In ecosystems, producers, consumers and decomposers are united by complex processes of transfer of substances and energy, which is contained in food created mainly by plants.
Transfer potential energy food created by plants through a number of organisms by eating some species by others is called a trophic (food) chain, and each link is called a trophic level.
All organisms that use the same type of food belong to the same trophic level.
In Fig.4. a diagram of the trophic chain is presented.
Fig.4. Food chain diagram.
Fig.4. Food chain diagram.
First trophic level form producers (green plants) that accumulate solar energy and create organic matter during the process of photosynthesis.
In this case, more than half of the energy stored in organic substances is consumed in the life processes of plants, turning into heat and dissipating in space, and the rest enters the food chain and can be used by heterotrophic organisms of subsequent trophic levels during nutrition.
Second trophic level form consumers of the 1st order - these are herbivorous organisms (phytophages) that feed on producers.
First-order consumers spend most of the energy contained in food to support their life processes, and the rest of the energy is used to build their own body, thereby transforming plant tissue into animal tissue.
Thus , 1st order consumers carry out the first, fundamental stage of transformation of organic matter synthesized by producers.
Primary consumers can serve as a source of nutrition for 2nd order consumers.
Third trophic level form consumers of the 2nd order - these are carnivorous organisms (zoophages) that feed exclusively on herbivorous organisms (phytophages).
Second-order consumers carry out the second stage of transformation of organic matter in food chains.
However, the chemical substances from which the tissues of animal organisms are built are quite homogeneous and therefore the transformation of organic matter during the transition from the second trophic level of consumers to the third is not as fundamental as during the transition from the first trophic level to the second, where plant tissues are transformed into animals.
Secondary consumers can serve as a source of nutrition for third-order consumers.
Fourth trophic level form consumers of the 3rd order - these are carnivores that feed only on carnivorous organisms.
Last level of the food chain occupied by decomposers (destructors and detritivores).
Reducers-destructors (bacteria, fungi, protozoa) in the process of their life activity decompose organic remains of all trophic levels of producers and consumers into mineral substances, which are returned to the producers.
All links of the food chain are interconnected and interdependent.
Between them, from the first to the last link, the transfer of substances and energy takes place. However, it should be noted that when energy is transferred from one trophic level to another, it is lost. As a result, the power chain cannot be long and most often consists of 4-6 links.
However, such food chains in their pure form are usually not found in nature, since each organism has several food sources, i.e. uses several types of food, and is itself used as a food product by numerous other organisms from the same food chain or even from different food chains.
For example:
Omnivorous organisms consume both producers and consumers as food, i.e. are simultaneously consumers of the first, second, and sometimes third order;
a mosquito that feeds on the blood of humans and predatory animals is at a very high trophic level. But the swamp sundew plant feeds on mosquitoes, which is thus both a producer and a consumer of a high order.
Therefore, almost any organism that is part of one trophic chain can simultaneously be part of other trophic chains.
Thus, trophic chains can branch and intertwine many times, forming complex food webs or trophic (food) webs , in which the multiplicity and diversity of food connections acts as an important mechanism for maintaining the integrity and functional stability of ecosystems.
In Fig.5. shows a simplified diagram of a power network for a terrestrial ecosystem.
Human intervention in natural communities of organisms through the intentional or unintentional elimination of a species often has unpredictable consequences. negative consequences and leads to disruption of ecosystem stability.
Fig.5. Scheme of the trophic network.
There are two main types of trophic chains:
pasture chains (grazing chains or consumption chains);
detrital chains (decomposition chains).
Pasture chains (grazing chains or consumption chains) are processes of synthesis and transformation of organic substances in trophic chains.
Pasture chains begin with producers. Living plants are eaten by phytophages (consumers of the first order), and the phytophages themselves are food for carnivores (consumers of the second order), which can be eaten by consumers of the third order, etc.
Examples of grazing chains for terrestrial ecosystems:
3 links: aspen → hare → fox; plant → sheep → human.
4 links: plants → grasshoppers → lizards → hawk;
nectar of plant flower → fly → insectivorous bird →
bird of prey.
5 links: plants → grasshoppers → frogs → snakes → eagle.
Examples of grazing chains for aquatic ecosystems:→
3 links: phytoplankton → zooplankton → fish;
5 links: phytoplankton → zooplankton → fish → predatory fish →
birds of prey.
Detrital chains (decomposition chains) are processes of step-by-step destruction and mineralization of organic substances in trophic chains.
Detrital chains begin with the gradual destruction of dead organic matter by detritivores, which successively replace each other in accordance with a specific type of nutrition.
At the last stages of destruction processes, reducers-destructors function, mineralizing the remains of organic compounds into simple inorganic substances, which are again used by producers.
For example, when decomposing dead wood, they successively replace each other: beetles → woodpeckers → ants and termites → destructive fungi.
Detritus chains are most common in forests where most(about 90%) of the annual increase in plant biomass is not consumed directly by herbivores, but dies and enters these chains in the form of leaf litter, then undergoing decomposition and mineralization.
In aquatic ecosystems, most of the matter and energy is included in grazing chains, and in terrestrial ecosystems Detrital chains are of greatest importance.
Thus, at the level of consumers, the flow of organic matter is divided into different groups of consumers:
living organic matter follows grazing chains;
dead organic matter goes along detrital chains.
Most living organisms eat organic food; this is the specificity of their life activity on our planet. Among this food are plants, the meat of other animals, their products and dead matter ready for decomposition. The process of nutrition itself in different species of plants and animals occurs in different ways, but the so-called They are always formed. They transform matter and energy, and nutrients can thus pass from one creature to another, carrying out the cycle of substances in nature.
in the forest
Forests of various kinds cover quite a lot of land surface. These are lungs and a tool for cleansing our planet. It is not for nothing that many progressive modern scientists and activists today oppose mass deforestation. The food chain in the forest can be quite diverse, but, as a rule, it includes no more than 3-5 links. In order to understand the essence of the issue, let us turn to the possible components of this chain.
Producers and consumers
- The first are autotrophic organisms that feed on inorganic food. They take energy and matter to create own bodies using gases and salts from their environment. As an example, green plants that receive nutrition from sunlight using photosynthesis. Or numerous types of microorganisms that live everywhere: in the air, in the soil, in the water. It is the producers who, for the most part, constitute the first link in almost any food chain in the forest (examples will be given below).
- The second are heterotrophic organisms that feed on organic matter. Among them are those of the first order that directly provide nutrition through plants and bacteria producers. Second order - those who eat animal food (predators or carnivores).
Plants
As a rule, the food chain in the forest begins with them. They act as the first link in this cycle. Trees and shrubs, grasses and mosses extract food from inorganic substances using sunlight, gases and minerals. A food chain in a forest, for example, may begin with a birch tree, the bark of which is eaten by a hare, which in turn is killed and eaten by a wolf.
Herbivores
Animals that feed on plant foods are found in abundance in various forests. Of course, for example, it is very different in its content from the land middle zone. They live in the jungle various types animals, many of which are herbivores, which means they constitute the second link food chain eating plant foods. From elephants and rhinoceroses to barely visible insects, from amphibians and birds to mammals. So, in Brazil, for example, there are more than 700 species of butterflies, almost all of them are herbivores.
The fauna, of course, is poorer in the forest belt of central Russia. Accordingly, there are much fewer power supply options. Squirrels and hares, other rodents, deer and moose, hares - this is the basis for such chains.
Predators or carnivores
They are called that because they eat flesh, feeding on the meat of other animals. IN food chain occupy a dominant position, often being the final link. In our forests these are foxes and wolves, owls and eagles, sometimes bears (but in general they belong to those who can eat both plant and animal food). A food chain can involve either one or several predators that eat each other. The final link, as a rule, is the largest and most powerful carnivore. In the middle forest, this role can be performed, for example, by a wolf. There are not too many such predators, and their population is limited by the nutritional base and energy reserves. Since, according to the law of conservation of energy, during the transition nutrients from one link to the next, up to 90% of the resource can be lost. This is probably why the number of links in most food chains cannot exceed five.
Scavengers
They feed on the remains of other organisms. Oddly enough, there are also quite a lot of them in the natural forest: from microorganisms and insects to birds and mammals. Many beetles, for example, use the corpses of other insects and even vertebrates as food. And bacteria are capable of decomposing the dead bodies of mammals in a relatively short time. short time. Scavenger organisms play a huge role in nature. They destroy matter by transforming it into inorganic substances, release energy, using it for their life activities. If it were not for scavengers, then, probably, the entire earthly space would be covered with the bodies of animals and plants that have died throughout time.
in the forest
To create a food chain in a forest, you need to know about the inhabitants who live there. And also about what these animals can eat.
- Birch bark - insect larvae - small birds - birds of prey.
- Fallen leaves are bacteria.
- Butterfly caterpillar - mouse - snake - hedgehog - fox.
- Acorn - mouse - fox.
- Cereals - mouse - eagle owl.
There is also a more authentic one: fallen leaves - bacteria - earthworms - mice - mole - hedgehog - fox - wolf. But, as a rule, the number of links is no more than five. The food chain in a spruce forest is slightly different from those in a deciduous forest.
- Cereal seeds - sparrow - wild cat.
- Flowers (nectar) - butterfly - frog - snake.
- Fir cone - woodpecker - eagle.
Food chains can sometimes intertwine with each other, forming more complex, multi-level structures that unite into a single forest ecosystem. For example, the fox does not disdain to eat both insects and their larvae, and mammals, thus several food chains intersect.
Lesson topic:“Who eats what? Food chains".
Lesson type:learning new material.
Textbook: “The world around us, grade 3, part 1” (author A.A. Pleshakov)
Goals and objectives of the lesson
Target:generalize students' knowledge about the diversity of the animal world, about groups of animals by type of nutrition, about power circuits, about reproduction and stages of development, adaptation to protection from enemies and protection of animals.
Tasks:
1. Contribute to the enrichment and development of subjective ideas about the life of animals.
2. To promote the development of children’s ability to draw up, “read” diagrams, and model environmental connections.
3. Contribute to the development of skills and abilities of independent and group work.
4. Create conditions for the development of logical thinking;
5. Cultivate a sense of responsibility for all living things that surround us, a feeling of love for nature.
Lesson equipment
Computer.
Worksheets with tasks. Cards with puzzles.
Multimedia projector.
Textbook: Pleshakov A.A. The world is around us. - M., Education, 2007.
Board
Progress of the lesson.
1 .Organizational moment.
2. Statement of the topic of the lesson and statement of the problem.
(Appendix slide 1)
Guys, look carefully at the slide. Think about how these representatives of wildlife are connected to each other. Based on this slide, who will determine the topic of our lesson?
(We will talk about who eats what.)
Right! If you look closely at the slide, you will see that all the items are connected by arrows in a chain according to the method of nutrition. In ecology, such chains are called ecological chains, or food chains. Hence the topic of our lesson “Who eats what?” Food chains.”
3. Updating knowledge.
To trace different food chains and try to compose them ourselves, we need to remember who eats what. Let's start with plants. What is special about their diet? Tell us based on the table.
(Appendix slide 3)
(Plants come from the air carbon dioxide. They absorb water and salts dissolved in it through their roots from the soil. When exposed to sunlight, plants convert carbon dioxide, water and salts into sugar and starch. Their specialty is that they cook their own food.)
Now let’s remember what groups animals are divided into based on their feeding method and how they differ from each other.
(Herbivorous animals eat plant foods. Insectivores eat insects. Carnivorous animals feed on the flesh of other animals, therefore they are also called carnivores. Omnivores eat plant and animal foods.)
(Appendix slide 4)
4. Discovery of new knowledge .
Food chains are the nutritional connections of all living things. There are a lot of food chains in nature. In the forest they are alone, completely different in the meadow and in the pond, others in the field and in the garden. I invite you to act as environmental scientists and engage in search activity. All groups will go to different places. Here are the routes of environmental scientists.
(Appendix slide 5)
Where you will have to work will be decided by drawing lots.
I invite one person from each group, and they pull out a card with the name of the place. The same guys receive sheets with arrows and 4 cards with pictures of plants and animals.
Now listen to the task. Each group, using cards, must create a food chain. The cards are attached to the sheet with arrows using paper clips. Immediately agree who will present your circuit to the class. Consider whether you will need all the cards.
At the signal, the guys begin to work in groups. Those who finished early are offered riddles.
(Appendix slide 6)
All finished chains are hung on a board.
A pine tree grows in the forest. A bark beetle lives under the bark of a pine tree and feeds on it. In turn, the bark beetle is food for woodpeckers. We had an extra picture - a goat. This is a domestic animal and is not included in this food chain.
Let's check the guys' work.
(Appendix slide 7)
Other groups explain their chains in the same way.
2) Field: rye – mouse – snake (extra – fish).
(Appendix slide 8)
3) Vegetable garden: cabbage - slugs - toad (extra one - bear).
(Appendix slide 9)
4) Garden: apple tree – apple aphid – ladybug(the extra one is the fox).
(Appendix slide 10)
5) Reservoir: algae - crucian carp - pike (extra - hare).
(Appendix slide 11)
All the chains are on our board. Let's see what parts they consist of. What is on each table? What comes first? On the second? On the third?
(Plant. Herbivorous animal. Carnivorous, insectivorous or omnivorous animal.)
5. Primary consolidation of knowledge.
1. Work according to the textbook. pp. 96-97.
Now, guys, let's get acquainted with the textbook article and test ourselves. Children open the textbook p. 96–97 and silently read the article “Food Chains”.
– What power circuits are given in the textbook?
Aspen - hare - wolf.
Oaks – wood mice – owls.
In what order are the links in the food chain located?
I link – plants;
II link – herbivorous animals;
III link – other animals.
(Appendix slide 12)
2) Repetition of the rules of behavior in the forest.
Here we are in the forest. Listen to the sounds of the forest, look at the diversity of its inhabitants. Do you know how to behave in the forest?
1. Do not break branches of trees and bushes.
2.Do not pick or trample flowers and medicinal plants.
3.Do not catch butterflies, dragonflies and other insects.
4.Do not destroy frogs and toads.
5.Do not touch bird nests.
6.Do not bring animals home from the forest.
Slide 6 (appendix) opens with images of an owl, mice and acorns. Students create a food chain by moving pictures.
Who is bigger in this food chain?
The largest of all is the owl, and the mouse is larger than the acorn.
If we had a magic scale and we weighed all the owls, mice and acorns, it would turn out that acorns are heavier than mice, and mice are heavier than owls. Why do you think?
Because there are very, very many acorns in the forest, many mice, and few owls.
And this is no coincidence. After all, one owl needs a lot of mice for food, and one mouse needs a lot of acorns. It turns out to be an ecological pyramid.
Summary conclusion :
In nature, everything and everyone is connected to each other. Food webs intertwine to form a food web. Plants and animals form ecological pyramids. At the base are plants, and at the top are predatory animals.
6 .Introduction to the concept of “power network”
Food chains in nature are not as simple as in our example. Other animals can also eat the hare. Which? (fox, lynx, wolf)
A mouse can become prey for a fox, owl, lynx, wild boar, or hedgehog.
Many herbivorous animals serve as food for various predators.
Therefore, power chains are branched; they can intertwine with each other, forming a complex power network.
7. Problem situation .
Guys, what will happen if all the trees on which the hare eats disappear in the forest? (The hare will have nothing to eat)
- What if there are no hares? (There will be no food for both the fox and the wolf)
– What will happen to the chain? (It'll collapse)
What conclusion can be drawn? (If you destroy even one link in a chain, the whole chain will collapse.)
8.Make several possible power circuits
9. Summary of the lesson. Generalization on the topic.
Reflection.
“Finish the sentence.”
Animals and plants are related to each other in ……………………
At the heart of the power supply chain are ………………………………..
And they end the chain – ………………………………………..
In nature, food chains intertwine with each other, forming
…………………………………………
Homemadeexercise.
1. Prepare a message about one of Birch’s friends;
2. Complete tasks No. 4 from the manual “ The world around us"(The figure shows a section of the garden. Make several possible food chains).
Target: expand knowledge about biotic factors environment.
Equipment: herbarium plants, stuffed chordates (fish, amphibians, reptiles, birds, mammals), insect collections, wet preparations of animals, illustrations various plants and animals.
Work progress:
1. Use the equipment and make two power circuits. Remember that the chain always starts with a producer and ends with a reducer.
Plants → insects→lizard → bacteria
Plants → grasshopper→ frog → bacteria
Remember your observations in nature and make two food chains. Label producers, consumers (1st and 2nd orders), decomposers.
Violet → Springtails→predatory mites→predatory centipedes→ bacteria
Producer - consumer1 - consumer2 - consumer2 - decomposer
Cabbage→ slug→ frog →bacteria
Producer – consumer1 - consumer2 - decomposer
What is a food chain and what underlies it? What determines the stability of a biocenosis? State your conclusion.
Conclusion:
Food (trophic) chain- a series of species of plants, animals, fungi and microorganisms that are connected to each other by the relationship: food - consumer (a sequence of organisms in which a gradual transfer of matter and energy occurs from source to consumer). Organisms of the next link eat the organisms of the previous link, and thus a chain transfer of energy and matter occurs, which underlies the cycle of substances in nature. With each transfer from link to link, a large part (up to 80-90%) of the potential energy is lost, dissipated in the form of heat. For this reason, the number of links (types) in the food chain is limited and usually does not exceed 4-5. The stability of a biocenosis is determined by its diversity species composition. Producers- organisms capable of synthesizing organic substances from inorganic ones, that is, all autotrophs. Consumers- heterotrophs, organisms that consume ready-made organic substances created by autotrophs (producers). Unlike decomposers
Consumers are not able to decompose organic substances into inorganic ones. Decomposers- microorganisms (bacteria and fungi) that destroy dead remains of living beings, turning them into inorganic and simple organic compounds.
3. Name the organisms that should be in the missing place in the following food chains.
1) Spider, fox
2) tree-eater caterpillar, snake hawk
3) caterpillar
4. From the proposed list of living organisms, create a trophic network:
grass, berry bush, fly, tit, frog, snake, hare, wolf, rotting bacteria, mosquito, grasshopper. Indicate the amount of energy that moves from one level to another.
1. Grass (100%) - grasshopper (10%) - frog (1%) - snake (0.1%) - rotting bacteria (0.01%).
2. Shrub (100%) - hare (10%) - wolf (1%) - rotting bacteria (0.1%).
3. Grass (100%) - fly (10%) - tit (1%) - wolf (0.1%) - rotting bacteria (0.01%).
4. Grass (100%) - mosquito (10%) - frog (1%) - snake (0.1%) - rotting bacteria (0.01%).
5. Knowing the rule for the transfer of energy from one trophic level to another (about 10%), build a pyramid of biomass for the third food chain (task 1). Plant biomass is 40 tons.
Grass (40 tons) -- grasshopper (4 tons) -- sparrow (0.4 tons) -- fox (0.04).
6. Conclusion: what the rules reflect ecological pyramids?
The rule of ecological pyramids very conditionally conveys the pattern of energy transfer from one level of nutrition to the next in the food chain. These graphic models were first developed by Charles Elton in 1927. According to this pattern, the total mass of plants should be an order of magnitude greater than that of herbivorous animals, and the total mass of herbivorous animals should be an order of magnitude greater than that of first-level predators, etc. to the very end of the food chain.
Laboratory work № 1
