Who in ecology are called consumers of the first order. Food chain. Ecosystem. Signs of an ecosystem
Phytophagous and carnivorous
The structure of living matter in an ecosystem. Biotic structure. Autotrophs and heterotrophs
Ecosystem. Signs of an ecosystem
Ecosystem homeostasis. Ecological succession. Types of natural and anthropogenic successions. Concepts of climax, stability and variability of ecosystems.
Populations in an ecosystem.
Producers. Consumers of the 1st and 2nd order. Detritivores. Decomposers.
Phytophagous and carnivorous.
The structure of living matter in an ecosystem. Biotic structure. Autotrophs and heterotrophs.
Ecosystem. Signs of an ecosystem.
Topic 3. Ecosystem. Ecosystem structure
Bioconsumption. Population and stability of the biosphere
Concepts of noosphere and technosphere
The term “ecosystem” was proposed by the English ecologist A. Tansley in 1935.
Ecosystem is any set of interacting living organisms and environmental conditions.
“Any unit (biosystem) that includes all the co-functioning organisms (biotic community) in a given area and interacts with the physical environment in such a way that the flow of energy creates well-defined biotic structures and the circulation of substances between living and nonliving parts is ecological system, or ecosystem"(Y. Odum, 1986).
Ecosystems are, for example, anthills, a patch of forest, a farm area, a spaceship cabin, a geographic landscape, or even the entire globe.
Ecologists also use the term “biogeocenosis”, proposed by the Russian scientist V.N. Sukachev. This term refers to the collection of plants, animals, microorganisms, soil and atmosphere on a homogeneous land area. Biogeocenosis is one of the variants of an ecosystem.
Between ecosystems, as well as between biogeocenoses, there are usually no clear boundaries, and one ecosystem gradually passes into another. Large ecosystems are made up of smaller ecosystems.
Rice. "Matryoshka" of ecosystems
In Fig. a “matryoshka” of ecosystems is shown. The smaller the size of the ecosystem, the more closely its constituent organisms interact. An organized group of ants lives in an anthill, in which all responsibilities are distributed. There are ants-hunters, guards, builders.
The anthill ecosystem is part of the forest biogeocenosis, and the forest biogeocenosis is part of the geographical landscape. The composition of the forest ecosystem is more complex; representatives of many species of animals, plants, fungi, and bacteria live together in the forest. The connections between them are not as close as those of ants in an anthill. Many animals spend only part of their time in the forest ecosystem.
Within the landscape, different biogeocenoses are connected by aboveground and underground movement of water in which minerals are dissolved. Water with minerals moves most intensively within a drainage basin - a reservoir (lake, river) and adjacent slopes, from which above-ground and underground waters flow into this reservoir. The ecosystem of the drainage basin includes several different ecosystems - forest, meadow, and arable land. The organisms of all these ecosystems may not have direct relationships and are connected through underground and aboveground water flows that move to the reservoir.
Within the landscape, plant seeds are transferred and animals move. A fox's hole or a wolf's lair are located in one biogeocenosis, and these predators hunt over a large territory consisting of several biogeocenoses.
Landscapes are united into physical-geographical regions (for example, the Russian Plain, the West Siberian Lowland), where different biogeocenoses are connected by a common climate, the geological structure of the territory and the possibility of settlement of animals and plants. Connections between organisms, including humans, in the ecosystems of a physical-geographical region and the biosphere are carried out through changes in the gas composition of the atmosphere and the chemical composition of water bodies.
Finally, all ecosystems of the globe are connected through the atmosphere and the World Ocean, into which the waste products of organisms enter, and form a single whole - biosphere.
The ecosystem includes:
1) living organisms (their totality can be called a biocenosis or biota of an ecosystem);
2) non-living (abiotic) factors - atmosphere, water, nutrients, light;
3) dead organic matter - detritus.
Of particular importance for identifying ecosystems are trophic , i.e. food relationships between organisms that regulate the entire energy of biotic communities and the entire ecosystem as a whole.
First of all, all organisms are divided into two large groups - autotrophs and heterotrophs.
Autotrophic organisms use inorganic sources for their existence, thereby creating organic matter from inorganic matter. Such organisms include photosynthetic green plants of land and aquatic environments, blue-green algae, some bacteria due to chemosynthesis, etc.
Since organisms are quite diverse in types and forms of nutrition, they enter into complex trophic interactions with each other, thereby performing the most important ecological functions in biotic communities. Some of them produce products, others consume them, and others convert them into inorganic form. They are called accordingly: producers, consumers and decomposers.
Producers- producers of products that all other organisms then feed on - these are terrestrial green plants, microscopic sea and freshwater algae, producing organic substances from inorganic compounds.
Consumers are consumers of organic substances. Among them there are animals that eat only plant foods - herbivores(cow) or eating only the meat of other animals – carnivores(predators), as well as those who use both – “ omnivores"(man, bear).
Reducers (destructors)– reducing agents. They return substances from dead organisms back to inanimate nature, decomposing organic matter into simple inorganic compounds and elements (for example, CO 2, NO 2 and H 2 O). By returning biogenic elements to the soil or aquatic environment, they thereby complete the biochemical cycle. This is done mainly by bacteria, most other microorganisms and fungi. Functionally, decomposers are the same consumers, which is why they are often called micro-consumers.
A.G. Bannikov (1977) believes that insects also play an important role in the processes of decomposition of dead organic matter and in soil-forming processes.
Microorganisms, bacteria and other more complex forms, depending on their habitat, are divided into aerobic, i.e. living in the presence of oxygen, and anaerobic– living in an oxygen-free environment.
All living organisms are divided into two groups according to their feeding method:
autotrophs(from Greek autos– himself and tropho- nutrition);
heterotrophs(from Greek heteros- another).
Autotrophs use inorganic carbon ( inorganic energy sources) and synthesize organic substances from inorganic ones; these are the producers of the ecosystem. According to the source (used) energy, they, in turn, are also divided into two groups:
Photoautotrophs– solar energy is used to synthesize organic substances. These are green plants that have chlorophyll (and other pigments) and absorb sunlight. The process by which its absorption occurs is called photosynthesis.
(Chlorophyll is a green pigment that causes plant chloroplasts to turn green. With its participation, the process of photosynthesis is carried out.
Choroplasts are green plastids that are found in the cells of plants and some bacteria. With their help, photosynthesis occurs.)
Chemoautotrophs– chemical energy is used to synthesize organic substances. These are sulfur bacteria and iron bacteria that obtain energy from the oxidation of sulfur and iron compounds (chemosynthesis). Chemoautotrophs play a significant role only in groundwater ecosystems. Their role in terrestrial ecosystems is relatively small.
Heterotrophs They use carbon from organic substances that are synthesized by producers, and together with these substances they obtain energy. Heterotrophs are consumers(from lat. consumo– consume), consuming organic matter, and decomposers, decomposing it into simple compounds.
Phytophagous(herbivores). These include animals that feed on living plants. Among the phytophages there are small animals, such as aphids or grasshoppers, and giants, such as the elephant. Almost all farm animals are phytophages: cows, horses, sheep, rabbits. There are phytophages among aquatic organisms, for example, the grass carp fish, which eats plants that overgrow irrigation canals. An important phytophage is the beaver. It feeds on tree branches, and from the trunks it builds dams that regulate the water regime of the territory.
Zoophagi(predators, carnivores). Zoophages are diverse. These are small animals that feed on amoebas, worms or crustaceans. And big ones, like a wolf. Predators that feed on smaller predators are called second-order predators. There are predator plants (sundew, bladderwort) that use insects as food.
Symbiotrophs. These are bacteria and fungi that feed on plant root secretions. Symbiotrophs are very important for the life of the ecosystem. Fungal threads entangling plant roots help absorb water and minerals. Symbiotrophic bacteria absorb nitrogen gas from the atmosphere and bind it into compounds available to plants (ammonia, nitrates). This nitrogen is called biological (as opposed to nitrogen from mineral fertilizers).
Symbiotrophs also include microorganisms (bacteria, single-celled animals) that live in the digestive tract of phytophagous animals and help them digest food. Animals such as a cow, without the help of symbiotrophs, are not able to digest the grass they eat.
Detritivores are organisms that feed on dead organic matter. These are centipedes, earthworms, dung beetles, crayfish, crabs, jackals and many others.
Some organisms use both plants and animals and even detritus for food, and are classified as euryphages (omnivores) - bear, fox, pig, rat, chicken, crow, cockroaches. Man is also a euryphage.
Decomposers- organisms that, in their position in the ecosystem, are close to detritivores, since they also feed on dead organic matter. However, decomposers - bacteria and fungi - break down organic matter into mineral compounds, which are returned to the soil solution and used again by plants.
Reducers need time to process corpses. Therefore, there is always detritus in the ecosystem - a supply of dead organic matter. Detritus is leaf litter on the surface of forest soil (preserved for 2–3 years), the trunk of a fallen tree (preserved for 5–10 years), soil humus (preserved for hundreds of years), deposits of organic matter at the bottom of the lake - sapropel - and peat in the swamp ( lasts for thousands of years). The longest-lasting detritus is coal and oil.
In Fig. shows the structure of an ecosystem, the basis of which is plants - photoautotrophs, and the table shows examples of representatives of different trophic groups for some ecosystems.
Rice. Ecosystem structure
Organic substances created by autotrophs serve as food and a source of energy for heterotrophs: phytophagous consumers eat plants, first-order predators eat phytophages, second-order predators eat first-order predators, etc. This sequence of organisms is called food chain, its links are located at different trophic levels (representing different trophic groups).
The trophic level is the location of each link in the food chain. The first trophic level is producers, all the rest are consumers. The second trophic level is herbivorous consumers; the third is carnivorous consumers, feeding on herbivorous forms; the fourth are consumers who consume other carnivores, etc. therefore, consumers can be divided into levels: consumers of the first, second, third, etc. orders (Fig.).
Rice. Food relationships of organisms in biogeocenosis
Only consumers specializing in a certain type of food are clearly divided into levels. However, there are species that eat meat and plant foods (humans, bears, etc.) that can be included in food chains at any level.
In Fig. Five examples of food chains are given.
Rice. Some food chains in ecosystems
The first two food chains represent natural ecosystems - terrestrial and aquatic. In the terrestrial ecosystem, predators such as foxes, wolves, and eagles that feed on mice or gophers complete the chain. In an aquatic ecosystem, solar energy, absorbed mainly by algae, passes to small consumers - daphnia crustaceans, then to small fish (roach) and, finally, to large predators - pike, catfish, pike perch. In agricultural ecosystems, the food chain can be complete when raising farm animals (third example), or shortened when plants are grown that are directly used by humans for food (fourth example).
The above examples simplify the actual picture, since the same plant can be eaten by different herbivores, and they, in turn, become victims of different predators. A plant leaf can be eaten by a caterpillar or slug, the caterpillar can become a victim of a beetle or an insectivorous bird, which can also peck the beetle itself. A beetle can also become a victim of a spider. Therefore, in real nature, it is not food chains that form, but food webs.
During the transition of energy from one trophic level to another (from plants to phytophages, from phytophages to first-order predators, from first-order predators to second-order predators) approximately 90% of the energy is lost through excrement and respiration. In addition, phytophages eat only about 10% of plant biomass, the rest replenishes the supply of detritus and is then destroyed by decomposers. Therefore, secondary biological products are 20–50 times less than primary ones.
Rice. Main types of ecosystems
(producers). Unlike decomposers, consumers are not able to decompose organic substances into inorganic ones.
An individual organism can be a consumer of different orders in different trophic chains, for example, an owl eating a mouse is simultaneously a consumer of the second and third order, and a mouse is a consumer of the first and second, since the mouse feeds on both plants and herbivorous insects.
Any consumer is heterotroph, since it is not able to synthesize organic substances from inorganic ones. The term “consumer (first, second, and so on) order” allows you to more accurately indicate the place of the organism in the food chain. Reducers (for example, fungi, decay bacteria) are also heterotrophs; they are distinguished from consumers by the ability to completely decompose organic substances (proteins, carbohydrates, lipids and others) to inorganic ones (carbon dioxide, ammonia, urea, hydrogen sulfide), completing the cycle of substances in nature, creating a substrate for the activity of producers (autotrophs).
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Excerpt characterizing Consumers
-Can I get a book? - he said.– Which book?
- Gospel! I have no.
The doctor promised to get it and began asking the prince about how he felt. Prince Andrei reluctantly, but wisely answered all the doctor’s questions and then said that he needed to put a cushion on him, otherwise it would be awkward and very painful. The doctor and the valet lifted the overcoat with which he was covered and, wincing at the heavy smell of rotten meat spreading from the wound, began to examine this terrible place. The doctor was very dissatisfied with something, changed something differently, turned the wounded man over so that he groaned again and, from the pain while turning, again lost consciousness and began to rave. He kept talking about getting this book for him as soon as possible and putting it there.
- And what does it cost you! - he said. “I don’t have it, please take it out and put it in for a minute,” he said in a pitiful voice.
The doctor went out into the hallway to wash his hands.
“Ah, shameless, really,” the doctor said to the valet, who was pouring water on his hands. “I just didn’t watch it for a minute.” After all, you put it directly on the wound. It’s such a pain that I’m surprised how he endures it.
“It seems we set it up, Lord Jesus Christ,” said the valet.
For the first time, Prince Andrei understood where he was and what had happened to him, and remembered that he was wounded and how at that moment when the carriage stopped in Mytishchi, he asked to go to the hut. Confused again from pain, he came to his senses another time in the hut, when he was drinking tea, and then again, repeating in his memory everything that had happened to him, he most vividly imagined that moment at the dressing station when, at the sight of the suffering of a person he did not love, , these new thoughts came to him, promising him happiness. And these thoughts, although unclear and indefinite, now again took possession of his soul. He remembered that he now had new happiness and that this happiness had something in common with the Gospel. That's why he asked for the Gospel. But the bad situation that his wound had given him, the new upheaval, again confused his thoughts, and for the third time he woke up to life in the complete silence of the night. Everyone was sleeping around him. A cricket screamed through the entryway, someone was shouting and singing on the street, cockroaches rustled on the table and on the icons, in the autumn a thick fly beat on his headboard and near the tallow candle, which had burned like a large mushroom and stood next to him.
In nature, populations of different species are integrated into macrosystems of a higher rank - into so-called communities, or biocenoses.
Biocenosis (from the Greek bios - life, koinos - general) is an organized group of interconnected populations of plants, animals, fungi and microorganisms living together in the same environmental conditions.
The concept of “biocenosis” was proposed in 1877 by the German zoologist K. Mobius. Moebius, studying oyster banks, came to the conclusion that each of them represents a community of living beings, all members of which are closely interconnected. Biocenosis is a product of natural selection. Its survival, stable existence in time and space depends on the nature of the interaction of the constituent populations and is possible only with the obligatory supply of radiant energy from the Sun from outside.
Each biocenosis has a certain structure, species composition and territory; it is characterized by a certain organization of food connections and a certain type of metabolism
But no biocenosis can develop on its own, outside and independently of the environment. As a result, certain complexes, collections of living and nonliving components, develop in nature. The complex interactions of their individual parts are supported on the basis of versatile mutual adaptability.
A space with more or less homogeneous conditions, inhabited by one or another community of organisms (biocenosis), is called a biotope.
In other words, a biotope is a place of existence, habitat, biocenosis. Therefore, a biocenosis can be considered as a historically established complex of organisms, characteristic of a specific biotope.
Any biocenosis forms a dialectical unity with a biotope, a biological macrosystem of an even higher rank - a biogeocenosis. The term “biogeocenosis” was proposed in 1940 by V. N. Sukachev. It is almost identical to the term “ecosystem”, widely used abroad, which was proposed in 1935 by A. Tansley. There is an opinion that the term “biogeocenosis” to a much greater extent reflects the structural characteristics of the macrosystem being studied, while the concept of “ecosystem” primarily includes its functional essence. In fact, there is no difference between these terms. Undoubtedly, V.N. Sukachev, formulating the concept of “biogeocoenosis”, combined in it not only the structural, but also the functional significance of the macrosystem. According to V.N. Sukachev, biogeocenosis- This a set of homogeneous natural phenomena over a known area of the earth's surface- atmosphere, rock, hydrological conditions, vegetation, fauna, microorganisms and soil. This set is distinguished by the specific interactions of its components, their special structure and a certain type of exchange of substances and energy among themselves and with other natural phenomena.
Biogeocenoses can be of very different sizes. In addition, they are characterized by great complexity - it is sometimes difficult to take into account all the elements, all the links. These are, for example, such natural groups as a forest, lake, meadow, etc. An example of a relatively simple and clear biogeocenosis is a small reservoir or pond. Its non-living components include water, substances dissolved in it (oxygen, carbon dioxide, salts, organic compounds) and soil - the bottom of a reservoir, which also contains a large number of various substances. The living components of a reservoir are divided into primary producers - producers (green plants), consumers - consumers (primary - herbivores, secondary - carnivores, etc.) and destroyers - destructors (microorganisms), which decompose organic compounds to inorganic ones. Any biogeocenosis, regardless of its size and complexity, consists of these main links: producers, consumers, destroyers and components of inanimate nature, as well as many other links. Connections of the most varied orders arise between them - parallel and intersecting, entangled and intertwined, etc.
In general, biogeocenosis represents an internal contradictory dialectical unity, in constant movement and change. “Biogeocenosis is not the sum of biocenosis and environment,” points out N.V. Dylis, “but a holistic and qualitatively isolated phenomenon of nature, acting and developing according to its own laws, the basis of which is the metabolism of its components.”
The living components of biogeocenosis, i.e., balanced animal-plant communities (biocenoses), are the highest form of existence of organisms. They are characterized by a relatively stable composition of fauna and flora and have a typical set of living organisms that retain their basic characteristics in time and space. The stability of biogeocenoses is supported by self-regulation, i.e. all elements of the system exist together, never completely destroying each other, but only limiting the number of individuals of each species to a certain limit. That is why such relationships have historically developed between species of animals, plants and microorganisms that ensure development and maintain their reproduction at a certain level. Overpopulation of one of them may arise for some reason as an outbreak of mass reproduction, and then the existing relationship between the species is temporarily disrupted.
To simplify the study of biocenosis, it can be conditionally divided into separate components: phytocenosis - vegetation, zoocenosis - fauna, microbiocenosis - microorganisms. But such fragmentation leads to an artificial and actually incorrect separation from a single natural complex of groups that cannot exist independently. In no habitat can there be a dynamic system that consists only of plants or only of animals. Biocenosis, phytocenosis and zoocenosis must be considered as biological unities of different types and stages. This view objectively reflects the real situation in modern ecology.
In the conditions of scientific and technological progress, human activity transforms natural biogeocenoses (forests, steppes). They are being replaced by sowing and planting of cultivated plants. This is how special secondary agrobiogeocenoses, or agrocenoses, are formed, the number of which on Earth is constantly increasing. Agrocenoses are not only agricultural fields, but also shelterbelts, pastures, artificially regenerated forests in cleared areas and fires, ponds and reservoirs, canals and drained swamps. Agrobiocenoses in their structure are characterized by a small number of species, but their high abundance. Although there are many specific features in the structure and energy of natural and artificial biocenoses, there are no sharp differences between them. In a natural biogeocenosis, the quantitative ratio of individuals of different species is mutually determined, since mechanisms regulating this ratio operate in it. As a result, a stable state is established in such biogeocenoses, maintaining the most favorable quantitative proportions of its constituent components. In artificial agrocenoses there are no such mechanisms; there, man has completely taken upon himself the responsibility for regulating the relationships between species. Much attention is paid to the study of the structure and dynamics of agrocenoses, since in the foreseeable future there will be practically no primary, natural, biogeocenoses left.
Based on their participation in the biogenic cycle of substances in biocenoses, three groups of organisms are distinguished:
1) Producers(producers) - autotrophic organisms that create organic substances from inorganic ones. The main producers in all biocenoses are green plants. The activities of producers determine the initial accumulation of organic substances in the biocenosis;
Consumers of the first order.
This trophic level is composed of direct consumers of primary production. In the most typical cases, when the latter is created by photoautotrophs, these are herbivores (phytophagous). The species and ecological forms representing this level are very diverse and are adapted to feeding on different types of plant food. Due to the fact that plants are usually attached to the substrate, and their tissues are often very strong, many phytophages have evolved a gnawing type of mouthparts and various types of adaptations for grinding and grinding food. These are the dental systems of the gnawing and grinding type in various herbivorous mammals, the muscular stomach of birds, especially well expressed in granivores, etc. n. The combination of these structures determines the ability to grind solid food. Gnawing mouthparts are characteristic of many insects and others.
Some animals are adapted to feeding on plant sap or flower nectar. This food is rich in high-calorie, easily digestible substances. The oral apparatus in species that feed in this way is designed in the form of a tube through which liquid food is absorbed.
Adaptations to feeding on plants are also found at the physiological level. They are especially pronounced in animals that feed on the rough tissues of the vegetative parts of plants, containing large amounts of fiber. In the body of most animals, cellulolytic enzymes are not produced, and the breakdown of fiber is carried out by symbiotic bacteria (and some protozoa of the intestinal tract).
Consumers partially use food to support life processes (“respiration costs”), and partially build their own body on its basis, thus carrying out the first, fundamental stage of transformation of organic matter synthesized by producers. The process of creation and accumulation of biomass at the level of consumers is designated as , secondary products.
Second order consumers.
This level unites animals with a carnivorous type of nutrition (zoophagous). Usually, all predators are considered in this group, since their specific features practically do not depend on whether the prey is a phytophage or a carnivore. But strictly speaking, only predators that feed on herbivores and, accordingly, represent the second stage of transformation of organic matter in food chains should be considered second-order consumers. The chemical substances from which the tissues of an animal organism are built are quite homogeneous, therefore the transformation during the transition from one level of consumers to another is not as fundamental as the transformation of plant tissues into animals.
With a more careful approach, the level of consumers of the second order should be divided into sublevels according to the direction of flow of matter and energy. For example, in the trophic chain “cereals - grasshoppers - frogs - snakes - eagles”, frogs, snakes and eagles constitute successive sublevels of consumers of the second order.
Plant material ( for example, nectar) → fly → spider → shrew → owl
Rosebush sap → aphid → ladybug → spider → insectivorous bird → bird of prey
Decomposers and detritivores (detritus food chains)
There are two main types of food chains – grazing and detrital. Above were examples of pasture chains in which the first trophic level is occupied by green plants, the second by pasture animals and the third by predators. The bodies of dead plants and animals still contain energy and “building material,” as well as intravital excretions, such as urine and feces. These organic materials are decomposed by microorganisms, namely fungi and bacteria, living as saprophytes on organic residues. Such organisms are called decomposers. They release digestive enzymes onto dead bodies or waste products and absorb the products of their digestion. The rate of decomposition may vary. Organic matter from urine, feces and animal carcasses is consumed within a few weeks, while fallen trees and branches can take many years to decompose. A very significant role in the decomposition of wood (and other plant debris) is played by fungi, which secrete the enzyme cellulose, which softens the wood, and this allows small animals to penetrate and absorb the softened material.
Pieces of partially decomposed material are called detritus, and many small animals (detritivores) feed on them, speeding up the decomposition process. Since both true decomposers (fungi and bacteria) and detritivores (animals) are involved in this process, both are sometimes called decomposers, although in reality this term refers only to saprophytic organisms.
Larger organisms can, in turn, feed on detritivores, and then a different type of food chain is created - a chain starting with detritus:
Detritus → detritivore → predator
Detritivores of forest and coastal communities include earthworm, woodlice, carrion fly larva (forest), polychaete, scarlet fly, holothurian (coastal zone).
Here are two typical detrital food chains in our forests:
Leaf litter → Earthworm → Blackbird → Sparrowhawk
Dead animal → Carrion fly larvae → Grass frog → Common grass snake
Some typical detritivores are earthworms, woodlice, bipeds and smaller ones (<0,5 мм) животные, такие, как клещи, ногохвостки, нематоды и черви-энхитреиды.
Food networks
In food chain diagrams, each organism is represented as feeding on other organisms of one type. However, actual food relationships in an ecosystem are much more complex, since an animal may feed on different types of organisms from the same food chain or even from different food chains. This is especially true for predators of the upper trophic levels. Some animals eat both other animals and plants; they are called omnivores (this is the case, in particular, with humans). In reality, food chains are intertwined in such a way that a food (trophic) web is formed. A food web diagram can only show a few of the many possible connections, and it usually includes only one or two predators from each of the upper trophic levels. Such diagrams illustrate nutritional relationships between organisms in an ecosystem and provide the basis for quantitative studies of ecological pyramids and ecosystem productivity.
Ecological pyramids.
Pyramids of numbers.
To study the relationships between organisms in an ecosystem and to graphically represent these relationships, it is more convenient to use not food web diagrams, but ecological pyramids. In this case, the number of different organisms in a given territory is first counted, grouping them by trophic levels. After such calculations, it becomes obvious that the number of animals progressively decreases during the transition from the second trophic level to subsequent ones. The number of plants at the first trophic level also often exceeds the number of animals that make up the second level. This can be depicted as a pyramid of numbers.
For convenience, the number of organisms at a given trophic level can be represented as a rectangle, the length (or area) of which is proportional to the number of organisms living in a given area (or in a given volume, if it is an aquatic ecosystem). The figure shows a population pyramid reflecting the real situation in nature. Predators located at the highest trophic level are called final predators.
Fourth trophic level Tertiary consumers
Third trophic level Secondary consumers
Second trophic level Primary consumers
First trophic Primary producers
level
Biomass pyramids.
The inconveniences associated with the use of population pyramids can be avoided by constructing biomass pyramids, which take into account the total mass of organisms (biomass) of each trophic level. Determining biomass involves not only counting numbers, but also weighing individual individuals, so it is a more labor-intensive process that requires more time and special equipment. Thus, the rectangles in the biomass pyramids represent the mass of organisms at each trophic level per unit area or volume.
When sampling - in other words, at a given point in time - the so-called standing biomass, or standing yield, is always determined. It is important to understand that this value does not contain any information about the rate of biomass production (productivity) or its consumption; otherwise errors may occur for two reasons:
1. If the rate of biomass consumption (loss due to consumption) approximately corresponds to the rate of its formation, then the standing crop does not necessarily indicate productivity, i.e. about the amount of energy and matter moving from one trophic level to another over a given period of time, for example, a year. For example, a fertile, intensively used pasture may have lower standing grass yields and higher productivity than a less fertile but poorly used pasture.
2. Small-sized producers, such as algae, are characterized by a high renewal rate, i.e. high growth and reproduction rates, balanced by their intensive consumption as food by other organisms and natural death. Thus, although standing biomass may be small compared to large producers (such as trees), productivity may not be less because trees accumulate biomass over a long period of time. In other words, phytoplankton with the same productivity as a tree will have much less biomass, although it could support the same mass of animals. In general, populations of large and long-lived plants and animals have a lower renewal rate compared to small and short-lived ones and accumulate matter and energy over a longer period of time. Zooplankton have greater biomass than the phytoplankton on which they feed. This is typical for planktonic communities of lakes and seas at certain times of the year; The biomass of phytoplankton exceeds the biomass of zooplankton during the spring “blooming”, but in other periods the opposite relationship is possible. Such apparent anomalies can be avoided by using energy pyramids.