Types of relationships between organisms

Animals and plants, fungi and bacteria do not exist in isolation from each other, but enter into complex relationships. There are several forms of interaction between populations.

Neutralism

Cohabitation of two species in the same territory, which has neither positive nor negative consequences for them.

In neutralism, cohabiting populations of different species do not influence each other. For example, we can say that a squirrel and a bear, a wolf and a cockchafer, do not directly interact, although live in the same forest.

Antibiosis

When both interacting populations or one of them experience a harmful, life-suppressing influence.

Antagonistic relationships can manifest themselves as follows:

1. Competition.

A form of antibiotic relationship in which organisms compete with each other for food resources, sexual partners, shelter, light, etc.

In competition for food, the species whose individuals reproduce faster wins. Under natural conditions, competition between closely related species weakens if one of them switches to a new food source (that is, they occupy a different ecological niche). For example, in winter, insectivorous birds avoid competition by searching for food in different places: on tree trunks, in bushes, on stumps, on large or small branches.

Displacement of one population by another: In mixed crops of different types of clover, they coexist, but competition for light leads to a decrease in the density of each of them. Thus, competition that arises between closely related species can have two consequences: either the displacement of one species by another, or different ecological specialization of species, which makes it possible to coexist together.

Suppression of one population by another: Thus, fungi that produce antibiotics suppress the growth of microorganisms. Some plants that can grow on nitrogen-poor soils secrete substances that inhibit the activity of free-living nitrogen-fixing bacteria, as well as the formation of nodules in legumes. In this way, they prevent the accumulation of nitrogen in the soil and the colonization of it by species that require large amounts of it.

3. Amensalism

A form of antibiotic relationship in which one organism interacts with another and suppresses its vital activity, while it itself does not experience any negative influences from the suppressed one (for example, spruce and lower tier plants). A special case is allelopathy - the influence of one organism on another, in which waste products of one organism are released into the external environment, poisoning it and making it unsuitable for the life of another (common in plants).

5. Predation

This is a form of relationship in which an organism of one species uses members of another species as a food source once (by killing them).

Cannibalism is a special case of predation - killing and eating one’s own kind (found in rats, brown bears, humans).

Symbiosis

A form of relationship in which the participants benefit from cohabitation or at least do not harm each other. Symbiotic relationships also come in a variety of forms.

1. Protocooperation is a mutually beneficial, but optional coexistence of organisms, from which all participants benefit (for example, hermit crab and sea anemone).

2. Mutualism is a form of symbiotic relationship in which either one of the partners or both cannot exist without a cohabitant (for example, herbivorous ungulates and cellulose-degrading microorganisms).

Lichens are an inseparable cohabitation of fungus and algae, when the presence of a partner becomes a condition of life for each of them. The hyphae of the fungus, entwining the cells and filaments of the algae, receive substances synthesized by the algae. Algae extract water and minerals from the fungal hyphae.

Many grasses and trees develop normally only when soil fungi (mycorrhiza) settle on their roots: root hairs do not develop, and the mycelium of the fungus penetrates into the root. Plants receive water and mineral salts from the fungus, which in turn receives organic substances.

3. Commensalism is a form of symbiotic relationship in which one of the partners benefits from cohabitation, while the other is indifferent to the presence of the first. There are two types of cohabitation:

Housing (some sea anemones and tropical fish). The fish sticks by clinging to large fish (sharks), uses them as a means of transportation and, in addition, feeds on their waste.

The use of structures and body cavities of other species as shelters is widespread. In tropical waters, some fish hide in the respiratory cavity (water lungs) of sea cucumbers (or sea cucumbers, order of echinoderms). The fry of some fish find refuge under the umbrella of jellyfish and are protected by their stinging threads. To protect the developing offspring, fish use the durable shell of crabs or bivalves. The eggs laid on the gills of the crab develop under conditions of an ideal supply of clean water passing through the gills of the host. Plants also use other species as habitats. These are the so-called epiphytes - plants that settle on trees. These can be algae, lichens, mosses, ferns, flowering plants. Woody plants serve as a place of attachment for them, but not as a source of nutrients.

Freeloading (large predators and scavengers). For example, hyenas follow lions, picking up the remains of their uneaten prey. There may be different spatial relationships between partners. If one partner is outside the cells of the other, they speak of ectosymbiosis, and if inside the cells, they speak of endosymbiosis.

EXAMINATION CARD No. 4
	Types of nutrition of living organisms.
	Theories of the origin of life.

Types of nutrition of living organisms:

There are two types of nutrition of living organisms: autotrophic and heterotrophic.

Autotrophs (autotrophic organisms) are organisms that use carbon dioxide as a carbon source (plants and some bacteria). In other words, these are organisms capable of creating organic substances from inorganic ones - carbon dioxide, water, mineral salts.

Heterotrophs (heterotrophic organisms) are organisms that use organic compounds (animals, fungi and most bacteria) as a carbon source. In other words, these are organisms that are not capable of creating organic substances from inorganic ones, but require ready-made organic substances.

Some living beings, depending on living conditions, are capable of both autotrophic and heterotrophic nutrition. Organisms with a mixed type of nutrition are called mixotrophs. Mixotrophs are organisms that can both synthesize organic substances from inorganic ones and feed on ready-made organic compounds (insectivorous plants, representatives of the euglena algae department, etc.)

Problems and exercises for the school course of general ecology 1

Continuation. See No. 15/2002

(Printed with abbreviations)

Ways of influence of organisms on the environment

1. It has rained. A bright hot sun came out from behind a cloud. In which area will the soil moisture content be greater after five hours (soil type is the same): a) on a freshly plowed field; b) in a ripe wheat field; c) in an ungrazed meadow; d) in a grazing meadow? Explain why.
(Answer: V. The thicker the vegetation cover, the less the soil heats up and, therefore, the less water will evaporate.)

2. Explain why ravines are more often formed in non-forest natural zones: steppes, semi-deserts, deserts. What human activities lead to the formation of ravines?
(Answer: The root systems of trees and shrubs, to a greater extent than of herbaceous vegetation, retain soil when it is washed away by water flows, therefore, in places where forest and shrub vegetation grow, ravines form less frequently than in fields, steppes and deserts. In the complete absence of vegetation (including grass), any flow of water will cause soil erosion. When vegetation is destroyed by humans (plowing, grazing, construction, etc.), increased soil erosion will always be observed.)

3.* It has been established that in summer, after the heat, more precipitation falls over the forest than over the nearby vast field.
(Answer: Why? Explain the role of the nature of vegetation in shaping the level of aridity in certain areas.
above open spaces the air heats up faster and stronger than above a forest.

4.* Rising upward, hot air turns raindrops into steam. As a result, when it rains, less water flows over a vast field than over a forest.
(Answer: goats eat not only grass, but also leaves and tree bark. Goats are capable of reproducing quickly. Having reached high numbers, they mercilessly destroy trees and shrubs. In countries with insufficient rainfall, this causes further drying of the climate. As a result, nature is impoverished, which negatively affects the country’s economy.)

Adaptive forms of organisms

1.* Why do wingless forms predominate among insects on small oceanic islands, while winged ones predominate on the nearby mainland or large islands?
(Answer: small oceanic islands are blown by strong winds. As a result, all small flying animals that are unable to withstand strong winds are blown into the ocean and die. In the course of evolution, insects living on small islands have lost the ability to fly.)

Adaptive rhythms of life

1. List the abiotic environmental factors known to you, the values ​​of which change periodically and regularly over time.
(Answer: illumination during the day, illumination throughout the year, temperature during the day, temperature throughout the year, humidity throughout the year and others.)

2. Select from the list those habitats in which animals do not have circadian rhythms (provided that they live only within one specific environment): lake, river, cave waters, soil surface, ocean floor at a depth of 6000 m, mountains, human intestines , forest, air, soil at a depth of 1.5 m, river bottom at a depth of 10 m, bark of a living tree, soil at a depth of 10 cm.
(Answer: waters of caves, ocean bottom, soil at a depth of 1.5 m.)

3. In what month do chinstrap Adélie penguins usually give birth in European zoos - May, June, October or February? Explain your answer.
(Answer: in October - in the Southern Hemisphere at this time it is spring.)

4. Why did the experiment with the acclimatization of the South American llama in the Tien Shan mountains (where the climate is similar to the usual conditions of the animal’s native places) end in failure?
(Answer: mismatch of annual cycles - baby animals were born in a new habitat in the fall (in the homeland of animals at this time it is spring) and died in the cold winter from lack of food.)

CHAPTER 2. COMMUNITIES AND POPULATIONS

Types of interactions between organisms

2. From the proposed list, make pairs of organisms that in nature can be in mutualistic (mutually beneficial) relationships with each other (the names of organisms can be used only once): bee, boletus mushroom, sea anemone, oak, birch, hermit crab, aspen, jay, clover , boletus mushroom, linden, nodule nitrogen-fixing bacteria.
(Answer: bee - linden; boletus mushroom - birch; sea ​​anemone - hermit crab; oak - jay;

3. boletus mushroom – aspen; clover is a nodule nitrogen-fixing bacteria.)
(Answer: From the proposed list, make pairs of organisms between which trophic (food) connections can form in nature (the names of organisms can be used only once): heron, willow, aphid, amoeba, brown hare, ant, aquatic bacteria, wild boar, frog, currant , sundew, antlion, mosquito, tiger.

4. heron - frog; hare - willow; aphid - currant; amoeba – aquatic bacteria; antlion - ant; tiger - boar; sundew - mosquito.)

(Answer: Lichens are an example of biotic relationships:

5. A.)

Pairs of organisms cannot serve as an example of a “predator-prey” relationship (choose the correct answer):
a) pike and crucian carp;
b) lion and zebra;
c) freshwater amoeba and bacteria;
d) antlion and ant;

(Answer: d) jackal and vulture.

6.

d.)
A. The interaction of two or more individuals, the consequences of which are negative for some and indifferent for others.
B. Interaction of two or more individuals, in which some use the leftover food of others without harming them.
B. Mutually beneficial interaction between two or more individuals.
D. Interaction of two or more individuals, in which some provide shelter to others, and this does not bring harm or benefit to the owner.
D. Cohabitation of two individuals that do not directly interact with each other.
E. The interaction of two or more individuals that have similar needs for the same limited resources, which leads to a decrease in the vital signs of the interacting individuals.
G. The interaction of two or more organisms, in which some feed on the living tissues or cells of others and receive from them a place of permanent or temporary habitat.

(Answer: H. The interaction of two or more individuals, in which some eat others.

7. 1 – B; 2 – D; 3 – E; 4 – A; 5 – G; 6 – B; 7 – F; 8 – Z.)
(Answer: A symbiotic relationship is formed between these fungi and the tree. Mushrooms quickly form a very branched mycelium and entwine tree roots with their hyphae. Thanks to this, the plant receives water and mineral salts from a huge area of ​​the soil surface. To achieve such an effect without mycelium, the tree would have to spend a lot of time, matter and energy on the formation of such an extensive root system. When planting in a new place, symbiosis with the fungus significantly increases the chances of the tree to take root safely.)

8.* Name the organisms that are human symbionts. What role do they play?
(Answer: representatives of bacteria and protozoa living in the human intestine. There are 250 billion microorganisms in 1 g of colon contents. Many substances that enter the human body with food are digested with their active participation. Without intestinal symbionts, normal development is impossible. A disease in which the number of symbiotic intestinal organisms decreases is called dysbiosis. Microorganisms also live in tissues, cavities and on the surface of human skin.)

9.* The relationship between an adult spruce and a neighboring oak seedling is an example:

(Answer: A.)

Laws and consequences of food relations

1. Match the proposed concepts and definitions:

A. An organism that actively seeks out and kills relatively large prey that are capable of fleeing, hiding, or resisting.
B. An organism (usually small in size) that uses living tissue or cells of another organism as a source of nutrition and habitat.
B. An organism that absorbs numerous food objects, usually of plant origin, for which it does not spend much effort searching.
D. An aquatic animal that filters water through itself with numerous small organisms that serve as food for it.
B. An organism that searches for and eats relatively small food objects that are not capable of running away or resisting.

(Answer: 1 – B; 2 – G; 3 – A; 4 – D; 5 – V.)

2. Explain why in China in the mid-twentieth century. Following the destruction of sparrows, the grain harvest sharply decreased. After all, sparrows are granivorous birds.
(Answer: adult sparrows feed mainly on seeds, but chicks need protein food for their development. While feeding their offspring, sparrows collect a huge number of insects, including pests of grain crops. The destruction of sparrows caused outbreaks of pests, which led to a reduction in harvests.)

Laws of competitive relations in nature

1. For each proposed pair of organisms, select a resource (from those given below) for which they can compete: lily of the valley - pine, field mouse - vole, wolf - fox, perch - pike, buzzard - tawny owl, badger - fox, rye – blue cornflower, saxaul – camel thorn, bumblebee – bee.
Resources: hole, nectar, wheat seeds, water, hares, light, small roaches, potassium ions, small rodents.
(Answer: lily of the valley and pine – potassium ions; field mouse and common vole – wheat seeds;

2.* wolf and fox are hares; perch and pike – small roach; the buzzard and the tawny owl are small rodents; badger and fox - hole; rye and cornflower - light; saxaul and camel thorn – water; bumblebee and bee - nectar.)
(Answer: Closely related species often live together, although it is generally accepted that the most intense competition exists between them.

3.* Why in these cases does not one species replace the other?
(Answer: 1 – very often closely related species living together occupy different ecological niches (they differ in the composition of their preferred food, in the method of obtaining food, use different microhabitats, are active at different times of the day); 2 – competition may be absent if the resource for which the species compete is in abundance; 3 – displacement does not occur if the number of a competitively stronger species is constantly limited by a predator or a third competitor; 4 - in an unstable environment in which conditions are constantly changing, they can alternately become favorable for one species or another.)

In nature, Scots pine forms forests on relatively poor soils in swampy or, conversely, dry places.

Planted by human hands, it grows well in rich soils with average moisture, but only if a person takes care of the plantings. Explain why this happens.

Usually, under these conditions, other tree species win the competition (depending on the conditions, this can be aspen, linden, maple, elm, oak, spruce, etc.). When caring for plantings, humans weaken the competitive power of these species by weeding, cutting down, etc.)
Populations
1. Select a value that evaluates the population density indicator:
a) 20 individuals;
b) 20 individuals per hectare;
c) 20 individuals per 100 breeding females;

(Answer: d) 20%;

2. e) 20 individuals per 100 traps;

e) 20 individuals per year.
b.)
Select a value that estimates the birth rate (or death rate) of the population:
a) 100 individuals;

(Answer: b) 100 individuals per year;

3. White hares and brown hares living in the same territory are:

a) one population of one species;
b) two populations of two species;
c) two populations of the same species;
d) one population of different species.

(Answer: b) 100 individuals per year;

4. Forest felling was carried out annually on an area of ​​100 km2. At the time of the organization of this reserve, 50 moose were recorded. After 5 years, the number of moose increased to 650 animals. After another 10 years, the number of moose decreased to 90 and stabilized in subsequent years at the level of 80–110 animals.
Determine the population density of moose: a) at the time of the creation of the reserve; b) 5 years after the creation of the reserve; c) 15 years after the creation of the reserve. Explain why the number of moose initially increased sharply, and later fell and stabilized.
(Answer: a – 0.5 individuals/km2; b – 6.5 individuals/km2; c – 0.9 individuals/km2. The number of moose has increased due to protection in the reserve. Later, the number decreased, since logging is prohibited in reserves. This led to the fact that after 15 years, small trees growing in old clearings grew, and the food supply for moose decreased.)

5. Game experts established that in the spring, 8 sables lived on an area of ​​20 km2 of taiga forest, of which 4 were females (adult sables do not form permanent pairs). Every year, one female gives birth to an average of three cubs. The average mortality rate of sables (adults and calves) at the end of the year is 10%. Determine the number of sables at the end of the year; density in spring and at the end of the year;
(Answer: annual mortality rate; birth rate per year.

6.* the number of sables at the end of the year is 18 individuals; density in spring – 0.4 individuals/km2;
(Answer: density at the end of the year 0.9 individuals/km2; mortality rate per year - 2 individuals (according to calculations - 1.8, but the real value, of course, will always be expressed as an integer); The birth rate per year is 12 individuals.)

7.* How can we explain the fact that if in a fight between two (non-fighting) dogs one exposes its unprotected neck, the other will not grab it, while in a fight between a lynx and a dog such behavior will be fatal for the dog that has exposed its neck?
(Answer: aggression between individuals of the same species, as a rule, is aimed at maintaining the hierarchical and spatial structure of the population, and not at the destruction of fellow tribesmen.

8.* A population, like a species, is a single whole, and the well-being of one individual largely determines the well-being of the population or species. The lynx will simply eat the dog.)
(Answer: In the forest, scientists evenly placed traps for white hares. A total of 50 animals were caught. They were tagged and released.
A week later the capture was repeated. We caught 70 hares, 20 of which were already marked. Determine the number of hares in the study area, assuming that the animals tagged for the first time are evenly distributed throughout the forest.
50 marked individuals were to be distributed among the total number of hares (X) living in the study area. Their share in the repeated sample should reflect their share in the total number, i.e. 50 is to X as 20 is to 70.
Solving the proportion:
50: X = 20: 70; X = 70x 50: 20 = 175.

Thus, the estimated number of hares in the study area is 175 individuals.

1. This method (Lincoln index, or Petersen index) is used to determine the number of secretive animals that cannot be counted directly. The result of the calculations may have a fractional value, but we must remember that the real number of animals is always expressed as an integer value. In addition, this method has its own errors, which must also be taken into account. It would be more logical to talk, for example, about a population of 170–180 individuals.)
(Answer: Demographic structure of the population

2. Explain why up to 30% of individuals can be removed from the wild boar population, without the risk of destroying it, while the permissible shooting of moose should not exceed 15% of the population size?
(Answer: The simple age structure of populations distinguishes organisms whose life cycle does not exceed one year, and reproduction occurs once in a lifetime and is timed to coincide with seasonal changes in the environment. These are, for example, annual plants, a number of insect species, etc. Otherwise, the age structure of populations may be complex.)

3. Explain why a significant spring death of adult shrews will lead to a sharp and prolonged decline in the population, while the complete destruction of all adult cockchafers emerging in the spring will not lead to a similar result.
(Answer: The shrew population in the spring is represented exclusively by adult animals of the previous year of birth. Chafer beetles, whose larvae develop in the soil over 3–4 years, have a complex age population structure. If adult individuals die one spring, they will be replaced the next year by beetles that have developed from another generation of larvae.)

4. Construct age pyramids reflecting the age composition of the population of Russia (140 million inhabitants) and Indonesia (190 million inhabitants), using the given data.

To be continued

1 The signs “*” and “**” indicate tasks of increased complexity that are cognitive and problematic in nature.

Living organisms are connected to each other in a certain way. The following types of connections between species are distinguished:

• trophic,
• topical,
• phoric,
• factory

The most important are trophic and topical connections, since they are the ones that hold organisms of different species near each other, uniting them into communities.

Trophic connections arise between species when one species feeds on another: living individuals, dead remains, waste products. Trophic connections can be direct or indirect. Direct connection manifests itself when lions feed on live antelopes, hyenas on the corpses of zebras, dung beetles on the droppings of large ungulates, etc. Indirect connection occurs when different species compete for the same food resource.

Topical connections manifest themselves in one species changing the living conditions of another species. For example, under a coniferous forest, as a rule, there is no grass cover.

Phoric connections occur when one species participates in the spread of another species. The transfer of seeds, spores, and pollen by animals is called zoochory, and small individuals - phoresia.

Factory connections consist in the fact that one species uses excretory products, dead remains, or even living individuals of another species for its structures. For example, when building nests, birds use tree branches, grass, down and feathers of other birds.

Types of relationships between organisms

The impact of one species on another can be positive, negative and neutral. In this case, different combinations of impact types are possible. There are:

Neutralism- cohabitation of two species on the same territory, which has neither positive nor negative consequences for them. For example, squirrels and moose do not have significant effects on each other.

Protocooperation- mutually beneficial, but not obligatory coexistence of organisms, from which all participants benefit. For example, hermit crabs and sea anemones. A coral sea anemone polyp, which has stinging cells that secrete poison, can settle on the shell of a crayfish. The sea anemone protects the crayfish from predatory fish, and the hermit crab, by moving, contributes to the spread of the sea anemones and an increase in their feeding space.

Mutualism (obligate symbiosis) - mutually beneficial cohabitation, when either one of the partners or both cannot exist without a cohabitant. For example, herbivorous ungulates and cellulose-degrading bacteria. Cellulose-degrading bacteria live in the stomach and intestines of herbivorous ungulates. They produce enzymes that break down cellulose, so they are essential for herbivores who do not have such enzymes. Herbivorous ungulates, for their part, provide bacteria with nutrients and a habitat with optimal temperature, humidity, etc.

Commensalism- a relationship in which one of the partners benefits from cohabitation, and the other is indifferent to the presence of the first. There are two forms of commensalism: sinoikia (tenancy) And trophobiosis (freeloading). An example of synoikia is the relationship between some sea anemones and tropical fish. Tropical fish take refuge from predators among the tentacles of sea anemones, which have stinging cells. An example of trophobiosis is the relationship between large predators and scavengers. Scavengers, such as hyenas, vultures, and jackals, feed on the remains of victims killed and partially eaten by large predators - lions.

Predation- a relationship in which one of the participants (predator) kills the other (prey) and uses him as food. For example, wolves and hares. The state of the predator population is closely related to the state of the prey population. However, when the population size of one prey species decreases, the predator switches to another species. For example, wolves can use hares, mice, wild boars, roe deer, frogs, insects, etc. as food.

A special case of predation is cannibalism- killing and eating one's own kind. It is found, for example, in rats, brown bears, and humans.

Competition- relationships in which organisms compete with each other for the same environmental resources when the latter are in short supply. Organisms may compete for food resources, sexual partners, shelter, light, etc. There are direct and indirect, intraspecific and interspecific competition. Indirect (passive) competition- consumption of environmental resources necessary for both types. Direct (active) competition- suppression of one type by another. Intraspecific competition- competition between individuals of the same species. Interspecific competition occurs between individuals of different but ecologically similar species. Its result can be either mutual adjustment two types, or substitution a population of one species of a population of another species that moves to another place, switches to another food, or goes extinct.

Competition leads to natural selection in the direction of increasing ecological differences between competing species and the formation of different ecological niches by them.

Amensalism- a relationship in which one organism influences another and suppresses its vital activity, while it itself does not experience any negative influences from the suppressed one. For example, spruce and lower tier plants. The dense crown of spruce prevents the penetration of sunlight under the forest canopy and suppresses the development of plants in the lower tier.

A special case of amensalism is allelopathy (antibiosis)- the influence of one organism on another, in which waste products of one organism are released into the external environment, poisoning it and making it unsuitable for the life of another. Allelopathy is common in plants, fungi, and bacteria. For example, the penicillium fungus produces substances that suppress the activity of bacteria. Penicillium is used to produce penicillin, the first antibiotic discovered in medicine. Recently, the concept of “allelopathy” has also included a positive effect.

In the course of evolution and development of ecosystems, there is a tendency to reduce the role of negative interactions at the expense of positive ones, increasing the survival of both species. Therefore, in mature ecosystems the proportion of strong negative interactions is less than in young ones.

Characteristics of the types of interaction between populations of different species are also given in the table:

Notes:

1. (0)—there is no significant interaction between populations.
2. (+) - a beneficial effect on growth, survival or other characteristics of the population.
3. (-) - inhibitory effect on growth or other characteristics of the population.
4. Types 2-4 can be considered "negative interactions", 7-9 can be considered "positive interactions", and types 5 and 6 can be classified as both groups.

There are several basic types of interactions between organisms. Like most biological categories, they are not concepts with absolutely clear boundaries, therefore there is no generally accepted single classification of them. As an example, consider the classification “+,0, -”

"- -" (Competition)- this is an interaction that boils down to the fact that one organism consumes a resource that would be available to another organism and could be consumed by it. One living creature deprives another of part of the resource, which, as a result, grows slower, leaves fewer descendants and has a greater chance of dying. Individuals of the same or different species can deprive each other of a potential resource. In the first case, mutual influence can be considered equal and symmetrical, since individuals of the same species have more similar resource needs than individuals of different species.

"0 -" (Amensalism)– relationships between individuals of different species, when individuals of one species, often by secreting special substances, have a depressing effect on individuals of another species. Strictly speaking, amensalism can be considered those cases of exposure when one organism produces a harmful effect (for example, releases a toxin) regardless of whether the organism being suppressed is present or not.

“+ -” (Predation)- can be defined as the eating of one organism (prey) by another organism (predator), and the victim must be alive before the predator attacks it. This definition excludes detritophagy (consumption of dead organic matter).

There are different classifications of predators. According to one of them (“taxonomic”), predators (in the proper sense of the word) eat animals, herbivores eat plants, and omnivores eat both.

“+ 0” Commensalism– the basis for this type of relationship can be shared space, substrate, shelter, movement, or most often food. Using the characteristics of the host’s lifestyle or structure, commensalism derives one-sided benefit from this. Its presence usually remains indifferent to the owner (for example, the dwelling of the Mediterranean carp fish in the body cavity of some species of sea cucumbers, which it uses as a refuge).

To the types of relationships listed above, you can add detritophagy (feeding on the remains of organisms). This type has a certain specificity, which is expressed in the fact that decomposers and detritivores do not control the rate at which their resources become available or are renewed; they are completely dependent on the speed with which some other factor (disease, aging) releases the resource that ensures their vital activity.



And this is one of the most aggressive predators of our fresh waters! Consider this fact: it pursues its prey so stubbornly that it loses control of itself, jumps out into very small places, even onto the shore, where it dies. Or another fact: in the second month of life, he already swallows the young of other fish. Many people believe that pike perch and pike are sworn enemies: they always fight. The war is that they strive to get each other out of a good hole...

Traveling along the Volga delta in a kulas - a single-seater boat, I turned into an erik, which struck me with its gloom and mystery. For this, apparently, he was called Leshachy. It is very small - only a hundred meters long, flows out of the Chilimny erik - quite wide, covered with patterned leaves of chilim - water chestnut, and flows into... It’s hard to say about this: it actually has no mouth. The banks are densely overgrown with young willows and old, blackened willow grass. At the end of Leshachy they connected with crowns bent over the water and formed a green tunnel, and then a dead end. Therefore, it was cool and dark here even at noon. Dried algae hung from the lower branches of trees and bushes, looking like large black-green clumps that had fallen here during high water. Even further away lay two half-sunken, spreading sedges, brought by the spring flood. The bark had long fallen off from them, and the water polished them, and they began to look like the yellowed bones of some long-extinct animals. Erik penetrates the thicket of willows and willows, the pile of dead sedge trees and immediately gives his water to the Big Kultuk.

I grabbed a branch touching the side of the kulas and stopped it. At that same moment it seemed that the goblin’s head would poke out through the living and dead trees and dried algae and ask in a sepulchral voice:

Why did you come to my kingdom? But seconds and minutes passed, the goblin did not appear. Having driven 30 m away from the dead end, I threw a spoon. It sank for a long time, and along the fishing line you could feel the spinner falling from branch to branch of the underwater parts of trees and bushes. Expecting that it was about to get hooked, I felt a tug, hooked it and began to reel in the line. Soon a bright green pike perch surfaced near the side and immediately fell into the landing net. He weighed 1.5 kg. The second cast brought another similar pike perch. To catch the third one, I had to make five casts. After that, no one was interested in my spinner anymore. Apparently, if there were pike perch left in Leshachy, I scared them away.

The next day I looked here again. After the first cast I caught a 3-kilogram pike, the next one after the tenth cast. There were no more bites. I released the pike back into the erik - I didn’t need fish then. On the third day, as expected, pike perch were biting in this erik, on the fourth - pike, on the fifth - pike perch again. How can we explain this “schedule”?

I happened to be there - in the vastness of the Volga delta - in one of the pits I alternately caught perches and small catfish: it seemed that they were not so much at odds with each other. On Zolotitsa, which flows into the White Sea, with a spinning rod, when casting far away, I caught anadromous trout, and when casting close-in, in small and quiet backwaters, I caught pike. But I don’t remember a case where pike perch and pike perch lived in the same hole or on the same stretch. They are always fighting. Today, for example, the pike “won” - which means there will be more of them in the pit or on the reach than pike perch. The next day there were more pike perch, they fought the pikes and drove them away.

These are by no means bloodless fights: first one side, then the other was bitten. Of course, the outcome of the fights is affected not only by the number and weight of individuals, but also by the size of the hole or reach and the amount of food in them.