Ecological groups of fish, amphibians, birds and mammals. Ecological groups of amphibians. Morphophysiological features. Ecological niche of amphibians

Amphibians are given a specific ecological “niche” - they are an important link in the food chains of humid land areas and aquatic biocenoses. Together with birds, amphibians take an active part in maintaining the natural ecological balance.

Sometimes living beings are classified into different groups, assessing the degree of their “usefulness” for their environment. In fact, there are neither “beneficial” nor “harmful” species in nature. Each species has its own ecological niche, position in food chains, place in the cycle of substances, etc. Each individual is a carrier of unique genetic information characteristic of its species. There is a close relationship between animal species. Moreover, each of them is endowed with its own usefulness for the biocenosis, which may not always be understood by us. Although representatives of some species may pose a certain danger to various members of the community - plants, animals, humans. This is especially evident when the ecological balance is disturbed (for example, during the “explosive” mass reproduction of insects or pathogens). In those natural biocenoses that include various types of amphibians, there are also no absolutely beneficial or harmful insects, birds, amphibians, plants, etc. Everything is an interconnected systemic whole. At the same time, amphibians play the role of defenders flora. After all, the food items they need are basically dangerous to the life of many plants, especially with uncontrolled reproduction. At the same time, amphibians practically do not consume the main plant pollinators. Here the “wise interrelation of interests” of representatives of flora and fauna is manifested. The ecological niches of amphibians and birds, constituting single biocenoses, are also interconnected.

Regulators of ecological balance

Birds have a fairly wide range of food items, but it is amphibians that are considered universal plant protectors. Important role Regulators of the ecological balance of amphibians are made possible by their omnivorous and unpretentious nature. For example, the diet of Russian northern frogs and toads includes locusts, weevils, bedbugs, bark beetles, leaf beetles and other beetles, including the most dangerous pest, the Colorado potato beetle. Amphibians destroy large quantities of cutworm caterpillars, moths, and slugs. The unpretentiousness of amphibians in terms of nutrition is also of great importance. They are in much more than birds, are able to eat insects with unpleasant smell and taste, hairy caterpillars, invertebrates with bright, repellent colors. The fact is that the amphibian body is equipped with excellent defense mechanisms against poisonous creatures. Therefore, in most cases, their innate life program does not include a reflex to the bright color of prey, which frightens other animals.

In addition, amphibians have an important hunting feature, which allows them and birds to complement each other in this joint activity. After all, birds that feed on insects hunt mainly during daylight hours and destroy pests active during this period. And many amphibians are able to restrain the excessive reproduction of representatives of many species of insects and mollusks, working at dusk and at night, when birds sleep. For example, an adult toad can eat up to 100 insects, their larvae and slugs in one night.

The advantage of cold-blooded amphibians

The activities of amphibians are especially important various types to curb (together with birds) the excessive proliferation of invertebrate vegetation destroyers during difficult periods of cold weather and lack of food. After all, birds, being warm-blooded animals, cannot starve for long. Birds need to constantly maintain their body temperature at a level of 39-410C, and for this they must burn enough food in their “furnaces”. When it gets colder, the energy consumption of the bird's body increases sharply. To keep warm, birds need to increase their nutrition, but just at this time insects hide and become inaccessible. Therefore, the birds either die from exhaustion or try to fly to areas with better weather conditions. Even short periods of cold weather and lack of food cause especially serious damage to chicks. However, birds are given an amazing ability - with great accuracy make long-term weather forecasts. In years when unfavorable living conditions are expected, including a decrease in the number of food items, birds lay fewer eggs than usual. As a result, when warming occurs and insects actively reproduce, feathered plant protectors become clearly insufficient. This is where all the benefits of the life activity of cold-blooded amphibians manifest themselves. Having easily survived the temporary cold snap and lack of food, they take revenge under favorable conditions. Amphibians begin to feed intensively, while curbing the excessive proliferation of plant pests.

In the diet of animals

Amphibians are not only consumers of food, but they themselves are objects of food. And thus amphibians are included in the general biological cycle. Among amphibians, the food items of various animals are mainly tadpoles and adult frogs. Tadpoles are eaten mainly by fish. Grown-up frogs are mainly eaten by birds, snakes, animals and large fish. After all, these amphibians do not hide in shelters during the daytime. They are fully equipped for active hunting of insects at this particular time. In addition, frogs are not provided with skin secretions with such protective properties as the caustic mucus of toads, toads, salamanders, etc. Frogs are consumed by a huge number of animals. First of all, these are many large predatory fish: catfish, pike perch, pike. For them, frogs and tadpoles are quite accessible mass food. The most common fish prey is the grass frog, which, in contrast to the green frog, lacks the behavioral mechanism of burying itself in mud for the winter. Therefore, it turns out to be the food link that expands the diet of fish at the expense of terrestrial food items. Many birds also feed on frogs, including storks, herons, crows, magpies, rooks, harrier gulls, terns, and grebes. For some of them, frogs make up a large proportion of their diet. Ornithologists estimate that at least 90 species of birds prey on frogs, 21 species prey on spadefoot spadefoots, and 18 species prey on toads. To a large extent, the nutrition of snakes is provided by frogs. Small quantities of frogs are consumed by hedgehogs, minks, shrews, foxes, and otters. Toads are eaten by raccoons and raccoon dogs, badgers, and hori. In years when the main food of these animals is scarce, the role of amphibians as food items increases. By feeding on a wide variety of invertebrates, amphibians accumulate organic substances in their bodies, which can then be used by larger vertebrates. Thus, the purpose of amphibians is also to use their lives to support the lives of other animals during unfavorable periods.

The number of most species of frogs in all habitats intended for them is in a certain balance (despite the participation of various animals in the diet). It is mainly due to the enormous fertility of frogs, which quickly restores the losses incurred. In addition, amphibians are distinguished by the relative longevity of individuals. In that part of the amphibians that were destined to avoid danger and survive, several generations can exist side by side, regularly producing offspring of the same fertile amphibians.

Man and amphibians

Amphibians are extremely important animals for humans. Firstly, by feeding on small animals, amphibians, especially frogs and toads, restrain the mass reproduction of agricultural pests. Thanks to this, they, along with insectivorous birds, are included in the category of crop protectors, friends of gardeners and gardeners. Secondly, amphibians destroy insects that are carriers of human diseases, for example, malaria mosquitoes. Thirdly, amphibians are actively used for experiments by many generations of physicians, biologists and scientists in related fields. They helped make a lot of important scientific discoveries in biology and other sciences, including bionics. In addition, amphibians are surprisingly touching, gentle and often very beautiful creatures. They admire the phenomenal capabilities of their body, graceful movements and complex behavior. Amphibians, like all living beings, require humane treatment and protection. Let's look at these questions in more detail.

"Utility coefficient" for a person

Living in a wide variety of places and feeding on insects and other invertebrates that are dangerous to plant life, amphibians bring great benefits to gardens, vegetable gardens, fields, forests and meadows (hayfields), and therefore to humans. Among pests that, if uncontrolled, can destroy almost the entire crop, insects occupy the first place. And the vast majority of frogs, toads, tree frogs and salamanders feed on them. In addition, these amphibians destroy countless slugs.

Scientists who studied the nutrition of our domestic amphibians once proposed a fairly simple formula for calculating the usefulness index for a person of a particular species:

V=t, where n is the number of animals eaten that are harmful to humans, u is the number of useful ones, t is the total number of animals eaten (harmful, beneficial and neutral, found in the stomach) and v is the coefficient of utility for humans.

For general guidance in this matter, the formula gives quite satisfactory results. “Utility coefficients” calculated using this formula as a percentage for some amphibians were as follows:

common newt - 98 lake frog - 50

tree frog - 66 toad - 49

sharp-faced frog - 46 crested newt - 11

grass frog - 59 Asia Minor frog - 27

spadefoot - 57 pond frog - 18

It should be borne in mind that the beneficial activity of amphibians for humans calculated using this formula is purely utilitarian. It fluctuates at different times and in different habitats. And of course, this formula does not reflect the importance of amphibians for ecosystems, biodiversity, etc.

A study of the food range of amphibians showed that they consume mainly insects harmful to plants. Due to the fact that in areas of mass reproduction there are more of them than other insects, in the stomachs of amphibians they make up 80–85% of all food eaten. Moreover, on the ground, insects are hunted mainly by salamanders and frogs. And tropical tree frogs and arboreal salamanders catch their prey on the branches of trees and shrubs. Their sticky tongue, which accurately hits the target, helps them grab insects on the fly. Tropical copepods use glider devices to help them hunt. Unlike many birds, amphibians are capable of eating “inedible” insect pests with an unpleasant odor, taste and bright protective coloring. Some amphibians are able to catch insects and their larvae in the ground. Therefore, plants - from roots to crowns - can be completely protected by amphibians. They have been recognized as having an independent and quite significant role in exterminating insects harmful to Agriculture.

Toads have one important feature - they are the most active consumers of slugs, these nocturnal plant pests and practically omnivorous animals. Slugs destroy the harvest of rye and wheat, peas and carrots, cabbage and potatoes, and tobacco. It is easier to list the crops that they do not eat. Moreover, pests do this from early spring to late autumn, on open ground or penetrating greenhouses and greenhouses. They are especially harmful at the time of harvest ripening, when chemical treatment of plants cannot be carried out. This is where toads demonstrate their beneficial abilities for humans. At dusk, choosing a more secluded path and making small dashes, toads go out hunting. The benefits to people of their night hikes are enormous. In the United States, they have roughly estimated the cost savings that toads bring night after night to farming and forestry. It turned out that this is billions of dollars a year! And every year the profit from each toad is 20 - 30 dollars. The usefulness of toads was also highly appreciated in Europe. It is not for nothing that in the 19th century, for example, in Paris there was a special market where gardeners and peasants bought hundreds of toads to release them into vegetable gardens, fields and orchards. Thus, they saved a huge share of their harvest.

After metamorphosis is completed, juveniles, for example, green toads, leave the water and actively engage in hunting. It makes a significant contribution to the eradication of agricultural pests. Of course, young toads mainly consume small animals, which adult amphibians do not pay attention to. But the little caterpillar manages to eat a lot of greenery before it grows to a size where it becomes “interesting” as a food item for adult animals. Thus, juvenile amphibians enter the ecological niche along with older ones, preventing the enormous damage caused by small plant pests.

Those amphibians that eat disease carriers bring great benefit to humans. Newts play a special role in the destruction of mosquito larvae. The purpose of newts to regulate the reproduction of mosquitoes is due to the fact that the habitat of these amphibians, and most importantly their predatory larvae, is most often small and stagnant warm bodies of water. And they are also breeding grounds for mosquitoes. This food “predilection” of newts in areas of mass breeding of malaria mosquitoes is of particular importance, bringing people dangerous disease.

"Martyrs of Science"

Both the first observations of schoolchildren in the biology classroom, and the largest studies of biologists, doctors and other scientists are very often associated with the use of frogs. Most instruments in experimental biology and medicine are designed for these “martyrs of science.” In addition, it was the frog that, more than 200 years ago, gave rise to the development of one of the most important branches of knowledge - the study of electricity. The frog was also of interest for bionics. The purpose of these studies is to use biological knowledge about perfect and unique “devices” and “instruments” of living organisms to solve engineering problems and develop technology. For example, the common frog is endowed with most interesting feature. She practically sees only moving objects, which helps the amphibian to instantly react and grab prey. At the same time, her eye filters out information about stationary objects and tunes only to a moving target. The study of these features of the frog's eye made it possible to create the retinatron device. It does not react to stationary objects and provides observation of moving objects, such as an airplane.

In recognition of the invaluable benefits that modest amphibians brought to the development of world science, monuments are even erected to them. One of the most famous is installed in front of the Pasteur Institute in Paris. With money raised by medical students, a monument was created in Tokyo.

Man inflicts damage on amphibian tribe

The amphibian tribe cannot be seriously threatened by their traditional enemies. The ecological balance inherent in nature is not disturbed naturally. At the same time, some species of amphibians are on the verge of extinction, which is mainly due to the anthropogenic factor - rapidly expanding human economic activity, as well as the consequences of unreasonable recreation and tourism. The recent decline in the populations of the most beneficial tailless amphibians – frogs and toads – has been especially serious. But the purpose of these eternal workers is to maintain balance in nature. Therefore, the increasing pace of technological progress, direct and indirect impact

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COURSE WORK

ECOLOGY OF AMPHIBIDES

Introduction

The relevance of this topic lies in the fact that at the moment there is a sharp decline in the number of representatives of this class of animals, the reasons for which have not been precisely established. Every year, herpetologists describe several dozen new species of animals from this class. The features of biology and ecology of most of them have not yet been studied, and they remain known only by their names. And the study of their biology is often of interest to specialists in other biological disciplines. The above can be confirmed by the discovery of polyploid species and hybrids among green frogs. Amphibians are also active regulators of the number of invertebrates, including those harmful from a human point of view.

Amphibians occupy a special place among other animals, since they represent the first and most simply organized terrestrial vertebrates.

Amphibians are the smallest class of vertebrates, including only about 3,400 species, grouped into 3 orders: legless, tailless and tailed.

Legless amphibians (Apoda) include approximately 165 species of tropical caecilians, most of which lead an underground lifestyle. Most likely, these are very ancient amphibians that have survived to this day thanks to their adaptation to an underground lifestyle, thus avoiding competition with other more advanced vertebrates.

Only about 340 species of tailed amphibians (Caudata, or Urodela) are known. These include salamanders and newts, which are found almost exclusively in the northern hemisphere.

Tailless amphibians (Anura) contain the largest number - about 2900 species, adapted to move on land by jumping with the help of elongated hind limbs. Among our amphibians, this includes various frogs, toads, spadefoots, fire-bellied fireflies, tree frogs, etc. Tailless animals are widespread on all continents except Antarctica.

	Family
Anurans		Lake frog
		grass frog
		sharp-faced frog
		Gray toad
		Green toad
	Garlics	Common spadefoot
	Toadstools	Red-bellied toad
Tailed	Salamanders	Siberian salamander
		Common newt
		Crested newt
Legless		Lazy snake
		Ringed caecilian

Table 1. Orders of amphibians

1. Origin and general information about amphibians

1.1 Emergence of amphibians

The oldest amphibians - Ichthyostegas - lived in the Upper Devonian about 300 - 320 million years ago. These primitive amphibians still retained many of the original and even common features (characters) with lobe-finned fish. Therefore, the origin of amphibians from lobe-finned fish is beyond any doubt. The abundance and prosperity of these animals was noted in the Carboniferous, Triassic and Cenozoic, when they were represented in many different forms. At the same time, in the Jurassic and Cretaceous periods, their development slowed down, their numbers and species diversity decreased. However, from the beginning of the Upper Carboniferous (in the Paleozoic) to the end of the Triassic (in the Mesozoic), amphibians predominated in the fauna of that time.

At the end of the Carboniferous period, one of the representatives of large amphibians appeared on Earth - Mastodonsaurus. It was a large predator that fed almost exclusively on fish and inhabited freshwater bodies of water (lakes and swamps). He led an aquatic lifestyle. Its habits and behavior were very similar to the lifestyle of ordinary frogs. He also could not exist without water, only occasionally and briefly crawling onto land. Therefore, when in the Permian period the climate became less humid, and bodies of water, including large lakes, began to dry up and disappear, the mass death of mastodonsaurs began, and by the beginning of the Triassic this large predator disappeared from the face of the Earth.

The name of the described group - amphibians - suggests that these animals, coming onto land, have not yet fully separated from life in the water. And in fact, many of them continued to lead an aquatic lifestyle, crawling onto land only for short time, and if they lived on land, then near the water, with which they were constantly connected. They, like fish, laid eggs, the entire development cycle of which took place in water. Amphibians went through only the very first stages of land development, but that is why their biology is still of great scientific interest, since the further evolution of these animals, their complete separation from the aquatic environment, laid the foundation for the emergence of the next group - higher vertebrates (reptiles). For the first time, reptiles began to reproduce on land, away from water. They now have eggs with a dense outer shell that protects them from drying out and mechanical damage.

1.2 Amphibian habitats

Currently on globe There are about 3000 species. Amphibians are usually found in and near freshwater bodies. Here they feed on invertebrate animals. In case of danger, they quickly jump into the water.

Some species of amphibians, such as grass frogs, frogs, and common toads, live mainly away from bodies of water. During the day they hide among clods of soil and other shelters, and at dusk they go out hunting. Only during the breeding season do they move to live in bodies of water.

All amphibians are active only in the warm season. When the temperature drops environment up to 4°C they fall into torpor. In a state of suspended animation, vital processes do not stop, but occur at a very low level, for example, the heart makes 1 - 2 contractions per minute. Amphibians usually winter at the bottom of reservoirs (frogs) or in various shelters on land (newts, toads).

1.3 External structure

The body shape of amphibians is different. Tailed amphibians are more similar to fish, have a laterally compressed body and a long, paddle-shaped tail; others, tailless or jumping (more than 75% of all amphibians), have a round or flat body, and no tail.

On the head of amphibians two large bulging eyes and a pair of nostrils are noticeable. The eyes and nostrils are located on elevations in most species. Therefore, a frog, for example, can breathe atmospheric air and navigate the space around it without getting out of the water. Unlike fish, amphibians have eyelids. The upper eyelid is mobile, the lower one has the appearance of a translucent nictitating membrane. The eyelids protect the eyes from clogging and help keep them moist.

In frogs, toads and most other tailless amphibians, eardrums are visible on the head, separating the middle ear cavity from the external environment.

The limbs of some amphibians are absent (caecilians - Apoda), while others are underdeveloped or, conversely, highly developed. Most amphibians have two pairs of legs (tailed amphibians may have only one pair). In tailless amphibians, the hind legs are longer and stronger than the front ones, which allows these animals to move by jumping. Swimming membranes are developed between the toes of the hind legs of tailless animals.

The peculiarity of amphibians is the absence of any hard outer coverings, which is why they are called naked reptiles. They have neither scales, like fish and reptiles, nor feathers, like birds, nor hair, like mammals; the majority are covered on the outside only with bare skin, and only a very few have some traces or semblance of horny formations on the skin. But in the skin of amphibians there are formations that are not typical for other vertebrates.

In the connective tissue layer of the skin of some amphibians there are small capsules filled with a gelatinous substance; in others, voluminous cavities are formed, adapted for the development and initial storage of embryos. Finally, some people sometimes develop ossifications or hard plates in their skin, somewhat similar to fish scales.

The coloring of some amphibians can change and is determined in most cases by the relative position and state of the special pigments of the cells contained in the skin. Contraction or expansion, change in shape, approaching the outer surface of the skin or moving away from it - all give one color or another to the skin and are caused both by changes in external conditions and by internal irritation.

Both in the upper and inner layers of all amphibians there are a lot of glands of various sizes and different purposes. The most interesting are the poisonous glands. They are located in the lower layer of the skin, have a spherical or oval shape, and secrete a mucous liquid containing a toxic substance. Amphibians, in which such glands are more developed, can voluntarily increase secretion, and use them as a means of defense. It has now been established that the poisons of some amphibians are very strong, but are not dangerous for humans and large animals, because they are contained in the mucus only in minor impurities. However, this poison can be fatal to many animals. Injecting toad venom into the blood of small birds quickly kills them; in the same way, the poisonous mucus of toads injected into the blood of puppies, guinea pigs, frogs and newts, has a lethal effect. Some toads, and especially salamanders, have very developed mucous glands, from which they can arbitrarily cause copious discharge, even splashing drops of poisonous liquid, this is what is connected popular belief as if the salamander does not burn in fire.

The elastic, very thin and uncoated skin of amphibians has great importance in their lives. Not a single amphibian drinks water in the usual way, but absorbs it exclusively through the skin. That is why they require proximity to water or dampness. Frogs removed from water quickly lose weight, become lethargic and soon die. If you put a wet rag near such frogs, exhausted by dryness, they begin to press their bodies against it and quickly recover. How large is the amount of water that frogs absorb through their skin can be seen from the following Thomson experiment. He took a dried tree frog and, after weighing it, found that its weight was 95 grams. After that, he wrapped it in a wet rag, and after an hour it already weighed 152 grams. Amphibians absorb water through their skin and sweat it out. Also, gas exchange occurs through the skin, which contains a huge number of capillaries. In a closed tin box, surrounded by a humid atmosphere, a frog can live for 20 - 40 days, even if the air supply to the lungs is cut off. Breathing through the skin occurs both in water and on land. Skin respiration is of particular importance at a time when the amphibian is in the water for a long time (hibernation, long stay in a reservoir in case of danger).

1.4 Features of the amphibian skeleton

The skeletal structure of amphibians is to some extent similar to that of fish. The skeleton of the head, torso and limbs is distinguished. The skeleton of the head is formed by fewer bones than in fish. The structure of the skull is varied. Here you can notice a gradual increase in bone formations due to cartilage and connective tissue. A characteristic feature of the entire class of amphibians are two articulated heads on the occipital part of the skull, which correspond to the two dimples of the first cervical vertebra. The skull is always flat, wide, the eye sockets are very large. The skull consists of the occipital bones, two frontal bones, and the main bone. In the lateral walls of the skull, for the most part, ossification does not occur at all, or the cartilage ossifies partially. The palatine bones are immovably connected to the skull; teeth sometimes sit on them, just like on the vomer and on the sphenoid bone. The lower jaw consists of two or more parts and never completely ossifies. The facial region is much larger than the cerebral region.

The spine of amphibians, due to their semi-terrestrial lifestyle, is more dissected compared to fish. It consists of the cervical, trunk, sacral and caudal sections. In fish-like amphibians, the vertebrae are exactly the same as in fish; in others, vertebrae develop with an articulated head in front and a dimple in the back, which results in full articulation. The transverse processes of the vertebrae in all amphibians are well developed, but real ribs usually do not develop; instead, there are only bone or cartilaginous appendages. The transverse processes of some are very long and replace the ribs.

The cervical region is formed by one vertebra that connects to the skull. The number of trunk vertebrae varies among amphibians. In some species, such as newts, poorly developed ribs articulate with the trunk vertebrae.

Most amphibians have a sacral section; it consists of one vertebra. The tail section of tailless amphibians is small (the vertebrae are fused into one bone). In tailed amphibians this section is well expressed.

The paired limbs of amphibians differ sharply from the paired fins of fish. If the fins of a fish are single-membered levers with their own muscles, then in the skeleton of the fore limb of amphibians the humerus, bones of the forearm and hand are distinguished, and in the skeleton of the hind limb - the femur, bones of the lower leg and bones of the foot. The support for the forelimbs is the skeleton of the shoulder girdle, consisting of paired shoulder blades, crow bones, and in most cases, also clavicles. Connected to the girdle of the forelimbs is the sternum, or sternum. The support of the hind limbs is the pelvic girdle, consisting of the pelvic bones, which are connected to the processes of the sacral vertebra or to the processes of the last trunk vertebra.

1.5 Amphibian musculature

The muscular system of amphibians is more complex than that of fish. It consists of different groups muscles. Tailless animals have the most developed muscles of the limbs, which are attached by tendons to the bones and cause their movement. In tailed amphibians, the muscles of the tail are most developed.

1.6 Metabolism

Underdeveloped lungs, a circulatory system with mixed blood and red blood cells containing nuclei, limit the supply of oxygen to the organs. Therefore, oxidative processes in tissues proceed slowly and little energy is released. As a result, the body temperature of amphibians is variable. Amphibians are cold-blooded animals.

These factors also influence the lifestyle of amphibians. All amphibians are sedentary.

2. Features of the structure of organ systems

2.1 Digestive system

Comprises oral cavity, pharynx, esophagus, stomach and intestines. Amphibians have a more developed stomach, and the duodenum, small and large intestines are prominent in the intestines. The liver ducts open into the duodenum along with the gallbladder duct, into which the pancreatic ducts open. The final digestion of food and absorption of nutrients into the blood occurs in the small intestine. Undigested food remains accumulate in the colon. The large intestine ends in the rectum, called the cloaca. The bladder also opens here (in defense, the frog can release a stream of accumulated urine), ureters and oviducts (in females).

Amphibians are able to endure fasting for a very long time; a toad planted in a damp place can remain without food for more than two years.

Figure 2.1. Organs of the digestive system

1 - esophagus; 2 --stomach; 3 - small intestine, 4 - rectum; 5 -- bladder; 6 - cloaca.

2.2Respiratory system

Most amphibians breathe using the lungs and skin (skin respiration was discussed above). The lungs of amphibians are poorly developed and imperfect. They have a small internal area of contact with the inhaled air. The lungs look like oblong sacs with thin elastic walls, in which many capillaries branch. Such lungs cannot fully supply the body with oxygen. Amphibians do not suck, but swallow air. The animal increases the volume of the oral cavity, and air enters it through the nostrils. As the floor of the mouth rises toward the roof of the mouth, the nostrils close and air is forced through the larynx into the lungs. Gas exchange occurs in the lungs: oxygen penetrates the capillaries, and carbon dioxide from the blood passes into the air, which is then released outside.

Pulmonary and skin respiration in amphibians is unequally developed. Those who spend most of their lives in water have less developed lungs and better skin respiration. Amphibian larvae breathe through gills. Some tailed amphibians retain gills for life.

1 - larynx 2 -lung

Figure 2.2 Organs of the respiratory system

2.3 Circulatory system

Due to the presence of lungs, the circulatory system of amphibians has a more complex structure than that of fish. The heart of amphibians consists of three chambers: two atria and one ventricle. Blood from all organs collects in the veins and enters the right atrium. This blood contains a lot of carbon dioxide and nutrients coming from the intestines. Blood from the lungs enters the left atrium. It is rich in oxygen.

When the atria contract, blood is pushed into the ventricle. Here it is partially mixed. A large artery departs from the ventricle; it is divided into branches that carry blood to all organs of the body (this is the systemic circulation), and branches through which blood goes to the lungs and skin (this is the pulmonary circulation). Thus, amphibians, unlike fish, have not one, but two circles of blood circulation - large and small.

Figure 2.3. Circulatory system

2.4 Excretory system

The excretory system of amphibians includes oblong red-brown kidneys, which are located in the body cavity on the sides of the spine, ureters and bladder. Substances that are unnecessary for the body, released from the blood, enter the cloaca through the ureters and are removed outside.

2.5 Nervous system

The amphibian brain is simple. It has an elongated shape and consists of two anterior hemispheres, the midbrain and the cerebellum, which is only a transverse bridge, as well as the medulla oblongata. In amphibians, the forebrain is more developed (later in evolution, the development of the forebrain will be observed), but there is still no cerebral cortex, gray matter, nerve cells are scattered over the entire surface, the cerebellum is weaker. Poor development of the cerebellum is associated with the uniformity of motor reactions of amphibians. The spinal cord is much better developed than the brain.

Figure 2.4. Organs of the nervous system

The behavior of amphibians is based on unconditioned reflexes, and conditioned ones are developed after a long combination of unconditioned and conditioned stimuli. The most developed senses are: vision, hearing, and smell. The tongue of most amphibians is well developed, and that of frogs differs significantly from the tongue of other vertebrates in that it is attached not by the rear, but by the front end and can be thrown out of the mouth. The teeth are adapted only for grasping and holding prey, but cannot be used for chewing it.

2.6 Reproductive organs of amphibians. Development of the embryo

Amphibians are dioecious animals. The ovaries of females and the testes of males are located in the body cavity.

After hibernation, all amphibians (with rare exceptions) accumulate in fresh water bodies. Soon the females begin to lay eggs. Some of them, for example brown frogs, deposit it near the shore of a reservoir in shallow, warm areas. Others, such as green frogs, lay their eggs at great depths, most often among aquatic plants. In frogs, the eggs are glued together into large clumps, and in toads - into long cords. Newts place single eggs (eggs) on the leaves or stems of aquatic plants. Fertilization in most amphibians is external. At the same time, the males release liquid with sperm into the water. After fertilization, embryos develop in the eggs.

Amphibians are anamniac, that is, their eggs do not have amniotic fluid, this is due to the development in aquatic environment. However, the eggs are surrounded by a thick layer of a transparent gelatinous substance. This shell is of great importance for the embryo. It protects the embryo from drying out, mechanical damage, prevents the eggs from approaching each other, thereby improving the access of oxygen, and it also protects them from being eaten by other animals; indeed, very few birds are able to swallow a gelatinous lump of frog spawn; The shell itself also protects the eggs from attacks by fish, shellfish and aquatic insects. In addition, this shell, like a lens, collects the sun's rays on the developing embryo. The eggs themselves are black, so they absorb heat well sun rays necessary for the development of the embryo.

After the embryo goes through the initial stages of its development (about a week in frogs and toads, two or three in newts), the larva breaks through the gelatinous membrane, feeding on it, and begins to lead an independent life in the water. The larva has a flat, flattened head, a rounded body and a paddle-shaped tail, trimmed at the top and bottom with a leathery fin. The original external gills grow on the head in the form of tree-like branched processes. After some time, these gills fall off and internal gills form in their place. The body narrows even more, the caudal fin increases, and limbs gradually begin to develop; In frog tadpoles the hind limbs grow first and then the forelimbs; in salamanders it is the other way around. Tadpoles at first feed mainly on plant foods, but gradually switch more and more to animal foods. At the same time, changes occur in the organization of the entire body: the tail, which at first is the only organ of movement, loses its importance and shortens as the limbs develop; the intestines become shorter and adapt to digestion animal food; the horny plates with which the tadpole's jaws are armed become sharper, gradually disappear and are replaced by real teeth. The ever-shortening tail finally disappears - and the tadpole turns into an adult frog.

In the development of the brain and sensory organs of amphibians, there is a great similarity with fish. The heart is formed in the larvae very early and immediately begins to act. Initially it is a simple bag, which is subsequently divided into separate parts. The aorta passes into the branchial arches and branches first in the external gills, and later in the internal ones. The blood flows back through a vein running along the tail, and then branches on the surface of the yolk sac and returns through the yolk veins back to the atrium. Later, the portal systems of the liver and kidneys gradually form. At the end of the larval stage, gill respiration is gradually replaced by pulmonary respiration; the anterior branchial arches turn into the cephalic arteries, and the middle ones form the aorta.

At the beginning of their lives, amphibians grow very quickly, but over time their growth slows down greatly. Frogs become mature only at 4-5 years of life, although the larvae of some amphibians (axolotls) reach maturity before metamorphosis, but continue to grow for another 10 years; others reach their present size only after 30 years.

3. Ecology of amphibians

3.1 Amphibians in nature and human life

Even in ancient times, people used the poison of toads and frogs to lubricate arrows. As mentioned above, the venom of most amphibians is safe for humans, but is lethal for small animals and birds. Also, some poisons are used in medicine.

Amphibians bring invaluable benefits to agriculture. Among the pests that destroy crops right at the root, the first place belongs to insects. The vast majority of frogs, tree frogs, toads and salamanders feed on insects, some willingly destroy mollusks, and finally, the largest amphibians do not disdain rodents. A study of amphibian food items in our country and around the world has shown that they eat mainly harmful insects. Frogs and toads most often eat what catches their eye, and since in areas of mass reproduction there are much more pests than any other insects, in the stomachs of amphibians they make up 80 - 85% of all food eaten.

Amphibians are the most versatile plant protectors. Firstly, they have an extremely wide range of readily eaten objects, much wider than that of birds. Most amphibians do not have food preferences. They eat everything indiscriminately, as long as the trophy moves and is edible. This is evidenced by the fairly diverse menu of our northern frogs and toads. They readily eat locusts and weevils, bugs, click beetles, bark beetles, various beetles, including Colorado beetles, cutworm caterpillars, moths and other butterflies. A significant proportion of tree frog trophies are flea beetles and leaf beetles. They also do not refuse shellfish. Secondly, amphibians, unlike birds, are insensitive to poisons, therefore they do not refuse poisonous ones that have bad smell or brightly, or rather frighteningly colored insects. They also do not refuse furry caterpillars, which the vast majority of birds avoid eating.

In addition, insectivorous birds feed only during daylight hours. Therefore, only those pests that are active during the day get into their stomachs. And frogs and salamanders hunt at any time of the day. They bring noticeable benefits in that they destroy nocturnal insects that are inaccessible to birds.

Slugs are among the nocturnal enemies of plants. These are omnivores. They eat rye, wheat, clover, vetch, peas, pumpkin, carrots, cabbage, potatoes, tobacco, tangerines and lemons. They penetrate greenhouses and greenhouses, strawberry plantations and rampage there when the crop is already ripe, and it is no longer possible to use chemicals. Amphibians do not shy away from slugs, and toads can be considered one of their most active enemies.

Amphibians are all-round hunters. Some of them forage in the water or from its surface. Most frogs and salamanders hunt on the ground. Tree frogs and tree salamanders, like birds, find their prey on the branches of bushes and in the crowns of trees. An amazing hunting weapon - the tongue - allows frogs and tree frogs to grab insects on the fly. Our pond and lake frogs “beat” the game, and tropical copepods overtake their prey in flight. Many amphibians have adapted to obtain food in the ground. In general, entire plants, from crown to roots, are under their protection.

Toads, tree frogs and salamanders bring considerable benefits by destroying blood-sucking insects: mosquitoes, flies, horse flies and gadflies that plague us in the summer. Among the bloodsuckers there are many carriers of pathogens of such dangerous diseases as malaria. The flies that live in our homes carry dangerous germs on their legs. Mosquitoes and flies are actively hunted by adult frogs, young frogs, and newt tadpoles. Toaded toads and water frogs destroy mosquito larvae and pupae.

Of course, amphibians, like any other predators, are not able to completely exterminate the population of any pest. But this is not required of them. It is enough that they sharply reduce the number of pests and keep it at an average or even low level.

The lack of thermoregulation and, in connection with this, insignificant energy consumption allow amphibians to spend only 40% of the energy resources of consumed food on the basic needs of the body. The remaining 60% goes towards building your own body. In this regard, amphibians as producers of biomass are significantly superior to warm-blooded animals, mammals and birds. That is why their role in ecological systems is so great. For the same reason, it is profitable to breed them and use them as food.

Many species of frogs and salamanders are edible and provide excellent nutritional value. They are included in the menu of residents of many countries, including Europe. In some countries, the number of amphibians, in particular frogs, has greatly decreased due to their excessive catching.

In some extremely rare cases, amphibians can cause harm. Bullfrogs cause significant damage to pond farms. Other species do not harm fisheries.

Lake and pond frogs are of great benefit. A significant part of their diet consists of predatory water beetles and their equally predatory larvae, which feed on fish fry. Thus, in our farms, frogs are useful because they destroy the worst enemies of young fish. The frogs themselves look askance at the juvenile carp, which is the main object of fish farming. This was confirmed by a specially conducted study: only 44 fry were found in 275 opened stomachs. Undoubtedly, the benefits brought by the destruction of predators significantly exceed the minor damage from frogs - lovers of the fish table, sometimes feasting on fry.

3.2 “Utility coefficient” for humans

Scientists who studied the nutrition of our domestic amphibians once proposed a fairly simple formula for calculating the usefulness index for a person of a particular species:

For general guidance in this matter, the formula gives quite satisfactory results. “Utility coefficients” calculated using this formula as a percentage for some amphibians were as follows:

common newt - 98 lake frog - 50

tree frog - 66 toad - 49

sharp-faced frog - 46 crested newt - 11

grass frog - 59 Asia Minor frog - 27

spadefoot - 57 pond frog - 18

3.3 Amphibians in science

The skin of frogs and toads secretes substances containing a huge number of different compounds. Some of them have been used by people for a long time. These are poisons. They are necessary for protection from predators, as well as various microorganisms. amphibian skeleton fish organ

In dosed form, poisons, as is known, can also be healing. Ancient oriental recipes mention poisons collected from the skin of some toads. Nowadays, scientists are particularly interested in frog poisons, which can reduce human blood pressure, dilate blood vessels, stimulate respiration and blood circulation, have a detrimental effect on helminths, accelerate the healing of wounds and protect them from suppuration. The final stage Such research should be the synthesis of these very complex compounds, which will ensure the mass production of these drugs.

Some laboratories are engaged in the isolation of protective substances. Perhaps over time they will be able to replace antibiotics that are losing their potency. Something has already been achieved: based on the components of frog venom, an effective medicine has been synthesized to combat skin fungi.

Currently, with the help of amphibians, the genetic apparatus of the cell, issues of organ regeneration, tissue compatibility, and much more are being studied. Let us only note that the first successful heart transplant in a frog was performed 53 years ago by the Soviet scientist N.P. Sinitsyn. His patients with heart transplants lived happily for many years and remained practically healthy.

Since ancient times, salamanders have been considered terribly poisonous animals. The many glands that are contained in her skin can abundantly secrete mucus, which is completely harmless, but from ancient times, according to prejudice, it was considered very poisonous. The myth that the salamander is not affected by fire is based on this same copious secretion of mucus. In reality, she is saved from its effects by the same abundantly secreted mucus.

The toxic properties of mucus, as you can see, have always been greatly exaggerated, but there is no doubt that this juice is fatal to many small animals: birds, reptiles and reptiles. The latest experiments show that the salamander's skin secretions are poisonous when injected into the bloodstream or taken orally. However, this poison is not dangerous for large animals and humans and causes only mild inflammation on the skin.

As a result of evolution, the ability to regenerate in many highly organized forms noticeably decreases and even completely disappears. In amphibians, a broken tail, a cut off finger, and even a whole leg grow back. The vitality of some amphibians is amazing; tailed amphibians are especially distinguished by this quality. A salamander or a newt can be completely frozen in water, in this state they become brittle and show absolutely no signs of life, but as soon as the ice melts, these animals awaken again and, as if nothing had happened, continue to live. When taken out of water and placed in a dry place, the newt shrinks and becomes a completely lifeless mass. But as soon as this dead lump is thrown into soda, a living newt appears again in complete well-being.

Spalanzani carried out very cruel experiments on these animals, cutting off their legs, tail, gouging out their eyes, etc., and it turned out that all these parts were completely restored, even several times. Blumenbach cut out 4/5 of the newt's eyes and was convinced that after 10 months a new eye formed, differing from the previous one only in smaller size. As for the tail and limbs, they are restored to the same size as before.

3.4 Impact of human activities

The amphibian tribe cannot be seriously threatened by their traditional enemies. The ecological balance inherent in nature is not disturbed naturally. At the same time, some species of amphibians are on the verge of extinction, which is mainly due to the anthropogenic factor - rapidly expanding human economic activity, as well as the consequences of unwise recreation and tourism. The recent decline in populations of the most beneficial tailless amphibians - frogs and toads - has been especially serious. But the purpose of these eternal workers is to maintain balance in nature. Therefore, the ever-increasing pace of technological progress, the direct and indirect impact of civilization, striking at amphibian populations, also disrupts the general ecological state Earth.

The number of reservoirs suitable for the normal life of amphibians, including their reproduction, is catastrophically decreasing. Drainage of swamps and other work to include unused ones in human agricultural activities drive tailless and tailed amphibians into the few “reservations” that have survived so far. When small bodies of water are destroyed and swamps are drained, the groundwater level decreases. The remaining reservoirs dry up, which is detrimental to the tadpoles. And the shallow lakes and swamps in winter time freeze to the bottom, causing the death of adults.

Reservoirs are not only drained, but become clogged and polluted by industrial, agricultural and household substances. Moreover, this happens not only as a result of economic activity, but also as a result of the “costs” of tourism and recreation for people who have not received environmental education. In addition, some species of amphibians, such as the reed toad, are close to extinction from coastal areas due to the fact that natural areas are not left there when creating places for recreation, equipping beaches, and laying roads.

To enrich the soil nutrients it is entered into a large number of fertilizers of natural and artificial origin, and to destroy field pests - toxic substances. All this falls with rain and melt water from small and large reservoirs, having a detrimental effect on their inhabitants and coastal living beings. This changes the ecological balance, which affects the food resources of various animals, including amphibians, affecting the very life of individuals. The so-called “chemical war,” while benefiting certain sectors of agriculture, turns into disaster for the peaceful inhabitants of the Earth.

In many countries, people pay with the loss of the number of their own living beings for some positive role of imported animals. Although his animals are no less useful to him, but in other industries. For example, the introduction of such large and aggressive animals as the aga toad or bullfrog from other areas is harmful to the population of amphibian hosts. When the giant aga toad (25 cm long) was brought to Australia from the USA, they counted only on its benefits. Due to its great gluttony, the toad helped actively fight sugar cane pests. But gradually her food habits began to have a negative impact on local animals. First, the snakes disappeared because they died from the poison of the toads after eating them. In this regard, rodents and insects began to actively reproduce, the numbers of which were kept in check by snakes. The number of bees, plant pollinators and honey collectors, to which the aga toad has a special predilection, has decreased. This is what human disruption of ecological balance can lead to.

Conclusion

Thus, hamphibians- animals that are extremely important to humans. Firstly, by feeding on small animals, amphibians, especially frogs and toads, restrain the mass reproduction of agricultural pests. Thanks to this, they, along with insectivorous birds, are included in the category of crop protectors, friends of gardeners and gardeners. Secondly, amphibians destroy insects that are carriers of human diseases, for example, malaria mosquitoes. Thirdly, amphibians are actively used for experiments by many generations of physicians, biologists and scientists in related fields. They helped make a lot of important scientific discoveries in biology and other sciences, including bionics. In addition, amphibians are amazingly touching, gentle and often very beautiful creatures. They admire the phenomenal capabilities of their body, graceful movements and complex behavior. Amphibians, like all living beings, require humane treatment and protection.

In Paris, near the Pasteur Institute, a monument to a frog was even erected with funds raised by medical students, as a sign of respect and gratitude for the truly invaluable services of this patient, inconspicuous creature, a favorite subject of physiological and pharmacological research. The second similar monument was erected in Tokyo.

Bibliography

1. Akimushkin I.I. Animal world: Birds, fish, amphibians and reptiles. 2nd ed., rev. and additional - M.: Mysl, 1989 - 462 p.: ill.

2. Bram A. E. Animal life. T. 1 - 6. - M., 1949

3. Makhlin M.D. About those who are not loved. -- Alma-Ata: “Kainar”, 1986

4. Nikishov A. I., Sharova I. Kh. Biology: Animals. Textbook for grades 7 - 8. educational institutions. 5th ed. - M.: Education, 1998 - 256 p.: ill.

5. Sergeev B.F. The world of amphibians. - M.: Kolos, 1983 - 191 p.

6. Animal life in seven volumes. Volume five. Edited by A.G. Bannikov's edition has been revised three times; M. Education 1985

7. Amphibians and reptiles. Ivanter E.V.; Petrozavodsk 1995

8. Amphibians and reptiles of the USSR. Bannikov A.G.; M. Thought 1971

9. Frog. Terentyev P.V.;M. 1950

10. Freaks of nature. Igor Akimushkin; M. Mysl 1981

11. Electronic resources: http://www.portal-slovo.ru/biology

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Conditions of existence and distribution. Amphibians belong to the group of poikilothermic (cold-blooded) animals, i.e. their body temperature is not constant and depends on the ambient temperature. The life of amphibians is highly dependent on environmental humidity.

This is determined by the large role of skin respiration in their life, complementing and sometimes even replacing imperfect pulmonary respiration. The bare skin of amphibians is always moist, since oxygen diffusion can only occur through a water film. Moisture from the surface of the skin constantly evaporates, and evaporation occurs the faster, the lower the environmental humidity. Evaporation from the surface of the skin constantly lowers body temperature, and the drier the air, the more the temperature will drop. The dependence of body temperature on air humidity in combination with poikilothermity (“cold-bloodedness”) leads to the fact that the body temperature of amphibians not only follows the temperature of the environment, as in fish or reptiles, but, due to evaporation, is usually 2-3° lower than it ( this difference can reach 8-9° when the air is drier).

The great dependence of amphibians on humidity and temperature determines their almost complete absence in deserts and subpolar countries and, conversely, a rapid increase in the number of species towards the equator and their exceptional richness in humid and warm tropical forests. So, if there are 12 species of amphibians in the Caucasus, then over vast areas Central Asia, 6 times larger than the Caucasus, only two species live - the green toad and the lake frog. Only a few species penetrate north to the Arctic Circle. Such are the grass and sharp-faced frogs and the Siberian four-toed newt.

Skin respiration plays a different role in different species of amphibians. Where the respiratory function of the skin is low, the skin becomes keratinized and evaporation from the surface decreases, and consequently, the body’s dependence on environmental humidity decreases. As a rule, the distribution of species by habitat is determined by the degree of skin participation in respiration.

Among our amphibians, the Ussuri clawed newt and the Semirechensk newt are among the species that constantly live in water, in which gas exchange occurs almost exclusively through skin respiration alone. Our green frogs do not move any significant distance from bodies of water, receiving more than 50% of the oxygen they need for breathing through their skin.

Land amphibians include almost all toads, which evaporate half as much water from the surface of the body as green frogs. Some land amphibians spend a significant part of their time buried in the ground, like our spadefoot spadefoot. A number of species live in trees; An example of a typical tree form is the tree frog, found in our region. southern regions the European part of Russia, the Caucasus and the Far East.

The peculiarity of the structure of the skin of amphibians has another ecological consequence - representatives of this class are not able to live in salt water with a concentration exceeding 1.0-1.5%, since their osmotic balance is disturbed.