Laws and consequences of food relations. Lesson topic: Laws of competitive relations in nature

Ecology teacher,

Municipal educational institution "Privolnenskaya Secondary School"

Lesson topic: “Laws and consequences of food relations in nature”

Goal: To study the laws and consequences of food relations in nature.

Tasks:

1. Familiarize yourself with diversity and find out the role of food relationships in nature.

2. Prove that food connections unite all living organisms into a single system and are one of the most important factors of natural selection.

Progress of the lesson.

I. Organizational moment.

II. Checking homework.

III. Learning new material

1. Providing the energy needs of organisms.

Life on Earth exists due to solar energy, which is transmitted to all other organisms that create food or trophic chain : from producers to consumers, and so 4-6 times from one trophic level to another.

Trophic level – the place of each link in food chain. The first trophic level is producers, all the rest are consumers: the second level is herbivorous consumers, the third is carnivorous consumers, etc. Consequently, consumers can be divided into levels: 1st, 2nd, etc. order .

Energy costs are associated primarily with maintaining metabolic processes (respiration costs), less for growth, and the rest is excreted in the form of excrement. As a result, most of the energy is converted into heat and dissipated in environment, and the next, more high level transmitted no more than 10% of the energy from the previous one.

However, such a strict picture of the transition of energy from level to level is not entirely real, since trophic chains intertwine, forming trophic networks.

Example: sea otters– sea urchins – brown algae.

There are two types of trophic chains: 1) grazing chains (pasture), 2) detrital chains (decomposition).

So, the flow of radiant energy in an ecosystem is distributed over two types of trophic chains. The end result is dissipation and loss of energy, which must be renewed for life to exist.

2. Trophic groups.

Nutritional relationships not only provide the energy needs of organisms. They play another important role in nature - they hold species V communities, regulate their numbers and influence the course of evolution. Food connections are extremely diverse.

Filling out the table " Comparative characteristics trophic groups"(Appendix 1.2)

2. Discussion.

Question . In what direction is the evolution of species going in the case of typical predators?

Sample answer : The progressive evolution of both predators and prey is aimed at improving the nervous system: sensory organs and muscular system, since selection maintains those properties that help them escape from predators, and in predators - those that help in obtaining food.

Question : In which direction does evolution go in the case of gathering?

Sample answer : The evolution of species follows the path of specialization: selection in prey maintains characteristics that make them less noticeable and less convenient for collection, namely protective and warning coloration, imitative similarity, mimicry.

For example, the smallest aquatic rotifers grow long shell spines in the presence of other, predatory rotifers. These spines greatly prevent predators from swallowing their prey, as they literally stand across their throats. The same defense occurs in peaceful Daphnia crustaceans - against other predatory crustaceans. The predator, having captured the daphnia, picks it up with its legs and turns it over to eat it from the soft ventral side. The thorns get in the way and the prey is often lost. It turned out that the victims grow spines in response to the presence of metabolic products of predators in the water. If there are no enemies in the pond, thorns do not appear on the victims.

4. Regulation of population numbers.

The first consequence of food relations is the regulation of population numbers.

In the 20s XX century Ch. Elton processed long-term data from a fur company extracting hare and lynx skins in Northern Canada. It turned out that after the “fruitful” years for hares, there was an increase in the number of lynx. Elton discovered the pattern of these fluctuations, their repeatability.

At the same time, independently of each other, two mathematicians, A. Lotka and V. Volterra, calculated that based on the interactions of predator and prey, oscillatory cycles in the numbers of both species could arise.

These data needed experimental verification, which is what I took on.

Demonstration.

In his research, Gause studied how the number of two types of ciliates changed in test tubes with hay infusion - one of the types of slipper ciliates that feed on bacteria, and the didinium ciliate that eats the slippers themselves. At first, the number of the slipper (prey) grew faster than the number of Didinium (predator). However, with a good food supply, didinium soon also began to multiply quickly. When the rate of eating shoes became equal to the rate of their reproduction, the growth in the number of this species stopped. The number of shoes in the test tubes began to decline sharply. After some time, having undermined their food supply, they stopped dividing and the didiniums began to die. When the number of predators decreased so much that they had almost no effect on the number of victims, the unhindered reproduction of the surviving slippers again led to an increase in their numbers. The cycle repeated. Thus, it was proven that predator-prey interactions can lead to regular cyclical fluctuations in their numbers.

The second consequence of food relations is that population fluctuations occur cyclically.

Adaptations of predator and prey arose during evolution as a result of selection. Could these adaptations have arisen if predator and prey had not interacted? ( Answers.) Thus, evolutionary changes occur in concert, that is, the evolution of one species partially depends on the evolution of another - this is called coevolution.

The third consequence of food relations is that coevolution occurs between populations of biologically related species.

Coevolution – joint development; the occurrence of two parallel processes that have a significant mutual influence.

Assignment training: characterize the species listed in the list as participants in food relations, and identify among them pairs that may be related by coevolutionary relations. List of species ( can be drawn up on a board, dictated or printed on cards): tiger, ladybug, wild boar, gadfly, leech, bream, antelope, aphid, pig fluke, cow.

Question: In what situations does a person act as a typical predator? Forager in relation to other species?

In nature, when the supply of familiar food is depleted, the predator switches to new look food. Man stubbornly “pursues” one species until it disappears from the face of the Earth. There are many sad examples: bison, aurochs, dodo... In the 70-80s. XX century The global cod fishery significantly exceeded its reproduction; as a result, production fell by 7–10 times. At the same time, the number of capelin increased sharply ( main victim cod). The fishermen switched to it and again overdid it. The cod began to run out of food and the adults began to eat their fry. Cod numbers continue to decline.

A “reasonable being” - a person - cannot assess the consequences of his activities?! There is an effect ecological boomerang – when the results are directly opposite to the initial direction of influence.

Therefore, it is important to be able to foresee the consequences of your activities and organize them in such a way as not to undermine natural reserves.

One of the first examples of the successful use of a predator to suppress pest numbers is the use of the rhodolia ladybug in the fight against the Australian grooved bug.

Student's Post on the Use of Ladybug Rhodolia

against the Australian mealybug.

IV. Fixing the material.

Do you think we need knowledge? biological laws? For what? Which ones are biological? ecological patterns did we find out today? ( Students repeat the noted consequences of food relationships.)

Like an apple on a platter
We have one Earth.
Take your time people
Scoop everything out to the bottom.
It's no wonder to get there
To hidden hiding places,
Loot all the wealth
In future centuries.
We common life grains,
Relatives of the same fate.
It's shameful for us to fatten
For the next day!
Understand this people
Like your own order
Otherwise there will be no Earth
And each of us. (Mikhail Dudin)

V. House. exercise: Ch. - § 9, Kr. - clause 3.3

Appendix 1.

Comparative characteristics of food groups

Appendix 2.

Predators Grazing

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Nutritional relationships not only provide the energy needs of organisms. They play another important role in nature - they hold species in communities, regulate their numbers and influence the course of evolution. Food connections are extremely diverse.

Typical predators spend a lot of energy tracking down their prey, catching it and catching it. They have developed special hunting behavior.

Lion hunt

They need many sacrifices throughout their lives. These are usually strong and active animals.

Life cycle of the bovine tapeworm

Gatherer animals spend energy searching for seeds or insects, i.e., small prey. Mastering the food they find is not difficult for them. They have developed search activity, but do not have hunting behavior.

Field mouse

Grazing species do not spend much effort searching for food; there is usually quite a lot of it around, and most of their time is spent absorbing and digesting food.

African elephant

IN aquatic environment A widespread method of acquiring food is filtration, and at the bottom - swallowing and passing soil along with food particles through the intestines.

Edible mussel (an example of a filter-feeding organism)

The consequences of food connections are most clearly manifested in predator-prey relationships.

If a predator feeds on large, active prey that can run away, resist, hide, then those who do it better than others survive, i.e. have sharper eyes, sensitive ears, developed nervous system, muscular strength. Thus, the predator selects for the improvement of victims, destroying the sick and weak. In turn, among predators there is also selection for strength, dexterity and endurance. The evolutionary consequence of these relationships is the progressive development of both interacting species: predator and prey.

If predators feed on inactive or small species that are not able to resist them, this leads to a different evolutionary result. Those individuals that the predator manages to notice die. Victims who are less noticeable or somehow inconvenient to capture win. This is how natural selection is carried out for protective coloring, hard shells, protective spines and needles and other means of salvation from enemies. The evolution of species moves towards specialization for these characteristics.

The most significant result of trophic relationships is the inhibition of species population growth. The existence of food relations in nature is opposed to the geometric progression of reproduction.

For each pair of predator and prey species, the result of their interaction depends primarily on their quantitative relationships. If predators catch and destroy their victims at approximately the same rate at which these victims reproduce, then they can restrain the growth of their numbers. These are the results of these relationships that are most often characteristic of sustainable natural communities. If the rate of reproduction of prey is higher than the rate of their consumption by predators, an outbreak of the species occurs. Predators can no longer contain its numbers. This also sometimes occurs in nature. The opposite result—the complete destruction of the prey by a predator—is very rare in nature, but in experiments and in human-disturbed conditions it occurs more often. This is due to the fact that with a decrease in the number of any type of prey in nature, predators switch to other, more accessible prey. Hunting only for rare species takes up too much energy and becomes unprofitable.

G. F. Gause (1910-1986)

In the first third of our century, it was discovered that predator-prey relationships can be the cause of regular periodic fluctuations in the numbers of each of the interacting species. This opinion was especially strengthened after the results of the research of the Russian scientist G. F. Gause. In his experiments, G. F. Gause studied how the number of two types of ciliates changed in test tubes, connected by relationship predator - prey. The victim was one of the species of slipper ciliates that feeds on bacteria, and the predator was a didinium ciliate that eats slippers.

At first, the number of the slipper grew faster than the number of the predator, which soon received a good food supply and also began to multiply quickly. When the rate of eating shoes became equal to the rate of their reproduction, the growth of the species' population stopped. And since didiniums continued to catch slippers and reproduce, soon the consumption of victims far exceeded their replenishment, and the number of slippers in the test tubes began to decline sharply. After some time, having undermined their food supply, they stopped dividing and the didiniums began to die. With some modifications of the experiment, the cycle repeated itself from the beginning. The unhindered reproduction of the surviving slippers again increased their abundance, and after them the didinium population curve went up. On the graph, the predator abundance curve follows the prey curve with a shift to the right, so that changes in their abundance are asynchronous.

Thus, it was proven that interactions between predator and prey can, under certain conditions, lead to regular cyclical fluctuations in the numbers of both species. The course of these cycles can be calculated and predicted, knowing some initial quantitative characteristics species. Quantitative laws of interaction between species in their food relationships are very important for practice. In fishing, harvesting of marine invertebrates, fur fishing, sport hunting, collection of ornamental and medicinal plants— wherever a person reduces the number of species he needs in nature, from an ecological point of view he acts in relation to these species as a predator. Therefore, it is important to be able to foresee the consequences of your activities and organize them so as not to undermine natural reserves.

In fishing and hunting, it is necessary that when the number of species decreases, fishing standards also decrease, as happens in nature when predators switch to more easily accessible prey. If, on the contrary, one strives with all one’s might to catch a declining species, it may not restore its numbers and cease to exist. Thus, as a result of overfishing, due to the fault of people, a number of species that were once very numerous have already disappeared from the face of the Earth: American bison, European tours, passenger pigeons and others.

When a predator of any species is accidentally or intentionally destroyed, outbreaks in the number of its victims first occur. This also leads to environmental disaster either as a result of the species undermining its own food supply, or as a result of the spread of infectious diseases, which are often much more destructive than the activities of predators. The phenomenon of an ecological boomerang occurs when the results turn out to be directly opposite to the initial direction of impact. Therefore, the competent use of natural resources environmental laws- the main way of interaction between man and nature.

Date of publication: 09.13.16

Litnevskaya Anna Andreevna Municipal educational institution-secondary school from Orlovskoye, Marksovsky district

Ecology teacher

Lesson topic:

LAWS AND CONSEQUENCES OF FOOD RELATIONSHIPS

Target: study the laws and consequences of food relations.

Tasks: emphasize the universality, diversity and extraordinary role of food relations in nature. Show that it is food connections that unite all living organisms into a single system and are also one of the most important factors natural selection.

Equipment: graphs reflecting fluctuations in numbers in the predator-prey relationship; herbarium specimens of insectivorous plants; wet preparations (tapeworms, liver fluke, leeches); collections of insects (ladybug, ant, gadfly, horsefly); images of herbivorous rodents, mammals (eagle, tiger, cow, zebra, baleen whales).

I. Organizational moment.

P. Test of knowledge. Test control.

1. Light-loving herbs growing under spruce are typical
representatives of the following type of interactions:

a) neutralism;

b) amenalism;

c) commensalism;

d) proto-cooperation.

2. Type of relationship between the following representatives
of the new world can be classified as “freeloading”:

a) hermit crab and sea anemone; b) crocodile and cowbird;

V)shark and sticky fish;

d) wolf and roe deer.

3. An animal that attacks another animal, but
eats only part of its substance, rarely causing death, relatively
goes to the number:

a) predators;

b) carnivores;

d) omnivores.

4. Coprophagia occurs:
a) in hares; b) in hippopotamuses;

c) in elephants;

d) in tigers.
5. Allelopathy is an interaction with the help of biologically active substances, characteristic of the following organisms:

a) plants;

b) bacteria;
c) mushrooms;
d) insects.

6. Do not enter into symbiotic relationships:

a) trees and ants;

b) legumes and rhizobium bacteria;

c) trees and mycorrhizal fungi;

d) trees and butterflies.

a) late blight;

b) tobacco mosaic virus;

c) champignon, honey fungus;

d) dodder, broomrape.

a) eat only the outer integument of the victim;

b) occupy a similar economic niche;

c) attack mainly weakened individuals;

d) have similar methods of hunting prey.

9. Wasp wasps are:

b) predators with traits of decomposers;

c) stem nematodes;

d) rust fungi.

a) mushrooms; b) worms;

b) broomrape;

c) white mistletoe;

d) smut.

a) amoeba - opaline - frog;

b) frog -> scorch - amoeba;

c) mushrooms - * frog -> scorch;

d) frog - * amoeba - scorch.

III. Learning new material. 1.The narrator.

Life on Earth exists due to solar energy, which is transmitted through plants to all other organisms that create a food, or trophic, chain: from producers to consumers, and so on 4-6 times from one trophic level to another.

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 level is herbivorous consumers; the third - carnivorous consumers feeding on herbivorous forms; the fourth is consumers who consume other carnivores, etc.

Consequently, consumers can be divided into levels: consumers of the first, second, third, etc. orders.

Energy costs are associated primarily with maintaining metabolic processes, which are called respiration costs; a smaller part of the expenditure goes towards growth, and the rest of the food is excreted in the form of excrement. Ultimately, most of the energy is converted into heat and dissipated in the environment, and no more than 10% of the energy from the previous one is transferred to the next, higher trophic level.

However, such a strict picture of the transfer of energy from level to level is not entirely realistic, since the trophic chains of ecosystems are complexly intertwined, forming trophic networks.

For example, sea otters eat sea urchins that eat brown algae; The destruction of otters by hunters led to the destruction of algae due to the growth of the hedgehog population. When otter hunting was banned, algae began to return to their habitats.

A significant part of heterotrophs are saprophages and sa-prophytes (fungi), which use the energy of detritus. Therefore, two types of trophic chains are distinguished: grazing chains, or grazing chains, which begin with the consumption of photosynthetic organisms, and detrital decomposition chains, which begin with the decomposition of the remains of dead plants, corpses and animal excrement. So, the flow of radiant energy in an ecosystem is distributed over two types of trophic networks. The end result: dissipation and loss of energy, which must be renewed for life to exist.

2. JobWithtextbookVsmallgroups.

Task 2. Indicate the features of the feeding relationships of typical predators. Give examples.

Task 3. Indicate the features of the food relationships of animal-gatherers. Give examples.

Task 4. Indicate the features of food relationships of grazing species. Give examples.

Note: the teacher should draw students' attention to the fact that in foreign language literature the term denoting relationships like

In this regard, it is necessary to keep in mind that the term “predator” is used in the literature on ecology in a narrow and broad sense.

Answer to task 1.

Use the owner as a permanent or temporary place of residence;

Answer to task 2.

Typical predators spend a lot of energy searching, tracking and capturing prey; They kill the victim almost immediately after the attack. Animals have developed special hunting behavior. Examples - representatives of the order Carnivora, Mustelidae, etc.

Answer to task 3.

Gatherer animals spend energy only searching for and collecting small prey. Foragers include many granivorous rodents, chicken birds, carrion vultures, and ants. Peculiar collectors - filter feeders and ground eaters of water bodies and soils.

Answer to task 4.

Grazing species feed on abundant food, which does not require a long search and is easily accessible. Usually these are herbivorous organisms (aphids, ungulates), as well as some carnivores ( ladybugs on aphid colonies).

3. D and s k u s s i .

Question. In what direction is the evolution of species going?

with typical predators? Sample answer.

The progressive evolution of both predators and their prey is aimed at improving the nervous system, including sensory organs, and the muscular system, since selection maintains in prey those properties that help them escape from predators, and in predators - those that help in getting food.

Question. In which direction does evolution go in the case of gathering?

Sample answer.

The evolution of species follows the path of specialization: selection in prey supports traits that make them less noticeable and less convenient for collection, namely protective or warning coloration, imitative resemblance, and mimicry.

V o n r O With. In what situations does a person act as a typical predator?

Sample answer.

When using commercial species(fish, game, fur-bearing and ungulate animals);

When destroying pests.

Note: the teacher should focus on the fact that in an ideal case, with the competent use of commercial objects (fish in the sea, wild boars and moose in the forest, wood), it is important to be able to foresee the consequences of this activity in order to stay on the fine line between acceptable and excessive use resource. The goal of human activity is to preserve and increase the number of “victims” (resource).

IV. Consolidationnew material.

Textbook,§9, questions 1-3. Answer to question 1.

Not always. The nesting territory can only accommodate a certain number of birds. The size of individual plots determines how many hanging nests will be occupied. The rate of reproduction of the pest may be so high that the available number of birds will not be able to significantly reduce its numbers.

Answer to question 2.

A simplification of the model is as follows: they did not take into account that prey can run and hide from predators, and predators can feed on different prey; in reality, the fertility of predators depends not only on the food supply, etc., that is, the relationships in nature are much more complex.

Answer to question 3.

The food supply for moose has improved and mortality from predators has decreased. Permission for moderate hunting is given if high elk numbers begin to negatively affect forest restoration.

V/Homework:§ 9, task 1; additional information.

Rice. 1. Cheetah in pursuit of prey

Typical predators spend a lot of effort to track down prey, catch it and catch it (Fig. 1). They have developed special hunting behavior. They need many sacrifices throughout their lives. These are usually strong and active animals.

Animal Gatherers spend energy searching for seeds or insects, i.e. small prey. Mastering the food they find is not difficult for them. They have developed search activity, but no hunting behavior.

grazing species do not spend much effort searching for food; there is usually quite a lot of it around, and most of their time is spent absorbing and digesting food.

In the aquatic environment, this method of acquiring food is widespread: filtration, and at the bottom - ingestion and passage of soil along with food particles through the intestines.

Rice. 2. Predator-prey relationships (wolves and reindeer)

The effects of food connections are most pronounced in relationships. predator - prey(Fig. 2).

If a predator feeds on large, active prey that can run away, resist, and hide, then those who do it better than others, that is, have sharper eyes, sensitive ears, a developed nervous system, and muscular strength, survive. Thus, the predator selects for the improvement of victims, destroying the sick and weak. In turn, among predators there is also selection for strength, agility and endurance. The evolutionary consequence of these relationships is the progressive development of both interacting species: predator and prey.

G.F. Gause
(1910 – 1986)

Russian scientist, founder of experimental ecology

If predators feed on inactive or small species that are not able to resist them, this leads to a different evolutionary result. Those individuals that the predator manages to notice die. Victims who are less noticeable or somehow inconvenient to capture win. This is how it works natural selection for protective coloring, hard shells, protective spines and needles and other weapons of salvation from enemies. The evolution of species moves towards specialization for these characteristics.

The most significant result of trophic relationships is the inhibition of species population growth. The existence of food relations in nature is opposed to the geometric progression of reproduction.

For each pair of predator and prey species, the result of their interaction depends primarily on their quantitative relationships. If predators catch and destroy their prey at approximately the same rate at which their prey reproduces, then they may hold back growth of their numbers. These are the results of these relationships that are most often characteristic of sustainable natural communities. If the rate of reproduction of prey is higher than the rate at which they are eaten by predators, population explosion kind. Predators can no longer contain its numbers. This also sometimes occurs in nature. The opposite result - the complete destruction of the prey by a predator - is very rare in nature, but in experiments and in human-disturbed conditions it occurs more often. This is due to the fact that with a decrease in the number of any type of prey in nature, predators switch to other, more accessible prey. Hunting only for a rare species takes up too much energy and becomes unprofitable.

In the first third of our century, it was discovered that predator-prey relationships can cause regular periodic fluctuations in numbers each of the interacting species. This opinion was especially strengthened after the results of the research of the Russian scientist G. F. Gause. In his experiments, G.F. Gause studied how the number of two species of ciliates, connected by a predator-prey relationship, changes in test tubes (Fig. 3). The victim was one of the species of slipper ciliates that feeds on bacteria, and the predator was a didinium ciliate that eats slippers.

Rice. 3. Progress in the number of ciliates-slippers
and the predatory ciliate didinium

At first, the number of the slipper grew faster than the number of the predator, which soon received a good food supply and also began to multiply quickly. When the rate of eating shoes became equal to the rate of their reproduction, the growth of the species' population stopped. And since didiniums continued to catch slippers and reproduce, soon the consumption of victims far exceeded their replenishment, and the number of slippers in the test tubes began to decline sharply. After some time, having undermined their food supply, they stopped dividing and the didiniums began to die. With some modifications of the experiment, the cycle repeated itself from the beginning. The unhindered reproduction of the surviving slippers again increased their abundance, and after them the didinium population curve went up. In the graph, the predator abundance curve follows the prey curve with a shift to the right, so that changes in their abundance are asynchronous.

Rice. 4. Decline in fish numbers as a result of overfishing:
red curve – world cod fishery; blue curve – the same for capelin

Thus, it was proven that interactions between predator and prey can, under certain conditions, lead to regular cyclic fluctuations in the numbers of both species. The course of these cycles can be calculated and predicted, knowing some of the initial quantitative characteristics of the species. Quantitative laws of interaction between species in their food relationships are very important for practice. In fishing, the extraction of marine invertebrates, fur fishing, sport hunting, the collection of ornamental and medicinal plants - wherever a person reduces the number of species he needs in nature, from an ecological point of view he acts in relation to these species as a predator. Therefore it is important be able to foresee consequences their activities and organize them in such a way as not to undermine natural resources.

In fishing and harvesting, it is necessary that when the number of species decreases, fishing rates also decrease, as happens in nature when predators switch to more easily accessible prey (Fig. 4). If, on the contrary, we strive with all our might to obtain a declining species, it may not restore its numbers and cease to exist. Thus, as a result of overfishing due to the fault of people, a number of species that were once very numerous have already disappeared from the face of the Earth: European aurochs, passenger pigeons and others.

When a predator of any species is accidentally or intentionally destroyed, outbreaks in the number of its victims first occur. This also leads to environmental disaster either as a result of the species undermining its own food supply, or - the spread infectious diseases, which are often much more destructive than the activities of predators. A phenomenon occurs ecological boomerang, when the results are directly opposite to the initial direction of influence. Therefore, the competent use of natural environmental laws is the main way of human interaction with nature.