query: which type of organism would occupy the bottom trophic level

pos: Trophic level Trophic level The trophic level of an organism is the position it occupies in a food chain. 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 chain starts at trophic level 1 with primary producers such as plants, can move to herbivores at level 2, carnivores at level 3 or higher, and typically finish with apex predators at level 4 or 5. The path along the chain can form

pos: Trophic level Trophic level The trophic level of an organism is the position it occupies in a food chain. 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 chain starts at trophic level 1 with primary producers such as plants, can move to herbivores at level 2, carnivores at level 3 or higher, and typically finish with apex predators at level 4 or 5. The path along the chain can form

pos: Trophic level 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. Trophic level The trophic level of an organism is the position it occupies in a food chain. 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 chain starts at trophic level 1 with primary producers such as plants, can move

pos: Trophic level either a one-way flow or a food "web". Ecological communities with higher biodiversity form more complex trophic paths. The word "trophic" derives from the Greek τροφή (trophē) referring to food or nourishment. The concept of trophic level was developed by Raymond Lindeman (1942), based on the terminology of August Thienemann (1926): "producers", "consumers" and "reducers" (modified to "decomposers" by Lindeman). The three basic ways in which organisms get food are as producers, consumers and decomposers. 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

pos: Ecotoxicology effects. Therefore, the term "Stress Biology" would seem more appropriate. Chemicals are shown to prohibit the growth of seed germination of an arrangement of different plant species. Plants are what make up the most vital trophic level of the biomass pyramids, known as the primary producers. Because they are at the bottom of the pyramid, every other organism in an ecosystem relies on the health and abundance of the primary producers in order to survive. If plants are battling problems with diseases relating to exposure to chemicals, other organisms will either die because of starvation or obtain the disease by

pos: Cross-boundary subsidy generally increase the population growth of the resident producers (plants) and detritivores (Polis et al. 1997). Increased growth at the producer level can result in a bottom-up trophic effect, in which increases in populations at lower trophic levels support a higher population of consumers than would otherwise be possible in a closed system (Polis et al. 1997). allochthonous detrital inputs can also have strong impacts on food web dynamics over a variety of temporal scales, ranging from seconds to millennia, as in the case of fossil fuel formation from build-up of detritus over millennia (Moore et al. 2004). Many food

pos: Food web from one trophic level into another and up through the hierarchy. 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. The amount can be less than one percent in animals consuming less digestible plants,

pos: Species–area relationship Species–area relationship The species–area relationship or species–area curve describes the relationship between the area of a habitat, or of part of a habitat, and the number of species found within that area. Larger areas tend to contain larger numbers of species, and empirically, the relative numbers seem to follow systematic mathematical relationships. The species–area relationship is usually constructed for a single type of organism, such as all vascular plants or all species of a specific trophic level within a particular site. It is rarely, if ever, constructed for all types of organisms if simply because of the prodigious data requirements.

pos: Trophic level their food to their own organic tissue (the ten-percent law). For this reason, food chains rarely extend for more than 5 or 6 levels. At the lowest trophic level (the bottom of the food chain), plants convert about 1% of the sunlight they receive into chemical energy. It follows from this that the total energy originally present in the incident sunlight that is finally embodied in a tertiary consumer is about 0.001% Both the number of trophic levels and the complexity of relationships between them evolve as life diversifies through time, the exception being intermittent mass extinction events. Food webs

pos: Theoretical ecology level, is a measure of the number of species encountered as energy or nutrients move from plants to top predators. Food energy flows from one organism to the next and to the next and so on, with some energy being lost at each level. At a given trophic level there may be one species or a group of species with the same predators and prey. In 1927, Charles Elton published an influential synthesis on the use of food webs, which resulted in them becoming a central concept in ecology. In 1966, interest in food webs increased after Robert Paine's experimental

pos: Effects of the Chernobyl disaster radiation on plants and trees in particular depends on numerous factors, including climatic conditions, the mechanism of radiation deposition, and the soil type. In turn, radiated vegetation affects organisms further up the food chain. In general, the upper-level trophic organisms received less contamination, due to their ability to be more mobile and feed from multiple areas. The amount of radioactive nuclides found to have been deposited into surrounding lakes has increased the normal baseline radioactive amounts by 100 percent. Most of the radionuclides in surrounding water areas were found in the sediments at the bottom of the lakes. There has

pos: Food web 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 which no other species kills directly for its food resource needs. The intermediate levels are filled with omnivores that feed on more than one trophic level and cause energy to flow through a number of food pathways starting from a basal species. In the simplest scheme, the first trophic level (level 1) is plants, then herbivores (level 2), and then carnivores (level 3). The trophic level is equal to one more than

pos: Trophic level plots of trophic level versus catch originally observed by Pauly and others in 1998. 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

pos: Ecological pyramid shaped (forest ecosystem). Energy pyramids begin with producers on the bottom (such as plants) and proceed through the various trophic levels (such as herbivores that eat plants, then carnivores that eat flesh, then omnivores that eat both plants and flesh, and so on). The highest level is the top of the food chain. The concept of pyramid of numbers ("Eltonian pyramid") was developed by Charles Elton (1927). Later, it would also be expressed in terms of biomass by Bodenheimer (1938). The idea of pyramid of productivity or energy relies on works of G. Evelyn Hutchinson and Raymond Lindeman (1942). A

pos: Lumbricus rubellus pH variations, and to direct the organism towards possible food sources. "Lumbricus rubellus" is a saprophage which feeds on organic material that is in a high state of decomposition. In ecosystems, earthworms such as "Lumbricus rubellus" increase the rate of transfer between trophic levels by making it easier for plants to uptake nutrients. In food chains, earthworms such as "Lumbricus rubellus" are primary consumers whose role is converting the energy synthesized by photosynthetic plants into food for animals at higher trophic levels. One significant biotic interaction of "Lumbricus rubellus" results from a relationship with vitamin B-producing microorganisms such as bacteria

pos: Trophic level as it grows up. The fisheries scientist Daniel Pauly sets the values of trophic levels to one in plants and detritus, two in herbivores and detritivores (primary consumers), three in secondary consumers, and so on. The definition of the trophic level, TL, for any consumer species is: where formula_2 is the fractional trophic level of the prey "j", and formula_3 represents the fraction of "j" in the diet of "i". In the case of marine ecosystems, the trophic level of most fish and other marine consumers takes value between 2.0 and 5.0. The upper value, 5.0, is unusual, even for

pos: Trophic level largely define ecosystems, and the trophic levels define the position of organisms within the webs. But these trophic levels are not always simple integers, because organisms often feed at more than one trophic level. For example, some carnivores also eat plants, and some plants are carnivores. A large carnivore may eat both smaller carnivores and herbivores; the bobcat eats rabbits, but the mountain lion eats both bobcats and rabbits. Animals can also eat each other; the bullfrog eats crayfish and crayfish eat young bullfrogs. The feeding habits of a juvenile animal, and, as a consequence, its trophic level, can change

pos: Trophic level 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. This is only an average, and plainly both modern and ancient human eating habits are complex and vary greatly. For example, a traditional Eskimo living

pos: Apex predator Apex predator An apex predator, also known as an alpha predator or top predator, is a predator at the top of a food chain, with no natural predators. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic levels. Food chains are often far shorter on land, usually limited to being secondary consumers – for example, wolves prey mostly upon large herbivores (primary consumers), which eat plants (primary producers). The apex predator concept is applied in wildlife management, conservation and ecotourism. Apex predators have a long evolutionary history, dating at least to the

pos: Ecological efficiency remaining is lost during transfer, broken down in respiration, or lost to incomplete digestion by higher trophic level. When organisms are consumed, 10% of the energy in the food is fixed into their flesh and is available for next trophic level (carnivores or omnivores). When a carnivore or an omnivore consumes that animal, only about 10% of energy is fixed in its flesh for the higher level. For example, the Sun releases 1000 J of energy, then plants take only 100 J of energy from sunlight; thereafter, a deer would take 10 J from the plant. A wolf eating the

pos: Food web 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. Food webs depict energy flow via trophic linkages. Energy flow is directional, which contrasts

neg: Forage fish a lower trophic level, and the organisms that eat it are at a higher trophic level. Forage fish occupy middle levels in the food web, serving as a dominant prey to higher level fish, seabirds and mammals. Ecological pyramids are graphical representations, along the lines of the diagram at the right, which show how biomass or productivity changes at each trophic level in an ecosystem. The first or bottom level is occupied by primary producers or autotrophs (Greek "autos" = self and "trophe" = food). These are the names given to organisms that do not feed on other organisms, but

neg: Integrated multi-trophic aquaculture profits and can reduce financial risks due to weather, disease and market fluctuations. Over a dozen studies have investigated the economics of IMTA systems since 1985. Typically, carnivorous fish or shrimp occupy IMTA's higher trophic levels. They excrete soluble ammonia and phosphorus (orthophosphate). Seaweeds and similar species can extract these inorganic nutrients directly from their environment. Fish and shrimp also release organic nutrients which feed shellfish and deposit feeders. Species such as shellfish that occupy intermediate trophic levels often play a dual role, both filtering organic bottom-level organisms from the water and generating some ammonia. Waste feed may also provide

neg: Food web 1942 by Raymond L. Lindeman. The basis of trophic dynamics is the transfer of energy from one part of the ecosystem to another. 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." A central question in the trophic dynamic

neg: Biodilution correlation of cadmium, lead, and nickel with an increase in trophic level Cadmium and lead are both non-essential metals that will compete for calcium within an organism, which is detrimental for organism growth. Most studies measure bioaccumulation and biodilution using the δ15N isotope of nitrogen. The δ15N isotopic signature is enriched up the food web. A predator will have a higher δ15N as compared to its prey. This trend allows the trophic position of an organism to be derived. Coupled to the concentration of a specific pollutant, such as mercury, the concentration verses trophic position can be accessed. While most

neg: Ecological pyramid Ecological pyramid An ecological pyramid (also trophic pyramid, eltonian pyramid, energy pyramid, or sometimes food pyramid) is a graphical representation designed to show the biomass or bio productivity at each trophic level in a given ecosystem. "Biomass pyramids" show how much biomass (the amount of living or organic matter present in an organism) is present in the organisms at each trophic level, while "productivity pyramids" show the procreation or turnover in biomass. There is also "pyramid of numbers" which represent the number of organisms in each trophic level. They may be upright (e.g. Grassland ecosystem), inverted (parasitic ecosystem) or dumbbell

neg: Integrated multi-trophic aquaculture co-cultured species each yield valuable commercial "crops". IMTA can synergistically increase total output, even if some of the crops yield less than they would, short-term, in a monoculture. "Integrated" refers to intensive and synergistic cultivation, using water-borne nutrient and energy transfer. "Multi-trophic" means that the various species occupy different trophic levels, i.e., different (but adjacent) links in the food chain. IMTA is a specialized form of the age-old practice of aquatic polyculture, which was the co-culture of various species, often without regard to trophic level. In this broader case, the organisms may share biological and chemical processes that may be

neg: Ecological yield matter may be converted into 10 kg of herbivores, which then may be converted to 1 kg of carnivores who exclusively eat herbivores. One can compute the trophic level of an organism as the weighted average of length of the predation chain from the organism to a primary producer. This trophic level determines an exponential multiplier to convert from primary producer biomass to the organism's biomass. One can measure the amount of wood removed from a forest by asking the company who removed it; typically only one company has the logging rights to any given plot of land. In order

neg: Fishing down the food web organism in a food web, starting at level 1 with primary producers, such as phytoplankton and seaweed, then moving through the primary consumers at level 2 that eat the primary producers to the secondary consumers at level 3 that eat the primary consumers, and so on. In marine environments, trophic levels range from two to five for the apex predators. The mean trophic level can then be calculated for fishery catches by averaging trophic levels for the overall catch using the datasets for commercial fish landings. Pauly's team used the catch data from the FAO which it fed into an

neg: G. Evelyn Hutchinson limnology. His student Raymond Lindeman furthered Hutchinson's model of the trophic dynamic concept. Together they looked at energy flows through the lake in the trophic levels of ecosystems. They followed the energy using Hutchinson's notation system in which each organism was given an integer to mark how many organisms the energy had to go through in order to reach it, this was designated as its trophic level. It then became possible to measure the efficiency of a given system, or the energy losses between ascending trophic levels. Hutchinson is also recognized as being the first to use radioisotopes as tracers

neg: Trophic level 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

neg: Persistent, bioaccumulative and toxic substances taken up at a higher rate than being removed from an organism. For PBTs this is caused mainly by a resistance to degradation, biotic and abiotic. PBTs usually are highly insoluble in water which allows them to enter organisms at faster rates through fats and other nonpolar regions on an organism. Bioaccumulation of a toxicant can lead to biomagnification through a trophic web which has resulted in massive concern in areas with especially low trophic diversity. Biomagnification results in higher trophic organisms accumulating more PBTs than those of lower trophic levels through consumption of the PBT contaminated lower trophic organisms.

neg: Dioxins and dioxin-like compounds compounds are first accumulated to microscopic organisms such as phytoplankton (plankton of plant character, e.g. algae). Phytoplankton is consumed by animal plankton, this by invertebrates such as insects, these by small fish, and further by large fish and seals. At every stage or trophic level, the concentration is higher, because the persistent chemicals are not "burned off" when the higher organism uses the fat of the prey organism to produce energy. Due to bioaccumulation and biomagnification, the species at the top of the trophic pyramid are most vulnerable to dioxin-like compounds. In Europe, the white-tailed eagle and some species of

neg: Soil food web the biomass of each functional group is calculated, usually in kg carbon/hectare. In order to calculate feeding rates, researchers assume that the population of the functional group is in equilibrium. At equilibrium, the reproduction of the group balances the rate at which members are lost through natural death and predation When feeding rate is known, the efficiency with which nutrients are converted into organism biomass can be calculated. This energy stored in the organism represents the amount available to be passed on to the next trophic level. After constructing the first soil flow webs, researchers discovered that nutrients and energy

neg: Relative species abundance Relative species abundance refers to how common or rare a species is relative to other species in a given location or community. Usually relative species abundances are described for a single trophic level. Because such species occupy the same trophic level they will potentially or actually compete for similar resources. For example, relative species abundances might describe all terrestrial birds in a forest community or all planktonic copepods in a particular marine environment. Relative species abundances follow very similar patterns over a wide range of ecological communities. When plotted as a histogram of the number of species represented by 1,

neg: Theoretical ecology within which a complex network of predator–prey interactions can be organised. A food web model is a network of food chains. Each food chain starts with a primary producer or autotroph, an organism, such as a plant, which is able to manufacture its own food. Next in the chain is an organism that feeds on the primary producer, and the chain continues in this way as a string of successive predators. The organisms in each chain are grouped into trophic levels, based on how many links they are removed from the primary producers. The length of the chain, or trophic

neg: Guild (ecology) similar niches (for example, "the insect community"). Nor is a guild the same as a trophic species, organisms of the same species that have mutual predators and prey. Guild (ecology) A guild (or ecological guild) is any group of species that exploit the same resources, or that exploit different resources in related ways. It is not necessary that the species within a guild occupy the same, or even similar, ecological niches. An ecological niche is defined as the role an organism plays in its community, i.e. decomposer, primary producer, etc. Guilds are defined according to the locations, attributes, or activities

neg: Trophic species and animal, and biological stages of an organism. The reassessment grouped similar species according to habit rather than genetics. This resulted in a ratio of predator to prey in food webs is generally 1:1. By assigning groups in a trophic manner, relationships are linear in scale. This allows for predicting the proportion of different trophic links in a community food web. Trophic species Trophic species are a group of organisms that are aggregated according to their common trophic (feeding) positions in a food web or food chain. Trophic species have identical prey and a shared set of predators in the

neg: Antarctic bottom water Antarctic bottom water The Antarctic bottom water (AABW) is a type of water mass in the Southern Ocean surrounding Antarctica with temperatures ranging from −0.8 to 2 °C (35 °F), salinities from 34.6 to 34.7 psu. Being the densest water mass of the oceans, AABW is found to occupy the depth range below 4000 m of all ocean basins that have a connection to the Southern Ocean at that level. The major significance of Antarctic bottom water is that it is the coldest bottom water, giving it a significant influence on the movement of the world's oceans. Antarctic bottom water

neg: Trophic level on a diet consisting primarily of seals would have a trophic level of nearly 5. In general, each trophic level relates to the one below it by absorbing some of the energy it consumes, and in this way can be regarded as resting on, or supported by, the next lower trophic level. Food chains can be diagrammed to illustrate the amount of energy that moves from one feeding level to the next in a food chain. This is called an energy pyramid. The energy transferred between levels can also be thought of as approximating to a transfer in biomass, so

neg: Chalkhill blue by 25% in the number of adults. Since this species is of Least Concern there are few conservation efforts being put forth. But in certain areas that have been having large decline or had large decline implemented conservation efforts. This species is considered by researchers to be an indicator species of calcareous grassland habitat quality and could also be a good model organism to help develop conservation programs for more At Risk species. All three countries have done research into the conservation of the calcareous grassland. Protecting this species would also lead to helping protect higher trophic level individuals that

neg: Trophic level across an entire area or ecosystem is calculated for year y as: where formula_5 is the catch of the species or group i in year y, and formula_6 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 at the higher trophic levels. Earlier reports found precipitous declines in mean trophic level of fisheries catch, in a process known as fishing down the food web. However, more recent work finds no relation between economic value and trophic level; and that mean trophic levels in

neg: Biomass (ecology) shows, for a given ecosystem, the relationship between biomass or biological productivity and trophic levels. An ecological pyramid provides a snapshot in time of an ecological community. The bottom of the pyramid represents the primary producers (autotrophs). The primary producers take energy from the environment in the form of sunlight or inorganic chemicals and use it to create energy-rich molecules such as carbohydrates. This mechanism is called primary production. The pyramid then proceeds through the various trophic levels to the apex predators at the top. When energy is transferred from one trophic level to the next, typically only ten percent

neg: Forage fish enormous ocean production of zooplankton. They are, in turn, central prey items for higher trophic levels. Forage fish may have achieved their dominance because of the way they live in huge, and often extremely fast cruising schools. Though forage fish are abundant, there are relatively few species. There are more species of primary producers and apex predators in the ocean than there are forage fish. Forage fish occupy central positions in the ocean food webs. The position that a fish occupies in a food web is called its trophic level (Greek "trophē" = food). The organisms it eats are at

neg: Salt marsh die-off in an ecological community. Much energy is lost from one trophic level to the next (about 90%); therefore, the success of higher levels is linked to lower ones and their supply of resources (Lindeman 1942). However, the abundance and distribution of organisms in an ecosystem is also affected by densities of consumers, which limit the success of organisms at lower trophic levels and thereby influence the abundance of these organisms (Hairston et al. 1960). Many ecologists argue that bottom-up and top-down control do not play equally critical roles in the structure and dynamics of populations in an ecosystem; however, data

neg: Trophic cascade 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 may occur if predators are effective enough in predation to reduce the abundance, or alter the behavior, of their prey, thereby releasing the next lower trophic level from predation (or herbivory if the intermediate trophic level is a herbivore). The trophic cascade is an ecological concept which has stimulated new research in many areas of ecology. For example, it can be important for understanding the knock-on effects of removing top predators

neg: Ecological efficiency deer would only take 1 J. A human eating the wolf would take 0.1J, etc. The ten percent law provides a basic understanding on the cycling of food chains. Furthermore, the ten percent law shows the inefficiency of energy capture at each successive trophic level. The rational conclusion is that energy efficiency is best preserved by sourcing food as close to the initial energy source as possible. Energy at n(th) level and, Energy at n(th) level Ecological efficiency Ecological efficiency describes the efficiency with which energy is transferred from one trophic level to the next. It is determined by a

neg: Axiidea the burrow. These two groups can be further divided based on whether they contain plant material within the burrow. Burrows tend to be narrow, and can range from Y or U shaped in certain species, to intricate branching tunnels and deep wells in other species. Burrows can also differ within the classifications of external characteristics, based on the feeding mode for each organism. There are three general trophic groups that the families within the infraorder Axiidea can fall into. The first trophic group are the detritophages, or deposit feeders. The other two trophic groups are the drift catchers, which collect

neg: Puzzle Link blocks which occupy some of a 9x10 block grid. The player clears these blocks by linking together two or more discrete sections of each block type. This linking is accomplished by firing one-block-width units of pipe from a player-controlled launcher at the bottom of the screen, which the player can only move left or right. The pipes have as many varieties as the number of block types in a given level, and the type of pipe being fired is determined by the first block hit by the first fired unit of a new pipe. An existing pipe can be canceled.

neg: Fishing down the food web progressively decreasing trophic levels. The trophic level of a fish is the position it occupies on the food chain. The article establishes the importance of the mean trophic level of fisheries as a tool for measuring the health of ocean ecosystems. In 2000, the Convention on Biological Diversity selected the mean trophic level of fisheries catch, renamed the "Marine Trophic Index" (MTI), as one of eight indicators of ecosystem health. However, many of the world's most lucrative fisheries are crustacean and mollusk fisheries, which are at low trophic levels and thus result in lower MTI values. Over the last 50

neg: Ecological efficiency the organism. Finally one half of the remaining energy is lost through respiration while the rest (63 units) is used for growth and reproduction. This energy expended for growth and reproduction constitutes to the net production of trophic level 1, which is equal to formula_2 units. Ecological efficiency is a combination of several related efficiencies that describe resource utilization and the extent to which resources are converted into biomass. Theoretically, it is easy to calculate ecological efficiency using the mathematical relationships above. It is often difficult, however, to obtain accurate measurements of the values involved in the calculation. Assessing ingestion,

neg: Autecology locate the prey species, but at this point relieving predation tends to make little difference to population size, as individuals continue to reproduce around replacement level as they were at a higher density prior to the introduction of a higher trophic level . Knowledge of species-level interactions, tolerances and habitat requirements is valuable for conservation of an endangered plant or animal species by ensuring its particular ecological requirements are met. With focus on individual organism, autecology has mechanistic links to several other biological fields, including ethology, evolution, genetics and physiology Autecology Autecology is an approach in ecology that seeks to

neg: Ecological pyramid such as fish and insects. This is explained as the phytoplankton reproduce very quickly, but have much shorter individual lives. One problem with biomass pyramids is that they can make a trophic level appear to contain more energy than it actually does. For example, all birds have beaks and skeletons, which despite having mass are not typically digested by the next trophic level. A "pyramid of productivity" is often more useful, showing the production or turnover (the rate at which energy or mass is transferred from one trophic level to the next) of biomass at each trophic level. Instead of

neg: Ecological pyramid "pyramid of numbers" shows graphically the population of each level in a food chain. It is an upright pyramid given in an ecosystem, where usually the producers are more in number than any other Trophic level. This shows the number of organisms in each trophic level without any consideration for their size. This type of pyramid can be convenient, as counting is often a simple task and can be done over the years to observe the changes in a particular ecosystem. However, some types of organisms are difficult to count, especially when it comes to some juvenile forms. Unit: number

neg: Food web 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/m), and energy (k cal m yr). 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.\ The size of each level in the pyramid generally represents biomass, which can be measured as the dry weight of an organism. Autotrophs may have the highest global proportion of biomass, but they are

neg: Trophic coherence the opposite of that suggested by the arrows, which indicate the order in which words are concatenated in sentences). The syntactic function of words is also shown with node colour. There is a clear relationship between syntactic function and trophic level: the mean trophic level of common nouns (blue) is formula_29, whereas that of verbs (red) is formula_30. This example illustrates how tropic coherence or incoherence might emerge from node function, and also that the trophic structure of networks provides a means of identifying node function in certain systems. There are various ways of generating directed networks with specified trophic

neg: Food web 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. These complex multitrophic interactions involve more than two trophic levels in a food web. Another example of a multi-trophic 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

neg: Ecometrics out of all the total energy intake is also the efficiency of conversion. The collective energy assimilated in one trophic level is the energy available to the succeeding level. There is consecutively less energy available to succeeding trophic levels. Consider a situation where 1000k calories are available to beef through grain feed and that their net production after consuming feed is 100k calories, only 100k calories would be available to the trophic level above, and beyond that 10k calories for the next. Agricultural production and consumption within the economy is the modern human ecosystem. This system has been made feasible

neg: Trophic coherence their diet, and hence with trophic level. This has been suggested as the reason for food-web coherence. However, food-web models based on a "niche axis" do not reproduce realistic trophic coherence, which may mean either that this explanation is insufficient, or that several niche dimensions need to be considered. The relation between trophic level and node function can be seen in networks other than food webs. The figure shows a word adjacency network derived from the book Green Eggs and Ham, by Dr Seuss. The height of nodes represents their trophic levels (according here to the edge direction which is

neg: Bioconcentration of chemical immediately interacting with and possibly having an effect on an organism. If organism-specific fugacity values are available, it is possible to create a food web model which takes trophic webs into consideration. This is especially pertinent for conservative chemicals that are not easily metabolized into degradation products. Biomagnification of conservative chemicals such as toxic metals can be harmful to apex predators like orca whales, osprey, and bald eagles. Bioconcentration factors facilitate predicting contamination levels in an organism based on chemical concentration in surrounding water. BCF in this setting only applies to aquatic organisms. Air breathing organisms do not

neg: Salt marsh die-off these factors depends on the abiotic and biotic conditions of each local or regional marsh system and its environment. Human activities can trigger trophic cascades (Jefferies 1997), which occur when the predators that limit abundance of prey and thereby enhance survival of the next lower trophic level are depleted (Strong 1992). Depletion of top predators releases their prey from consumer control and leads to population declines of the next lower trophic level, often the primary producers. Trophic cascades occur across a minimum of three trophic levels and can impact community dynamics in a variety of systems (Estes et al. 1998).

neg: Fishing down the food web the size of the fish captured and their trophic level. The trophic level of fishes usually increases with their size, and fishing tends to selectively capture the larger fishes. This applies both between species as well as within species. When the fishing is intense, the relative abundance of the larger fish positioned high in the food chain is reduced. Consequently, over time, small fishes start to dominate the fisheries catches, and the mean trophic level of the catches declines. Recently the market value of small forage fishes and invertebrates, which have low trophic levels, has sharply increased to the point

neg: Trophic mutualism of the leafcutter ant that engage in trophic mutualism with a fungus. These ants cultivate a certain type of fungus by providing it with leaves and other nutrients. In turn, the ants will feed on a special nutrient that is only created by the fungus they nurture. This trophic mutualism was studied in detail in the 1970s and since. Trophic mutualism Trophic mutualism is a key type of ecological mutualism. Specifically, "trophic mutualism" refers to the transfer of energy and nutrients between two species. This is also sometimes known as resource-to-resource mutualism. Trophic mutualism often occurs between an autotroph and

neg: Foundation species a similar and differing taxa (McKenzie Flats study and Eastern hemlock study, respectively); however, there are many other examples in which removal of foundation species could decrease species diversity within the same or differing taxa. Foundation species In ecology, the term foundation species is used to refer to a species that has a strong role in structuring a community. A foundation species can occupy any trophic level in a food web (i.e., they can be primary producers, herbivores or predators). The term was coined by Paul K. Dayton in 1972, who applied it to certain members of marine invertebrate and

neg: Lake ecosystem trophic levels. Typically, these processes operate only between two trophic levels, with no effect on the others. In some cases, however, aquatic systems experience a trophic cascade; for example, this might occur if primary producers experience less grazing by herbivores because these herbivores are suppressed by carnivores. Bottom-up processes are functioning when the abundance or diversity of members of higher trophic levels is dependent upon the availability or quality of resources from lower levels. Finally, a combined regulating theory, , combines the predicted influences of consumers and resource availability. It predicts that trophic levels close to the lowest trophic levels

neg: Trophic cascade to food chains with more than or fewer than three trophic levels. Lauri Oksanen argued that the top trophic level in a food chain increases the abundance of producers in food chains with an odd number of trophic levels (such as in Hairston, Smith and Slobodkin's three trophic level model), but decreases the abundance of the producers in food chains with an even number of trophic levels. Additionally, he argued that the number of trophic levels in a food chain increases as the productivity of the ecosystem increases. Although the existence of trophic cascades is not controversial, ecologists have long

neg: Atlantic puffin was reduced to 16% of its previous level. The Atlantic puffin and other pelagic birds are excellent bioindicators of the environment as they occupy a high trophic level. Heavy metals and other pollutants are concentrated through the food chain and, as fish are the primary food source for Atlantic puffins, there is great potential for them to bioaccumulate heavy metals such as mercury and arsenic. Measurements can be made on eggs, feathers or internal organs and beached bird surveys, accompanied by chemical analysis of feathers, can be effective indicators of marine pollution by lipophilic substances as well as metals. In

neg: Biomass (ecology) level in the food chain. The fourth trophic level consists of predatory fish, marine mammals and seabirds that consume forage fish. Examples are swordfish, seals and gannets. Apex predators, such as orcas, which can consume seals, and shortfin mako sharks, which can consume swordfish, make up the fifth trophic level. Baleen whales can consume zooplankton and krill directly, leading to a food chain with only three or four trophic levels. Marine environments can have inverted biomass pyramids. In particular, the biomass of consumers (copepods, krill, shrimp, forage fish) is larger than the biomass of primary producers. This happens because the

neg: Biomagnification which then may be eaten by bigger fish, large birds, animals, or humans. The substances become increasingly concentrated in tissues or internal organs as they move up the chain. Bioaccumulants are substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted. Although sometimes used interchangeably with "bioaccumulation", an important distinction is drawn between the two, and with bioconcentration. Thus, bioconcentration and bioaccumulation occur within an organism, and biomagnification occurs across trophic (food chain) levels. Biodilution is also a process that occurs to all trophic

neg: Ecological efficiency transfer in both autotrophs and heterotrophs. Energy transfer between trophic levels is generally inefficient, such that net production at one trophic level is generally only 10% of the net production at the preceding trophic level (the Ten percent law). Due to non-predatory death, egestion, and respiration, a significant amount of energy is lost to the environment instead of being absorbed for production by consumers. The figure approximates the fraction of energy available after each stage of energy loss in a typical ecosystem, although these fractions vary greatly from ecosystem to ecosystem and from trophic level to trophic level. The loss

neg: Trophic coherence their trophic coherence. The position of the nodes on the vertical axis corresponds to their trophic level. In the network on the left, nodes fall into distinct (integer) trophic levels, so the network is maximally coherent formula_17. In the one on the right, many of the nodes have fractional trophic levels, and the network is more incoherent formula_18. The degree to which empirical networks are trophically coherent (or incoherent) can be investigated by comparison with a null model. This is provided by the "basal ensemble", which comprises networks in which all non-basal nodes have the same proportion of basal nodes

neg: Trophic cascade debated how ubiquitous they are. Hairston, Smith and Slobodkin argued that terrestrial ecosystems, as a rule, behave as a three trophic level trophic cascade, which provoked immediate controversy. Some of the criticisms, both of Hairston, Smith and Slobodkin's model and of Oksanen's later model, were: Antagonistically, this principle is sometimes called the "trophic trickle". Although Hairston, Smith and Slobodkin formulated their argument in terms of terrestrial food chains, the earliest empirical demonstrations of trophic cascades came from marine and, especially, aquatic ecosystems. Some of the most famous examples are: The fact that the earliest documented trophic cascades all occurred in

neg: Trophic level formula_8 is the catch at year y, formula_9 is the mean trophic level of the catch at year y, formula_10 is the catch, formula_11 the mean trophic level of the catch at the start of the series being analyzed, and formula_12 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”

neg: Non-trophic networks Non-trophic networks Any action or influence that species have on each other is considered a biological interaction. These interactions between species can be considered in several ways. One such way is to depict interactions in the form of a network, which identifies the members and the patterns that connect them. Species interactions are considered primarily in terms of trophic interactions, which depict which species feed on others. Currently, ecological networks that integrate non-trophic interactions are being built. The type of interactions they can contain can be classified into six categories: mutualism, commensalism, neutralism, amensalism, antagonism, and competition. Observing and estimating

neg: Trophic coherence formula_2. Each node formula_3 can be assigned a trophic level formula_4 according to where formula_6 is formula_3's in-degree, and nodes with formula_8 (basal nodes) have formula_9 by convention. Each edge has a "trophic difference" associated, defined as formula_10. The "trophic coherence" of the network is a measure of how tightly peaked the distribution of trophic distances, formula_11, is around its mean value, which is always formula_12. This can be captured by an "incoherence parameter" formula_13, equal to the standard deviation of formula_11: where formula_16 is the number of edges in the network. The figure shows two networks which differ in

neg: Bioaccumulation this is the expedition of Sir Douglas Mawson, where his exploration companion died from eating the liver of one of their dogs. Coastal fish (such as the smooth toadfish) and seabirds (such as the Atlantic puffin) are often monitored for heavy metal bioaccumulation. In some eutrophic aquatic systems, biodilution can occur. This trend is a decrease in a contaminant with an increase in trophic level and is due to higher concentrations of algae and bacteria to "dilute" the concentration of the pollutant. Bioaccumulation Bioaccumulation is the accumulation of substances, such as pesticides, or other chemicals in an organism. Bioaccumulation occurs

neg: Carbon diet 1 kilogram of edible produce. If an organism is placed high on the trophic level the greater the loss of energy due to digestion and metabolism. A cow needs to eat a lot of food in order to maintain its body mass and muscle tissue, but the nutritional benefits of the food is diminished once it is digested and metabolized. A diet developed around plant based food items are seen as energy efficient as they utilize the Sun’s energy for photosynthesis. Based on an average 2,000 kcal diet, the high meat diet had 2.5 times as many greenhouse gas emissions

neg: Biodilution heavy metals bioaccumulate, under certain conditions, heavy metals and organic pollutants have the potential to biodilute, making a higher organism less exposed to the toxin. Biodilution Biodilution, sometimes referred to as bloom dilution, is the decrease in concentration of an element or pollutant with an increase in trophic level. This effect is primarily observed during algal blooms whereby an increase in algal biomass reduces the concentration of pollutants in organisms higher up in the food chain, like zooplankton or daphnia. The primary elements and pollutants of concern are heavy metals such as mercury, cadmium, and lead. These toxins have been

neg: Trophic level large fish, though it occurs in apex predators of marine mammals, such as polar bears and killer whales. In addition to observational studies of animal behavior, and quantification of animal stomach contents, trophic level can be quantified through stable isotope analysis of animal tissues such as muscle, skin, hair, bone collagen. This is because there is a consistent increase in the nitrogen isotopic composition at each trophic level caused by fractionations that occur with the synthesis of biomolecules; the magnitude of this increase in nitrogen isotopic composition is approximately 3–4‰. In fisheries, the mean trophic level for the fisheries catch

neg: Krill Krill Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word "", meaning "small fry of fish", which is also often attributed to species of fish. Krill are considered an important trophic level connection – near the bottom of the food chain – because they feed on phytoplankton and (to a lesser extent) zooplankton, converting these into a form suitable for many larger animals for which krill make up the largest part of their diets. In the Southern Ocean, one species, the Antarctic krill, "Euphausia superba",

neg: Clostridium botulinum coast of Poland, and Russia. The type-E "C. botulinum" was suggested to be a true Aquatic ecosystem|aquatic organism, which was indicated by the correlation between the level of type-E contamination and flooding of the land with seawater. As the land dried, the level of type E decreased and type B became dominant. In soil and sediment from the United Kingdom, "C. botulinum" type B predominates. In general, the incidence is usually lower in soil than in sediment. In Italy, a survey conducted in the vicinity of Rome found a low level of contamination; all strains were proteolytic "C. botulinum" types

neg: Ecological efficiency of energy by a factor of one half from each of the steps of non-predatory death, defecation, and respiration is typical of many living systems. Thus, the net production at one trophic level is formula_1 or approximately ten percent that of the trophic level before it. For example, assume 500 units of energy are produced by trophic level 1. One half of that is lost to non-predatory death, while the other half (250 units) is ingested by trophic level 2. One half of the amount ingested is expelled through defecation, leaving the other half (125 units) to be assimilated by

neg: Environmental issues in Uruguay normal body functioning, the excess amounts of the heavy metals found in the bay and the surrounding Rìo de la Plata estuary, resulted in the build-up of their concentration in the muscle, and liver tissues of the fish. The contamination then travels up the food chains, from one organism to another, thus affecting wide range of organisms, and greatly increasing the concentrations with each trophic level, in the process called biomagnification. Humans, by virtue of being high in the food chain, may find in their food, the concentration of the heavy metals, exceed their natural demand, by orders of magnitude

neg: Trophic mutualism Trophic mutualism Trophic mutualism is a key type of ecological mutualism. Specifically, "trophic mutualism" refers to the transfer of energy and nutrients between two species. This is also sometimes known as resource-to-resource mutualism. Trophic mutualism often occurs between an autotroph and a heterotroph. Although there are many examples of trophic mutualisms, the heterotroph is generally a fungus or bacteria. This mutualism can be both obligate and opportunistic. Ecologists first began to understand trophic mutualisms in the mid-20th century with the investigation of nutrient abundance and distribution. One of the first trophic mutualisms was discovered in 1958 by Professor Leonard Muscatine

neg: Upwelling and low trophic levels are well-represented by high species diversity. However, the intermediate trophic level is only represented by one or two species. This trophic layer, which consists of small, pelagic fish usually makes up about only three to four percent of the species diversity of all fish species present. The lower trophic layers are very well-represented with about 500 species of copepods, 2500 species of gastropods, and 2500 species of crustaceans on average. At the apex and near-apex trophic levels, there are usually about 100 species of marine mammals and about 50 species of marine birds. The vital intermediate

neg: Ecological efficiency 250%, and soy results in 415% of input calories converted to calories able to be utilized by humans. This disparity in efficiency reflects the reduction in production from moving up trophic levels. Thus, it is more energetically efficient to form a diet from lower trophic levels. The Ten percent law of transfer of energy from one trophic level to the next was introduced by Raymond Lindeman (1942). According to this law, during the transfer of organic food energy from one trophic level to the next higher level, only about ten percent of the transferred energy is stored as flesh. The

neg: Sediment-dwelling organism live in and disturb the sediment. The deepest burrowers are the ghost shrimps – "Thalassinidea" – which go as deep as 3 metres into the sediment at the bottom of the ocean. Sediment-dwelling organism A sediment-dwelling organism is a creature or micro-organism which lives mainly inside sediment – the layer of small particles at the bottom of a body of water. These are collectively known as infauna, as opposed to epifauna – the benthic organisms which live on the surface of the sediment. Such creatures are found in the fossil record and include lingulata, trilobites and worms. They made burrows

neg: Ediacaran type preservation impressions in the sediment below, in combination with the formation of iron sulfides and pyrite to form a "death mask" mantling the organisms. An alternative hypothesis, which accounts for the occurrence of this preservational mode into the Cambrian and its increasing scarcity thereafter, links the preservation of the fossils to the higher silica content of oceans before sponges, diatoms and other silica sinks became widespread. The rate of cementation of the overlying substrate, relative to the rate of decomposition of the organism, determines whether the top or bottom surface of an organism is preserved. Most disc-shaped fossils decomposed before the

neg: Krill inedible exoskeleton. In 2011, the US Food and Drug Administration published a letter of no objection for a manufactured krill oil product to be generally recognized as safe (GRAS) for human consumption. Krill Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word "", meaning "small fry of fish", which is also often attributed to species of fish. Krill are considered an important trophic level connection – near the bottom of the food chain – because they feed on phytoplankton and (to a lesser extent) zooplankton,

neg: Cretoxyrhina By the Mid-Turonian about 91 Ma, however, pliosaurs became extinct. It is thought that the radiation of sharks like "Cretoxyrhina" may have been a major contributing factor to the acceleration of their extinction. However, the ecological void left behind was quickly filled by emerging mosasaurs, which also came to occupy the highest trophic levels. Large mosasaurs like "Tylosaurus", which reached an excess of over in length, may have provided strong competition with "Cretoxyrhina", and evidence of interspecific interactions such as bite marks from either have been found. Sharks that occupy a similar ecological role with "Cretoxyrhina" such as "Cardabiodon" and

neg: Foundation species Foundation species In ecology, the term foundation species is used to refer to a species that has a strong role in structuring a community. A foundation species can occupy any trophic level in a food web (i.e., they can be primary producers, herbivores or predators). The term was coined by Paul K. Dayton in 1972, who applied it to certain members of marine invertebrate and algae communities. It was clear from studies in several locations that there were a small handful of species whose activities had a disproportionate effect on the rest of the marine community and they were therefore

neg: Trophic coherence single in-neighbour randomly from among those already there. Every node then has an integer temporary trophic level formula_66. The remaining formula_67 edges are introduced as follows. Each pair of nodes formula_68 has two temporary trophic distances associated, formula_69 and formula_70. Each of these candidate edges is accepted with a probability that depends on this temporary distance. Klaise and Johnson use because they find the distribution of trophic distances in several kinds of networks to be approximately normal, and this choice leads to a range of the parameter formula_44 in which formula_73. Once all the edges have been introduced, one must

neg: Food web 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. 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. It was once thought that omnivory was rare, but recent evidence suggests otherwise. This realization has made trophic classifications more complex. The trophic level concept was introduced in a historical landmark paper on trophic dynamics in

neg: Hart Lake (Oregon) also receives a steady flow of fresh water from Honey Creek. As a result, Hart Lake has the most stable water level within the Warner Lakes chain. Any outflow during high water drains into Anderson Lake, just north of Hart Lake. The water in Hart Lake is quite murky due to suspended particles stirred up from the shallow bottom by wave action. However, water clarity is not a good indicator of the lake's trophic state. The amount of nutrients in the lake is very high; nitrate and phosphorus levels indicate a hypereutrophic condition. This is counterbalanced by the chlorophyll level

neg: Mixotroph Mixotroph A mixotroph is an organism that can use a mix of different sources of energy and carbon, instead of having a single trophic mode on the continuum from complete autotrophy at one end to heterotrophy at the other. Possible combinations are photo- and chemotrophy, litho- and organotrophy, auto- and heterotrophy or other combinations of these. Mixotrophs can be either eukaryotic or prokaryotic. They can take advantage of different environmental conditions. If a trophic mode is obligate, then it is always necessary for sustaining growth and maintenance; if facultative, it can be used as a supplemental source. Some organisms have

neg: Hydrogen isotope biogeochemistry the same tissues is also important, as different tissues fractionate deuterium differently. In aquatic systems, tracking trophic interactions is valuable for not only understanding the ecology of the system, but also for determining the degree of terrestrial input. The patterns of deuterium enrichment consistent within trophic levels is a useful tool for assessing the nature of these interactions in the environment. Biological deuterium fractionation through metabolism is very organism and pathway dependent, resulting in a wide variability in fractionations. Despite this, some trends still hold. Hydrogen isotopes tend to fractionate very strongly in autotrophs relative to heterotrophs during lipid biosynthesis

neg: Clavariaceae such as dark-colored "Clavulina", are typically found on only a single continent, and may be quite rare. The trophic status of the Clavariaceae has been debated in the scientific literature. It has been variously described as saprotrophic, mycorrhizal, or unknown. Experimental techniques commonly employed to determine trophic strategy, such as stable isotope analysis and phylogenetic analysis of environmental sequences (DNA that is released from an organism into the environment), have not often been used with Clavariaceae species. Birkebak and colleagues suggest that, excluding lignicolous (wood-decaying) species, the Clavariaceae are biotrophic. A 2008 estimate placed 7 genera and 120 species in

neg: Fishing down the food web an international treaty aimed at sustaining biodiversity which has been adopted by 193 member countries, selected the mean trophic level of fisheries catch as one of eight indicators for immediate testing. They renamed it the "Marine Trophic Index" (MTI), and have mandated that member countries report over time on changes in ocean trophic levels as a primary indicator of marine biodiversity and health. The Marine Trophic Index is a measure of the overall health and stability of a marine ecosystem or area. The index is also a proxy measure for overfishing and an indication of how abundant and rich the

neg: Ecosystem animals while still alive and enters the plant-based trophic system, or it is consumed after it has died, and enters the detritus-based trophic system. In aquatic systems, the proportion of plant biomass that gets consumed by herbivores is much higher. In trophic systems photosynthetic organisms are the primary producers. The organisms that consume their tissues are called primary consumers or secondary producers—herbivores. Organisms which feed on microbes (bacteria and fungi) are termed microbivores. Animals that feed on primary consumers—carnivores—are secondary consumers. Each of these constitutes a trophic level. The sequence of consumption—from plant to herbivore, to carnivore—forms a food chain.

neg: Trophic coherence new edge is placed from formula_34 to formula_3. The new node is given a temporary trophic level formula_37. Then a further formula_38 new in-neighbours formula_39 are chosen for formula_3 from among those in the network according to their trophic levels. Specifically, for a new candidate in-neighbour formula_39, the probability of being chosen is a function of formula_42. Johnson "et al" use where formula_44 is a parameter which tunes the trophic coherence: for formula_45 maximally coherent networks are generated, and formula_13 increases monotonically with formula_44 for formula_48. The choice of formula_38 is arbitrary. One possibility is to set to formula_50, where

neg: Persistent, bioaccumulative and toxic substances The toxicity of this class of compounds is high with very low concentrations of a PBT required to enact an effect on an organism compared to most other contaminants. This high toxicity along with the persistence allows for the PBT to have detrimental effects in remote areas around the globe where there is not a local source of PBTs. The bioaccumulation and magnification along with the high toxicity and persistence has the ability to destroy and/or irreparably damage trophic systems, especially the higher trophic levels, globally. It is this reason that PBTs have become an area of focus in global