauls in specific habitats. A key principle underlying the shape of these pyramids, particularly the energy pyramid, is Lindeman's approximation of trophic transfer efficiency, which posits that approximately 10% of the energy from one is transferred to the next, with the remainder lost primarily as heat through respiration and other processes; this "10% rule," derived from empirical data on aquatic systems, explains the exponential decline in available energy and thus the pyramidal form. Inverted pyramids can occur, however, especially for : in oceanic ecosystems, the pyramid is often inverted because producers have low standing due to their rapid turnover rates (high but short lifespans), while consumers maintain higher supported by continuous production. By contrast, a forest ecosystem typically exhibits an upright pyramid of numbers, with abundant primary producers and herbivores like vastly outnumbering sparse top carnivores such as eagles. Despite their utility in visualizing trophic organization, ecological pyramids have notable limitations, as they assume a steady-state without accounting for temporal fluctuations in population sizes or seasonal variations in productivity. They also overlook detrital pathways, where much of the enters the food web through decomposers rather than direct , potentially underrepresenting microbial contributions. Additionally, these models simplify complex food webs by focusing on linear trophic levels, ignoring omnivory or occupying multiple levels, which can lead to misleading representations in dynamic or diverse systems.

Functional Dynamics

Energy Flow and Transfer

Energy enters food webs primarily through , where autotrophs such as plants and algae capture solar energy via , or in certain environments like deep-sea hydrothermal vents, through using from inorganic compounds. This energy flows unidirectionally through successive trophic levels, from producers to herbivores, carnivores, and higher-order consumers, in accordance with the first and second . Unlike nutrients, which can cycle, energy cannot be recycled and is progressively dissipated as through metabolic processes at each transfer. The foundational equation for distinguishes gross primary production (GPP), the total fixed by autotrophs, from net primary production (NPP), the available to the rest of the after accounting for autotrophic respiration:
GPP=NPP+Ra\text{GPP} = \text{NPP} + R_a
where RaR_a represents autotrophic respiration. This NPP forms the base for higher trophic levels, with subsequent transfers governed by trophic , where production at the next level (Pi+1P_{i+1}) is a of at the current level (IiI_i):
Pi+1=e×IiP_{i+1} = e \times I_i
Here, ee is the transfer , typically ranging from 0.1 to 0.2 (10-20%), as formalized in Lindeman's trophic-dynamic model. These efficiencies reflect production-to- conversion factors, where only a portion of ingested is assimilated into . Energy losses occur primarily through respiration, which releases heat during metabolism; egestion, the undigested waste excreted as feces; and mortality, where uneaten deaths contribute to detritus rather than direct transfer. These mechanisms ensure that standing crop—the biomass present at any time—remains lower than throughput, the total energy flowing through the system over time, limiting the length and productivity of food webs. Respiration alone accounts for the majority of losses, often 60-90% at each level, enforcing the observed 10-20% transfer rule. Transfer efficiencies vary by pathway; for instance, microbial loops in aquatic systems exhibit higher efficiencies (up to 30-50% in some bacterial-protozoan transfers) due to rapid turnover and direct carbon channeling to higher consumers like . In contrast, food chains involving large mammals, such as predator-prey dynamics in terrestrial , show lower efficiencies (often below 10%) owing to greater metabolic demands, longer generation times, and higher respiration losses in endothermic organisms. These differences highlight how pathway structure influences overall energy flow and productivity.

Nutrient Cycling and Material Flux

Nutrient cycling in food webs represents the closed-loop circulation of essential elements through biological communities, integrating processes within the food web with broader geological and chemical dynamics to sustain productivity. The primary biogeochemical cycles involved are those of carbon (C), nitrogen (N), and phosphorus (P), which are tightly coupled and fundamental to life on , influencing everything from to atmospheric composition. In food webs, these cycles operate through the uptake of inorganic nutrients by autotrophs, their incorporation into , and subsequent transfers and returns that prevent depletion despite ongoing biological demands. Nutrient flux paths begin with producers absorbing elements from , , or air—such as carbon via , nitrogen through root uptake or fixation, and phosphorus from dissolution—converting them into organic forms. These nutrients then transfer upward through the food web via herbivory and predation, where consumers portions into their tissues while excreting or egesting the rest, maintaining elemental flow across trophic levels. Ultimately, nutrients return to the pool available for reuse through of dead and direct , closing the loop and enabling sustained cycling rather than linear loss. This recycling contrasts with energy flow, which dissipates irreversibly as heat across trophic levels. Decomposers, primarily and fungi, play a pivotal role in release by breaking down into simpler compounds, facilitating mineralization that returns elements to inorganic forms for uptake. During , immobilization occurs when microbes temporarily bind into their , potentially slowing availability, while mineralization rates determine the pace of release, influenced by factors like , , and organic substrate quality. The balance between immobilization and mineralization governs availability, with diverse microbial communities enhancing overall cycling efficiency in food webs. The dynamics of these cycles can be quantified through nutrient turnover rates, approximated as the ratio of inputs plus biological fixation to outputs plus losses in steady-state ecosystems, reflecting the of relative to external fluxes. Stoichiometric ratios, such as the of C:N:P = 106:16:1 observed in oceanic plankton, further illustrate balanced elemental demands across food web components, guiding nutrient transfers and limiting potential imbalances. Bottlenecks in cycling arise from limiting elements that constrain food web productivity; for instance, often limits in freshwater lakes, where low availability reduces algal growth and cascades through higher trophic levels. Such limitations highlight how food web structure and function depend on the rate of supply relative to demand. In soil-based food webs, the exemplifies these processes, with symbiotic fixation by introducing bioavailable N into the system via root nodules, supporting plant growth and subsequent transfers to herbivores and predators. However, by soil microbes converts nitrate back to gaseous N2, representing a key loss pathway that can reduce overall N retention and affect long-term fertility.

Multitrophic Interactions

Multitrophic interactions encompass the dynamic exchanges among organisms across multiple trophic levels in food webs, influencing , community structure, and processes. These interactions extend beyond direct predation to include indirect effects that propagate through the network, often amplifying or dampening responses at distant levels. Trophic levels provide the foundational framework for these interactions, where energy and matter flow from producers to consumers and decomposers, but the strength and direction of controls vary based on environmental and biotic factors. A primary distinction in multitrophic regulation is between top-down and bottom-up controls. Top-down control occurs when predators exert influence on lower trophic levels by suppressing populations, thereby releasing primary producers from pressure. In contrast, bottom-up control arises when resource availability at the base of the food web limits higher-level consumers, constraining the entire chain. Empirical studies in diverse ecosystems, such as lakes and grasslands, demonstrate that the relative dominance of these controls can shift with gradients; for instance, enrichment often strengthens bottom-up effects in oligotrophic systems. Key multitrophic interactions include apparent competition, , and effects. Apparent competition arises when two prey species share a common predator, leading to indirect negative effects where an increase in one prey boosts predator numbers, suppressing the other. involves competitors within the same preying on each other, complicating food web stability by blending predation and competition dynamics. disproportionately affect community structure through strong interactions, such as a predator maintaining diversity by preventing dominance of a single prey type. Trophic cascades represent alternating effects that propagate through trophic levels, often initiated by changes in top predator abundance. In marine systems, sea otters (Enhydra lutris) exemplify this by preying on sea urchins (Strongylocentrotus spp.), which in turn reduces overgrazing on kelp forests, enhancing algal biomass and habitat complexity. Similarly, the reintroduction of gray wolves (Canis lupus) in Yellowstone National Park in 1995 triggered a cascade, reducing elk (Cervus elaphus) browsing pressure on riparian willows (Salix spp.) and aspen (Populus tremuloides), allowing vegetation recovery and benefiting beaver (Castor canadensis) populations. These cascades highlight how apex predator restoration can restructure entire ecosystems. Temporal aspects further modulate multitrophic interactions, with seasonal shifts and phenological mismatches altering interaction strengths. Seasonal variations in resource availability can intensify top-down control during peak productivity periods, while phenological mismatches—such as asynchrony between predator and prey life cycles due to —may weaken trophic links, reducing cascade propagation. For example, in temperate forests, spring outbreaks can disrupt predator-prey synchrony, leading to transient booms in plant damage before predator populations respond. Such dynamics underscore the need to consider time scales in understanding food web resilience.

Types of Food Webs

Grazing Food Webs

Grazing food webs are trophic networks in which energy and nutrients flow from living primary producers—such as vascular plants, , or —directly to herbivores and onward to carnivores and apex predators. This contrasts with detrital pathways by focusing on the consumption of intact, photosynthetically active biomass rather than decomposed material. These webs underpin energy dynamics in ecosystems where autotrophs capture efficiently, supporting consumer populations through successive trophic transfers. Seminal work by Lindeman (1942) highlighted the grazing pathway as a key model for understanding trophic efficiency in aquatic systems, influencing subsequent ecological theory. Characteristic of habitats with elevated primary productivity, grazing food webs dominate in terrestrial biomes like grasslands and forests, as well as marine pelagic zones where blooms sustain vast consumer . Herbivores in these systems exert strong selective pressure on producers, driving the of anti-herbivory defenses such as silica-rich tissues in grasses or polyphenolic compounds in woody , which in turn shape community structure and diversity. Energy transfer across trophic levels remains inefficient, with approximately 10% of assimilated energy passing to the next level due to metabolic losses, resulting in steep ecological pyramids and typically short chains limited to 3–5 levels. This inefficiency underscores the high turnover rates at basal levels, where producer far exceeds that of consumers. In oceanic pelagic environments, classical grazing webs centered on large-celled are often augmented by the , wherein viruses, , and heterotrophic protists recycle dissolved from , bridging gaps in direct and boosting overall carbon flux to higher consumers. A prominent terrestrial example is the savanna food web, where perennial grasses and forbs are grazed by migratory herbivores like zebras (Equus quagga) and Thomson's gazelles (Eudorcas thomsonii), which form the prey base for predators including lions (Panthera leo) and spotted hyenas (Crocuta crocuta), illustrating how seasonal dynamics maintain web stability. In marine settings, coral reef webs feature turf algae and symbiotic consumed by (Scaridae) and surgeonfish (), which are predated by jacks () and sharks, with herbivory critical for preventing algal overgrowth and preserving coral dominance. Human-induced , often from intensive management, disrupts these webs by reducing , compacting soils, and triggering trophic cascades that diminish and predator populations while favoring . In arid grasslands, such pressures have led to significant declines, impairing resilience and services like forage provision. Restoration efforts, including , can mitigate these effects by mimicking natural herbivory patterns and allowing recovery.

Detrital Food Webs

Detrital food webs are ecological networks centered on the processing of , which consists of dead from plants, animals, and their wastes, serving as the primary energy base. These webs begin with decomposers such as and fungi that break down the detritus, releasing nutrients and simpler organic compounds, which are then consumed by detritivores like earthworms, , and nematodes. Energy subsequently flows to predators that feed on these detritivores, forming a chain that recycles materials back into the . These food webs are particularly dominant in environments like forests, soils, and aquatic sediments, where living is often low relative to accumulated dead . Unlike grazing webs, detrital pathways feature longer food chains due to high levels of omnivory among detritivores and , allowing for more trophic levels and potentially greater overall energy retention through microbial processing. In terrestrial systems, they process the majority of plant , as herbivores typically consume only a small fraction—often less than 10%—leaving most for . Key processes in detrital food webs involve microbial breakdown, where and fungi mineralize organic compounds, liberating nutrients like and for reuse. Detritivores are often classified into functional groups based on particle size preferences: shredders (e.g., ) fragment coarse like leaves, collectors (e.g., blackflies) filter fine particles, and scrapers (e.g., some snails) graze on attached microbial films. These activities enhance rates and nutrient availability, with microbes providing essential microbial links by supplying and other resources to higher trophic levels. Detrital and food webs frequently integrate, with detritus from grazing pathways entering and vice versa, creating parallel energy channels; for instance, in headwater streams, allochthonous detritus supplies over 90% of the energy base, supplementing limited in-stream . In ecosystems, leaf litter is decomposed by fungi and , then ingested by earthworms and millipedes, which in turn support predatory birds and mammals. Similarly, in deep-sea sediments, sinking particulate from surface waters fuels benthic communities, where microbes and small process organic aggregates before transfer to larger predators like polychaetes and . One key advantage of detrital food webs is their role in stabilizing ecosystems by buffering fluctuations in live , as the steady supply of accumulated provides a reliable source amid seasonal or disturbance-related variability in growth. This pathway also enhances cycling, ensuring sustained fertility in nutrient-poor environments like soils and sediments.

Quantitative and Modeling Approaches

Network Analysis and Complexity

In food web network analysis, are represented as nodes in a , with trophic interactions depicted as edges pointing from prey to predators, capturing the flow of and through the . This graph-theoretic framework allows for the quantification of structural properties, distinguishing food webs from random by their non-random patterns of connectivity. Key metrics of complexity include connectance and linkage density. Connectance CC, defined as the fraction of possible directed links that are realized, is calculated as C=LS(S−1)C = \frac{L}{S(S-1)}, where LL is the number of trophic links and SS is the number of ; it measures the overall of interactions relative to the maximum possible. Linkage density LDLD, given by LD=LSLD = \frac{L}{S}, represents the average number of feeding links per and scales with network size in empirical webs. Additional indices such as intervality assess the chain-like ordering of diets along a trophic axis, where consumer resource sets form consecutive intervals with minimal gaps or overlaps. Nestedness evaluates how the diets of are subsets of those of generalists, promoting hierarchical in the interaction matrix. Empirical food webs consistently exhibit low connectance, typically ranging from 0.1 to 0.2, indicating sparse connectivity despite potential for denser links, which contrasts with higher values in random graphs. They also display compartmentalization into semi-isolated modules, where interactions are concentrated within subgroups of , enhancing local coherence while limiting cross-module links. These patterns arise from ecological constraints like body size hierarchies and behaviors, rather than chance. Data for constructing these networks derive primarily from empirical studies using gut content analysis, which identifies prey through direct examination of digestive tracts, and stable isotope analysis, which traces trophic positions via ratios of carbon and nitrogen isotopes in tissues. These methods provide complementary insights: gut contents reveal specific links, while isotopes quantify average trophic transfers over time. A representative example is the Ythan Estuary food web in Scotland, comprising 92 species and 409 links, where network analysis revealed significant modularity with distinct compartments among invertebrate and vertebrate predators, reflecting habitat partitioning in this coastal ecosystem.

Stability and Resilience Metrics

In food web ecology, stability refers to the persistence of community structure and function in the face of perturbations, with local stability describing the return to equilibrium after small-scale disturbances via mechanisms like negative feedback loops, while global stability encompasses recovery from large-scale disruptions that may shift the system to alternative states. Resilience, a key component of stability, quantifies the rate at which a food web recovers its pre-disturbance dynamics, often measured as the return time or speed of rebound from disequilibrium. These concepts highlight how structural features like interaction strengths and trophic levels influence a web's ability to maintain biodiversity and ecosystem services under stress. A foundational theoretical insight into stability comes from Robert May's 1972 analysis, which showed that in randomly constructed food webs, increasing —through more and connections—tends to reduce local stability when interaction strengths are moderate. Key metrics for assessing stability include robustness to deletion, defined as the proportion of secondary extinctions triggered by primary loss, where empirical webs demonstrate higher robustness against random removals (up to 50% tolerance in some cases) compared to targeted deletions of highly connected . Other metrics encompass reaction norms, which evaluate how responses to varying environmental pressures affect overall persistence, and the dampening of oscillations, where faster decay of fluctuations indicates greater dynamical stability in response to events. These measures collectively reveal how food web buffers against collapse, with quantitative thresholds often derived from matrix analyses of interaction matrices. Empirical studies underscore that functional redundancy—multiple species performing similar roles—and modularity—compartmentalized interaction clusters—bolster stability by distributing risks and localizing perturbation effects, as observed in diverse aquatic and terrestrial webs where modular structures reduced secondary extinctions by 20-30% in simulations validated against field data. Conversely, high levels of omnivory, where predators consume across trophic levels, can destabilize webs by amplifying trophic loops and increasing oscillation amplitudes, though moderate omnivory in life-history contexts may enhance persistence. Illustrative examples highlight these dynamics: in the Antarctic Southern Ocean, of (Euphausia superba), a keystone basal , has cascaded to declines in top predators like and seals, demonstrating low global stability in relatively simple polar webs due to limited redundancy. In contrast, diverse stream food webs exhibit enhanced resilience, with omnivorous linking modules to buffer loss, maintaining over 80% functionality after simulated extinctions in empirical networks from . Trade-offs in stability arise as high often promotes long-term persistence through alternative energy pathways but can delay recovery speeds from acute disturbances, as complex interactions slow coordinated responses; this context-dependency reconciles the diversity-stability debate, with meta-analyses of 100+ webs showing positive stability effects in 60% of diverse systems yet prolonged recovery (up to 2-3 times longer) compared to simpler ones.

Mathematical Models

Mathematical models of food webs provide theoretical frameworks for simulating the dynamics of interactions, population abundances, and energy flows within . These models extend classical predator-prey equations to multispecies systems and incorporate network structures to predict emergent properties such as stability and patterns. By integrating empirical data on trophic links and physiological constraints, they enable forecasts of ecosystem responses to perturbations like species invasions or environmental changes. A foundational approach involves extensions of the Lotka-Volterra equations to multispecies food webs, where population dynamics for species ii are described by the ordinary differential equation: dNidt=riNi(1−NiKi)−∑jaijNiNj\frac{dN_i}{dt} = r_i N_i \left(1 - \frac{N_i}{K_i}\right) - \sum_j a_{ij} N_i N_j Here, rir_i is the intrinsic growth rate, KiK_i the carrying capacity, and aija_{ij} the interaction coefficient representing predation or competition effects from species jj on ii. This formulation captures logistic growth modified by trophic interactions, allowing analysis of coexistence and oscillations in complex webs. Niche models offer a complementary method for predicting trophic links without explicit dynamics, assigning each species a one-dimensional niche value and connecting predators to prey whose niches fall within a random contiguous subset, constrained by connectance levels observed in nature. These models generate realistic network topologies, such as intervality and degree distributions, outperforming random or cascade alternatives in matching empirical food webs. Network generation in food web models includes random models, where links are assigned probabilistically based on connectance; cascade models, which impose a feeding hierarchy by ordering species and allowing predators to consume lower-ranked prey with probability proportional to rank; and static models that fix structures for dynamic simulations. Allometric scaling integrates body size effects, scaling interaction strengths with predator-prey mass ratios (typically 100-10,000:1), which enhances model realism by reflecting metabolic constraints on foraging. Simulation tools facilitate implementation of these models, with ordinary differential equation (ODE)-based approaches using R packages like deSolve to numerically integrate Lotka-Volterra systems for temporal dynamics. Agent-based models, such as those in the abmR package, simulate individual-level behaviors in spatial contexts, incorporating movement and rules to capture heterogeneity in large-scale webs. Validation against empirical data involves comparing simulated topologies and dynamics to observed networks from field studies, assessing fit via metrics like linkage density and predictions of success or risks under perturbations. For instance, niche models accurately forecast link presence in 70-80% of cases when calibrated to real connectance. Recent advances incorporate stochasticity through noise terms in differential equations to model demographic variability, improving persistence estimates in fluctuating environments. Climate variables are integrated via parameter adjustments for temperature-dependent rates, while Bayesian networks quantify uncertainty in link strengths using prior distributions from meta-analyses. As of 2025, emerging methods include environmental DNA (eDNA) for reconstructing trophic links non-invasively and AI-driven large language models for automated species grouping and parameterization. Examples include Gaia hypothesis-inspired models that emphasize feedback loops for global stability, simulating how trophic complexity buffers against perturbations to maintain . Meta-analysis databases like EcoBase aggregate Ecopath models, enabling cross-system validation and parameterization of dynamic simulations with mass-balanced flux data.

Historical Development and Applications

Evolution of the Concept

The concept of the food web emerged from early ecological thought rooted in 18th- and 19th-century , where scientists sought to understand nature as an interconnected governed by divine order. , in his 1749 work Oeconomia Naturae, described the "economy of nature" as a balanced of interdependent organisms, with each fulfilling a specific role in a harmonious whole, laying foundational ideas for trophic interactions without explicit diagramming. This perspective influenced later views of ecological balance, though it emphasized static equilibrium over dynamic processes. A pivotal shift toward interconnected networks occurred in the late 19th century with Stephen A. Forbes' 1887 essay "The Lake as a Microcosm," which portrayed freshwater ecosystems as integrated communities where organisms form a "living whole" through mutual dependencies, introducing the notion of a web-like structure rather than isolated elements. Forbes highlighted how predation, competition, and resource flows create a balanced "machine" in isolated lakes, anticipating modern food web complexity. In the early 20th century, Charles S. Elton formalized trophic structure in his 1927 book Animal Ecology, introducing the concepts of food chains—linear sequences of predators and prey—and trophic levels, which grouped organisms by their feeding roles (producers, herbivores, carnivores). Elton also described ecological pyramids of numbers, , and , emphasizing how these chains interconnect into broader "food cycles" within communities. Building on this, Raymond L. Lindeman's 1942 paper "The Trophic-Dynamic Aspect of " advanced energy flow models, applying thermodynamic principles to quantify efficiency across trophic levels in a , marking a transition from descriptive chains to quantitative dynamics. The mid-20th century saw ecosystem ecology flourish through the work of Eugene P. Odum and , who in the 1950s integrated food webs into holistic ecosystem studies, as detailed in Eugene's 1953 textbook Fundamentals of Ecology. Their research on energy flows, including studies at Eniwetok Atoll, emphasized self-regulating systems where food webs drive nutrient cycling and stability. further innovated with energy circuit diagrams in works like his 1972 paper, using symbolic representations to model complex trophic interactions and energy transformations in ecosystems. By the 1960s, Robert T. Paine's experimental removals of the keystone predator in intertidal zones demonstrated how individual species can disproportionately structure food webs, revealing non-linear effects on diversity and community composition. This work, published in 1966, shifted focus from uniform chains to influential nodes within networks. In the , ecologists increasingly recognized detrital pathways—decomposition-based flows—as integral to food webs, moving beyond grazing chains to include microbial and roles, as evidenced in studies of terrestrial and aquatic systems. This incorporation highlighted the dominance of detrital energy in many ecosystems, enriching web models with parallel trophic routes. Culminating these developments, Stuart L. Pimm's 1982 book Food Webs synthesized stability analyses, using mathematical approaches to explore how connectance, loop lengths, and perturbations affect resilience, establishing quantitative benchmarks for web persistence up to the early 1980s.

Modern Applications in Conservation and Management

In conservation efforts, food web concepts underpin trophic rewilding strategies, which involve reintroducing apex predators to restore top-down trophic cascades and ecosystem functions. For instance, the reintroduction of gray wolves in Yellowstone National Park has demonstrated how such interventions can regulate herbivore populations, reduce overbrowsing, and promote riparian vegetation recovery, thereby enhancing biodiversity across trophic levels. Similarly, food web models are employed to assess the impacts of invasive species, revealing how invasions disrupt trophic structures by altering interaction strengths and leading to cascading extinctions in native communities. In , ecosystem-based fisheries approaches integrate food web analyses to prevent and maintain balance among . These models simulate multispecies interactions to set sustainable harvest limits, as seen in the North Atlantic where incorporating trophic linkages has improved cod resilience by accounting for prey-predator dynamics. In , enhancing food web complexity supports ; for example, promoting diverse predator-prey networks in agricultural landscapes reduces reliance on pesticides by fostering natural enemy populations that regulate herbivores. Climate change poses significant threats to food webs through structural shifts, such as phenological mismatches where warming alters timing between consumers and resources, potentially reducing and transfer efficiency. Resilience planning in marine protected areas (MPAs) leverages food web insights to buffer these effects; studies show MPAs enhance community stability during heatwaves by preserving key trophic interactions, aiding recovery of assemblages post-disturbance. Advanced monitoring tools have revolutionized food web mapping, with stable isotope analysis tracing energy flows and trophic positions non-invasively across ecosystems. (eDNA) metabarcoding complements this by detecting trophic links through genetic traces in or , enabling rapid reconstruction of interaction networks even for cryptic . Global databases, such as the Global Web Database, aggregate these data to facilitate comparative analyses and inform large-scale conservation. Case studies illustrate practical applications; in the , food web models have guided management by quantifying nutrient-driven shifts in plankton-fish interactions, supporting targeted reductions in nitrogen loads to restore pelagic balance. In the Amazon, deforestation fragments arboreal food webs, with modeling showing diminished trophic diversity and increased vulnerability to cascades, emphasizing the need for habitat connectivity to sustain canopy-dependent . Looking ahead, integrating into food web forecasting enables real-time predictions of disruptions, such as invasion spread or climate-induced collapses, by processing vast datasets on interactions. These advancements carry policy implications, informing targets like those in the Kunming-Montreal Framework by prioritizing interventions that bolster web resilience for global ecosystem services.

References

  1. https://www.nature.com/scitable/knowledge/library/food-web-concept-and-applications-84077181/
  2. https://education.nationalgeographic.org/resource/food-web/
  3. https://www.chesapeakebay.net/discover/ecosystem/food-web
  4. https://lab.rockefeller.edu/cohenje/assets/file/181PimmLawtonCohenNature1991.pdf
  5. https://pressbooks.uwf.edu/envrioscience/chapter/3-1-energy-flow-through-ecosystems/
  6. https://www.cpp.edu/respect/resources/documents_5th/gr5.fw_content_background.pdf
  7. https://opened.cuny.edu/courseware/lesson/851/student/?section=8
  8. https://deepblue.lib.umich.edu/bitstream/handle/2027.42/74199/j.1461-9563.2008.00427.x.pdf%3Bsequence=1
  9. https://www.seagrant.sunysb.edu/ifishny/pdfs/lessons/inclass/elementary/foodweb-background.pdf
  10. https://aquaticecology.tamu.edu/wp-content/uploads/sites/3/2012/07/W-Polis-1996-Book-What-food-webs-tell-us.pdf
  11. https://www.pnas.org/doi/10.1073/pnas.1409077111
  12. https://www.journals.uchicago.edu/doi/10.1086/381964
  13. https://www.noaa.gov/education/resource-collections/marine-life/aquatic-food-webs
  14. https://www.epa.gov/sites/default/files/documents/foodchainsandfoodwebs.pdf
  15. https://pressbooks.umn.edu/introbio/chapter/ecosystemenergy/
  16. https://faculty.fiu.edu/~trexlerj/Advanced_Ecology/Morin_ch6.pdf
  17. https://pmc.ncbi.nlm.nih.gov/articles/PMC130560/
  18. https://www.diva-portal.org/smash/get/diva2:1248133/FULLTEXT02
  19. https://pmc.ncbi.nlm.nih.gov/articles/PMC7660400/
  20. https://aquaticecology.tamu.edu/wp-content/uploads/sites/3/2012/07/Hoeinghaus_et_al_2008_Oikos.pdf
  21. https://pmc.ncbi.nlm.nih.gov/articles/PMC3158938/
  22. https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1930126
  23. https://sites.lsa.umich.edu/globalchange/lectures/flow-of-energy/
  24. https://opened.cuny.edu/courseware/lesson/852/student/?section=11
  25. https://www.biologydiscussion.com/ecosystem/ecological-pyramids-and-its-limitations-biology/56295
  26. https://www.geeksforgeeks.org/biology/ecological-pyramid-its-types/
  27. https://www.khanacademy.org/science/biology/ecology/intro-to-ecosystems/a/energy-flow-primary-productivity
  28. https://socio.health/ecology-environment-urban-development/laws-of-thermodynamics-energy-flow-ecosystems/
  29. https://energy.sustainability-directory.com/term/energy-flow-in-ecosystems/
  30. https://besjournals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2005.00983.x
  31. https://fiveable.me/ap-enviro/unit-1/energy-flow-10-percent-rule/study-guide/TRmVEr5JN1FSSPwzXICg
  32. https://www.khanacademy.org/science/hs-bio/x230b3ff252126bb6:energy-and-matter-in-biological-systems/x230b3ff252126bb6:flow-of-matter-and-energy-through-ecosystems/a/matter-and-energy-in-ecosystems
  33. https://www.savemyexams.com/dp/biology/ib/23/sl/revision-notes/interaction-and-interdependence/transfer-of-energy-and-matter/energy-losses/
  34. https://tos.org/oceanography/assets/docs/20-2_pomeroy.pdf
  35. https://fiveable.me/ap-enviro/unit-1/food-chains-food-webs/study-guide/4fCgW98LwgSPkma8myW5
  36. https://www.sciencedirect.com/science/article/pii/S0048969724014116
  37. https://esajournals.onlinelibrary.wiley.com/doi/10.1890/100001
  38. https://www.pnas.org/doi/10.1073/pnas.0914281107
  39. https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.3328
  40. https://esajournals.onlinelibrary.wiley.com/doi/10.1002/eap.2684
  41. https://www.science.org/doi/10.1126/sciadv.aaw9371
  42. https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecs2.1554
  43. https://www.nature.com/scitable/knowledge/library/the-nitrogen-cycle-processes-players-and-human-15644632/
  44. https://www.nature.com/scitable/knowledge/library/the-nitrogen-cycle-processes-players-and-human-15644632
  45. https://academic.oup.com/bioscience/article/53/7/633/219782
  46. https://www.pnas.org/doi/10.1073/pnas.1621037114
  47. https://www.annualreviews.org/doi/10.1146/annurev-ecolsys-121415-032246
  48. https://pmc.ncbi.nlm.nih.gov/articles/PMC2981949/
  49. https://pressbooks.calstate.edu/biol102/chapter/energy-flow-through-ecosystems/
  50. https://opened.cuny.edu/courseware/lesson/852/overview
  51. https://bg.copernicus.org/preprints/bg-2015-66/
  52. https://pmc.ncbi.nlm.nih.gov/articles/PMC2685430/
  53. https://study.com/academy/lesson/the-food-web-ecosystem-of-coral-reefs.html
  54. https://www.nature.com/articles/s41467-023-40809-6
  55. https://extension.sdstate.edu/lasting-effects-overgrazing-rangeland-ecosystems
  56. https://www.frontiersin.org/journals/sustainable-food-systems/articles/10.3389/fsufs.2022.945514/full
  57. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/detrital-food-web
  58. https://research.fs.usda.gov/treesearch/download/66060.pdf
  59. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/detrital-food-web
  60. https://academic.oup.com/book/4275/chapter/146154655
  61. https://www.sciencedirect.com/science/article/pii/S0031405604701948
  62. https://wernberglab.org/wp-content/uploads/2019/12/vilas-et-al-2020-jms-kelp-carbon-uptake-by-arctic-deep-sea-food-webs.pdf
  63. https://www.pnas.org/doi/10.1073/pnas.192407699
  64. https://www.sciencedirect.com/science/article/pii/S2666389920301070
  65. https://www.pnas.org/doi/10.1073/pnas.0603844103
  66. https://besjournals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2656.2008.01362.x
  67. https://pmc.ncbi.nlm.nih.gov/articles/PMC4424665/
  68. https://pmc.ncbi.nlm.nih.gov/articles/PMC9848559/
  69. https://www.sciencedirect.com/science/article/abs/pii/S014111362200215X
  70. https://www.sciencedirect.com/science/article/abs/pii/S0022519301924609
  71. https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.13651
  72. https://www.sciencedirect.com/science/article/abs/pii/S0022519310006387
  73. https://www.science.org/doi/10.1126/sciadv.adv3841
  74. https://www.nature.com/articles/238413a0
  75. https://pnas.org/doi/10.1073/pnas.192407699
  76. https://link.springer.com/article/10.1007/s10144-018-0628-3
  77. https://www.nature.com/articles/ncomms8379
  78. https://royalsocietypublishing.org/doi/10.1098/rspb.1997.0172
  79. https://www.researchgate.net/publication/6807845_Modelling_Southern_Ocean_ecosystems_Krill_the_food-web_and_the_impacts_of_harvesting
  80. https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2656.14121
  81. https://pmc.ncbi.nlm.nih.gov/articles/PMC4734619/
  82. https://www.sciencedirect.com/science/article/pii/S0092824084800440
  83. https://www.pnas.org/doi/10.1073/pnas.0603039103
  84. https://besjournals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2009.01644.x
  85. https://pubmed.ncbi.nlm.nih.gov/17040325/
  86. https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.14014
  87. https://www.sciencedirect.com/science/article/abs/pii/B9780124200029000044
  88. https://pmc.ncbi.nlm.nih.gov/articles/PMC8928887/
  89. https://nsojournals.onlinelibrary.wiley.com/doi/10.1111/ecog.07546
  90. https://www.sciencedirect.com/science/article/pii/S1574954115001648
  91. https://www.biorxiv.org/content/10.1101/2025.05.18.654761v2
  92. https://www.sciencedirect.com/science/article/pii/S1470160X25003292
  93. https://doi.org/10.7551/mitpress/9780262194983.003.0024
  94. https://ecobase.ecopath.org/
  95. https://esajournals.onlinelibrary.wiley.com/doi/10.1890/0012-9623%25282007%252988%255B72%253AAHOTES%255D2.0.CO%253B2
  96. https://www.tandfonline.com/doi/full/10.1080/00033790.2025.2514438
  97. https://people.wku.edu/charles.smith/biogeog/FORB1887.htm
  98. https://www.journals.uchicago.edu/doi/abs/10.1086/384945
  99. https://esajournals.onlinelibrary.wiley.com/doi/10.1890/0012-9623%25282007%252988%255B50%253AUFCAFW%255D2.0.CO%253B2
  100. https://www.oxfordbibliographies.com/abstract/document/obo-9780199830060/obo-9780199830060-0190.xml
  101. https://www.environmentandsociety.org/sites/default/files/key_docs/madison-3-2.pdf
  102. https://www.lubchencomengelab.com/uploads/1/1/9/0/119053103/estes_et_al-2016-ecology.pdf
  103. http://www.csun.edu/~msteele/classes/marine_ecology/readings/Paine_1966.pdf
  104. https://www.researchgate.net/publication/250078156_Understanding_Food_Chains_and_Food_Webs_1700-1970
  105. https://link.springer.com/book/10.1007/978-94-009-5925-5
  106. https://www.pnas.org/doi/10.1073/pnas.1502556112
  107. https://pmc.ncbi.nlm.nih.gov/articles/PMC8609295/
  108. https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1196329/full
  109. https://www.sciencedirect.com/science/article/abs/pii/S235224961530029X
  110. https://www.sciencedirect.com/science/article/abs/pii/S0169534722001422
  111. https://www.nature.com/articles/s41598-023-28507-1
  112. https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2019.00395/full
  113. https://www.canberra.edu.au/globalwebdb/
  114. https://pmc.ncbi.nlm.nih.gov/articles/PMC9110573/
  115. https://pmc.ncbi.nlm.nih.gov/articles/PMC12513428/
  116. https://www.pnas.org/doi/10.1073/pnas.2220283120
  117. https://www.cbd.int/gbf/targets
Add your contribution
Related Hubs
Contribute something
User Avatar
No comments yet.