What determines the number of trophic levels. Trophic levels, types, meaning, patterns and definition of the food chain
Level 1, producers
2 level, hare
3rd level, fox
4th level, eagle
Trophic level- a unit denoting the remoteness of an organism from producers in the food (trophic) chain. Word trophic comes from Greek τροφή (trophē) - food.
Both the number of trophic levels and their complexity of study are increasing, with the exception of periodic mass extinctions.
Levels
There are several levels in the food chain. The food chain starts at level 1 - it contains producers such as plants. At level 2 are herbivores that feed on producers. Carnivores are found at level 3. Sometimes the food chain ends with apex predators, which are at trophic levels 4 or 5. Ecological communities with higher biodiversity form more complex trophic pathways.
Ways to get food
The concept of "trophic level" was introduced by Raymond Lindemann in 1942, based on the terminology of August Tienmann (1926), who called the ways of obtaining food:
Trophic levels are not always defined by natural integers because organisms often feed on different foods and are at more than one trophic level. For example, some carnivores also eat plants. A large predator can eat both smaller predators and herbivores. Killer whales are top predators, but they are divided into separate species that prey on specific prey - tuna, small sharks and seals. Daniel Poli presented the calculations of trophic levels:
T L i = 1 + ∑ j (T L j ⋅ D C i j) (\displaystyle TL_(i)=1+\sum _(j)(TL_(j)\cdot DC_(ij))\ !},where T L j (\displaystyle TL_(j)) is the trophic prey level j, a D C i j (\displaystyle DC_(ij)) is a share j in the body's diet i.
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§ 8. Trophic levels. Ecological pyramids
The concept of trophic levels. Trophic level- This is a group of organisms that occupy a certain position in the overall food chain. To organisms that receive their energy from the sun through the same number of steps belong to one trophic level.
Such a sequence and subordination of groups of organisms connected in the form of trophic levels is a flow of matter and energy in an ecosystem, the basis of its organization.
Trophic structure of the ecosystem. As a result of the sequence of energy transformations in food chains, each community of living organisms in an ecosystem acquires a certain trophic structure. The trophic structure of the community reflects the ratio between producers, consumers (separately of the first, second, etc. orders) and decomposers, expressed either by the number of individuals of living organisms, or ph biomass, or the energy contained in them, calculated per unit area per unit time.
The trophic structure is usually depicted as ecological pyramids. This graphic model was developed in 1927 by the American zoologist Charles Elton. The base of the pyramid is the first trophic level - the level of producers, and the next floors of the pyramid are formed by subsequent levels - consumers of various orders. The height of all blocks is the same, and the length is proportional to the number, biomass or energy at the corresponding level. There are three ways to build ecological pyramids.
1. Pyramid of numbers(numbers) reflects the number of individual organisms at each level. For example, to feed one wolf, you need at least a few hares that he could hunt; to feed these hares, you need a fairly large number of various plants. Sometimes pyramids of numbers can be inverted, or inverted. This applies to forest food chains, when trees serve as producers, and insects as primary consumers. In this case, the level of primary consumers is numerically richer than the level of producers (a large number of insects feed on one tree).
2. Pyramid of biomass- the ratio of the masses of organisms of different trophic levels. Usually, in terrestrial biocenoses, the total mass of producers is greater than each subsequent link. In turn, the total mass of first-order consumers is greater than second-order consumers, and so on. If the organisms do not differ too much in size, then the graph usually shows a stepped pyramid with a tapering top. So, for the formation of 1 kg of beef, 70-90 kg of fresh grass is needed.
In aquatic ecosystems, it is also possible to obtain an inverted or inverted biomass pyramid, when the biomass of producers is less than that of consumers, and sometimes decomposers. For example, in the ocean, with a fairly high productivity of phytoplankton, its total mass at a given moment may be less than that of consumer consumers (whales, large fish, mollusks).
Pyramids of numbers and biomass reflect static systems, i.e., characterize the number or biomass of organisms in a certain period of time. They do not provide complete information about the trophic structure of the ecosystem, although they allow solving a number of practical problems, especially those related to maintaining the stability of ecosystems. The pyramid of numbers makes it possible, for example, to calculate the allowable value of catching fish or shooting animals during the hunting period without consequences for their normal reproduction.
3. Pyramid of energy reflects the magnitude of the energy flow, the speed of passage of the mass of food through the food chain. The structure of the biocenosis is largely influenced not by the amount of fixed energy, but by the rate of food production.
It has been established that the maximum amount of energy transferred to the next trophic level can in some cases be 30% of the previous one, and this is at best. In many biocenoses, food chains, the value of the transferred energy can be only 1%.
In 1942, the American ecologist R. Lindeman formulated the law of the pyramid of energies (the law of 10 percent), according to which, on average, about 10% of the energy received by the previous level of the ecological pyramid passes from one trophic level through food chains to another trophic level. The rest of the energy is lost in the form of thermal radiation, movement, etc. Organisms, as a result of metabolic processes, lose about 90% of all energy in each link of the food chain, which is spent on maintaining their vital functions.
If a hare ate 10 kg of plant matter, then its own weight could increase by 1 kg. A fox or a wolf, eating 1 kg of hare, increases its mass by only 100 g. In woody plants, this proportion is much lower due to the fact that wood is poorly absorbed by organisms. For grasses and algae, this value is much higher, since they do not have hard-to-digest tissues. However, the general regularity of the process of energy transfer remains: much less energy passes through the upper trophic levels than through the lower ones.
That is why food chains usually cannot have more than 3-5 (rarely 6) links, and ecological pyramids cannot consist of a large number of floors. To the final link of the food chain, as well as to the top floor of the ecological pyramid, there will be so little energy that it will not be enough if the number of organisms increases.
This statement can be explained by looking at where the energy of the consumed food is spent (C). Part of it goes to building new cells, i.e. for growth (P). Part of the energy of food is spent on ensuring energy metabolism 7 or on breathing (i?) . Since the digestibility of food cannot be complete, i.e. 100%, then part of the undigested food in the form of excrement is removed from the body (F). The balance sheet will look like this:
C = R+R + F .
Considering that the energy spent on respiration is not transferred to the next trophic level and leaves the ecosystem, it becomes clear why each subsequent level will always be less than the previous one.
That is why large predatory animals are always rare. Therefore, there are also no predators that would feed on wolves. In this case, they simply would not feed themselves, since the wolves are not numerous.
The trophic structure of an ecosystem is expressed in complex food relationships between its constituent species. Ecological pyramids of numbers, biomass and energy, depicted in the form of graphical models, express the quantitative ratios of organisms that differ in the way they feed: producers, consumers and decomposers.
1. Define a trophic level. 2. Give examples of organisms belonging to the same trophic level. 3. By what principle are ecological pyramids built? 4. Why can't a food chain include more than 3 - 5 links?
General Biology: Textbook for the 11th grade of the 11-year-old comprehensive school, for basic and advanced levels. N.D. Lisov, L.V. Kamlyuk, N.A. Lemeza and others. Ed. N.D. Lisova.- Minsk: Belarus, 2002.- 279 p.
Contents of the textbook General Biology: Textbook for Grade 11:
- § 2. Population - a structural unit of the species. Population characteristics
- § 6. Ecosystem. Relationships between organisms in an ecosystem. Biogeocenosis, structure of biogeocenosis
- § 7. The movement of matter and energy in an ecosystem. Circuits and power networks
- § 9. Circulation of substances and energy flow in ecosystems. Productivity of biocenoses
- § 13. Prerequisites for the emergence of the evolutionary theory of Ch. Darwin
- § 14. General characteristics of the evolutionary theory of Ch. Darwin
- § 18. Development of evolutionary theory in the post-Darwinian period. Synthetic theory of evolution
- § 19. Population - an elementary unit of evolution. Background of evolution
- § 27. Development of ideas about the origin of life. Hypotheses for the origin of life on Earth
- § 32. The main stages in the evolution of flora and fauna
- § 33. Diversity of the modern organic world. Principles of taxonomy
- § 35. Formation of ideas about the origin of man. Man's place in the zoological system
- § 36. Stages and directions of human evolution. human predecessors. The oldest people
- § 38. Biological and social factors of human evolution. Qualitative differences of a person
Chapter 1. Species - a unit of existence of living organisms
Chapter 2. Relationships of species, populations with the environment. ecosystems
Chapter 3
Chapter 4
Chapter 5. Origin and development of life on Earth
Chapter 6
Stable biogeochemical cycles of matter and energy in the biosphere of our planet are formed as a result of the biological diversity of the set of substances consumed by organisms and the products of vital activity released into the natural environment. The basis of the biological cycle of substances is trophic levels, which are represented by specific types of living organisms, divided into three main groups: producers, consumers and decomposers. The trophic level is made up of populations of organisms that perform the same trophic functions in the ecosystem and have a different species composition (from the Greek trophe - “nutrition”).
First trophic level level of primary production- form autotrophs. These are organisms that synthesize organic substances (carbohydrates, fats, proteins, nucleic acids) from inorganic compounds using the energy of the Sun. Primary production is the biomass of plant tissues. Primary producers are plants, photoautotrophic bacteria and chemosynthetic bacteria (chemotrophs). Chemotrophs are microorganisms that synthesize organic matter at the expense of the energy of oxidation of ammonia, hydrogen sulfide and other substances present in water and soil.
The second trophic level is consumers (heterotrophs):
1) the first order - phytophages - use plants as food;
2) the second order - they eat animal food.
At the third trophic level - decomposers. These are organisms that decompose waste products and dead organisms into minerals, carbon dioxide and water. Consumers are also involved in the mineralization of organic matter.
All organisms use the biomass of previous trophic levels for food, losing energy with losses for respiration, body heating, for various forms of activity, for excrement.
There are relationships between species of different trophic levels that form a system of trophic chains (food chains). The use of resources at each trophic level depends on the species diversity of the ecosystem.
Species diversity may decrease in contaminated areas, causing a simplification of the trophic structure.
Today, violations of the structure of biocenoses due to environmental pollution are recorded. Toxicants are transmitted through food chains and contribute to the death of animals, birds, aquatic organisms, and also accumulate in food products consumed by humans.
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Food chains and trophic levels are considered integral components of the biological cycle. It contains many elements. Let's take a closer look at the trophic levels of an ecosystem.
Terminology
The food chain is the movement of energy, which is contained in plant foods, through a number of organisms as a result of eating each other. Only plants form organic matter from inorganic matter. The trophic level is a complex of organisms. Between them there is an interaction in the process of transferring nutrients and energy from the source. Trophic chains (trophic level) imply a certain position of organisms at a particular stage (link) during this movement. Marine and terrestrial biological structures have many differences. One of the main ones can be called the fact that in the first food chains are longer than in the second.
steps
The first trophic level is represented by autotrophs. They are also called producers. The second trophic level is made up of the original consumers. At the next stage are consumers, which are consumed by herbivorous organisms. These consumers are called secondary. These, for example, include primary predators, carnivores. Also, the 3rd trophic level includes consumers of the 3rd order. They consume, in turn, weaker predators. As a rule, there is a limited number of trophic levels - 4 or 5. Rarely there are more than six. This food chain is usually closed by decomposers or decomposers. They are bacteria, microorganisms that decompose organic residues.
Consumers: general information
They are not just "eaters" that the food chain contains. Satisfaction of their needs by them is carried out through a system of feedback (positive) communication. Consumers affect the trophic levels of the ecosystem that are higher. For example, the consumption of vegetation in the African savannas by large herds of antelope, together with fires during the dry season, increases the rate of return of nutrients to the soil. Subsequently, during the rainy season, the restoration of herbaceous plantations and their production increase.
The example of Odum is quite interesting. It describes the impact of consumers on producers in a marine ecosystem. Crabs that eat detritus and algae tend to their herbs in several ways. They break up the soil, thus increasing the circulation of water near the roots and introducing oxygen and necessary elements into the anaerobic coastal zone. In the process of constant processing of bottom silts rich in organic matter, crabs help to improve the conditions for the development and growth of benthic algae. One trophic level is made up of organisms that receive energy through the same number of steps.
Structure
Food consumed at each trophic level is not fully assimilated. This is due to its significant losses at the stages of metabolic processes. In this regard, the production of organisms in the next trophic level is less than in the previous one. Within a biological system, organic compounds containing energy are formed by autotrophic organisms. These substances are a source of energy and the necessary components for heterotrophs. The following example is simple: an animal consumes plants. In turn, the animal can be eaten by another larger representative of the fauna. In this way, energy can be transferred through several organisms. The next one uses the previous one, which supplies energy and nutrients. It is this sequence that forms the food chain, in which the trophic level acts as a link.
Producers of the 1st order
The initial trophic level contains autotrophic organisms. They mainly include green spaces. Some prokaryotes, in particular blue-green algae, as well as a few species of bacteria, also have the ability to photosynthesize. However, their contribution to the trophic level is insignificant.
Thanks to the activity of photosynthetics, solar energy is converted into chemical energy. It lies in organic molecules, from which, in turn, tissues are built. A relatively small contribution to the production of organic matter is made by chemosynthetic bacteria. They extract energy from inorganic compounds. Algae are the main producers in aquatic ecosystems. Often they are small unicellular organisms that form phytoplankton in the surface layers of lakes and oceans. Most of the primary production on land comes in more highly organized forms. They belong to gymnosperms and angiosperms. Due to them, meadows and forests are formed.
Consumers 2, 3 orders
Food chains can be of two types. In particular, detritus and pasture structures are distinguished. Examples of the latter are described above. They have green plants on the first level, grazing animals on the second, and predators on the third. However, the bodies of dead plants and animals still contain energy and "building material" along with lifetime secretions (urine and feces). All these organic materials are decomposed due to the activity of microorganisms - bacteria and fungi. They live on organic remains as saprophytes.
Organisms of this type are called decomposers. They secrete digestive enzymes into waste products or dead bodies, and then the products of digestion are absorbed. Decomposition can occur at different rates. Consumption of organic compounds of faeces, urine, animal corpses is carried out within a few weeks. At the same time, fallen branches or trees can decompose for years.
Detritivores
Fungi play an important role in the process of wood decay. They secrete the enzyme cellulase. It has a softening effect on wood, which makes it possible for small animals to penetrate and absorb the material. Fragments of decomposed material are called detritus. They feed on many small living organisms (detritophages) and accelerate the process of destruction.
Since two types of organisms are involved in decomposition (fungi and bacteria, as well as animals), they are often combined under one name - "decomposers". But in reality, this term applies only to saprophytes. Detritophages, in turn, can be consumed by larger organisms. In this case, a chain of a different type is formed - starting with detritus. The detritophages of coastal and forest communities include woodlice, earthworms, carrion fly larvae, crimson, sea cucumbers, and polychaetes.
food web
In system diagrams, each organism can be represented as consuming others of a particular type. But the nutritional relationships that exist in the biological structure have a much more complex structure. This is due to the fact that the animal can consume organisms of various types. However, they may belong to the same food chain or belong to different ones. This is especially evident among predators that are at high levels of the biological cycle. There are animals that consume other representatives of the fauna and plants at the same time. Such individuals belong to the category of omnivores. In particular, such is the person. In the existing biological system, the interweaving of food chains is quite common. As a result, a new multicomponent structure is formed - a network. Only some of all possible relationships can be reflected in the diagram. As a rule, it contains only one or two predators belonging to the upper trophic levels. In the flow of energy and circulation within the framework of a typical structure, there can be two ways of exchange. On the one hand, the interaction is carried out between predators, on the other hand, between decomposers and detritivores. The latter can consume dead animals. At the same time, live decomposers and detritivores can act as food for predators.
The transfer of food energy from its source - autotrophs (plants) - through a number of organisms, occurring by eating some organisms by others, is called food chain. With each transfer, most (80-90%) potential energy is lost, turning into heat. Therefore, the shorter the food chain (the closer the organism is to its beginning), the greater the amount of energy available to the population. Food chains can be divided into two main types: pasture chain, which starts with a green plant and progresses to grazing herbivores (i.e., organisms that eat living plant cells or tissues) and carnivores (organisms that eat animals), and detrital chain, which goes from dead organic matter to microorganisms, and then to detritus feeders and their predators. Food chains are not isolated from each other, but are closely intertwined with each other, forming the so-called food webs. In complex natural communities, organisms that receive their energy from the Sun through the same number of steps are considered to belong to one trophic level. So, green plants occupy the first trophic level (the level of producers), herbivores - the second (the level of primary consumers), primary predators that eat herbivores - the third (the level of secondary consumers), and secondary predators - the fourth (the level of tertiary consumers).
Food chains are familiar to each of us: a person eats large fish, and they eat small fish that eat zooplankton, which feed on phytoplankton that capture solar energy, or a person can eat the meat of cows that eat grass that captures solar energy, he can use and a much shorter food chain by feeding on crops that capture the sun's energy. In the latter case, a person is the primary consumer at the second trophic level. In the food chain grass - cows - man, he is a secondary consumer at the third trophic level. But more often a person is both a primary and secondary consumer, since his diet usually includes a mixture of plant and animal foods.
With each transfer of food, part of the potential energy is lost. First of all, plants capture only a small fraction of the incoming solar energy. Therefore, the number of consumers (e.g. humans) that can survive on a given primary production output is highly dependent on chain length, moving to each successive link in our traditional agricultural food chain reduces the available energy by about an order of magnitude (i.e. 10 times ). Therefore, if the meat content in the diet increases, then the number of people who can be fed decreases. If it turns out that a lot of new mouths will have to be fed on the basis of existing primary production, then meat should be completely abandoned or its consumption should be sharply reduced.
Some substances do not dissipate as they move along the chain, but rather accumulate. This so-called concentration in the food chain (bioconcentration) most clearly demonstrate persistent radionuclides and pesticides.
The tendency of some radionuclides, the by-products of nuclear fission, to increase in concentration with each stage of the food chain was discovered in the 50s. Extremely small (trace) amounts of radioactive J, P, Cs, Se in the Columbia River were concentrated in the tissues of fish and birds. It was found that the accumulation factor (the ratio of the amount of substance in tissues and the environment) of radioactive phosphorus in goose eggs is 2 million. Thus, safe releases into the river can become extremely dangerous for the upper links of the food chain.
Example: DDT(4,4 - dichlorodiphenyl trichloromethylmethane). To reduce the number of mosquitoes on Long Island, the swamps have been pollinating DDT for many years. Insect control specialists did not use concentrations that would be directly lethal to fish and other animals, but they did not consider environmental processes and the long-term persistence of DDT residues. Instead of being washed off into the sea, the poisonous residues adsorbed on the detring were concentrated in the tissues of detring-feeders and small fish, and further - in predators of a higher order (fish-eating birds). The concentration coefficient (the ratio of DDT content in the body to the content in water, expressed in parts per million) for fish-eating animals is about 500,000. In fish and birds, accumulation is facilitated by significant fat accumulation, in which DDT is concentrated. Birds are particularly susceptible to DDT poisoning, as this poison (and other insecticides, which are chlorinated hydrocarbons), by reducing the concentration of steroid hormones in the blood, disrupts the formation of eggshells; the thin shell bursts before the chick develops. Thus, very small doses that are harmless to an individual turn out to be lethal to the population.
The principles of biological accumulation must be taken into account in any decisions related to the release of pollutants into the environment. Many non-biological factors, however, can decrease or increase the concentration factor. So, a person receives less DDT than a bird, because. when processing and cooking food, some of this substance is removed.
Trophic level is a collection of organisms that occupy a certain place in the food web.
I trophic level - always plants,
II trophic level - primary consumers
III trophic level - secondary consumers, etc.
Detritophages can be at II and higher trophic levels.
Typically, there are 3-4 trophic levels in an ecosystem.
Trophic structure can be measured and expressed either as yield per vine (per unit area) or as the amount of energy recorded per unit area per unit time at successive trophic levels.
Trophic structure and trophic function can be represented graphically as ecological pyramids, the basis of which is the first level (the level of producers), and subsequent levels form the floors and the top of the pyramid. Ecological pyramids can be classified into three main types:
pyramid of numbers reflecting the number of individual organisms;
biomass pyramid characterizing the total dry mass, calorie content or other measure of the total amount of living matter;
energy pyramid showing the amount of energy flow and "productivity" at successive trophic levels. With each transition from one trophic level to another within the food chain or web, work is done and heat energy is released into the environment, and the amount of high-quality energy used by organisms of the next trophic level decreases. The percentage of high quality energy passing from one trophic level to another ranges from 2 to 30%. Most of the energy is lost to the environment as low quality thermal energy. The longer the food chain, the more useful energy is wasted. The Energy Flow Pyramid explains why more people can be fed by reducing the food chain to direct grain consumption (rice-human) than by using grain-eating animals as food. To avoid protein (protein) malnutrition, a vegetarian diet should consist of a variety of plants.
Pyramids of numbers It is possible to collect all samples of organisms in an ecosystem and count the abundance of all species found at each trophic level. Such information is necessary to create a pyramid of numbers. For example, a million phytoplangton in a small pond can feed 10,000 zooplangton, which in turn can feed 100 perch, enough to feed one person for a month.
Rice. 3.2 Pyramid of numbers
But for some ecosystems, population pyramids have a different shape. For example, in a forest, a small number of large trees, such as the evergreen sequoia, provide food for a huge number of small-sized phytophagous insects and birds - first-order consumers.
biomass pyramid characterizing the mass of living matter (per unit area or volume). Each trophic level of a food chain or web contains a certain amount of biomass. In terrestrial ecosystems, the following applies biomass pyramid rule: the total mass of plants exceeds the mass of all herbivores, and their mass exceeds the entire biomass of predators.
For the ocean, the biomass pyramid rule is invalid - the pyramid has inverted (inverted) view. The ecosystem of the ocean is characterized by the incandescence of biomass at high levels, in predators. Predators live for a long time, and the rate of turnover of their regeneration is low, but for producers - phytoplankton algae, the turnover rate is hundreds of times higher than the biomass reserve.
Rice. 3.3 Biomass pyramid
Pyramids of numbers and biomass can be reversed (or partially reversed), i.e. the base may be smaller than one or more of the upper floors. This happens when the average size of producers is less than the size of consumers. On the contrary, the energy pyramid will always narrow towards the top, provided that we take into account all sources of food energy in the system.
