Subject . Diversity of animals in nature
Target . Continue to form the concept of "animals-living organisms", provide students with objective, age-appropriate information about the diversity of the animal world, begin to form the concept of "insects", "amphibians", "fish", "reptiles", "birds", "animals", form the ability to describe animals of different groups, to identify them by essential features.
To develop students' cognitive interest, observation, attention,
oral speech.
To educate and instill a caring attitude towards all living things, the ability to feel and protect the world around.
Equipment. Animal name cards, animal illustrations, pair work cards, multimedia projector, electronic presentation.
Lesson type : a lesson in the assimilation of new knowledge.
During the classes
Ι. Organizing time.
Now check it out buddy
Are you ready to start the lesson?
Everything is in place
Everything is fine,
Pen, book and notebook?
Is everyone seated correctly?
Is everyone watching closely?
Everyone wants to receive
Just a high score.
You have leaves, on the leaves depict the sun, a cloud or a cloud with rain, depending on the mood with which you came to the lesson.
ΙΙ. Updating the basic knowledge of students
Guys, let's remember what you already know about the natural environment.
Tell me, what is nature like? (Alive and non-living)
What is inanimate nature? (Water, sun, air, soil, stars, mountains, rainbow)
And now our weather forecaster will tell you about changes in inanimate nature for the next day
Synoptic. - Hello, dear children! I want to tell you about the weather for the next day. Cloudy weather is expected, light snow, western wind, temperature at night -7, in the daytime -1.
Winter does not want to give way to spring. But still, there is a spring freshness in the air. And let's remember the signs of early spring.
It shines brighter and warms ... (Sun)
It's getting longer... (Day)
The frost weakens, begins to melt ... (Snow)
Spring flowed along the roads ...... (brooks)
Well done guys, you know the signs of spring well. But still dress warmly! Thank you for your attention!
front poll.
How are living organisms different from non-living things? Who belongs to wildlife?
Prove that animals are living organisms.
How are animals different from plants?
Why are animals constantly moving, moving? (To find food, escape from enemies)
What do plants eat? What do animals eat?
ΙΙΙ . Message about the topic and purpose of the lesson.
And now we will solve a crossword puzzle to find out the topic of today's lesson.
(Using an electronic presentation)
1. There is a hoofed giant.
Neck like a crane
With horns, spotted,
But not very fast. (Giraffe)
2. The tail is fluffy, quick dexterity,
Golden red fur.
If hungry, cheat
Kur thinks the best.
(Fox)
3. He looks like a sheepdog.
Every tooth is a sharp knife!
He runs, baring his mouth,
Ready to attack the sheep.
(Wolf)
4. He builds a house on the rock.
Isn't it scary to live there?
Though beauty is all around
but such height!
No, the owner is not afraid
roll down a steep cliff -
two mighty wings
at the owner...
(Eagle.)
5. Although I'm not a hammer -
I knock on wood:
It has every corner
I want to explore.
I walk in a red hat
And a great acrobat.
(Woodpecker)
6. Bright pink outfit,
The eyes are burning with the sun -
So slim, gentle, lovely
Leggy princess. (Flamingo)
7. In the water - alive,
On land, it's dead.
(Fish)
8. I walk in a fluffy coat,
I live in a dense forest.
In a hollow on an old oak
I chew nuts.
(Squirrel)
Which keyword happened? (Animals) Today in the lesson we will continue to study the topic “Animals are part of wildlife” Or rather, today you will learn how diverse the animal world is. We will go on a journey with you, find out into which groups scientists divided animals.
The epigraph of today's lesson will be the words of the famous children's writer Nikolay Sladkov.
“The main wealth of nature is its secrets and beauty, they lead to a meeting with the beautiful, amazing and mysterious” N. Sladkov.
ΙV. Motivation of educational activity.
Since the dawn of mankind, there has been a mutual relationship between humans and animals. Many peoples deified some animals. For example, in ancient egypt the cat was revered as the Goddess Bast, the patroness of the night and hunting. Aboriginal tribes in Australia and Africa believe that they are descended from animals. Primitive people were completely dependent on animals, which served as a source of food for them, gave them clothes, and warned of danger. Therefore, people from ancient times took care of animals and protected them. I urge you, my students, to respect all living things.
v. Primary perception and awareness of new material.
1. Explanation of new material (Working with electronic presentation)
The science of animals is called zoology. Scientists zoologists divide the animal kingdom into several groups.
What are the animals? We will try to answer this question today.
1) The first group.
Animals of the first group have three pairs of legs. These are insects. Their body is protected by a dense chitinous cover and is divided into three sections: head, chest and abdomen.
They have well-developed eyesight, and some have an ear for music and a delicate sense of smell. Beautiful representatives of this group are butterflies. Now we will listen to a short message about them.
Butterflies only live when they live well. It will be a little bad, windy. Damp - immediately and die. They will fall into a special dream: they see nothing, hear nothing, feel nothing. And then everything bad, unpleasant passes by them, as if it, bad, does not exist at all. There are no hard and cloudy days in the life of butterflies - only bright, warm, sunny days. All life among flowers and sunbeams. That is probably why they so carelessly and cheerfully flutter over the meadow.
Reading a textbook article about insects, working with questions.
2) The second group is amphibians.
These are animals that can live both in water and on land. They have neither strong claws, nor large teeth, nor a hard shell; their coloring performs a protective function.
Why do you think these animals are called that? Let's read the textbook article.
List the main features of amphibians.
3) The third group is reptiles.
These are animals that move mainly by crawling or dragging their belly along the ground. The skin is covered with horny scales or shields that protect the body from drying out. These animals have a good sense of smell. Most of them lay eggs and are predators.
Let's read an article about these animals and select the essential features that are characteristic of them.
4) Pisces
These are animals whose body is covered with scales, have a streamlined shape, can swim, and have fins. They are diverse: round, flat, large, small. Fish lay eggs. They breathe oxygen, getting it from the water through the gills.
Now let's listen to the dialogue of two fish.
(Scene "Perch and Burbot")
Perch. - Miracles under the ice. All fish are sleepy, you alone, Burbot, cheerful and playful, what is the matter with you?
Burbot. - And what is for all fish winter - winter, but for me, Burbot, winter is summer.
You, perches, doze, and we, burbots, play weddings, caviar with a sword, rejoice, have fun.
Perch. - Come on, perch brothers, to Burbot for the wedding! Let's disperse our sleep, have fun .
Reading an article, working with questions.
5) Birds. These animals can fly, their body is covered with feathers. They reproduce by laying eggs. Birds have well-developed sense organs, mainly sight and hearing.
Today the guys have prepared a message about birds.
Birds are song and flight!
Birds are children of the air, conquerors of the air ocean. They rise above clouds and mountains, fly over seas and deserts.
Birds are the children of the rainbow: their feathers are painted in all conceivable and inconceivable colors.
Birds are messengers of joy. Every year they bring spring to us on wings.
Birds are our faithful helpers, defenders of our forests and fields, orchards and orchards.
Birds are mystery and beauty. Birds are our childhood friends. Beautiful poems and songs, legends and fairy tales are composed about birds. We can't do without birds. It is impossible even to imagine our Earth without birds!
That's what birds are.
Reading become textbook "Birds"
6) Animals or mammals.
These are animals whose body is covered with wool. They have a well-developed sense of smell, hearing, sight, touch. Among them there are predators, herbivores and omnivores. All animals feed their young with milk.
Reading textbook article.
Guys, there are other groups of animals. These are spiders, crustaceans, mollusks, worms. You will learn more about them in high school.
PHYSICAL MINUTE
Hamster-hamster, hamster
Hamster, hamster, hamster,
Striped barrel.
Hamster gets up early
Washes cheeks, rubs neck.
Hamster sweeps the house
And goes to charge.
One two three four five!
Homka wants to become strong. (Children imitate all the movements of a hamster.)
VΙ Consolidation and comprehension of knowledge.
1) Guys, a letter from animals came to our class today, the animals are asking for help to determine which group they belong to. But, unfortunately, they forgot to identify themselves. Therefore, we need now to guess who it is and say to which group it belongs.
I live in a large family in nests suspended from tree branches, we make our nests from paper, which we get by chewing pieces of wood. I feed on the nectar of flowers. If I bite a person, I will hurt him. A small swelling forms at the site of the bite. (Wasp)
My life is impossible without water. I live in a river or lake. My body is covered in scales. In length, I reach a meter, or even more. I hunt other fish, I have very sharp teeth and a long head. I am the heroine of the Russians folk tales. (Pike)
Most of all I live in water, heavily overgrown with plants, I move on the ground by jumping .. I eat insects, spiders, snails. My larvae are tadpoles, they live and develop in the water. (frog)
I have no legs, I have a body about a meter long. I move with lateral bending movements of the body. I am a predatory animal. My food is frogs, mice and others. My bites are not poisonous. I am easily recognized by the yellow spots on my head. (Oh)
I can fly, agile and agile. I have a yellow belly and a blue cap on my head. I don't fly to warm countries. In winter, it is difficult for me to find food, and I fly closer to human habitation. Where seeds, cereals and delicacy - bacon are waiting for me in the feeder. (tit)
I am called the master of the forest for my great stature and strength. I am an omnivore. I look clumsy, but I run fast. I stock up for the winter subcutaneous fat and I go into hibernation. (Bear)
2) - And now we will play a game of attention. The whole class will be divided into six teams. Names of teams by groups of animals. I show a card with the name of an animal, and the team whose name matches the group of this animal raises the card up.
3) Work in pairs. Hand out task cards. It is necessary to connect the name of the animal with the group to which this animal belongs with arrows.
4) The game "Decipher the name of the animal" (Working with an electronic presentation.)
VΙΙ. The result of the lesson.
Guys, tell me, what groups are all animals divided into?
What are the characteristics of insects? Birds? Amphibians? Reptiles? Pisces? Animals?
And what animals are not on Earth now? Can existing animals disappear from our planet?
Why might they be extinct?
Many countries are taking measures to protect endangered species of animals by creating reserves. Rare and endangered animals are listed in the Red Book, prohibiting hunting for them.
Everything, everything
Needed in the world!
And midges are no less needed than elephants!
You can't do without absurd monsters
And even without predators
Evil and ferocious.
Everything in the world is needed!
Need everything -
Who makes honey
And who makes the poison.
Bad things in a cat without a mouse
A mouse without a cat
No better business.
Yes, if we are with someone
Not very friendly.
We still really need each other!
Our lesson is coming to an end. You were very active today. I especially want to note the messages that you have prepared, as well as the most active guys.
On the leaves, depict the sun, or a cloud, or a cloud with rain, depending on what mood you are in right now. Thank you for your work.
VΙΙ. Homework.
MAKEEVSKAYA COMPREHENSIVE SCHOOL Ι-ΙΙΙ STAGES № 53
Lesson
in natural history
(course "I and Ukraine")
3rd grade
Theme "Diversity of animals in nature"
Animals have structural features that help them survive in different habitats. It can be strong legs to run and jump; streamlined body shape and wide wings to fly; fins and flippers to swim; poisonous stings for protection from enemies or killing prey and many other adaptive features.
A huge variety of animals live on Earth. They differ in appearance and internal structure, size, lifestyle. Some animals are covered with hair, others with feathers, others with scales, others have shells, and many have no hard body parts at all.
But animals have common features. All of them consume prepared organic food. Animal growth usually stops after a certain period of development.
Many animals actively move: crawl, jump, run, fly, swim. But among them there are also sedentary, leading an attached lifestyle, for example, coral polyps. The ability of most animals to actively move distinguishes them from other organisms.
IN animal kingdom There are two sub-regions: unicellular, or the simplest, and multicellular(Fig. 32). The sub-kingdom of unicellular organisms includes organisms consisting of one cell, for example, the common amoeba, radiolarians.
The sub-kingdom of multicellular animals includes animals whose bodies are built from a large number of different cells: muscle, nerve, etc. Due to this, animals are able to actively respond to external influences. Animals with a well-developed nervous system, such as animals and birds, have complex behavior.
Rice. 32. Diversity of the Animal Kingdom
In nature, animals constantly interact with each other and with other organisms: plants, bacteria, fungi. Animals pollinate many plants. In turn, plants serve as food for herbivorous animals. Along with bacteria, animals are involved in the formation of soil, the decomposition of dead organisms.
The animal world plays an important role in people's lives. From pets, a person receives a significant proportion of food, as well as leather, wool, silk, and wax. Many birds and predatory insects destroy pests of cultivated plants.
Among animals there are causative agents of a number of diseases of humans, domestic animals, plants.
Some animals are carriers of pathogens of various diseases. So, taiga ticks are very dangerous for humans. They serve as carriers of pathogens of encephalitis - a serious disease of the human nervous system.
It is very important that every person be attentive to the animal world and strive to reduce Negative influence on nature.
Remember
- How are animals different from other organisms?
- What role do animals play in nature?
- What is the importance of animals in human life?
New concepts
Kingdom Animals. Unicellular and multicellular animals.
Think!
My laboratory
The diversity of the animal world has been declining in recent decades. main reason extinction of animals has become human activity. By cutting down forests, plowing up steppes, draining swamps, a person destroys the habitats of animals, and they die. And only after many animals disappeared, people realized that it was irrevocable.
The initiative to save endangered animals was shown by the International Union for Conservation of Nature. In 1966, a list of rare and endangered animals was compiled. They were included in a special Red Book. It is so named because the color red is a signal of prohibition, understandable to people all over the world.
In Russia, the national Red Book, which includes animals, was first published in 1983. This official directory, containing information about the condition of animals in need of special protection. In the Red Book Russian Federation used a special system of dividing animals into categories: 0 - probably extinct animals; 1 - endangered; 2 - declining in number; 3 - rare; 4 - undefined by status; 5 - recoverable.
Today in Russia there is almost no mollusk left - tiun pearl oyster; beetle - Tebler's beetles; butterflies - Mongolian bear; fish - kaluga; reptile - the Mediterranean tortoise; birds - white-backed albatross, pink pelican, yellow-billed heron, Far Eastern stork, mountain goose, Japanese crane, fish owl; mammals - red wolf, bandaging, leopard, snow leopard, Japanese whale, bison, gazelle (Fig. 33).
Rice. 33. Endangered Animals
Reserves are of great importance for the conservation of animals listed in the Red Book. These are protected natural areas where any economic activity is completely prohibited: mining, felling trees and shrubs, hunting, fishing, haymaking, picking berries and mushrooms.
In 1916, one of the first in our country, the Barguzinsky Reserve was founded. It is located on the northeast coast of Lake Baikal. More than half of the area of the reserve is occupied by dark coniferous taiga. The Barguzin sable lives here. Its dark chocolate fur with bluish underfur has long been considered the most beautiful and expensive in the world. Loud fame almost killed the Barguzin sable.
Conclusions to chapter 2
The organisms that inhabit the Earth make up the organic world. ¦ It distinguishes several independent kingdoms.
Kingdom Bacteria - non-nuclear, mostly unicellular AND organisms. Decay bacteria and soil bacteria destroy complex organic substances, turning them into simpler ones. Thus, bacteria are involved in the cycle of substances in the nature of Herod. Humans use bacteria economic activity. Bacteria are pathogenic.
Kingdom Fungi are unicellular or multicellular organisms. For food, they use ready-made organic matter. Mushrooms are of great importance in nature and play an essential role in human life.
The plant kingdom includes two large groups: lower plants and higher plants. The main feature of green plants is the ability to photosynthesis. Lower plants - algae - have a relatively simple structure. Among them are unicellular and multicellular. The body of algae (thallus) is not divided into tissues and organs. The higher plants include mosses, club mosses, horsetails, ferns, gymnosperms and angiosperms. Their body is divided into organs, each of which performs certain functions. Among higher plants, angiosperms have the highest organization.
The Animal Kingdom includes unicellular and multicellular organisms that consume ready-made organic substances. Most animals are able to actively move. Constantly interacting with plants, bacteria, fungi, animals participate in the cycle of substances in nature.
Fish, crayfish, whales, jellyfish, live on the ground and in the air, animals and, and in the soil - earthworms, moles and bears. The habitat for some animals are other living organisms and plants.
photo: Bill Gracey
The fauna of our planet is represented by unique organisms: from single-celled crumbs, which can only be seen with a microscope, to giant whales, whose mass reaches 150 tons. Thanks to constant evolution, animal organisms are endowed with unique properties: they move, feed, defend themselves from enemies, reproduce and raise offspring in various conditions.
Animal classification
The following taxa are distinguished in the animal kingdom:
Family;
Species are grouped into a genus, families into a series, classes into a type. In addition to these taxa, intermediate concepts are used: subtypes, subclasses, and others. All living organisms are divided into:
Protozoa;
insects;
Amphibians;
reptiles;
Mammals.
photo:David Shannon
Meaning of animals
Representatives of the animal world are of great importance for the entire planet: they participate in the cycle of substances in nature, pollinate plants, and are distributors of fruits and seeds. act as natural orderlies, in addition, they regulate the number of herbivorous organisms. : animals are bred and hunted for meat, skins, fur, milk and eggs, animals are used for research, medical and scientific purposes. On laboratory mice, hamsters, rats and guinea pigs investigate the effect of some medicines, monkeys are attracted in experiments with table cells. Bee and snake venom are used for medicinal purposes.
photo: Rob Escott
Features of the resettlement of animals
Various factors influence the population density of representatives of the animal world. These include climate, terrain, human activities and the relationship between different types. Adaptability to environmental conditions is expressed in the characteristics of living organisms. So, in order to find favorable conditions for living, feeding and reproduction, many organisms travel great distances. These movements are called migrations. As an example, the following example can be given: fish of the salmon order grow up in the sea, and breed in the upper reaches of rivers. The fry of these fish hatched from the eggs are carried by the river current back to the sea, where their further growth takes place.
photo: Jiya Aggarwal
If you move from the poles to the equator, it becomes noticeable that the number of species of living organisms is increasing. The largest is . For example, there are more than 40 species of parrots alone, and thousands of species of butterflies.
Evolution of biodiversity
In the history of the animal world, there have always been periods of decline and increase in biodiversity. They are characterized by the appearance of new species that appeared to replace others. Scientists learn about these stages through archaeological excavations: fossils and prints. So, in the Precambrian, 670 million years BC, soft-bodied invertebrates, annelids and intestinal worms dominated. The Cambrian and Silurian, 590-438 million years BC, are characterized by shelled marine invertebrates, insects reigned during the Late Carboniferous and Cenozoic, amphibians dominated the Carboniferous and Triassic, reptiles were most numerous in the Permian and Cretaceous, and mammals flourished in the Cenozoic.
The flourishing and extinction of species is a natural process that occurs under the influence of climate change in certain regions and on the entire planet as a whole. Scientists suggest that most species of living organisms will die out sooner or later. Some are transformed into more evolutionarily advanced species, but others will not be able to adapt to new environmental conditions. The latter are in danger of extinction.
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In biology, all living organisms that have existed and still exist on our Earth are divided into four huge groups called kingdoms. These are bacteria, plants, fungi and animals. Each kingdom includes a great variety of genera and species, consisting of a large number of units. Amazes the imagination and the huge diversity of the animal world. In turn, animals are divided into unicellular and multicellular, invertebrate and vertebrate organisms. And the science that studies them is called zoology (a branch of biology).
Animal diversity: classification
Invertebrates usually include worms, molluscs, echinoderms, crustaceans, arachnids, and insects. These animals (yes, worms are also animals!) do not have a pronounced spine inside or outside. Sometimes there is a chitinous shell that performs this role. Vertebrates include fish, birds, mammals (man belongs to the last class, because he feeds his young with breast milk).
Invertebrates: worms
shellfish
The variety of mollusk animals is also great. This group includes more than 130 thousand species. And they live almost everywhere, even on trees. But most of them live in the world's oceans at various depths. Some of them are hundreds of years old. Mollusks feed on plants, small animals, and organic waste. Almost all of them have protection in the form of a shell (except, for example, squid, which is also a mollusk, but it also has the rudiments of a shell). People have been using shellfish as food for a long time. Some representatives of this group are even delicacies.
Echinoderms
These are (1500 species), which got their name due to the presence of rays on the body (many have five, but some even have up to 50 pieces). The stars that live in the sea vary in size and appearance. Feature starfish - the ability to regenerate (like lizards). If a limb is torn off from an animal, then a new one grows at a speed in its place. And from the torn off beam, under favorable conditions, a new individual develops. Most starfish are predators.
(800 species) are also echinoderms. The body of hedgehogs is covered with needles various sizes. And the length of the processes can reach up to 30 centimeters. Hedgehogs move with the help of needles. And among them there are very poisonous, dangerous for other animals.
Crustaceans
The body of these animals consists of armored segments: the head, chest and abdomen. Limbs, located on the abdomen and chest, allow crayfish to move along the surface. Their eyes consist of many small eyes, and on the head there are several pairs of jaws.
Arachnids and insects
The diversity of animals living on Earth is well represented by these groups, of which there are more than 27 thousand species. These two groups are related. Only insects have six legs, while spiders have eight. All insects also have wings, even in their infancy. Spiders do not have wings. Also, the structure of the body varies: insects have a head, chest and abdomen, and spiders have a cephalothorax and abdomen.
Vertebrates
The variety of animals living on our planet is easy to imagine by studying the order of vertebrates. These are fish covered with scales. There are a great many of their species, among which are very ancient ones that have inhabited the waters of the ocean since time immemorial (sharks, these are amphibians, reptiles, birds, and mammals that inhabit the world around us.
The variety of animals is so great that even an experienced zoologist will not give an exact answer to the question of how many species of animals exist in nature. Because there is no definitive answer: new ones are constantly being opened, some existing species. The cycle of nature is carried out, including an endless variety of animals (see photo above).
We are surrounded by a huge world of living beings - plants, animals, microorganisms - forming various combinations in various parts of our planet. Both the species themselves and their complexes - biocenoses arose long before the appearance of man as a biological species. With each epoch in the history of the Earth, this world has changed more and more. In place of the first primitive groups of organisms, new groups advanced in morphophysiological terms, possessing broader evolutionary potentials, came, and this continues as long as there is life on Earth. All this is the result of organic evolution, which can be called in one word - biodiversity.
Biodiversity is hundreds of thousands of species, and diversity within populations of each species, and diversity of biocenoses, that is, diversity is observed at every level - from genes to ecosystems. This phenomenon has long interested man. First, out of simple curiosity, and then quite consciously and often for practical purposes, a person studies his living environment. This process has no end, since with each century new tasks arise and the ways of understanding the composition and structure of the biosphere change. They are solved by the whole complex of biological sciences.
The study of the diversity of the organic world of our planet has become especially relevant after the role of diversity itself in maintaining the stability of the biosphere began to be clarified. Her condition, which seemed unshakable and her inexhaustible resources, turned out to be so disturbed for a short time that it began to cause reasonable alarm for mankind. The growing pressure of human economic activity on the biosphere, the direct, although sometimes unconscious destruction of many plant and animal species, and changes in the habitat of other species can ultimately lead to catastrophic consequences.
Therefore, the increased interest in studying the role of biodiversity in the stability of the biosphere, from which a person receives resources for his existence, is understandable. Sustainable nature management is the rational use of the gene pool of plants and animals in combination with its long-term conservation, this goal can be achieved only with a clear understanding of the processes taking place in the biosphere, the relationships and interdependencies between the components of ecosystems, and above all from the knowledge of the diversity that surrounds us.
All animals, like other living organisms, are united by scientists into systematic groups on the basis of kinship. The smallest of them is the view. All white hares living in the taiga, mixed forests or tundra belong to the same species - the white hare. A species in zoology is a collection of animals that are similar to each other in all essential features of structure and life, living in a certain territory and capable of producing fertile offspring. Each animal, which has only its inherent structural and behavioral features, is called an individual. Similar species are combined into genera, genera - into families, families - into orders. Larger systematic groups of animals - classes, types.
The study of the species richness of the animal world of our planet has a long history, but only in 1758 the famous scientist Carl Linnaeus listed all the animals known at that time, giving them their own Latin names. In the more than two centuries that have passed since the publication of the tenth edition of Linnean's System of Nature, our knowledge of the animal world of the Earth has increased immeasurably and continues to grow at a rapid pace. Although the process of studying the faunas of various parts of the globe is far from being completed, it is already possible to present the results of this study.
In the literature, one can also find predictive data on the number of animal species in the world. Thus, many believe that after the completion of work on the study of the species composition of insects, there will be more than 1.5 million species. The same applies to roundworms and some other classes of animals. But even so, their species richness is literally stunning. As one would expect, the number of animal species in different parts of the globe is not the same. In the direction from the flat areas of the tropical zone to high latitudes and high altitudes of mountain ranges, a decrease in diversity is clearly manifested. This phenomenon is called the main diversity gradient. As a rule, this concerns not only the general diversity of the animal world, but also the number of species of specific taxa - orders, families, genera - in the faunas of the tropical and temperate zones of the Earth.
We are used to talking about the luxurious nature of the tropics and its poverty in the north. But everything is not so simple. Many theories or hypotheses have been proposed to explain the phenomenon of biological diversity. If biological diversity is the result of evolution at all, then why did evolution take place at such different rates in the tropics and beyond the Arctic Circle, on the plains and in the highlands, in shallow waters and in deep depressions of the World Ocean? Many attempts have been made to elucidate the causal relationships of biodiversity with environmental factors.
Factors affecting biodiversity
Depending on how environmental factors act on organisms - through the physical environment alone, through the physical and biotic environments, or through only one biotic environment, these factors or mechanisms are divided into primary, secondary and tertiary. Of course, the mechanisms themselves are not independent and act in concert and consistently. For some organisms, some factors are more important, for others, others. Let us briefly consider the hypotheses that explain biological diversity.
It has long been believed that the diversity of the animal world increases with the age of the communities in which the species live. That is, evolutionary time is called the first in a series of reasons acting on diversity. In temperate zones, especially in the northern hemisphere, habitats are poor in species, because, due to Quaternary glaciation and other geological disturbances, animal species had too little time to adapt and fully develop their habitat. In the tropics, on the other hand, communities are highly diverse, since they have not experienced external influences and evolution went unhindered, which led to species richness. This hypothesis is similar to another one, which takes into account the time required for the dispersal of species, but not for speciation, that is, a shorter ecological time. The following example gives us some idea of this. If we are dealing with a recently formed site like a forest fire, then its species composition is poor because there was simply not enough time for it to be populated by species from neighboring habitats. A classic example of this kind is the story of the settlement of animals on the island of Krakatau after a catastrophic volcanic eruption that destroyed all life on the island in 1883. It took only 50 years for the formation of a new fauna, but this fauna turned out to be much poorer than the previous one, despite the fact that the island is located in a tropical zone and the distances to the nearest islands are very small.
The most common of all hypotheses is the one that links species richness with climate stability, that is, with its slight seasonal fluctuations. This is exactly the climate of the tropics, especially the equatorial zone. An environment with a stable climate favors specialized species occupying narrow ecological niches. Recall that an ecological niche is a reflection of the place occupied by an organism or species in a community, and this concept includes, in addition to resistance to physical environmental factors, also interactions with other organisms. This means that more species that do not compete due to available resources can fit in one area. We add that in areas with a stable climate, the primary (vegetative) production of ecosystems is also stable and large, which ensures the coexistence of a larger number of species than in areas with unstable productivity.
The complexity of the habitat structure is also important. For many groups of animals, in particular for birds, spatial heterogeneity plays a primary role. This can be seen at least from the fact that more species of birds live in the forest (multi-tiered structure) than in the meadow. For marine animals living in the intertidal zone, where the bottom consists of particles of various sizes, there are more species of invertebrates than in the same shallow water with a monotonous muddy bottom. Thus, there is a correlation between the structural complexity of the habitat and the species diversity of the fauna.
Species diversity can be determined by the productivity of habitats. Food is more abundant and varied in more productive habitats, so there are also more opportunities for consumer specialization than in less productive habitats. Many ecologists attribute an important role in the formation of species-rich communities to such a biotic mechanism as competition. Ch. Darwin pointed out the role of competition as a driving force in the process of speciation. Competition leads to divergence in ecological niches, and specialized species have narrow niches, which contributes to the emergence of high diversity. Particularly intense interspecific competition is observed in communities such as tropical rainforests. They are distinguished by the highest biological diversity and small size of species populations. It is known that from 50 to 100 species of trees can grow on 1 ha of such a forest. The high diversity of plants, in turn, favors the development of animal diversity, especially birds and insects, while many species are rare and the number of individuals of one species is small.
Finally, biodiversity researchers assign an important place among its mechanisms to predation. This mechanism lies in the fact that predators feed on prey that have the largest number in the area, that is, the most common, so-called background species. In this case, predators act as a rarefaction factor. Therefore, they make possible the local coexistence of species, weakening the competition between them and leading to the multiplication of various prey.
In all likelihood, none of the environmental factors, taken in isolation, is able to explain the cause of the diversity of species in a particular landscape zone of the globe. Recently, a work based on a comparison of the number of species of certain groups of insects in the territory of the Russian Plain was devoted to a special discussion of the correlation between climate and diversity. The authors came to the conclusion that the problem of the relationship between climate and biodiversity is still at the descriptive stage of study. In addition, they believe that the evidence base that would link the response of biota to global warming is still insufficient. The last statement is important in the sense that it casts doubt on the statements of many ecologists who talk about the global consequences of global warming caused by human activity.
The studies on the basis of which certain hypotheses were proposed were carried out on various groups of animals with different environmental requirements. As a result, the conclusions of the authors often do not agree. Different groups of organisms have different correlations of diversity with vegetation structure, environmental stability, moisture conditions, etc. Therefore, diversity is the result of contradictions, a compromise between the genetically inherent potential for shaping and the resources of the environment. In a general sense, we can say that evolution is directed towards increasing diversity. The evolution of diversity is a self-propelled process, it creates the prerequisites for the further evolution of diversity, so it can be argued that diversity generates diversity by the feedback principle.
How many types of animals inhabit the Earth?
One million, ten million, fifty? We don't know. More than a million living creatures have been scientifically described, named and cataloged. This includes almost all large, conspicuous to the eye and accessible representatives of the fauna - birds, mammals and reptiles.
Judging by the number of annually discovered "new" insects, we know only a small part of their total number. In some collections collected under the canopy of the tropical jungle, about 90% of insect species were previously unknown to science. Therefore, according to the estimates of a number of scientists, there can be up to 50 million species of insects alone, plus a myriad of mollusks, worms, crustaceans, and similar small living creatures.
Compared to this wealth, 40 thousand species of vertebrates - fish, amphibians, reptiles, birds and mammals, including us - make up more than a modest part of the animal world. This is also clearly seen in the systematization of animals into groups with similar characteristics, each of which is called a type. In total, there are 32 types of animals, and vertebrates make up only a small part of one of them. All other phyla cover an astonishing variety of living beings, from plant-like sponges to intelligent octopuses. Many of them we know at best by name.
The application of new collection methods or the exploration of previously neglected places can also produce a sudden surge in the number of new species. In recent decades, the interstitial fauna of sea coasts (animals living among grains of sand in the tidal zone) has turned out to be such a "gold mine". Not so long ago, completely unexpected discoveries were accidentally made, which turned out to be sensational, at least for zoologists. This is, of course, not about Bigfoot or sea monsters. In 1938, coelacanth was caught - the first living representative of the lobe-finned fish considered extinct about 70 million years ago, from which amphibians originated. Extinct even earlier; in the Devonian, the class of molluscs Monoplacophora was also considered, interesting topics that imprints of places to which muscles were attached were found on their shells. This indicates an elementary segmentation of their body and, according to some scientists, indicates the connection of mollusks with annelids. And since 1952, we know these animals not only in the form of fossils. They live today! Representatives of the genera Neopilina and Vema were found in the Pacific Ocean at a depth of several thousand meters. True, the supposed relationship with annelids has not yet been confirmed.
A little later, another sensation: for the first time they found gastropods with a bivalve shell. It was tempting to see them as a link between gastropods and bivalves. But this assumption was not confirmed either. Meanwhile, two more species of these unusual snails were discovered. They were found not in hard-to-reach sea depths, but in shallow water - off the coast of Japan and Australia, in the Gulf of California and off the island of Jamaica. As you can see, the history of zoological discoveries on Earth is not over. Mammal researchers can still hope for luck - quite recently, in 1938, a new species of whale, the Tasmanian beaked whale, was described. Then the sea suddenly washed ashore several animals. And yet, in small and already well-studied groups, such discoveries are very rare.
In the classes of birds and mammals, the number of species has even decreased. This happened not so much due to extinction, but due to the fact that over time, scientists abandoned too fractional division and many species were combined. Thus, the total number of known and not yet known species of animals is, apparently, two or even three million. Incredible variety! But this is only a small fraction of the species that arose and disappeared in the process of evolution. Some of the once dominant groups of animals, at one time so numerous that scientists determine the age of geological layers by their fossil remains, have completely died out. Of the others, which also flourished in the past, such as the brachiopods, only miserable crumbs have survived. But even in such ancient classes as crustaceans, insects, fish, and even in relatively young classes of birds and mammals, the number of extinct species is much greater than the number of our "contemporaries".
The distribution of animals on land, in fresh water bodies and seas is extremely uneven. The sea is the cradle of life, the earliest stages of the evolution of the animal world took place here. Many ancient groups never found their way to land or fresh water. This applies to the cephalopods, echinoderms, and tunicates that thrive in the seas to this day, as well as to some small surviving groups and to many extinct branches of the animal kingdom. But, despite the vast expanses of the World Ocean, it would be a gross mistake to conclude that the number of marine species exceeds the number of freshwater or terrestrial ones.
The millions of years that have passed since their appearance, and the relative constancy of environmental conditions, it would seem, allowed marine animals to exist much longer and opened up unlimited scope for development before them. But no! It is precisely because of these circumstances that the number of species in the sea is relatively small: the constancy of conditions over a large area and for a long time contributes to the preservation, and not to the fragmentation of any group of animals. A huge number of species of terrestrial animals is the result of the most diverse conditions of their existence. It is surprising and little understood why for insects that have adapted to the most incredible land conditions, the way back to the sea turned out to be inaccessible. On all coasts, except perhaps the coldest, we will find many species of insects, but in the thickness of the sea water they are not. True, in the open sea you can find bugs Halobatidae, reminiscent of water striders from our puddles and ponds. They also rush on the surface of the water, but that's all. Spiders did not become real marine inhabitants either, although some of them settled in coral reefs.
Of course, there are species that differ little in their requirements for environment. However, as a rule, such differences are still expressed quite clearly. The very fact of the existence of many specialized species indicates that animals were able to adapt to almost any food and any climatic conditions within the boundaries determined by the biochemical laws of the body. As a result of this process, which lasted hundreds of millions of years, animals populated the globe from pole to pole. They resist the snow storms of the long polar night, live in circumpolar reservoirs and sea depths at a temperature of about 0°C. Life does not stop in hot springs, where the water temperature reaches and sometimes exceeds 50°C. However, in most animals, even at temperatures slightly below 50 °C, enzymatic systems break down and proteins change irreversibly. It seems to us unbearable heat that the animals of the steppes and deserts can withstand, which are located directly on the surface of the soil, because it heats up much more than air. True, many desert dwellers leave their underground shelters only at night or in the evening.
