Question 28. Food chain. Types of food chains.
FOOD CHAIN(trophic chain, food chain), the interconnection of organisms through food-consumer relationships (some serve as food for others). In this case, a transformation of matter and energy occurs from producers(primary producers) through consumers(consumers) to decomposers(converters of dead organic matter into inorganic substances assimilated by producers). There are 2 types of food chains - pasture and detritus. The pasture chain begins with green plants, goes to grazing herbivorous animals (consumers of the 1st order) and then to the predators that prey on these animals (depending on the place in the chain - consumers of the 2nd and subsequent orders). The detrital chain begins with detritus (a product of the breakdown of organic matter), goes to microorganisms that feed on it, and then to detritivores (animals and microorganisms involved in the process of decomposition of dying organic matter).
An example of a pasture chain is its multi-channel model in the African savanna. Primary producers are grass and trees, 1st order consumers are herbivorous insects and herbivores (ungulates, elephants, rhinoceroses, etc.), 2nd order are predatory insects, 3rd order are carnivorous reptiles (snakes, etc.), 4th – carnivorous mammals and predator birds. In turn, detritivores (scarab beetles, hyenas, jackals, vultures, etc.) at each stage of the grazing chain destroy the carcasses of dead animals and the food remains of predators. The number of individuals included in the food chain in each of its links consistently decreases (the rule of the ecological pyramid), i.e., the number of victims each time significantly exceeds the number of their consumers. Food chains are not isolated from one another, but are intertwined with each other to form food webs.
Question 29. What are ecological pyramids used for? Name them.
Ecological pyramid- graphic images of the relationship between producers and consumers of all levels (herbivores, predators, species that feed on other predators) in the ecosystem.
The American zoologist Charles Elton suggested schematically depicting these relationships in 1927.
In a schematic representation, each level is shown as a rectangle, the length or area of which corresponds to the numerical values of a link in the food chain (Elton’s pyramid), their mass or energy. Rectangles arranged in a certain sequence create pyramids of various shapes.
The base of the pyramid is the first trophic level - the level of producers; subsequent floors of the pyramid are formed by the next levels of the food chain - consumers of various orders. The height of all blocks in the pyramid is the same, and the length is proportional to the number, biomass or energy at the corresponding level.
Ecological pyramids are distinguished depending on the indicators on the basis of which the pyramid is built. At the same time, the basic rule has been established for all pyramids, according to which in any ecosystem there are more plants than animals, herbivores than carnivores, insects than birds.
Based on the rule of the ecological pyramid, it is possible to determine or calculate the quantitative ratios of different species of plants and animals in natural and artificially created ecological systems. For example, 1 kg of mass of a sea animal (seal, dolphin) requires 10 kg of eaten fish, and these 10 kg already need 100 kg of their food - aquatic invertebrates, which, in turn, need to eat 1000 kg of algae and bacteria to form such a mass. IN in this case the ecological pyramid will be sustainable.
However, as you know, there are exceptions to every rule, which will be considered in each type of ecological pyramid.
The first ecological schemes in the form of pyramids were built in the twenties of the 20th century. Charles Elton. They were based on field observations of a number of animals of different size classes. Elton did not include primary producers and did not make any distinction between detritivores and decomposers. However, he noted that predators are usually larger than their prey, and realized that this ratio is extremely specific only to certain size classes of animals. In the forties, the American ecologist Raymond Lindeman applied Elton's idea to trophic levels, abstracting from the specific organisms that comprise them. However, while it is easy to distribute animals into size classes, it is much more difficult to determine which trophic level they belong to. In any case, this can only be done in a very simplified and generalized manner. Nutritional relationships and the efficiency of energy transfer in the biotic component of an ecosystem are traditionally depicted in the form of stepped pyramids. This provides a clear basis for comparing: 1) different ecosystems; 2) seasonal states of the same ecosystem; 3) different phases ecosystem changes. There are three types of pyramids: 1) pyramids of numbers, based on counting organisms at each trophic level; 2) biomass pyramids, which use the total mass (usually dry) of organisms at each trophic level; 3) energy pyramids, taking into account the energy intensity of organisms at each trophic level.
Types of ecological pyramids
pyramids of numbers- at each level the number of individual organisms is plotted
The pyramid of numbers displays a clear pattern discovered by Elton: the number of individuals making up a sequential series of links from producers to consumers is steadily decreasing (Fig. 3).
For example, to feed one wolf, you need at least several hares he could hunt; To feed these hares, you need a fairly large variety of plants. In this case, the pyramid will look like a triangle with a wide base tapering upward.
However, this form of a pyramid of numbers is not typical for all ecosystems. Sometimes they can be reversed, or upside down. This applies to forest food chains, where trees serve as producers and insects serve 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), therefore the pyramids of numbers are the least informative and least indicative, i.e. the number of organisms of the same trophic level largely depends on their size.
biomass pyramids- characterizes the total dry or wet mass of organisms at a given trophic level, for example, in units of mass per unit area - g/m2, kg/ha, t/km2 or per volume - g/m3 (Fig. 4)
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 that of second-order consumers, etc.
In this case (if the organisms do not differ too much in size) the pyramid will also have the appearance of a triangle with a wide base tapering upward. However, there are significant exceptions to this rule. For example, in the seas, the biomass of herbivorous zooplankton is significantly (sometimes 2-3 times) greater than the biomass of phytoplankton, represented mainly by unicellular algae. This is explained by the fact that algae are very quickly eaten by zooplankton, but they are protected from being completely eaten away by the very high rate of division of their cells.
In general, terrestrial biogeocenoses, where producers are large and live relatively long, are characterized by relatively stable pyramids with a wide base. In aquatic ecosystems, where producers are small in size and have short life cycles, the pyramid of biomass can be inverted or inverted (with the tip pointing down). Thus, in lakes and seas, the mass of plants exceeds the mass of consumers only during the flowering period (spring), and during the rest of the year the opposite situation can occur.
Pyramids of numbers and biomass reflect the statics of the system, that is, they characterize the number or biomass of organisms in a certain period of time. They do not provide complete information about the trophic structure of an ecosystem, although they allow solving a number of practical problems, especially related to maintaining the sustainability of ecosystems.
The pyramid of numbers allows, for example, to calculate the permissible amount of fish catch or shooting of animals during the hunting season without consequences for their normal reproduction.
energy pyramids- shows the amount of energy flow or productivity at successive levels (Fig. 5).
In contrast to the pyramids of numbers and biomass, which reflect the statics of the system (the number of organisms at a given moment), the pyramid of energy, reflecting the picture of the speed of passage of food mass (amount of energy) through each trophic level of the food chain, gives the most complete picture of the functional organization of communities.
The shape of this pyramid is not affected by changes in the size and metabolic rate of individuals, and if all energy sources are taken into account, the pyramid will always have a typical appearance with a wide base and a tapering apex. When constructing a pyramid of energy, a rectangle is often added to its base to show the influx of solar energy.
In 1942, the American ecologist R. Lindeman formulated the law of the energy pyramid (the law of 10 percent), according to which, on average, about 10% of the energy received at 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. As a result of metabolic processes, organisms 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 may increase by 1 kg. A fox or wolf, eating 1 kg of hare meat, 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 herbs and seaweed this value is much greater, since they do not have difficult-to-digest tissues. However, the general pattern of the process of energy transfer remains: much less energy passes through the upper trophic levels than through the lower ones.
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 occurs differently in different species of plants and animals, but the so-called are always formed. They transform matter and energy, and nutrients can thus pass from one creature to another, carrying out the circulation of substances in nature.
In the woods
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. An example is green plants that get their food from sunlight through 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 obtain 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 different kinds animals, many of which are herbivores, which means they constitute the second link in the food chain, feeding on 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 of 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. a short time. Scavenger organisms play a huge role in nature. They destroy matter by transforming it into Not organic matter, 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 woods
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.
To any living creature on our planet for normal development food is needed. Nutrition is the process of receiving energy and necessary chemical elements into a living organism. The source of food for some animals is other plants and animals. The process of transferring energy and nutrients from one living organism to another occurs by eating one by another. Some animals and plants serve as food for others. Thus, energy can be transferred through several links.
The set of all links in this process is called power circuit. An example of a food chain can be seen in the forest, when a bird eats a worm and then itself becomes food for a lynx.
All types of living organisms, depending on the place they occupy, are divided into three types:
- producers;
- consumers;
- decomposers.
Producers are living organisms that produce their own nutrients. For example, plants or algae. To produce organic substances, producers can use sunlight or simple inorganic compounds, such as carbon dioxide or hydrogen sulfide. Such organisms are also called autotrophic. Autotrophs are the first link of any food chain and form its basis, and the energy received by these organisms supports each subsequent link.
Consumers
Consumers are the next link. The role of consumers is played by heterotrophic organisms, that is, those that do not produce organic substances on their own, but use other organisms as food. Consumers can be divided into several levels. For example, the first level includes all herbivores, some types of microorganisms, as well as plankton. Rodents, hares, moose, wild boars, antelopes and even hippos - all belong to the first level.
The second level includes small predators, such as: wild cats, minks, ferrets, plankton-eating fish, owls, snakes. These animals serve as food for third-level consumers - larger predators. These are animals such as fox, lynx, lion, hawk, pike, etc. Such predators are also called apex predators. Top predators do not necessarily eat only those at the previous level. For example, a small fox can become prey for a hawk, and a lynx can hunt both rodents and owls.
Decomposers
These are organisms that process animal waste products and their dead flesh into inorganic compounds. These include some types of fungi, decay bacteria. The role of decomposers is to close the cycle of substances in nature. They return water and simple inorganic compounds to the soil and air, which producers use for their life activities. Decomposers process not only dead animals, but also, for example, fallen leaves that begin to rot in the forest or dry grass in the steppe.
Trophic networks
All food chains exist in constant relationship with each other. The collection of several food chains constitutes a trophic web. This is a kind of pyramid consisting of several levels. Each level is formed by certain links in the food chain. For example, in chains:
- fly - frog - heron;
- grasshopper - snake - falcon;
The fly and grasshopper will belong to the first trophic level, the snake and frog to the second, and the heron and falcon to the third.
Types of food chains: examples in nature
They are divided into pasture and detritus. Pastoral food chains distributed in steppes and the world's oceans. The beginning of these chains are producers. For example, grass or algae. Next come first-order consumers, for example, herbivores or baby fish and small crustaceans that feed on algae. Next in the chain are small predators, such as foxes, minks, ferrets, perches, and owls. Superpredators, such as lions, bears, and crocodiles, complete the chain. Superpredators are not prey for other animals, but after their death they serve as food material for decomposers. Decomposers participate in the process of decomposition of the remains of these animals.
Detrital food chains originate from rotting organic matter. For example, from decaying leaves and remaining grass or from fallen berries. Such chains are common in deciduous and mixed forests. Fallen rotting leaves - woodlice - raven. Here is an example of such a food chain. Most animals and microorganisms can simultaneously be links in both types of food chains. An example of this is the woodpecker feeding on bugs that decompose dead wood. These are representatives of the detrital food chain. And the woodpecker itself can become prey for a small predator, for example, a lynx. Lynx can also hunt rodents - representatives of the pasture food chain.
Any food chain cannot be very long. This is due to the fact that only 10% of the energy of the previous level is transferred to each subsequent level. Most of them consist of 3 to 6 links.
The transfer of energy by living organisms eating each other is called a food chain. These are specific relationships between plants, fungi, animals, and microorganisms that ensure the circulation of substances in nature. Also called a food chain.
Structure
All organisms feed, i.e. receive energy that powers life processes. The trophic chain system is formed by links. A link in the food chain is a group of living organisms connected to a neighboring group through the “food-consumer” relationship. Some organisms are food for other organisms, which in turn are also food for a third group of organisms.
There are three types of links:
- producers - autotrophs;
- consumers - heterotrophs;
- decomposers (destructors) - saprotrophs.
Rice. 1. Links in the food chain.
All three links form one chain. There can be several consumers (consumers of the first, second order, etc.). The basis of the chain can be producers or decomposers.
Producers include plants that convert organic substances with the help of light into organic substances, which, when eaten by plants, enter the body of the first-order consumer. The main characteristic of the consumer is heterotrophy. At the same time, consumers can consume both living organisms and dead ones (carrion).
Examples of consumers:
- herbivores - hare, cow, mouse;
- predators - leopard, owl, walrus;
- scavengers - vulture, Tasmanian devil, jackal.
Some consumers, including humans, occupy an intermediate position, being omnivores. Such animals can act as consumers of the first, second and even third order. For example, a bear eats berries and small rodents, i.e. is simultaneously a consumer of the first and second orders.
Reducers include:
- mushrooms;
- bacteria;
- protozoa;
- worms;
- insect larvae.
Rice. 2. Decomposers.
Decomposers feed on the remains of living organisms and their metabolic products, returning inorganic substances to the soil that producers consume.
Kinds
Food chains can be of two types:
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- pasture (grazing chain);
- detrital (decomposition chain).
Pasture chains are characteristic of meadows, fields, seas, and reservoirs. The beginning of the grazing chain is autotrophic organisms - photosynthetic plants.
Next, the chain links are arranged as follows:
- First-order consumers are herbivores;
- second-order consumers are predators;
- third-order consumers are larger predators;
- decomposers.
In marine and oceanic ecosystems, grazing chains are longer than on land. They may include up to five consumer orders. The basis of marine chains is photosynthetic phytoplankton.
The following links are formed by several consumers:
- zooplankton (crustaceans);
- small fish (sprats);
- large predatory fish (herring);
- large predatory mammals (seals);
- apex predators (killer whales);
- decomposers.
Detritus chains are characteristic of forests and savannas. The chain begins with decomposers that feed on organic remains (detritus) and are called detriophages. These include microorganisms, insects, and worms. All these living organisms become food for top predators, for example, birds, hedgehogs, and lizards.
Examples of two types of food chains:
- pasture : clover - hare - fox - microorganisms;
- detrital : detritus - fly larvae - frog - snake - hawk - microorganisms.
Rice. 3. Example of a food chain.
The top of the food chain is always occupied by a predator, which is the last-order consumer in its range. The number of top predators is not regulated by other predators and depends only on external factors environment. Examples are killer whales, monitor lizards, and large sharks.
What have we learned?
We found out what food chains there are in nature and how the links are located in them. All living organisms on Earth are interconnected by food chains through which energy is transferred. Autotrophs themselves produce nutrients and are food for heterotrophs, which, when dying, become a breeding ground for saprotrophs. Decomposers can also become food for consumers and produce nutrient medium for producers, without interrupting the food chain.
Test on the topic
Evaluation of the report
Average rating: 4.7. Total ratings received: 203.
Target: expand knowledge about biotic environmental factors.
Equipment: herbarium plants, stuffed chordates (fish, amphibians, reptiles, birds, mammals), insect collections, wet preparations of animals, illustrations various plants and animals.
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, it is lost most of(up to 80-90%) of potential energy 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 the diversity of its 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, grass 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 do the rules of ecological pyramids reflect?
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
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