Abstract on the topic “The driving forces of evolution. The struggle for existence and natural selection"
Plan
Struggle for existence.
Forms of struggle for existence
Natural selection is the leading driving force of evolution.
Forms of natural selection.
The creative role of natural selection.
sexual selection.
Struggle for existence.
The struggle for existence is one of the factors of evolution and one of the main concepts in the theory of evolution by Charles Darwin.
Struggle for existence - the whole set of relationships between individuals and various environmental factors. These relationships determine the success or failure of a given individual in the struggle for existence.
According to Darwin, the struggle for existence is the result, on the one hand, of the tendency to unlimited reproduction, and on the other hand, of the limited natural resources, that is, the discrepancy between the intensity of reproduction and the means of life leads to a struggle for existence.
Here are examples of high fecundity of species:
The cholera bacillus per day can give offspring weighing 100 tons;
The offspring of a pair of birds the size of a sparrow with a life expectancy of 4 years can cover the entire globe in 35 years;
The offspring of one dandelion in 10 years can cover an area 15 times larger than the land of the globe (example of K. A. Timiryazev);
The offspring of a pair of flies will eat a dead horse as soon as a lion (example of K. Linnaeus), etc.
The fertility of the species is the higher, the higher the probability of extermination of offspring.
The breeding potential is high, but the number of adults of the species is constant. Why? Because most of the individuals die before reaching the age of maturity in the struggle for means of life.
What does the expression "The individual has achieved success in the struggle for existence" mean? The highest reward in this competition is the leaving of offspring, the transfer of genes to the next generations, and not just the preservation of life. Failure in the fight is not always the death of a given individual, but more often non-participation in reproduction. The result of the struggle for existence is natural selection.
Ch. Darwin singled out three forms of the struggle for existence: intraspecific, interspecific, struggle with adverse environmental conditions.
Forms of struggle for existence
Intraspecific - the toughest and sharpest, because all individuals of the same species need the same and, moreover, limited resources : food, living space, shelters, breeding grounds.
Conclusion: the form of this struggle determines the prosperity of the species as a whole and contributes to its improvement.
Example: Dandelion population.
Interspecific - occurs acutely if the species belong to the same genus and need the same conditions of existence.
Example: The gray rat is larger and more aggressive and has replaced the black rat in human settlements.
Interspecific struggle includes relationships like:
predator → prey
plant →herbivore
Conclusion: the form of this struggle leads to the evolution of both interacting species, to the development of mutual adaptations in them. It also intensifies and intensifies the intraspecific struggle.
Fight against adverse environmental conditions also enhances intraspecific competition, since individuals of the same species compete for food, light, heat, etc.
Conclusion: The winners are the fittest individuals (with efficient metabolism and physiological processes). If biological features are inherited, then species adaptations to the environment will be improved.
NB! Task number 1
Characteristics of the forms of the struggle for existence.
| form of wrestling | The result of the struggle | Examples from the animal kingdom | Examples from the plant kingdom |
| Intraspecific | |||
| Interspecies | |||
| With environmental conditions |
Natural selection is the leading driving force of evolution.
The factors of the evolutionary process considered by us are undirected, largely random. The only directional factor is natural selection. It is a consequence of various types of relationships of living beings among themselves and with environmental conditions, that is, a consequence of the struggle for existence. What is natural selection?
Natural selection - a process in which the most adapted individuals of each species predominantly survive and leave offspring and the less adapted die.
Selection characteristics:
A necessary prerequisite is hereditary variability;
Character - directed, it is always directed towards greater adaptability to environmental conditions;
The selection factor is the natural environment with its own conditions;
Genetic essence - consists in the non-random preservation of certain genotypes in a population and their selective participation in the transfer of genes to the next generation;
The result is the transformation of the gene pool of the population, the formation of fitness;
The consequence is an increase in the diversity of forms of organisms; successive complication of the organization in the course of progressive evolution; extinction of less adapted species.
Thus, natural selection is able to purposefully select from generation to generation individuals that are more adapted to the conditions of their habitat.
The Darwinian concept of natural selection was further developed in the works of S. S. Chetverikov, I. I. Shmalgauzen, R. Fisher, S. Wright, F. G. Dobzhansky and others.
Natural selection is sufficiently fully revealed only in sufficiently large populations, since as the number decreases, the role of random factors increases.
Forms of natural selection.
Natural selection in nature acts in different directions and accordingly leads to different results. Therefore, it is customary to distinguish between several forms of natural selection. Let's describe them.
Driving (directed, leading) selection - a form of selection that favors only one direction of variability and does not favor all its other variants.
Under the control of driving selection, the gene pool of the population changes as a whole, that is, there is no separation of daughter forms (divergence). As a result of driving selection in the gene pool of a population, mutations are accumulated and distributed, providing a change in the phenotype in a given direction. In a population, under the influence of driving selection from generation to generation, a trait changes in a certain direction.
Let us give examples of the action of motive selection. For example, an increase in body size in a horse (remember the phylogenetic series of a horse), a decrease in the body size of elephants on the islands of the Mediterranean Sea, industrial melanism (darkening of the animal body in industrial centers), the development of insect resistance to pesticides, etc.
Stabilizing selection - observed during long-term preservation of constant environmental conditions.
Stabilizing selection favors the preservation in the population of the optimal phenotype under given conditions, which becomes predominant and acts against the manifestation of phenotypic variability. In this case, the population remains phenotypically homogeneous, but its gene pool can change based on the appearance of mutations with the same average value, but with a narrower reaction rate. Examples of stabilizing selection are the preservation of the size and shape of a flower in insect-pollinated plants, since the flowers must correspond to the size of the body of the pollinating insect, or the preservation of relict species (tuatara, coelacanth, ginkgo, etc.). Thus, stabilizing selection guards the constancy of species, ensuring their phenotypic immutability.
disruptive (from lat.disruptus - torn)tearing selection - occurs when different parts of the range of a given species, or population, have different environmental conditions. This form of selection favors two or more directions of variability (classes of phenotypes), but does not favor the average (intermediate) phenotype. Under the action of tearing selection within a population, polymorphism usually arises - several distinctly different phenotypic forms. The action of disruptive selection within a species leads to the isolation of populations from each other, up to their isolation as new species. Sometimes disruptive selection is considered as a special case of driving selection, since, unlike stabilizing selection, it leads to a change in the phenotypic appearance of a population.
Driving and stabilizing selection act in medium-sized populations, and disruptive selection - in large populations or ranges. Propulsive and stabilizing selection are closely related to each other and often replace each other.
For example, on oceanic islands, flies with normal wings are blown into the ocean and die. An advantage in long-winged, which resist the wind, and in organisms with underdeveloped (rudimentary) wings, moving to a crawling lifestyle.
The creative role of natural selection.
Critics of Darwinism attributed to selection the role of a "sieve" or "gravedigger", eliminating or sorting out changes in populations. Such a result of the action of selection actually exists in nature. But selection not only (!) eliminates the less adapted, but also determines:
direction of evolution;
the pace of evolution.
The same material supplied by mutations, waves of life and other factors of evolution, depending on the direction of selection, can lead to different results. Acting for an unlimited time (millions and billions of years), natural selection, together with other evolutionary factors, genetic drift and isolation, has created a huge variety of species in wildlife adapted to life. This is the creative role of natural selection.
Circumstances favoring natural selection:
High frequency of manifestation of uncertain hereditary changes
The abundance of individuals of a species, increasing the likelihood of beneficial changes
Unrelated crossing, increasing the range of variability in the offspring
Isolation of a group of individuals that prevents them from interbreeding with the rest of the mass of organisms in a given population
Wide distribution of the species.
6. Sexual selection.
sexual selection- a form of natural selection in some species of animals, based on the rivalry of one sex for mating with individuals of the other sex.
Through sexual selection, sexual dimorphism and developed secondary sex characteristics(bright plumage, branched horns, etc.). These signs can be harmful to both the individual and for the species (e.g. heavy forked antlers in deer, heavy bright tail in some birds). Why, then, does selection preserve, and often exacerbate, these traits?
NB! Task number 2 Using the textbook and other information resources, complete the table in the workbook.
Comparison of artificial and natural selection
| Indicators | artificial selection | Natural selection |
| Initial material for selection | ||
| The Path of Favorable Change | ||
| The Path of Unfavorable Changes | ||
| Nature of action | ||
| Selection result | ||
| Selection Forms |
Lesson summary
(lesson using ICT). Teacher: Vorobyov D.S.
The purpose of the lesson: to form the concept of the struggle for existence and natural selection as interrelated processes and as one of the central concepts of Ch. Darwin's theory of evolution; to acquaint with the forms of the struggle for existence and natural selection.
Tasks
1. Educational: Form a system of knowledge about the struggle for existence and natural selection and their role in evolution.
2. Developing: to continue work on teaching students the ability to select the main thing, using various sources of information; draw up the work in the form of a summary diagram; publicly defend the results of creative activity;
3. educational: to form an understanding of the development of one's intellect as a value characteristic of a modern personality;
4. didactic: create conditions for comprehending new educational information and its application in educational situations, checking the level of assimilation of the system of knowledge and skills.
Lesson type: lesson on the application of knowledge and skills, collective forms of work
Teaching methods: reproductive, partially exploratory.
Form of organization of educational activities: group.
Equipment: personal computer with overhead projector; table "Struggle for existence", herbarium specimens of plants, collection of insects, multimedia presentation
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Lesson summary
"Struggle for existence and natural selection"
(lesson using ICT).Teacher: Vorobyov D.S.
The purpose of the lesson: to form the concept of the struggle for existence and natural selection as interrelated processes and as one of the central concepts of Ch. Darwin's theory of evolution; to acquaint with the forms of the struggle for existence and natural selection.
Tasks
- Educational:Form a system of knowledge about the struggle for existence and natural selection and their role in evolution.
2. Developing: to continue work on teaching students the ability to select the main thing, using various sources of information; draw up the work in the form of a summary diagram; publicly defend the results of creative activity;
3. educational: to form an understanding of the development of one's intellect as a value characteristic of a modern personality;
4. didactic:create conditions for comprehending new educational information and its application in educational situations, checking the level of assimilation of the system of knowledge and skills.
Lesson type: lesson on the application of knowledge and skills, collective forms of work
Teaching methods : reproductive, partially exploratory.
Form of organization of educational activities: group.
Equipment : personal computer with overhead projector; table "Struggle for existence", herbarium specimens of plants, collection of insects, multimedia presentation
Teacher activity | Student activities |
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I. Testing knowledge. 1. Testing. 1) The elementary unit of evolution is: a) population; b) an individual; c) view; d) biocenosis. Answer: a). 2) Elementary evolutionary material is supplied by: a) mutations; b) modifications; c) population waves; d) selection. Answer: a). a) natural selection; b) isolation; c) migration; d) mutations. Answer: a). 4) Genetic drift is: a) an increase in the number of individuals; 6) random changes in the concentration of genes in a population; c) migration of individuals from population to population; d) free interbreeding between individuals in a population. Answer: b). 6) Genetic balance in a population is: a) the constancy of the number of all individuals in the population; b) the constancy of the frequencies of occurrence of various alleles; c) equal number of females and males; d) the balance of fertility and mortality in the population. Answer: b). 7) Sharp fluctuations in the number of populations: a) do not affect the frequency of alleles in the gene pool of the population; b) change the gene pool of the population; c) always lead to the loss of dominant alleles; d) are usually associated with the loss of recessive alleles. Answer: b). 2. Written answer on the card. Exercise. Indicate the numbers of sentences in which errors were made, correct them. 1. In different populations of the same species, the frequency of mutant genes is the same(not the same). 2..
Both closely located and distant populations of the same species do not differ from each other(may differ significantly). 4. This is explained by the fact that only directed changes in the gene pool occur in populations of one species.(not only directed, but also undirected, random changes in gene frequency). 5. With the migration of animals and plants, the gene pool of the newly formed population is much larger(less) the gene pool of the parent population. 3. Written answer at the blackboard. Exercise. Make a diagram "Causes that violate the genetic balance in populations." | Differentiated job Level A - 1 task Level B - 2 task Level C - 3 task (individual, differentiated work) |
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II. Learning new material
(Slide 4) | Work in 3 groups by sections(CSR) Intraspecific struggle Interspecies struggle Fight against adverse conditions Attachment 1, paragraph 57c 206-207 Information search 1.disk "General biology grade 11" Cyril and Methodius 2. Ecology 10-11 |
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III. Consolidation and application of knowledge. Systematization of knowledge gained by students. Appendix 2. Slides 5-11 | Group reports on the work done. Filling in the table - Appendix 2 |
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IV. Learning new material 1. Performing tasks in groups. 1st group read the text on p. 233-236 of the textbook and defines the signs of motive selection. 2nd group read the text on p. 236-237 of the textbook and defines signs of stabilizing selection. 3rd group works with additional literature material(see the list of references for the lesson)and identifies signs of disruptive selection (slides 12-17) | Collective creative work, taking into account the abilities of students |
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V. Fixing the material Fill out and explain
| protect your part of the circuit- |
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VI. Reflection of the assimilation of the material. 1. The reasons that lead to the death of many dandelion individuals and prevent this species from occupying the entire globe are listed: a) the fruits, along with hay, enter the stomach of a sheep; b) many birds eat fruits; c) herbivorous animals feed on seedlings; d) trampling people, cars, tractors; e) interfere with other taller plants; f) dandelions crowd each other out; g) seeds die in deserts, on rocks; Z.) seeds die in the middle lane if they fall i) plants die from severe frosts and drought; j) plants die from pathogenic plants and viruses. Specify the forms of struggle for the existence of dandelions (intraspecific: ...; interspecific: ...; struggle against adverse environmental conditions: ...). 2. Definition of forms of natural selection. Determine what form of natural selection these examples can be attributed to:
| Test work. Checking the results. |
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VII. Homework:paragraph 57, 58 questions p.207 No. 1-3-reproductive level. Advanced level-Based on your own observations, prepare examples describing the struggle for existence between organisms: a) of the same species; b) different types. | Students write down their homework according to their ability. |
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VIII. Evaluation and summing up the lesson. Have you achieved your goals and objectives? What difficulties did you encounter? Self-esteem. Annex 3 | self-esteem |
Attachment 1
C. Darwin first came to the idea that the driving force of the entire evolutionary process is the result of the interaction of organisms with each other and with the external environment.
C. Darwin drew attention to the fact that all living organisms have the ability to reproduce practically "unlimited". As an illustration, he considered the example of the reproduction of an elephant - one of the slowest breeding animals. Even in this case, from one pair of elephants at the usual rate of reproduction in 740-750 years, about 19 million animals should appear.
In the overwhelming majority of cases, the rate of reproduction of organisms is much higher. For example, the offspring that one daphnia is potentially capable of producing over the summer reaches an astronomical size - more than 10 million individuals, which exceeds the mass of the Earth.
At the same time, an unlimited increase in the number of organisms in nature is not observed. What is the reason for this phenomenon? Most individuals die at different stages of development and leave no descendants behind. It is known that death is the more intense, the higher the reproduction of individuals of a given species.
Beluga spawns about a million eggs during spawning, and only a small part of them go through a full development cycle and reach adulthood. The same applies to
plants.
According to Darwin, the discrepancy between the possibility of unlimited reproduction of species and limited resources is the main reason for the struggle for existence. The death of descendants occurs for various reasons. Sometimes it can be random (forest fire, flood, intervention
person).
However, as a rule, death is selective. It should not be thought that an organism with unfavorable signs must necessarily be left without offspring or die. There is simply a high probability that this particular organism will leave fewer descendants or die. Consequently, organisms with a set of properties that provide them with the greatest adaptability to living conditions are more likely to survive and reproduce more efficiently.
2. Forms of struggle for existence.
Darwin distinguished three forms of the struggle for existence: intraspecific, interspecific, and the struggle against adverse conditions of inorganic nature.
C. Darwin pointed out that the struggle for life is especially stubborn between organisms within the same species, and substantiated his assertion by the fact that they have similar characteristics and experience the same needs. A vivid example of intraspecific struggle is the competition between coniferous forest trees of the same age. The tallest trees, with their widely spread crowns, intercept the bulk of the sun's rays, and their powerful root system absorbs dissolved nutrients from the soil to the detriment of weaker neighbors. Intraspecific struggle intensifies with an increase in population density. With an abundance of chicks in some bird species (many species of gulls, petrels), the stronger ones push the weaker ones out of the nest, dooming them to death from predators or starvation.
Interspecific struggle should be understood as competition between individuals of different species. Interspecific struggle is especially acute in those cases when species that live in similar ecological conditions and use the same food sources are confronted.
As a result of interspecific competition, either the displacement of one of the opposing species occurs, or the adaptation of species to different conditions within the same range, or their territorial separation. For example, gray and black rats are different species of the same genus. In human settlements in Europe, the gray rat completely replaced the black rat, which is now found in forest areas and deserts. The gray rat is larger, swims better and, most importantly, more aggressive, as a result of which it gains the upper hand in fights with the black one.
In the forest, under the protection of light-loving species - pines, birch, aspen - spruce seedlings develop well at first, which freeze in open areas, but then, as the crowns of young spruce trees close, seedlings of light-loving species die.
The interspecific struggle for existence includes the unilateral use of one species by another, the so-called "predator-prey" relationship (fish that eat plankton).
Examples of the struggle for existence are not reduced to the struggle in the literal sense. Thus, the form of the struggle for existence is the favoring of one species to another without prejudice to itself (birds and mammals distribute fruits and seeds), mutual favoring of different species to each other (flowers and their pollinators).
In the forest, there are also benefits from the joint growth of plants. Here, in comparison with open places, its own thermal, water and air regime is created: less sharp temperature fluctuations, higher relative humidity - shade-tolerant shrubs, grasses, mosses, ground algae grow under the canopy of trees of the upper tiers.
The third form of the struggle for existence is the struggle against unfavorable external conditions. Factors of inanimate nature have a direct impact on the evolution of living things. Plants in the desert are said to be "drought-fighting", referring to the development of numerous adaptations that help them extract water and nutrients from the soil (special root system) or reduce transpiration rate (special leaf structure).
The conditions of the inorganic world have a significant influence on the evolution of organisms, not only in themselves, their influence can strengthen or weaken interspecies relations from within. With a lack of territory, heat or light, intraspecific struggle intensifies and, conversely, with an excess of resources necessary for life, it weakens.
Annex 2
Comparative characteristics of the forms of the struggle for existence
Forms of wrestling for existence | Definition | Examples | Causes | Significance for evolution |
signs | driving selection | Stabilizing selection | Disruptive selection |
|
C. Darwin | I.I. Schmalhausen | |||
Validity conditions | Gradual and unsharp change in the conditions of existence of organisms | In the constant constant conditions of existence | Under rapidly changing conditions of existence |
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Orientation | Schemes of action of forms of natural selection Eliminated forms on population curves (elimination) | |||
In favor of individuals with deviations from the average norm | against individuals with emerging brief deviations from the mean | against individuals with average values of the trait |
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Action result | the emergence of a new average norm of a sign | preservation and maintenance of the value of the average norm of the trait | the formation of new average norms instead of one |
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Examples | Industrial mechanism; Sustainability to pesticides; -microorganisms and antibiotics | Down syndrome; sustainable relic | Polymorphism; early flowering fast growing |
Literature:
1. Kamensky A.A. General biology: a textbook for grades 10-11. Bustard 2009
2. Vysotskaya, L.V. General biology: a textbook for grades 10-11 with in-depth study of biology /L. V. Vysotskaya, S. M. Glagolev, A. O. Ruvinsky and others - M: Education, 2001. - S. 265-266.
3. Green, N. Biology: in 3 volumes / N. Green, W. Stout, D. Taylor; ed. R. Sopera. - M: Mir, 1990. - S. 290.
4. Sivoglazov, V. I. General biology. A basic level of. Grades 10-11 / V. I. Sivoglazov, I. B. Agafonova, E. T. Zakharova. -M.: Bustard, 2005.
slide 2
Lesson Objectives:
- To form an idea of the forms of the struggle for existence.
- To form an idea of the forms of natural selection.
slide 3
2. Natural selection
3. Tasks
1. Struggle for existence
4. Homework
slide 4
On average, each mouse gives birth to 50 mice per year. For ease of calculation, we will assume that each
a mouse gives birth to 25 females and 25 males a year. Thus, the offspring of one female after 5 years is 829425 individuals.
Explain why the number of mice on the planet is not noticeably increasing.
slide 5
The discrepancy between the number of individuals appearing in the population and the means of their livelihood
inevitably leads to a struggle for existence. Under the expression "struggle for existence" understand the complex and diverse relationships of individuals within species, between species and with inorganic nature.
slide 6
Intraspecific struggle
It arises due to the fact that individuals of the same species need similar food sources, which are also limited, in similar conditions for reproduction, in the same shelters. Darwin considered intraspecific struggle the most intense.
Pines in an even-aged forest stand
Slide 8
Fight against adverse factors of inanimate nature
It is observed in any part of the range of the species in cases where external environmental conditions worsen (daily and seasonal fluctuations in temperature and humidity), as well as wherever individuals find themselves in conditions of excessive heat or cold, dryness or humidity.
Slide 9
The result of the struggle for existence is natural selection. Natural selection is a process
as a result of which, predominantly individuals with hereditary changes that are useful under given conditions, survive and leave behind offspring.
Slide 10
Stabilizing selection
Operates under constant environmental conditions. The importance of this form was pointed out by the outstanding Russian scientist I.I. Schmalhausen. Stabilizing selection is aimed at maintaining the previously established average trait or property: the size of the body or its individual parts in animals, the size and shape of a flower in plants, the concentration of glucose in the blood in vertebrates, etc. Stabilizing selection preserves the fitness of the species, eliminating sharp deviations in the severity of the trait from the average norm, thereby protecting the existing genotype from the destructive effect of the mutation process.
slide 11
The action of the stabilizing form of natural selection explains the stability of the size and shape of flowers in insect-pollinated plants. This is due to the fact that the flowers must correspond to the structure and size of the body of pollinating insects. A bumblebee is not able to penetrate a too narrow corolla of a flower, a butterfly's proboscis will not be able to touch too short stamens in plants with a long corolla. Thanks to stabilizing selection, relict animals have survived to this day: the coelacanth fish coelacanth, a representative of the ancient reptiles of the hatteria, and the gymnosperm plant gingo.
slide 12
driving selection
It contributes to a shift in the average value of a feature or property and leads to the emergence of a new average norm instead of the existing one, which has ceased to correspond to new conditions. The driving form acts when the environmental conditions change.
Slide 14
Tearing (disruptive) selection
It operates under conditions that favor the extreme variants of the trait, but not favorable for the average state. This selection is effective when, with increased competition, relatively narrow adaptations to external conditions turn out to be favorable and the population tends to be divided into smaller groups.
slide 15
Disruptive selection
An example of tearing selection is the case of the formation of various populations of the large rattle plant in connection with mowing. This form of selection occurs when plants with medium flowering periods are eliminated from the original population. Ultimately, a single population splits into two, located on the same territory, but which turn out to be isolated from each other in terms of reproduction.
slide 16
Speaking of natural selection as a whole, one should not lose sight of its creative role. accumulating
beneficial for the population and species of hereditary changes and discarding harmful, natural selection gradually creates new, more perfect and perfectly adapted to the environment species. Natural selection is the main driving force of evolution.
Slide 17
Task 1 Define the forms of relationships between organisms:
- In thickened crops of kok-saghyz, seeds that germinate faster receive more nutrients and water. Already after 20-30 days, those plants that fall under the rosettes of leaves of previously sprouted plants die.
- Cereal breads are often affected by the bug (yellow-green bug). The telenomus lays its egg in the turtle's egg, and the telenomus larva eats its contents.
- After heavy snowfalls in the tundra, it is difficult for deer to get reindeer moss from under the snow, and many animals die of starvation.
- Usually the prey of wolves are less swift-footed and weaker deer.
Slide 18
Task 2
In the winter of 1898, after heavy rain and snowfall, researcher H.K. Bumpus collected and brought to the laboratory 136 stunned house sparrows. Of these, 72 survived and 64 died. Bumpus measured in all individuals the total body length, wingspan, body weight, beak and head length, humerus, femur, skull width and keel length. His measurements showed that in surviving birds all these signs are closer to the average values than in the dead ones. The result of what form of natural selection did the scientist reveal?
Slide 19
Task 3
- Many species of butterflies in non-industrialized areas have light colored bodies and wings. The development of industry, the associated pollution of tree trunks and the death of lichens living on their bark, led to a sharp increase in the frequency of occurrence of black (melanistic) butterflies. In the vicinity of some cities, black butterflies became predominant in a short time, while relatively recently they were completely absent there.
- Complete the scheme for the formation of a new dark-colored butterfly.
Topic: The struggle for existence and natural selection
Tasks: - consider the types of struggle for existence and natural selection, their significance in nature and human life
Develop the ability to generalize and compare, give examples, work independently with educational material, reproduce material using graphic reference notes;
Equipment: textbook, diagram, presentation
Lesson type: learning new material
During the classes:
I . Organizing time
Greetings. Checking absentees, checking readiness for the lesson; Attunement to the perception of the topic of the lesson; voicing the purpose and topic of the lesson
II . Checking the actualization of students' knowledge
Frontal survey on the topic: General individual variability and excess offspring
III . Explanation of new material
Target: talk about the struggle for existence, its forms.
Student goal: listen carefully to the teacher; write down new terms in a notebook
Plan:
1. Struggle and its causes
2. Intraspecific struggle
3. Interspecies struggle
4. Combating abiotic factors
As you have already studied earlier, Charles Darwin put forward 3 driving forces of evolution, one of which is the struggle for existence. The struggle for existence is a consequence of the causes: the unlimited ability of living organisms to reproduce; limited natural resources.
Under the struggle is meant a direct collision, leading to the displacement of some of them. This is the whole complex of complex relationships between organisms, including mutual assistance, passive competition, and the whole spectrum of symbiotic relationships. Traditionally, the fight is divided into 3 types: intraspecific, interspecific and the fight against abiotic factors.
Intraspecific struggle. It flows between individuals of the same species. There are three main directions of intraspecific struggle: the struggle for food, for the attention of the female, for the territory.
An example is the mating tournaments of deer or other animals. Figure 47.
Plant competition for light in a pine or spruce forest. It is believed that this is the most acute form in which the most individuals die. This type of struggle in many animals appears even before birth. In multiparous animals, for example, cats, dogs, mice, there are usually several cubs in one litter, they are not the same, differing in weight and size. This suggests that already at the embryonic level (that is, when the cubs are still in the womb), they compete for nutrients coming from the mother's body. Babies that get more nutrients and develop faster are more likely to be born healthy and strong.
After birth, competition increases. For example, chicks compete for food brought by their parents. The more cubs one pair has, the more acute the struggle for existence, the more dead cubs. This mechanism prevents overpopulation.
Fight for territory: the more individuals of the same species in the territory, the higher the mortality rate.
Interspecific struggle exists between individuals of different species. A classic example is the predator-prey relationship (wolf hare, cat mouse). These are the most diverse and multifaceted interactions. These include:
Competition between closely related species that need similar conditions, such as different species of antelope in the savannah.
In plants, this type of competition is clearly expressed in systematically distant groups. Thus, deciduous and coniferous plants (pine and birch) compete in the forest, and monocots and dicots (clover and couch grass) compete in the meadow. It is generally accepted that the struggle for existence is more acute between closely related species that need similar conditions. After all, they compete not only for food resources, but also for territory.
Intraspecific and interspecific struggle can be divided into direct and indirect. In a direct fight, an open clash of individuals occurs. For example, males of many species (roosters, beetles, dogs, cats, walruses) organize tournaments. Many animals fight for territory (bears, lions). As a result of starvation (pike) or due to other reasons (change of leader in a pride of lions), adults destroy the young of their own species.
Indirect struggle takes place without open clashes. This is how bird species compete, the males of which call the female by singing. Migratory birds may not encounter open clashes when settling in nesting sites. The “fastest” who returned from wintering earlier will get the best plots. There are even more examples of intraspecific indirect control in plants. Thus, wind-pollinated species produce more light pollen and displace their relatives, in which pollen was not enough. And when pollinated by insects, the most attractive flowers for pollinating insects get an advantage.
It includes all the complex and diverse relationships of organisms with their environment. This is a struggle for survival in natural disasters (floods, early frosts, prolonged snowfall, volcanic gases, etc.); adaptation to a sharp change in daily temperatures in mountainous areas; to seasonal changes (dropping foliage, hibernation or molting); adaptation to soil depletion or excess of any elements in it, excessive or insufficient moisture, and many others. others
Thus, in the course of the struggle for existence, individuals better adapted to environmental conditions survive and leave offspring. The intraspecific struggle is most acute, and the other two forms often intensify it. There is no 100% destruction of all individuals with unfavorable traits. As a result of accidents, some of them are still preserved and leave a few offspring. The struggle for existence leads to natural selection.
IV . Pinning a new topic
Fill in the table - forms of the struggle for existence
V . Homework
Learn paragraph 18-19