Food chains and trophic levels. Trophic levels

Are you familiar with such concepts as consumers, decomposers and producers? If not, then our article is for you. In fact, these organisms are well known to everyone. Who are they? Let's figure it out together.

The concept of the trophic chain

All components of the ecosystem are closely interconnected. Thanks to this, various communities are formed in nature. The structure of any ecosystem includes an abiotic and biotic part. The first is a collection of living organisms. It is called biocenosis. The abiotic part includes mineral and organic compounds.

The functioning of any ecosystem is associated with energy transformation. Its main source is sunlight. Photosynthetic organisms use it to synthesize organic substances. Heterotrophs obtain energy from the breakdown of organic substances. Only a small part of it is used for growth. And the rest is spent for existence of life processes.

As a result, sequences are formed in which individuals of some species, their remains or waste products are a source of nutrition for others. These are called trophic or food chains.

Trophic levels

Each power chain consists of a certain number of links. It has been established that when moving from one to another, part of the energy is constantly lost. Therefore, the number of links is usually 4-5. The position of a population of individual species in the food chain is called the trophic level.

What are consumers

All organisms are grouped into groups. These include representatives of absolutely all kingdoms of living nature, regardless of their level of organization. Let's look at each of them.

Consumers: orders

Heterotrophs occupy different levels in the food chain. All herbivorous species are the Next level are carnivores. They are already second-order consumers.

Consider this hierarchy at specific example. Let's say the trophic network looks like: mosquito, frog, stork. Which one of them is a consumer of the first order? This is a frog. Then the stork is a consumer of the second order. In nature, there are heterotrophs that feed on both plants and animals. Such consumers can simultaneously be at several trophic levels.

Producers

Speaking about what consumers are, we paid attention to the type of food they eat. Let us consider another group of the trophic network from this perspective. Producers are a group of organisms that are autotrophs. They are able to synthesize organic substances from minerals.

There are two types of producers: autotrophs and chemotrophs. The first use the energy of sunlight to create organic matter. These are plants, cyanobacteria, and some protozoa. Chemotrophs have the ability to oxidize various chemical compounds. At the same time, energy is generated, which they use to produce waste products. These include nitrogen-fixing, sulfur, and iron bacteria.

The presence of producers is a necessary condition development of any ecosystem. This fact is explained by the fact that photosynthetic organisms are a source of energy.

Decomposers

Another role in the ecosystem belongs to heterotrophic organisms, which feed on organic matter from the remains or waste products of other species, which they decompose into minerals. This function is performed by decomposers. Representatives of this group are bacteria and fungi.

It is at the level of producers in the ecosystem that energy accumulation occurs. It then passes through consumers and producers, where it is consumed. At each subsequent trophic level, part of the energy is dissipated as heat.

Types of power circuits

The energy in an ecosystem is divided into two streams. The first is directed to consumers from producers, the second - from dead organic matter. Depending on this, trophic networks of pasture and detritus types are distinguished. In the first case, the initial trophic level consists of producers who transfer energy to consumers of different levels. The pasture chain ends with decomposers.

The detrital chain begins with dead organic matter and continues with saprotrophs, which are representatives of consumers. The last link in this chain is also decomposers.

Within any ecosystem, many trophic chains simultaneously exist. All of them are inseparable from each other and are closely intertwined. This happens because representatives of the same species can simultaneously be links in different chains. Thanks to this, trophic networks are formed. And the more branched they are, the more stable the ecosystem.

Food chains and trophic levels are considered integral components biological cycle. There are many elements involved. Next, let's take a closer look at the trophic levels of the ecosystem.

Terminology

A food chain is the movement of energy contained in plant foods through a number of organisms as a result of them eating each other. Only plants form organic matter from inorganic matter. A trophic level is a complex of organisms. Interaction occurs between them in the process of transferring nutrients and energy from the source. Trophic chains (trophic level) presuppose a certain position of organisms at one or another stage (link) during this movement. Marine and terrestrial biological structures differ in many ways. One of the main ones is that in the former the food chains are longer than in the latter.

steps

The first trophic level is represented by autotrophs. They are also called producers. The second trophic level consists of the original consumers. At the next stage are consumers who consume herbivorous organisms. These consumers are called secondary. These include, for example, primary predators, carnivores. Also, the 3rd trophic level includes consumers of the 3rd order. They, in turn, consume weaker predators. As a rule, there is a limited number of trophic levels - 4 or 5. There are rarely 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. They satisfy their needs through a feedback (positive) feedback system. Consumers influence higher trophic levels of the ecosystem. So, for example, the consumption of vegetation in African savannas by large herds of antelopes, together with fires during the dry period, helps to increase the rate of return of nutrients to the soil. Subsequently, during the rainy season, herbaceous regeneration and production increases.

Odum's example is quite interesting. It describes the effects of consumers on producers in a marine ecosystem. Crabs, which consume detritus and algae, "look after" their grasses in several ways. They break up the soil, thereby increasing the circulation of water near the roots and introducing oxygen and necessary elements into the anaerobic coastal zone. In the process of constantly processing bottom silts rich in organic matter, crabs help improve conditions for the development and growth of benthic algae. One trophic level consists of organisms that obtain energy through the same number of steps.

Structure

Food consumed at each trophic level is not completely assimilated. This is due to its significant losses at the stages of metabolic processes. In this regard, the production of organisms included in the next trophic level is less than in the previous one. Within a biological system, organic compounds containing energy are produced by autotrophic organisms. These substances are a source of energy and necessary components for heterotrophs. A simple example is the following: an animal consumes plants. In turn, the animal can be eaten by another larger representative of the fauna. 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 is the link.

1st order producers

The initial trophic level contains autotrophic organisms. These 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 consists of 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. They are often represented by 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 contain 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 " construction material"along with intravital excretions (urine and feces). All these organic materials undergo decomposition due to the activity of microorganisms - bacteria and fungi. They live on organic debris 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 from feces, urine, and animal corpses occurs over several weeks. However, fallen branches or trees can take years to decompose.

Detritivores

Fungi play a significant role in the process of wood decay. They secrete the enzyme cellulase. It has a softening effect on the wood, which makes it possible for small animals to penetrate and absorb the material. Fragments of decayed material are called detritus. Many small living organisms (detritivores) feed on it and accelerate the process of destruction.

Since two types of organisms (fungi and bacteria, as well as animals) participate in decomposition, they are often combined under one name - “decomposers”. But in reality this term applies only to saprophytes. Detritivores, in turn, can be absorbed by larger organisms. In this case, a chain of a different type is formed - starting with detritus. Detritivores of coastal and forest communities include woodlice, earthworm, carrion fly larva, scarlet fly, sea cucumber, and polychaete.

food web

In systems diagrams, each organism can be represented as consuming others belonging to a certain type. But the food connections existing in the biological structure have a much more complex structure. This is due to the fact that the animal can consume a variety of organisms different types. Moreover, they may belong to the same food chain or belong to different ones. This is especially evident among predators located at high levels of the biological cycle. There are animals that consume other fauna and plants at the same time. Such individuals belong to the category of omnivores. In particular, this is how humans are. In the existing biological system, intertwined food chains are quite common. As a result, a new multicomponent structure is formed - a network. The diagram can only reflect some of all possible connections. As a rule, it contains only one or two predators belonging to the upper trophic levels. In the flow of energy and circulation within typical structure there may be two ways of exchange. On the one hand, interaction occurs between predators, on the other, between decomposers and detritivores. The latter can consume dead animals. At the same time, living decomposers and detritivores can act as food for predators.

Every organism must receive energy to live. For example, plants consume energy from the sun, animals eat plants, and some animals eat other animals.

A food (trophic) chain is the sequence of who eats whom in a biological community () to obtain nutrients and energy that support life.

Autotrophs (producers)

Autotrophs- living organisms that make their own food, that is, their own organic compounds, from simple molecules such as carbon dioxide. There are two main types of autotrophs:

• Photoautotrophs (photosynthetic organisms), such as plants, process energy from sunlight to produce organic compounds - sugars - from carbon dioxide in progress . Other examples of photoautotrophs are algae and cyanobacteria.

• Chemoautotrophs obtain organic matter through chemical reactions, which involve inorganic compounds (hydrogen, hydrogen sulfide, ammonia, etc.). This process is called chemosynthesis.

Autotrophs are the basis of every ecosystem on the planet. They make up the majority of food chains and webs, and the energy obtained through photosynthesis or chemosynthesis supports all other organisms ecological systems. When it comes to their role in food chains, autotrophs can be called producers or producers.

Heterotrophs (consumers)

Heterotrophs, also known as consumers, cannot use solar or chemical energy to produce their own food from carbon dioxide. Instead, heterotrophs obtain energy by consuming other organisms or their byproducts. People, animals, fungi and many bacteria are heterotrophs. Their role in food chains is to consume other living organisms. There are many species of heterotrophs with different ecological roles, from insects and plants to predators and fungi.

Destructors (reducers)

Another consumer group should be mentioned, although it does not always appear in food chain diagrams. This group consists of decomposers, organisms that process dead organic matter and waste, turning them into inorganic compounds.

Decomposers are sometimes considered a separate trophic level. As a group, they feed on dead organisms coming from different trophic levels. (For example, they are able to process decaying plant matter, the body of a squirrel malnourished by predators, or the remains of a deceased eagle.) In a sense, the trophic level of decomposers runs parallel to the standard hierarchy of primary, secondary, and tertiary consumers. Fungi and bacteria are key decomposers in many ecosystems.

Decomposers, as part of the food chain, play an important role in maintaining a healthy ecosystem because they return nutrients and moisture, which are subsequently used by producers.

Levels of the food (trophic) chain

Diagram of the levels of the food (trophic) chain

A food chain is a linear sequence of organisms that transfer nutrients and energy from producers to top predators.

The trophic level of an organism is the position it occupies in the food chain.

First trophic level

The food chain starts with autotrophic organism or producer, producing its own food from a primary energy source, usually solar or energy from hydrothermal vents at mid-ocean ridges. For example, photosynthetic plants, chemosynthetic plants, etc.

Second trophic level

Next come the organisms that feed on autotrophs. These organisms are called herbivores or primary consumers and consume green plants. Examples include insects, hares, sheep, caterpillars and even cows.

Third trophic level

The next link in the food chain are animals that eat herbivores - they are called secondary consumers or carnivorous (predatory) animals(for example, a snake that feeds on hares or rodents).

Fourth trophic level

In turn, these animals are eaten by larger predators - tertiary consumers(for example, an owl eats snakes).

Fifth trophic level

Tertiary consumers are eaten quaternary consumers(for example, a hawk eats owls).

Every food chain ends with an apex predator or superpredator - an animal with no natural enemies (for example, a crocodile, polar bear, shark, etc.). They are the "masters" of their ecosystems.

When any organism dies, it is eventually eaten by detritivores (such as hyenas, vultures, worms, crabs, etc.) and the rest is decomposed by decomposers (mainly bacteria and fungi), and energy exchange continues.

Arrows in a food chain show the flow of energy, from the sun or hydrothermal vents to top predators. As energy flows from body to body, it is lost at each link in the chain. The collection of many food chains is called food web.

The position of some organisms in the food chain may vary because their diet is different. For example, when a bear eats berries, it acts as a herbivore. When it eats a plant-eating rodent, it becomes a primary predator. When a bear eats salmon, it acts as a superpredator (this is due to the fact that salmon is the primary predator, since it feeds on herring, which eats zooplankton, which feeds on phytoplankton, which produces own energy thanks to sunlight). Think about how people's place in the food chain changes, even often within a single meal.

Types of food chains

In nature, as a rule, there are two types of food chains: pasture and detritus.

Grassland food chain

Grassland food chain diagram

This type of food chain begins with living green plants to feed the herbivores on which carnivores feed. Ecosystems with this type of circuit are directly dependent on solar energy.

Thus, the grazing type of food chain depends on the autotrophic capture of energy and its movement along the links of the chain. Most ecosystems in nature follow this type of food chain.

Examples of grazing food chains:

• Grass → Grasshopper → Bird → Hawk;
• Plants → Hare → Fox → Lion.

Detrital food chain

Detrital food chain diagram

This type of food chain begins with decaying organic material - detritus - which is consumed by detritivores. Then, predators feed on detritivores. Thus, such food chains are less dependent on direct solar energy than grazing ones. The main thing for them is the influx of organic substances produced in another system.

For example, this type of food chain is found in decomposing litter.

Energy in the food chain

Energy is transferred between trophic levels when one organism feeds on and receives nutrients from another. However, this movement of energy is inefficient, and this inefficiency limits the length of food chains.

When energy enters a trophic level, some of it is stored as biomass, as part of the body of organisms. This energy is available for the next trophic level. Typically, only about 10% of the energy that is stored as biomass at one trophic level is stored as biomass at the next level.

This principle of partial energy transfer limits the length of food chains, which typically have 3-6 levels.

At each level, energy is lost in the form of heat, as well as in the form of waste and dead matter that decomposers use.

Why does so much energy leave the food web between one trophic level and the next? Here are some of the main reasons for inefficient energy transfer:

• At each trophic level, a significant portion of energy is dissipated as heat as organisms perform cellular respiration and move around in daily life.
• Some organic molecules that organisms feed on cannot be digested and are excreted as feces.
• Not all individual organisms in a trophic level will be eaten by organisms from the next level. Instead, they die without being eaten.
• Feces and uneaten dead organisms become food for decomposers, who metabolize them and convert them into their energy.

So, none of the energy actually disappears - it all ends up producing heat.

Food chain meaning

1. Food chain studies help understand feeding relationships and interactions between organisms in any ecosystem.

2. Thanks to them, it is possible to evaluate the mechanism of energy flow and the circulation of substances in the ecosystem, as well as understand the movement toxic substances in the ecosystem.

3. Studying the food chain provides insight into biomagnification issues.

In any food chain, energy is lost every time one organism is consumed by another. Due to this, there should be many more plants than herbivores. There are more autotrophs than heterotrophs, and therefore most of them are herbivores rather than carnivores. Although there is intense competition between animals, they are all interconnected. When one species goes extinct, it can affect many other species and have unpredictable consequences.

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TROPHIC LEVEL, a collection of organisms united by a type of nutrition. The concept of the trophic level allows us to understand the dynamics of energy flow and the trophic structure that determines it.

Autotrophic organisms (mainly green plants) occupy the first trophic level (producers), herbivores occupy the second (first-order consumers), predators that feed on herbivores occupy the third (second-order consumers), and secondary predators occupy the fourth (third-order consumers). Organisms of different trophic chains, but receiving food through an equal number of links in the trophic chain, are at the same trophic level. Thus, a cow and a weevil of the genus Siton that feed on alfalfa leaves are consumers of the first order. The actual relationships between trophic levels in a community are very complex. Populations of the same species, participating in different trophic chains, can be at different trophic levels, depending on the source of energy used. At each trophic level, the food consumed is not completely assimilated, since a significant part of it is spent on metabolism. Therefore, the production of organisms of each subsequent trophic level is always less than the production of the previous trophic level, on average 10 times. The relative amount of energy transferred from one trophic level to another is called community ecological efficiency or food chain efficiency.

The relationship between different trophic levels (trophic structure) can be depicted graphically as ecological pyramid, the basis of which is the first level (the level of producers).

Ecological pyramid can be of three types:
1) pyramid of numbers - reflects the number of individual organisms at each level;
2) biomass pyramid - total dry weight, energy content, or other measure of the total amount of living matter;
3) pyramid of energy - the amount of energy flow.

The base in the pyramids of numbers and biomass may be smaller than subsequent levels (depending on the ratio of the sizes of producers and consumers). The pyramid of energy always narrows upward. In terrestrial ecosystems, a decrease in the amount of available energy is usually accompanied by a decrease in biomass and the number of individuals at each trophic level.

Pyramid of numbers (1) shows that if a boy were to eat only veal for one year, then he would need 4.5 calves, and to feed the calves it is necessary to sow a 4 hectare field with alfalfa (2x10 (7) plants). (2) In the biomass pyramid (3) the number of individuals is replaced by biomass values.

In the pyramid of energy solar energy taken into account Lucerne uses 0.24% solar energy. To accumulate production, calves use 8% of the energy accumulated by alfalfa throughout the year. 0.7% of the energy accumulated by calves is used for the development and growth of a child during the year. As a result, just over one millionth of the solar energy falling on a 4-hectare field is used to feed a child for one year. (according to Yu. Odum)

Ministry of Education and Science Russian Federation

Federal state budget educational institution

higher vocational education

"Vladimirsky

State University

named after Alexander Grigorievich and Nikolai Grigorievich Stoletov"

(VlGU)

Department of Ecology

Practical work.

by discipline:

"Ecology"

Completed:

Art. gr. VT-110

Shchegurov R.N.

Accepted:

Zabelina O.N.

Vladimir 2013

Theoretical part. Ecosystem concept Ecosystem- is any set of interacting living organisms and environmental conditions. Ecosystems are, for example, an anthill, a patch of forest,

geographical landscape or even the entire globe. Ecosystems consist of living and nonliving components, called biotic and abiotic, respectively. The biotic component is

Autotrophs type of food

They are divided into autotrophic and heterotrophic organisms. synthesize the organic substances they need from inorganic ones. Based on the source of energy for synthesis, they are divided into two types: photoautotrophs and chemoautotrophs. Photoautotrophs used for the synthesis of organic substances

solar energy Chemical energy is used to synthesize organic substances. These are sulfur bacteria and iron bacteria that obtain energy from the oxidation of iron and sulfur compounds. Chemoautotrophs play a significant role only in ecosystems groundwater. Their role in terrestrial ecosystems is relatively small.

Heterotrophs They use organic substances that are synthesized by autotrophs, and together with these substances they obtain energy. Heterotrophs thus depend for their existence on autotrophs, and understanding this dependence is necessary for understanding ecosystems.

The nonliving, or abiotic, component of an ecosystem mainly includes, firstly, soil or water, and secondly, climate.

Food chains and trophic levels

Within an ecosystem, energy-containing organic substances are created by autotrophic organisms and serve as food (a source of matter and energy) for heterotrophs. A typical example: an animal eats a plant. This animal, in turn, can be eaten by another animal, and in this way energy can be transferred through a number of organisms - each subsequent one feeds on the previous one, supplying it with raw materials and energy. This sequence is called food chain , and each of its links is trophic level .

With each subsequent transfer most of(80 - 90%) of potential energy is lost, turning into heat(10% rule). Therefore, the shorter the food chain, the large quantity energy available to the population. Energy losses during transfer are associated with a limitation on the number of links in the trophic chain, which usually does not exceed 4 - 5, since the longer the food chain, the lower the production of its last link in relation to the production of the initial one.

The first trophic level is occupied by producers , which are autotrophs, are mainly green plants. Some prokaryotes, namely blue-green algae and a few species of bacteria, also photosynthesize, but their contribution is relatively small. Photosynthetics convert solar energy into chemical energy contained in the organic molecules from which their tissues are built. Chemosynthetic bacteria also make a small contribution to the production of organic matter.

Organisms of the second trophic level are called primary consumers , third - secondary consumers . All consumers are heterotrophs.

There are two main types of food chains - grazing and detrital. IN pasture food chains, the first trophic level is occupied by green plants, the second by grazing animals and the third by predators.

However, the bodies of dead animals and plants (detritus) still contain energy, as do intravital excretions, for example, urine and feces. These organic materials decompose decomposers. Thus, detrital food the chain begins with dead organic remains and goes further to the organisms that feed on them. For example, a dead animal ® carrion fly larva ® grass frog.

In food chain diagrams, each organism is represented as feeding on other organisms of the same type. However, the actual food relationships in an ecosystem are much more complex, since animals can feed on different types of organisms from the same or different food chains. Therefore, food chains are not isolated from each other, they are closely intertwined and form food webs .

Ecological pyramids

Ecological pyramids express the trophic structure of an ecosystem in geometric shape. They are constructed by superposition of rectangles of the same width, but the length of the rectangles must be proportional to the value of the measured parameter. In this way, pyramids of numbers, biomass and energy can be obtained.

These pyramids reflect two fundamental characteristics of any biocenosis when they show its trophic structure:

their height is proportional to the length of the food chain in question, i.e. the number of trophic levels it contains;

their shape more or less reflects the efficiency of energy transformations during the transition from one level to another.

Pyramids of numbers represent the simplest approximation to the study of the trophic structure of an ecosystem. A basic rule has been established according to which in any environment, when moving from one trophic level to another, the number of individuals decreases and their size increases (Fig. 1.1).

Rice. 1.1. Ecological pyramid of numbers

In conclusion, we note that the pyramid of numbers does not ideally reflect the trophic relationships in the community, since it does not take into account either the size or mass of the individual.

Biomass pyramid more fully reflects the food relationships in the ecosystem, since it shows the biomass (dry mass) in this moment at each level of the food chain (Fig. 1.2).

Rice. 1.2. Biomass pyramids. Type A is the most common.

Type B refers to inverted pyramids (see text). The numbers mean

products expressed in g/m2

It is important to understand that the amount of biomass does not contain any information about the rate of its formation or consumption.

For producers small sizes, such as algae, are characterized by a high reproduction rate, which is balanced by their intensive consumption as food by other species and natural death. Thus, although their biomass may be small compared to large producers (trees), their productivity may be no less, since trees accumulate biomass over a long period of time. One possible consequence of this is the inverted pyramid of biomass shown in Figure 1.2, which describes the English Channel community. Zooplankton have greater biomass than the phytoplankton on which they feed.

Such inconveniences can be avoided by using energy pyramids. Pyramids of energy in the most fundamental way they reflect the relationships between organisms at different trophic levels. Each step of the energy pyramid reflects the amount of energy (per unit area or volume) that passed through a certain trophic level over a certain period (Fig. 1.3).

Rice. 1.3. Pyramid of energy. The numbers indicate the quantity

energy at each trophic level in kJ/m 2 year

Energy pyramids allow us to compare not only different ecosystems, but also the relative importance of populations within the same ecosystem, without ending up with inverted pyramids.

Ecosystem Productivity

Any ecosystem is characterized by a certain biomass. Under biomass imply the total mass of all living matter, plant and animal, present at a given specific moment in the ecosystem or any part of it. Biomass is usually expressed in units of mass in terms of dry matter or energy contained in a given mass (J, cal). Biomass accumulated over a certain period of time (usually a year) is called biological productivity. In other words, productivity is the rate of accumulation of organic matter (it includes all the growth of plant tissue, i.e. roots, leaves, etc., as well as the increase in the mass of animal tissue over a given period of time).

Ecosystem productivity is divided into primary and secondary. Primary productivity , or primary production, is the rate of accumulation of organic matter by autotrophic organisms.

Primary productivity is in turn divided into gross and net. Gross primary production - this is the total mass of organic matter synthesized by producers over a certain period of time.

Part of the synthesized organic matter is used by plants or other producers to maintain their own vital functions, i.e. consumed during breathing. If we subtract from gross primary production organic matter, spent on the respiration of producers, we get pure primary production .It is available to heterotrophs (consumers and decomposers), which, by eating organic matter synthesized by autotrophs, create secondary products .