The land-air environment is characterized by the features of ecological conditions that have formed specific adaptations in land plants and animals, which is reflected in a variety of morphological, anatomical, physiological, biochemical and behavioral adaptations.

The low density of atmospheric air makes it difficult to maintain the shape of the body, because plants and animals have formed a support system. In plants, these are mechanical tissues (bast and wood fibers) that provide resistance to static and dynamic loads: wind, rain, snow cover. The stressed state of the cell wall (turgor), caused by the accumulation of fluid with high osmotic pressure in the vacuoles of cells, determines the elasticity of leaves, grass stems, and flowers. In animals, the body is supported by the hydroskeleton (in roundworms), the external skeleton (in insects), and the internal skeleton (in mammals).

The low density of the medium facilitates the movement of animals. Many terrestrial species are capable of flight (active or gliding) - birds and insects, there are also representatives of mammals, amphibians and reptiles. Flight is associated with movement and search for prey. Active flight is possible due to modified forelimbs, developed pectoral muscles. In gliding animals, skin folds have formed between the fore and hind limbs, which stretch and play the role of a parachute.

The high mobility of air masses has formed in plants the oldest method of pollinating plants by the wind (anemophily), which is characteristic of many plants in the middle band and settling with the help of the wind. This ecological group of organisms (aeroplankton) has adapted due to the large relative surface area due to parachutes, wings, outgrowths and even cobwebs, or due to very small sizes.

Low atmospheric pressure, which is normally 760 mmHg (or 101,325 Pa), small pressure drops, have formed sensitivity to strong pressure drops in almost all land inhabitants. The upper limit of life for most vertebrates is about 6,000 m. A decrease in atmospheric pressure with an increase in altitude reduces the solubility of oxygen in the blood. This increases the frequency of breathing, and as a result, rapid breathing leads to dehydration. This simple dependence is not typical only for rare species of birds and some invertebrates.

The gas composition of the ground-air environment is characterized by a high oxygen content (more than 20 times higher than in the aquatic environment). This allows the animals to have very high metabolic rates. Therefore, only on land could homoithermia (the ability to maintain a constant body temperature, mainly due to internal energy) arise.

The value of temperature in the life of organisms is determined by the influence on the rate of biochemical reactions. Increasing the temperature (up to 60 °C) of the environment causes protein denaturation in organisms. A strong drop in temperature leads to a decrease in the metabolic rate and, as a critical condition, freezing of water in cells (ice crystals in cells violate the integrity of intracellular structures). Basically, on land, living organisms can exist only within 0 ° - +50 °, tk. these temperatures are compatible with the course of basic life processes. However, each species has its own upper and lower lethal temperature values, the value of temperature inhibition and temperature optimum.

Organisms whose vital activity and activity depend on external heat (microorganisms, fungi, plants, invertebrates, cyclostomes, fish, amphibians, reptiles) are called poikilotherms. Among them are stenotherms (cryophiles - adapted to small differences in low temperatures and thermophiles - adapted to small differences in high temperatures) and eurytherms, which can exist within a large temperature amplitude. Adaptations to endure low temperatures, which make it possible to regulate metabolism for a long time, are carried out in organisms in two ways: a) the ability to biochemical and physiological rearrangements - the accumulation of antifreezes that lower the freezing point of liquids in cells and tissues and therefore prevent the formation of ice; change in the set, concentration and activity of enzymes, change; b) endurance to freezing (cold resistance) is a temporary cessation of the active state (hypobiosis or cryptobiosis) or the accumulation of glycerol, sorbitol, mannitol in the cells, which prevent the crystallization of the liquid.

Eurytherms have a well-developed ability to transition into a latent state with significant temperature deviations from the optimal value. After cold oppression, organisms at a certain temperature restore normal metabolism, and this temperature value is called the temperature threshold of development, or the biological zero of development.

The basis of seasonal rearrangements in species - eurytherms, which are widespread, is acclimation (shift of the temperature optimum), when some genes are inactivated and others are switched on, which are responsible for replacing some enzymes with others. This phenomenon is found in different parts of the range.

In plants, metabolic heat is extremely negligible; therefore, their existence is determined by the air temperature within the habitat. Plants adapt to tolerate fairly large temperature fluctuations. The main thing in this case is transpiration, which cools the surface of the leaves when overheated; leaf blade reduction, leaf mobility, pubescence, wax coating. Plants adapt to cold conditions with the help of growth forms (dwarfing, cushion growth, trellis), coloring. All this applies to physical thermoregulation. Physiological thermoregulation is the fall of leaves, the death of the ground part, the transfer of free water to a bound state, the accumulation of antifreeze, etc.).

Poikilothermic animals have the possibility of evaporative thermoregulation associated with their movement in space (amphibians, reptiles). They choose the most optimal conditions, produce a lot of internal (endogenous) heat in the process of muscle contraction or muscle trembling (warm up the muscles during movement). Animals have behavioral adaptations (posture, shelters, burrows, nests).

Homeothermal animals (birds and mammals) have a constant body temperature and are little dependent on the ambient temperature. They are characterized by adaptations based on a sharp increase in oxidative processes as a result of the perfection of the nervous, circulatory, respiratory and other organ systems. They have biochemical thermoregulation (when the air temperature drops, lipid metabolism increases; oxidative processes increase, especially in skeletal muscles; there is a specialized brown adipose tissue in which all the released chemical energy goes to the formation of ATP, and to warm the body; the amount of food consumed increases) . But such thermoregulation has climatic limitations (unfavorable in winter, in polar conditions, in summer in the tropical and equatorial zones).

Physical thermoregulation is environmentally beneficial (reflex constriction and expansion of skin blood vessels, thermal insulation effect of fur and feathers, countercurrent heat exchange), because is carried out due to the preservation of heat in the body (Chernova, Bylova, 2004).

Behavioral thermoregulation of homoiterms is characterized by diversity: change in posture, search for shelters, construction of complex burrows, nests, migrations, group behavior, etc.

Light is the most important environmental factor for organisms. The processes that occur under the action of light are photosynthesis (1-5% of the incident light is used), transpiration (75% of the incident light is used to evaporate water), synchronization of vital activity, movement, vision, vitamin synthesis.

The morphology of plants and the structure of plant communities are organized for the most efficient absorption of solar energy. The light-receiving surface of plants on the Earth is 4 times larger than the surface of the planet (Akimova and Khaskin, 2000). For living organisms, the wavelength is important, because. rays of different lengths have different biological significance: infrared radiation (780 - 400 nm) acts on the thermal centers of the nervous system, regulating oxidative processes, motor reactions, etc., ultraviolet rays (60 - 390 nm) acting on integumentary tissues, contribute to the production of various vitamins, stimulate cell growth and reproduction.

Visible light is of particular importance, because For plants, the qualitative composition of light is important. In the spectrum of rays emit photosynthetic active radiation (PAR). The wavelength of this spectrum lies within 380 - 710 (370 - 720 nm).

The seasonal dynamics of illumination is associated with astronomical patterns, the seasonal climatic rhythm of a given area, and is expressed differently at different latitudes. For the lower tiers, the phenological state of vegetation is also superimposed on these regularities. Of great importance is the daily rhythm of changes in illumination. The course of radiation is disturbed by changes in the state of the atmosphere, clouds, etc. (Goryshina, 1979).

The plant is an opaque body that partially reflects light, absorbs and transmits. In the cells and tissues of the leaves there are various formations that provide absorption and transmission of light. To increase the productivity of the plant, they increase the total area and the number of photosynthetic elements, which is achieved by the multi-storey arrangement of leaves on the plant; tiered arrangement of plants in the community.

In relation to the strength of illumination, three groups are distinguished: light-loving, shade-loving, shade-tolerant, which differ in anatomical and morphological adaptations (in light-loving plants, the leaves are smaller, mobile, pubescent, have a waxy coating, thick cuticle, crystalline exclusions, etc. in shade-loving plants, the leaves are large , chloroplasts are large and numerous); physiological adaptations (different values ​​of light compensation).

The response to day length (light duration) is called photoperiodism. In plants, such important processes as flowering, seed formation, growth, transition to a state of dormancy, leaf fall are associated with seasonal changes in day length and temperature. For flowering of some plants, a day length of more than 14 hours is needed, for others 7 hours are enough, and others bloom regardless of the length of the day.

For animals, light is informational. First of all, according to daily activity, animals are divided into diurnal, twilight, and nocturnal. The organs that help to navigate in space are the eyes. Different organisms have different stereoscopic vision - in humans, the total vision is 180 ° - stereoscopic-140 °, in the rabbit - total 360 °, stereoscopic 20 °. Binocular vision is mainly characteristic of predatory animals (cats and birds). In addition, phototaxis (movement to light) is determined by the reaction to light,

reproduction, navigation (orientation to the position of the Sun), bioluminescence. Light is a signal to attract individuals of the opposite sex.

The most important environmental factor in the life of terrestrial organisms is water. It is necessary to maintain the structural integrity of cells, tissues, the whole organism, because. is the main part of the protoplasm of cells, tissues, plant and animal juices. Thanks to water, biochemical reactions are carried out, the supply of nutrients, gas exchange, excretion, etc. The water content in the body of plants and animals is quite high (83-86% in grass leaves, 79-82% in tree leaves, 40-55% in tree trunks, in the bodies of insects - 46-92%, amphibians - up to 93%, mammals - 62-83%).

Existence in a land-air environment poses an important problem for organisms to maintain water in the body. Therefore, the form and function of land plants and animals are adapted to protect against desiccation. In the life of plants, the intake of water, its conduction and transpiration, water balance are important (Walter, 1031, 1937, Schafer, 1956). Changes in water balance are best reflected by the sucking power of the roots.

The plant can absorb water from the soil as long as the sucking power of the roots can compete with the sucking power of the soil. A highly branched root system provides a large area of ​​contact between the absorbing part of the root and soil solutions. The total length of the roots can reach 60 km. The sucking power of the roots varies depending on the weather, on environmental properties. The larger the suction surface of the roots, the more water is absorbed.

According to the regulation of water balance, plants are divided into poikihydric (algae, mosses, ferns, some flowering plants) and homoihydric (most higher plants).

In relation to the water regime, ecological groups of plants are distinguished.

1. Hygrophytes are terrestrial plants that live in humid habitats with high air humidity and soil water supply. Characteristic signs of hygrophytes are thick, slightly branched roots, air-filled cavities in tissues, and open stomata.

2. Mesophytes - plants of moderately humid habitats. Their ability to tolerate soil and atmospheric drought is limited. They can be found in arid habitats - rapidly developing in a short period. Characterized by a well-developed root system with numerous root hairs, regulation of the intensity of transpiration.

3. Xerophytes - plants of dry habitats. These are drought-resistant plants, dry-bearers. Steppe xerophytes can lose up to 25% of water without damage, desert xerophytes - up to 50% of the water they contain (for comparison, forest mesophytes wither when 1% of the water contained in the leaves is lost). According to the nature of the anatomical, morphological and physiological adaptations that ensure the active life of these plants with a lack of moisture, xerophytes are divided into succulents (they have fleshy and succulent leaves and stems, are able to accumulate large amounts of water in tissues, develop a small sucking force and absorb moisture from atmospheric precipitation) and sclerophytes (dry-looking plants that intensively evaporate moisture have narrow and small leaves that sometimes roll into a tube, are able to withstand severe dehydration, the sucking power of the roots can be up to several tens of atmospheres).

In different groups of animals, in the process of adaptation to the conditions of terrestrial existence, the main thing was the prevention of water loss. Animals get water in different ways - through drinking, with juicy food, as a result of metabolism (due to the oxidation and breakdown of fats, proteins and carbohydrates). Some animals can absorb water through covers of moist substrate or air. Water losses occur as a result of evaporation from the integument, evaporation from the mucous membranes of the respiratory tract, excretion of urine and undigested food debris. Animals that receive water through drinking depend on the location of water bodies (large mammals, many birds).

An important factor for animals is air humidity, because. this indicator determines the amount of evaporation from the surface of the body. That is why the structure of the integument of the body matters for the water balance of the animal organism. In insects, a decrease in water evaporation from the body surface is provided by an almost impenetrable cuticle and specialized excretory organs (Malpighian tubes), which secrete an almost insoluble metabolic product, and spiracles, which reduce water loss through the gas exchange system - through the trachea and tracheoles.

In amphibians, the bulk of water enters the body through the permeable skin. Skin permeability is regulated by a hormone secreted by the posterior pituitary gland. Amphibians excrete very large amounts of dilute urine that is hypotonic to body fluids. In dry conditions, amphibians can reduce water loss in the urine. In addition, these animals can accumulate water in the bladder and subcutaneous lymphatic spaces.

Reptiles have many adaptations of different levels - morphological (keratinized skin prevents water loss), physiological (lungs located inside the body, which reduces water loss), biochemical (uric acid is formed in the tissues, which is excreted without much loss of moisture, tissues are able to tolerate an increase in concentration salts by 50%).

In birds, the evaporation rate is low (the skin is relatively impermeable to water, there are no sweat glands and feathers). Birds lose water (up to 35% of body weight per day) when breathing due to high ventilation in the lungs and high body temperature. Birds have a process of reabsorbing water from some of the water in their urine and faeces. Some sea birds (penguins, gannets, cormorants, albatrosses), which eat fish and drink sea water, have salt glands located in their eye sockets, with the help of which excess salts are excreted from the body.

In mammals, the organs of excretion and osmoregulation are paired, complexly arranged kidneys, which are supplied with blood and regulate the composition of the blood. This ensures a constant composition of the intracellular and interstitial fluid. Relatively stable osmotic pressure of blood is maintained due to the balance between the intake of water with drinking and the loss of water with exhaled air, sweat, excreted by feces and urine. Responsible for the fine regulation of osmotic pressure is the antidiuretic hormone (ADH), which is secreted from the posterior pituitary gland.

Among animals, groups are distinguished: hygrophiles, in which the mechanisms for regulating water metabolism are poorly developed or absent at all (these are moisture-loving animals that need high humidity - springtails, wood lice, mosquitoes, other arthropods, terrestrial mollusks and amphibians); xerophiles, which have well-developed mechanisms for regulating water metabolism and adaptation to water retention in the body, living in arid conditions; mesophiles living in conditions of moderate humidity.

Relief is an indirectly acting ecological factor in the ground-air environment. All landforms affect the distribution of plants and animals through changes in the hydrothermal regime or soil moisture.

In the mountains at different heights above sea level, climatic conditions change, resulting in altitudinal zonation. Geographical isolation in the mountains contributes to the formation of endemics, the preservation of relic species of plants and animals. River floodplains contribute to the northward movement of more southern groups of plants and animals. Of great importance is the exposure of the slopes, which creates conditions for the spread of heat-loving communities to the north along the southern slopes, and cold-loving communities to the south along the northern slopes (“rule of advance”, V.V. Alyokhina).

The soil exists only in the ground-air environment and is formed as a result of the interaction of the age of the territory, parent rock, climate, topography, plants and animals, and human activities. Of ecological importance is the mechanical composition (size of mineral particles), chemical composition (pH of aqueous solution), soil salinity, soil richness. Soil characteristics also act on living organisms as indirect factors, changing the thermo-hydrological regime, causing plants (primarily) to adapt to the dynamics of these conditions and influencing the spatial differentiation of organisms.

General characteristics. In the course of evolution, the ground-air environment was mastered much later than the water. Life on land required such adaptations that became possible only with a relatively high level of organization of both plants and animals. A feature of the land-air environment of life is that the organisms that live here are surrounded by a gaseous environment characterized by low humidity, density and pressure, high oxygen content. As a rule, animals in this environment move along the soil (solid substrate), and plants take root in it.

In the ground-air environment, the operating environmental factors have a number of characteristic features: higher light intensity in comparison with other environments, significant temperature fluctuations, changes in humidity depending on the geographical location, season and time of day.

In the process of evolution, living organisms of the terrestrial-air environment have developed characteristic anatomical, morphological, physiological, behavioral and other adaptations. For example, organs have appeared that provide direct assimilation of atmospheric oxygen during respiration (lungs and tracheae of animals, stomata of plants). Received a strong development of skeletal formations (animal skeleton, mechanical and supporting tissues of plants) that support the body
under conditions of low density of the medium. Adaptations have been developed to protect against adverse factors, such as the frequency and rhythm of life cycles, the complex structure of integuments, thermoregulation mechanisms, etc. seeds, fruits and pollen of plants, flying animals.

Low air density determines its low lifting force and insignificant bearing capacity. All inhabitants of the air environment are closely connected with the surface of the earth, which serves them for attachment and support. The density of the air medium does not provide high resistance to organisms when they move along the surface of the earth, however, it makes it difficult to move vertically. For most organisms, staying in the air is associated only with dispersal or the search for prey.

The small lifting force of air determines the limiting mass and size of terrestrial organisms. The largest animals living on the surface of the earth are smaller than the giants of the aquatic environment. Large mammals (the size and weight of a modern whale) could not live on land, as they were crushed by their own weight.

Low air density creates a slight resistance to movement. 75% of all land animal species are capable of active flight.

Winds increase the return of moisture and heat to animals and plants. With wind, heat is more easily tolerated and frosts are harder, and organisms dry out and cool faster. The wind causes a change in the intensity of transpiration in plants, plays a role in the pollination of anemophilous plants.

Gas composition of air- oxygen - 20.9%, nitrogen - 78.1%, inert gases - 1%, carbon dioxide - 0.03% by volume. Oxygen increases the metabolism of terrestrial organisms.

Light mode. The amount of radiation reaching the Earth's surface is determined by the geographic latitude of the area, the length of the day, the transparency of the atmosphere and the angle of incidence of the sun's rays. Illumination on the Earth's surface varies widely.

Trees, shrubs, plant crops shade the area, create a special microclimate, weakening the radiation.

Thus, in different habitats, not only the intensity of radiation, but also its spectral composition, the duration of illumination of plants, the spatial and temporal distribution of light of different intensities, etc. . In relation to light, three main groups of plants are distinguished: light-loving (heliophytes), shade-loving (sciophytes) and shade-tolerant.

Plants of the ground-air environment have developed anatomical, morphological, physiological, and other adaptations to various conditions of the light regime:

An example of anatomical and morphological adaptations is a change in appearance under different light conditions, for example, the unequal size of leaf blades in plants related in systematic position, living under different lighting conditions (meadow bell Cumpanula patula and forest bell C. trachelium, field violet Viola arvensis, growing in fields, meadows, edges, and forest violets - V. mirabilis).

In heliophyte plants, the leaves are oriented towards reducing the arrival of radiation during the most “dangerous” daytime hours. Leaf blades are located vertically or at a large angle to the horizontal plane, so during the day the leaves receive mostly gliding rays.

In shade-tolerant plants, the leaves are arranged so as to receive the maximum amount of incident radiation.

A peculiar form of physiological adaptation with a sharp lack of light is the loss of the plant's ability to photosynthesis, the transition to heterotrophic nutrition with ready-made inorganic substances. Sometimes such a transition became irreversible due to the loss of chlorophyll by plants, for example, orchids of shady spruce forests (Goodyera repens, Weottia nidus avis), aquatic worms (Monotropa hypopitys).

Physiological adaptations of animals. For the vast majority of terrestrial animals with day and night activity, vision is one of the ways of orientation, which is important for the search for prey. Many animal species also have color vision. In this regard, adaptive features arose in animals, especially victims. These include protective, masking, and warning coloration, protective resemblance, mimicry, etc. The appearance of brightly colored flowers of higher plants is also associated with the characteristics of the visual apparatus of pollinators and, ultimately, with the light regime of the environment.

Water regime. Moisture deficiency is one of the most significant features of the land-air environment of life. The evolution of terrestrial organisms took place by adapting to the extraction and conservation of moisture.

() cages (rain, hail, snow), in addition to providing water and creating moisture reserves, often play another ecological role. For example, during heavy rains, the soil does not have time to absorb moisture, water flows quickly in strong streams and often carries weakly rooted plants, small animals and fertile soil into lakes and rivers.

Hail also has a negative effect on plants and animals. Crops of agricultural crops in some fields are sometimes completely destroyed by this natural disaster.

The ecological role of snow cover is diverse, for plants whose renewal buds are in the soil or near its surface, for many small animals, snow plays the role of a heat-insulating cover, protecting it from low winter temperatures. For large animals, winter snow cover often prevents them from foraging and moving around, especially when an ice crust forms on the surface. Often, during snowy winters, the death of roe deer and wild boars is observed.

A large amount of snowfall also has a negative effect on plants. In addition to mechanical damage in the form of snow breaks or snowfalls, a thick layer of snow can lead to dampening of plants, and during snowmelt, especially in a long spring, to wetting of plants.

Temperature regime. A distinctive feature of the ground-air environment is the large range of temperature fluctuations. In most land areas, daily and annual temperature amplitudes are tens of degrees.

Terrestrial plants occupy a zone adjacent to the soil surface, i.e., to the “interface”, on which the transition of incident rays from one medium to another takes place - from transparent to opaque. A special thermal regime is created on this surface: during the day there is strong heating due to the absorption of heat rays, at night - strong cooling due to radiation. Therefore, the surface air layer experiences the sharpest diurnal temperature fluctuations, which are most pronounced over bare soil.

In the ground-air environment, life conditions are complicated by the existence of weather changes. Weather is the continuously changing state of the atmosphere near the earth's surface, up to about 20 km altitude. Weather variability is manifested in the constant variation of environmental factors: temperature, air humidity, cloudiness, precipitation, strength, wind direction. The long-term weather regime characterizes the climate of the area. The climate is determined by the geographical conditions of the area. Each habitat is characterized by a certain ecological climate, i.e., the climate of the surface air layer, or ecoclimate.

Geographical zonality and zonality. The distribution of living organisms on Earth is closely related to geographical zones and zones. On the surface of the globe, 13 geographical zones are distinguished, which change from the equator to the poles and from the oceans to the depths of the continents. Within the belts, latitudinal and meridional, or longitudinal natural zones are distinguished. The former stretch from west to east, the latter from north to south. Each climatic zone is characterized by a peculiar vegetation and animal population. Tropical forests, floodplains, prairies and forests of the subtropics and transition zone are the most rich in life and productive. Deserts, meadows and steppes are less productive. One of the important conditions for the variability of organisms and their zonal distribution on earth is the variability of the chemical composition of the environment. Along with horizontal zonality, altitudinal or vertical zonality is clearly manifested in the terrestrial environment. The vegetation of the mountainous countries is richer than on the adjacent plains. Adaptations to life in the mountains: plants are dominated by a pillow-shaped life form, perennials, which have developed adaptations to strong ultraviolet radiation and reduced transpiration. In animals, the relative volume of the heart increases, and the content of hemoglobin in the blood increases. Animals: mountain turkeys, mountain finches, larks, vultures, rams, goats, chamois, yaks, bears, lynxes.

Life on land required such adaptations that were possible only in highly organized living organisms. The ground-air environment is more difficult for life, it is characterized by a high oxygen content, a small amount of water vapor, low density, etc. This greatly changed the conditions of respiration, water exchange and movement of living beings.

The low air density determines its low lifting force and insignificant bearing capacity. Air organisms must have their own support system that supports the body: plants - a variety of mechanical tissues, animals - a solid or hydrostatic skeleton. In addition, all the inhabitants of the air environment are closely connected with the surface of the earth, which serves them for attachment and support.

Low air density provides low movement resistance. Therefore, many land animals have acquired the ability to fly. 75% of all terrestrial creatures, mainly insects and birds, have adapted to active flight.

Due to the mobility of air, the vertical and horizontal flows of air masses existing in the lower layers of the atmosphere, passive flight of organisms is possible. In this regard, many species have developed anemochory - resettlement with the help of air currents. Anemochory is characteristic of spores, seeds and fruits of plants, protozoan cysts, small insects, spiders, etc. Organisms passively transported by air currents are collectively called aeroplankton.

Terrestrial organisms exist in conditions of relatively low pressure due to the low density of air. Normally, it is equal to 760 mmHg. As altitude increases, pressure decreases. Low pressure may limit the distribution of species in the mountains. For vertebrates, the upper limit of life is about 60 mm. A decrease in pressure entails a decrease in oxygen supply and dehydration of animals due to an increase in the respiratory rate. Approximately the same limits of advance in the mountains have higher plants. Somewhat more hardy are the arthropods that can be found on glaciers above the vegetation line.

Gas composition of air. In addition to the physical properties of the air environment, its chemical properties are very important for the existence of terrestrial organisms. The gas composition of air in the surface layer of the atmosphere is quite homogeneous in terms of the content of the main components (nitrogen - 78.1%, oxygen - 21.0%, argon - 0.9%, carbon dioxide - 0.003% by volume).

The high oxygen content contributed to an increase in the metabolism of terrestrial organisms compared to primary aquatic ones. It was in the terrestrial environment, on the basis of the high efficiency of oxidative processes in the body, that animal homeothermia arose. Oxygen, due to its constant high content in the air, is not a limiting factor for life in the terrestrial environment.

The content of carbon dioxide can vary in certain areas of the surface layer of air within fairly significant limits. Increased air saturation with CO? occurs in zones of volcanic activity, near thermal springs and other underground outlets of this gas. In high concentrations, carbon dioxide is toxic. In nature, such concentrations are rare. The low content of CO 2 inhibits the process of photosynthesis. Under indoor conditions, you can increase the rate of photosynthesis by increasing the concentration of carbon dioxide. This is used in the practice of greenhouses and greenhouses.

Air nitrogen for most inhabitants of the terrestrial environment is an inert gas, but individual microorganisms (nodule bacteria, nitrogen bacteria, blue-green algae, etc.) have the ability to bind it and involve it in the biological cycle of substances.

Moisture deficiency is one of the essential features of the ground-air environment of life. The whole evolution of terrestrial organisms was under the sign of adaptation to the extraction and conservation of moisture. The modes of environmental humidity on land are very diverse - from the complete and constant saturation of air with water vapor in some areas of the tropics to their almost complete absence in the dry air of deserts. The daily and seasonal variability of water vapor content in the atmosphere is also significant. The water supply of terrestrial organisms also depends on the mode of precipitation, the presence of reservoirs, soil moisture reserves, the proximity of groundwater, and so on.

This led to the development of adaptations in terrestrial organisms to various water supply regimes.

Temperature regime. The next distinguishing feature of the air-ground environment is significant temperature fluctuations. In most land areas, daily and annual temperature amplitudes are tens of degrees. The resistance to temperature changes in the environment of terrestrial inhabitants is very different, depending on the particular habitat in which they live. However, in general, terrestrial organisms are much more eurythermic than aquatic organisms.

The conditions of life in the ground-air environment are complicated, in addition, by the existence of weather changes. Weather - continuously changing states of the atmosphere near the borrowed surface, up to a height of about 20 km (troposphere boundary). Weather variability is manifested in the constant variation of the combination of such environmental factors as temperature, air humidity, cloudiness, precipitation, wind strength and direction, etc. The long-term weather regime characterizes the climate of the area. The concept of "Climate" includes not only the average values ​​of meteorological phenomena, but also their annual and daily course, deviation from it and their frequency. The climate is determined by the geographical conditions of the area. The main climatic factors - temperature and humidity - are measured by the amount of precipitation and the saturation of the air with water vapor.

For most terrestrial organisms, especially small ones, the climate of the area is not so much important as the conditions of their immediate habitat. Very often, local elements of the environment (relief, exposition, vegetation, etc.) change the regime of temperatures, humidity, light, air movement in a particular area in such a way that it differs significantly from the climatic conditions of the area. Such modifications of the climate, which take shape in the surface layer of air, are called the microclimate. In each zone, the microclimate is very diverse. Microclimates of very small areas can be distinguished.

The light regime of the ground-air environment also has some features. The intensity and amount of light here are the greatest and practically do not limit the life of green plants, as in water or soil. On land, the existence of extremely photophilous species is possible. For the vast majority of terrestrial animals with diurnal and even nocturnal activity, vision is one of the main ways of orientation. In terrestrial animals, vision is essential for finding prey, and many species even have color vision. In this regard, the victims develop such adaptive features as a defensive reaction, masking and warning coloration, mimicry, etc. In aquatic life, such adaptations are much less developed. The emergence of brightly colored flowers of higher plants is also associated with the peculiarities of the apparatus of pollinators and, ultimately, with the light regime of the environment.

The relief of the terrain and the properties of the soil are also the conditions for the life of terrestrial organisms and, first of all, plants. The properties of the earth's surface that have an ecological impact on its inhabitants are united by "edaphic environmental factors" (from the Greek "edafos" - "soil").

In relation to different properties of soils, a number of ecological groups of plants can be distinguished. So, according to the reaction to the acidity of the soil, they distinguish:

1) acidophilic species - grow on acidic soils with a pH of at least 6.7 (plants of sphagnum bogs);

2) neutrophilic - tend to grow on soils with a pH of 6.7–7.0 (most cultivated plants);

3) basiphilic - grow at a pH of more than 7.0 (mordovnik, forest anemone);

4) indifferent - can grow on soils with different pH values ​​(lily of the valley).

Plants also differ in relation to soil moisture. Certain species are confined to different substrates, for example, petrophytes grow on stony soils, and pasmophytes inhabit free-flowing sands.

The terrain and the nature of the soil affect the specifics of the movement of animals: for example, ungulates, ostriches, bustards living in open spaces, hard ground, to enhance repulsion when running. In lizards that live in loose sands, the fingers are fringed with horny scales that increase support. For terrestrial inhabitants digging holes, dense soil is unfavorable. The nature of the soil in certain cases affects the distribution of terrestrial animals that dig holes or burrow into the ground, or lay eggs in the soil, etc.

Water as a habitat has a number of specific properties, such as high density, strong pressure drops, relatively low oxygen content, strong absorption of sunlight, etc. Reservoirs and their individual sections differ, in addition, in the salt regime, the speed of horizontal movements (currents) , the content of suspended particles. For the life of benthic organisms, the properties of the soil, the mode of decomposition of organic residues, etc. are important. Therefore, along with adaptations to the general properties of the aquatic environment, its inhabitants must also be adapted to various particular conditions. The inhabitants of the aquatic environment received a common name in ecology hydrobionts. They inhabit the oceans, continental waters and groundwater. In any reservoir, zones can be distinguished according to the conditions.

In the ocean and its constituent seas, two ecological areas are primarily distinguished: the water column - pelagial and the bottom benthal (Fig. 38). Depending on the depth, benthal is divided into sublittoral zone - an area of ​​​​smooth decrease in land to a depth of about 200 m, bathyal– steep slope area and abyssal zone– an area of ​​the oceanic bed with an average depth of 3–6 km. Even deeper areas of the benthal, corresponding to the depressions of the ocean floor, are called ultraabyssal. The edge of the coast that is flooded at high tide is called littoral. Above the level of the tides, the part of the coast moistened by the splashes of the surf is called supralittoral.

Rice. 38. Ecological zones of the World Ocean

It is natural that, for example, the inhabitants of the sublittoral live in conditions of relatively low pressure, daytime sunlight, and often quite significant changes in temperature. The inhabitants of the abyssal and ultra-abyssal depths exist in darkness, at a constant temperature and a monstrous pressure of several hundred, and sometimes about a thousand atmospheres. Therefore, the mere indication of which zone of the Bentali is inhabited by one or another species of organisms already indicates what general ecological properties it should have. The entire population of the ocean floor was named benthos.

Organisms that live in the water column, or pelagial, are pelagos. The pelagial is also divided into vertical zones corresponding in depth to the benthal zones: epipelagial, bathypelagial, abyssopelagial. The lower boundary of the epipelagic zone (no more than 200 m) is determined by the penetration of sunlight in an amount sufficient for photosynthesis. Photosynthetic plants cannot exist deeper than these zones. Only microorganisms and animals live in the twilight bathyal and dark abyssal depths. Different ecological zones are also distinguished in all other types of water bodies: lakes, swamps, ponds, rivers, etc. The variety of hydrobionts that have mastered all these habitats is very large.

Density of water is a factor that determines the conditions for the movement of aquatic organisms and pressure at different depths. For distilled water, the density is 1 g/cm3 at 4°C. The density of natural waters containing dissolved salts may be higher, up to 1.35 g/cm 3 . The pressure increases with depth by approximately 1 10 5 Pa (1 atm) for every 10 m on average.

Due to the sharp pressure gradient in water bodies, hydrobionts are generally much more eurybatic than land organisms. Some species, distributed at different depths, endure pressure from several to hundreds of atmospheres. For example, holothurians of the genus Elpidia and worms Priapulus caudatus inhabit from the coastal zone to the ultraabyssal. Even freshwater inhabitants, such as ciliates-shoes, suvoyi, swimming beetles, etc., withstand up to 6 10 7 Pa (600 atm) in the experiment.

However, many inhabitants of the seas and oceans are relatively wall-to-wall and confined to certain depths. Stenobatnost most often characteristic of shallow and deep-sea species. Only the littoral is inhabited by the annelid worm Arenicola, mollusk molluscs (Patella). Many fish, for example from the anglerfish group, cephalopods, crustaceans, pogonophores, starfish, etc., are found only at great depths at a pressure of at least 4 10 7–5 10 7 Pa (400–500 atm).

The density of water makes it possible to lean on it, which is especially important for non-skeletal forms. The density of the medium serves as a condition for soaring in water, and many hydrobionts are adapted precisely to this way of life. Suspended organisms hovering in water are combined into a special ecological group of hydrobionts - plankton ("planktos" - soaring).

Rice. 39. An increase in the relative surface of the body in planktonic organisms (according to S. A. Zernov, 1949):

A - rod-shaped forms:

1 – diatom Synedra;

2 – cyanobacterium Aphanizomenon;

3 – peridinean alga Amphisolenia;

4 – Euglena acus;

5 – cephalopod Doratopsis vermicularis;

6 – copepod Setella;

7 – larva of Porcellana (Decapoda)

B - dissected forms:

1 – mollusk Glaucus atlanticus;

2 – worm Tomopetris euchaeta;

3 – Palinurus crayfish larva;

4 – larvae of monkfish Lophius;

5 – copepod Calocalanus pavo

Plankton includes unicellular and colonial algae, protozoa, jellyfish, siphonophores, ctenophores, winged and keeled mollusks, various small crustaceans, larvae of bottom animals, fish eggs and fry, and many others (Fig. 39). Planktonic organisms have many similar adaptations that increase their buoyancy and prevent them from sinking to the bottom. These adaptations include: 1) a general increase in the relative surface of the body due to a decrease in size, flattening, elongation, the development of numerous outgrowths or bristles, which increases friction against water; 2) a decrease in density due to the reduction of the skeleton, the accumulation in the body of fats, gas bubbles, etc. In diatoms, reserve substances are deposited not in the form of heavy starch, but in the form of fat drops. The night light Noctiluca is distinguished by such an abundance of gas vacuoles and fat droplets in the cell that the cytoplasm in it looks like strands that merge only around the nucleus. Siphonophores, a number of jellyfish, planktonic gastropods, and others also have air chambers.

Seaweed (phytoplankton) hover passively in the water, while most planktonic animals are capable of active swimming, but to a limited extent. Planktonic organisms cannot overcome currents and are transported by them over long distances. many kinds zooplankton however, they are capable of vertical migrations in the water column for tens and hundreds of meters, both due to active movement and by regulating the buoyancy of their body. A special kind of plankton is the ecological group neuston ("nein" - to swim) - the inhabitants of the surface film of water on the border with the air.

The density and viscosity of water greatly affect the possibility of active swimming. Animals capable of fast swimming and overcoming the force of currents are combined into an ecological group. nekton ("nektos" - floating). Representatives of nekton are fish, squid, dolphins. Rapid movement in the water column is possible only in the presence of a streamlined body shape and highly developed muscles. The torpedo-shaped form is developed by all good swimmers, regardless of their systematic affiliation and the method of movement in the water: reactive, by bending the body, with the help of the limbs.

Oxygen mode. In oxygen-saturated water, its content does not exceed 10 ml per 1 liter, which is 21 times lower than in the atmosphere. Therefore, the conditions for the respiration of hydrobionts are much more complicated. Oxygen enters the water mainly due to the photosynthetic activity of algae and diffusion from the air. Therefore, the upper layers of the water column, as a rule, are richer in this gas than the lower ones. With an increase in temperature and salinity of water, the concentration of oxygen in it decreases. In layers heavily populated by animals and bacteria, a sharp deficiency of O 2 can be created due to its increased consumption. For example, in the World Ocean, depths rich in life from 50 to 1000 m are characterized by a sharp deterioration in aeration - it is 7-10 times lower than in surface waters inhabited by phytoplankton. Near the bottom of water bodies, conditions can be close to anaerobic.

Among the aquatic inhabitants there are many species that can tolerate wide fluctuations in the oxygen content in the water, up to its almost complete absence. (euryoxybionts - "oxy" - oxygen, "biont" - inhabitant). These include, for example, freshwater oligochaetes Tubifex tubifex, gastropods Viviparus viviparus. Among fish, carp, tench, crucian carp can withstand very low saturation of water with oxygen. However, a number of types stenoxybiont – they can exist only at a sufficiently high saturation of water with oxygen (rainbow trout, brown trout, minnow, ciliary worm Planaria alpina, larvae of mayflies, stoneflies, etc.). Many species are able to fall into an inactive state with a lack of oxygen - anoxybiosis - and thus experience an unfavorable period.

Breathing of hydrobionts is carried out either through the surface of the body, or through specialized organs - gills, lungs, trachea. In this case, the covers can serve as an additional respiratory organ. For example, loach fish consumes on average up to 63% of oxygen through the skin. If gas exchange occurs through the integument of the body, then they are very thin. Breathing is also facilitated by increasing the surface. This is achieved in the course of the evolution of species by the formation of various outgrowths, flattening, elongation, and a general decrease in body size. Some species with a lack of oxygen actively change the size of the respiratory surface. Tubifex tubifex worms strongly elongate the body; hydras and sea anemones - tentacles; echinoderms - ambulacral legs. Many sedentary and inactive animals renew the water around them, either by creating its directed current, or by oscillatory movements contributing to its mixing. For this purpose, bivalve mollusks use cilia lining the walls of the mantle cavity; crustaceans - the work of the abdominal or thoracic legs. Leeches, larvae of ringing mosquitoes (bloodworm), many oligochaetes sway the body, leaning out of the ground.

Some species have a combination of water and air respiration. Such are lungfish, discophant siphonophores, many pulmonary molluscs, crustaceans Gammarus lacustris, and others. Secondary aquatic animals usually retain the atmospheric type of breathing as more energetically favorable and therefore need contact with the air, for example, pinnipeds, cetaceans, water beetles, mosquito larvae, etc.

The lack of oxygen in water sometimes leads to catastrophic phenomena - zamoram, accompanied by the death of many hydrobionts. winter freezes often caused by the formation of ice on the surface of water bodies and the termination of contact with air; summer- an increase in water temperature and a decrease in the solubility of oxygen as a result.

The frequent death of fish and many invertebrates in winter is typical, for example, for the lower part of the Ob River basin, whose waters, flowing from the swampy spaces of the West Siberian Lowland, are extremely poor in dissolved oxygen. Sometimes zamora occur in the seas.

In addition to a lack of oxygen, deaths can be caused by an increase in the concentration of toxic gases in water - methane, hydrogen sulfide, CO 2, etc., formed as a result of the decomposition of organic materials at the bottom of reservoirs.

Salt mode. Maintaining the water balance of hydrobionts has its own specifics. If for terrestrial animals and plants it is most important to provide the body with water in conditions of its deficiency, then for hydrobionts it is no less important to maintain a certain amount of water in the body when it is in excess in the environment. An excessive amount of water in the cells leads to a change in their osmotic pressure and a violation of the most important vital functions.

Most aquatic life poikilosmotic: the osmotic pressure in their body depends on the salinity of the surrounding water. Therefore, the main way for aquatic organisms to maintain their salt balance is to avoid habitats with unsuitable salinity. Freshwater forms cannot exist in the seas, marine forms do not tolerate desalination. If the salinity of the water is subject to change, the animals move in search of a favorable environment. For example, during the desalination of the surface layers of the sea after heavy rains, radiolarians, marine crustaceans Calanus and others descend to a depth of 100 m. Vertebrates, higher crayfish, insects and their larvae that live in water belong to homoiosmotic species, maintaining a constant osmotic pressure in the body, regardless of the concentration of salts in the water.

In freshwater species, the body juices are hypertonic relative to the surrounding water. They are in danger of becoming overwatered unless their intake is prevented or the excess water is removed from the body. In protozoa, this is achieved by the work of excretory vacuoles, in multicellular organisms, by the removal of water through the excretory system. Some ciliates every 2–2.5 minutes release an amount of water equal to the volume of the body. The cell expends a lot of energy on “pumping out” excess water. With an increase in salinity, the work of vacuoles slows down. Thus, in Paramecium shoes, at a water salinity of 2.5% o, the vacuole pulsates with an interval of 9 s, at 5% o - 18 s, at 7.5% o - 25 s. At a salt concentration of 17.5% o, the vacuole stops working, since the difference in osmotic pressure between the cell and the external environment disappears.

If the water is hypertonic in relation to the body fluids of hydrobionts, they are threatened with dehydration as a result of osmotic losses. Protection against dehydration is achieved by increasing the concentration of salts also in the body of hydrobionts. Dehydration is prevented by water-impervious covers of homoiosmotic organisms - mammals, fish, higher crayfish, aquatic insects and their larvae.

Many poikilosmotic species go into an inactive state - suspended animation as a result of water deficiency in the body with increasing salinity. This is characteristic of species living in pools of sea water and in the littoral: rotifers, flagellates, ciliates, some crustaceans, Black Sea polychaetes Nereis divesicolor, etc. Salt hibernation- a means to survive unfavorable periods in conditions of variable salinity of water.

Truly euryhaline There are not so many species that can live in an active state in both fresh and salt water among aquatic inhabitants. These are mainly species inhabiting river estuaries, estuaries and other brackish water bodies.

Temperature regime water bodies are more stable than on land. This is due to the physical properties of water, primarily the high specific heat capacity, due to which the receipt or release of a significant amount of heat does not cause too sharp temperature changes. Evaporation of water from the surface of reservoirs, which consumes about 2263.8 J/g, prevents overheating of the lower layers, and the formation of ice, which releases the heat of fusion (333.48 J/g), slows down their cooling.

The amplitude of annual temperature fluctuations in the upper layers of the ocean is no more than 10–15 °C, in continental water bodies it is 30–35 °C. Deep layers of water are characterized by constant temperature. In equatorial waters, the average annual temperature of the surface layers is +(26–27) °C, in polar waters it is about 0 °C and lower. In hot ground springs, the water temperature can approach +100 °C, and in underwater geysers at high pressure on the ocean floor, a temperature of +380 °C has been recorded.

Thus, in reservoirs there is a fairly significant variety of temperature conditions. Between the upper layers of water with seasonal temperature fluctuations expressed in them and the lower ones, where the thermal regime is constant, there is a zone of temperature jump, or thermocline. The thermocline is more pronounced in warm seas, where the temperature difference between the outer and deep waters is greater.

Due to the more stable temperature regime of water among hydrobionts, to a much greater extent than among the population of the land, stenothermy is common. Eurythermal species are found mainly in shallow continental water bodies and in the littoral of the seas of high and temperate latitudes, where daily and seasonal temperature fluctuations are significant.

Light mode. There is much less light in water than in air. Part of the rays incident on the surface of the reservoir is reflected into the air. The reflection is stronger the lower the position of the Sun, so the day under water is shorter than on land. For example, a summer day near the island of Madeira at a depth of 30 m is 5 hours, and at a depth of 40 m it is only 15 minutes. The rapid decrease in the amount of light with depth is due to its absorption by water. Rays with different wavelengths are absorbed differently: red ones disappear close to the surface, while blue-green ones penetrate much deeper. The deepening twilight in the ocean is first green, then blue, blue and blue-violet, finally giving way to constant darkness. Accordingly, green, brown and red algae replace each other with depth, specialized in capturing light with different wavelengths.

The color of animals changes with depth in the same way. The inhabitants of the littoral and sublittoral zones are most brightly and diversely colored. Many deep-seated organisms, like cave ones, do not have pigments. In the twilight zone, red coloration is widespread, which is complementary to the blue-violet light at these depths. Additional color rays are most fully absorbed by the body. This allows the animals to hide from enemies, since their red color in blue-violet rays is visually perceived as black. Red coloration is typical for such animals of the twilight zone as sea bass, red coral, various crustaceans, etc.

In some species that live near the surface of water bodies, the eyes are divided into two parts with different ability to refract rays. One half of the eye sees in the air, the other half in the water. Such "four-eyedness" is characteristic of the whirling beetles, the American fish Anableps tetraphthalmus, one of the tropical species of blennies Dialommus fuscus. This fish sits in recesses at low tides, exposing part of its head from the water (see Fig. 26).

The absorption of light is the stronger, the lower the transparency of water, which depends on the number of particles suspended in it.

Transparency is characterized by the maximum depth at which a specially lowered white disk with a diameter of about 20 cm (Secchi disk) is still visible. The most transparent waters are in the Sargasso Sea: the disk is visible to a depth of 66.5 m. In the Pacific Ocean, the Secchi disk is visible up to 59 m, in the Indian Ocean - up to 50, in shallow seas - up to 5-15 m. The transparency of rivers is on average 1–1 .5 m, and in the most muddy rivers, for example, in the Central Asian Amu Darya and Syr Darya, only a few centimeters. The boundary of the photosynthesis zone therefore varies greatly in different water bodies. In the clearest waters euphotic zone, or zone of photosynthesis, extends to depths of no more than 200 m, twilight, or dysphotic, the zone occupies depths up to 1000–1500 m, and deeper, in aphotic zone, sunlight does not penetrate at all.

The amount of light in the upper layers of water bodies varies greatly depending on the latitude of the area and the time of year. Long polar nights greatly limit the time available for photosynthesis in the Arctic and Antarctic basins, and the ice cover makes it difficult for light to reach all freezing water bodies in winter.

In the dark depths of the ocean, organisms use the light emitted by living beings as a source of visual information. The glow of a living organism is called bioluminescence. Luminous species are found in almost all classes of aquatic animals from protozoa to fish, as well as among bacteria, lower plants and fungi. Bioluminescence appears to have reappeared multiple times in different groups at different stages of evolution.

The chemistry of bioluminescence is now fairly well understood. The reactions used to generate light are varied. But in all cases, this is the oxidation of complex organic compounds (luciferins) using protein catalysts (luciferase). Luciferins and luciferases have different structures in different organisms. During the reaction, the excess energy of the excited luciferin molecule is released in the form of light quanta. Living organisms emit light in impulses, usually in response to stimuli coming from the external environment.

Luminescence may not play a special ecological role in the life of the species, but may be a by-product of the vital activity of cells, as, for example, in bacteria or lower plants. It receives ecological significance only in animals with a sufficiently developed nervous system and organs of vision. In many species, the luminous organs acquire a very complex structure with a system of reflectors and lenses that amplify the radiation (Fig. 40). A number of fish and cephalopods, unable to generate light, use symbiotic bacteria that multiply in special organs of these animals.

Rice. 40. Luminous organs of aquatic animals (according to S. A. Zernov, 1949):

1 - deep-sea anglerfish with a flashlight over the toothed mouth;

2 - distribution of luminous organs in fish of this family. Mystophidae;

3 - the luminous organ of the fish Argyropelecus affinis:

a - pigment, b - reflector, c - luminous body, d - lens

Bioluminescence has mainly a signal value in the life of animals. Light signals can be used for orientation in the flock, attracting individuals of the opposite sex, luring victims, for masking or distraction. The flash of light can be a defense against a predator, blinding or disorienting it. For example, deep-sea cuttlefish, escaping from an enemy, release a cloud of luminous secretion, while species that live in illuminated waters use a dark liquid for this purpose. In some bottom worms - polychaetes - the luminous organs develop by the period of maturation of the reproductive products, and the females glow brighter, and the eyes are better developed in males. In predatory deep-sea fish from the anglerfish order, the first ray of the dorsal fin is shifted to the upper jaw and turned into a flexible "rod", carrying at the end a worm-like "bait" - a gland filled with mucus with luminous bacteria. By regulating the flow of blood to the gland and therefore the supply of oxygen to the bacterium, the fish can arbitrarily cause the "bait" to glow, imitating the movements of the worm and luring the prey.

In terrestrial environments, bioluminescence is developed only in a few species, most of all in beetles from the firefly family, which use light signaling to attract individuals of the opposite sex at twilight or at night.

Ways of orientation of animals in the aquatic environment. Living in constant twilight or darkness greatly limits the possibilities visual orientation hydrobionts. In connection with the rapid attenuation of light rays in water, even the owners of well-developed organs of vision orient themselves with their help only at close range.

Sound travels faster in water than in air. Sound Orientation is generally better developed in aquatic organisms than the visual one. A number of species pick up even very low frequency vibrations (infrasounds), arising when the rhythm of the waves changes, and descends in advance before the storm from the surface layers to the deeper ones (for example, jellyfish). Many inhabitants of water bodies - mammals, fish, mollusks, crustaceans - make sounds themselves. Crustaceans accomplish this by rubbing different parts of the body against each other; fish - with the help of a swim bladder, pharyngeal teeth, jaws, rays of the pectoral fins and in other ways. Sound signaling is most often used for intraspecific relationships, for example, for orientation in a flock, attracting individuals of the opposite sex, etc., and is especially developed in inhabitants of muddy waters and great depths, living in darkness.

A number of hydrobionts look for food and navigate using echolocation– perception of reflected sound waves (cetaceans). Many receive reflected electrical impulses producing discharges of different frequencies when swimming. About 300 species of fish are known to be able to generate electricity and use it for orientation and signaling. The freshwater water elephant fish (Mormyrus kannume) sends out up to 30 pulses per second to detect invertebrates it preys on the liquid sludge without the aid of sight. The frequency of discharges in some marine fish reaches 2000 impulses per second. A number of fish also use electric fields for defense and attack (electric stingray, electric eel, etc.).

For depth orientation perception of hydrostatic pressure. It is carried out with the help of statocysts, gas chambers and other organs.

The most ancient way of orientation, characteristic of all aquatic animals, is perception of the chemistry of the environment. The chemoreceptors of many aquatic organisms are extremely sensitive. In the thousand-kilometer migrations that are typical for many species of fish, they are guided mainly by smells, finding spawning or feeding grounds with amazing accuracy. It has been experimentally proven, for example, that salmon, artificially deprived of the sense of smell, do not find the mouth of their river, returning to spawn, but they are never mistaken if they can perceive odors. The subtlety of the sense of smell is extremely great in fish that make especially distant migrations.

Specifics of adaptations to life in drying up reservoirs. On Earth, there are many temporary, shallow reservoirs that arise after river floods, heavy rains, snow melt, etc. In these reservoirs, despite the brevity of their existence, various aquatic organisms settle.

Common features of the inhabitants of drying up pools are the ability to produce numerous offspring in a short time and endure long periods without water. At the same time, representatives of many species are buried in silt, passing into a state of reduced vital activity - hypobiosis. This is how shields, cladocerans, planarians, low bristle worms, mollusks and even fish behave - loach, African protopterus and South American lungfish lepidosiren. Many small species form cysts that withstand drought, such as sunflowers, ciliates, rhizopods, a number of copepods, turbellarians, nematodes of the genus Rhabditis. Others experience an unfavorable period in the stage of highly resistant eggs. Finally, some small inhabitants of drying water bodies have a unique ability to dry up to the state of a film, and when moistened, resume growth and development. The ability to tolerate complete dehydration of the body was found in rotifers of the genera Callidina, Philodina, etc., tardigrades Macrobiotus, Echiniscus, nematodes of the genera Tylenchus, Plectus, Cephalobus, etc. These animals inhabit micro-reservoirs in moss and lichen cushions and are adapted to abrupt changes in the humidity regime.

Filtration as a type of food. Many aquatic organisms have a special nature of nutrition - this is the sieving or sedimentation of particles of organic origin suspended in water and numerous small organisms (Fig. 41).

Rice. 41. The composition of planktonic food of ascidia from the Barents Sea (according to S. A. Zernov, 1949)

This method of feeding, which does not require much energy to search for prey, is characteristic of laminabranch mollusks, sessile echinoderms, polychaetes, bryozoans, ascidians, planktonic crustaceans, etc. (Fig. 42). Filter-feeding animals play an important role in the biological treatment of water bodies. Mussels inhabiting an area of ​​1 m 2 can drive 150–280 m 3 of water per day through the mantle cavity, precipitating suspended particles. Freshwater daphnia, cyclops or the most massive crustacean Calanus finmarchicus in the ocean filter out up to 1.5 liters of water per individual per day. The littoral zone of the ocean, especially rich in accumulations of filtering organisms, works as an effective cleaning system.

Rice. 42. Filtering devices of hydrobionts (according to S. A. Zernov, 1949):

1 – Simulium midge larvae on a stone (a) and their filtering appendages (b);

2 – filtering leg of the crustacean Diaphanosoma brachyurum;

3 – gill slits of the ascidian Phasullia;

4 – crustacean Bosmina with filtered intestinal contents;

5 – food current of ciliates Bursaria

The properties of the environment largely determine the ways of adaptation of its inhabitants, their way of life and ways of using resources, creating a chain of cause-and-effect dependencies. Thus, the high density of water makes possible the existence of plankton, and the presence of organisms hovering in the water is a prerequisite for the development of a filtration type of nutrition, in which a sedentary lifestyle of animals is also possible. As a result, a powerful mechanism of self-purification of water bodies of biospheric significance is formed. It involves a huge number of hydrobionts, both benthic and pelagic, from unicellular protozoa to vertebrates. According to calculations, all the water in the lakes of the temperate zone is passed through the filtration apparatus of animals from several to tens of times during the growing season, and the entire volume of the World Ocean is filtered for several days. Disturbance of the activity of filter feeders by various anthropogenic influences poses a serious threat to maintaining the purity of waters.

The ground-air environment is the most difficult in terms of environmental conditions. Life on land required such adaptations that were possible only with a sufficiently high level of organization of plants and animals.

The low density of air determines its low lifting force and negligible disputability. The inhabitants of the air environment must have their own support system that supports the body: plants - a variety of mechanical tissues, animals - a solid or, much less often, a hydrostatic skeleton. In addition, all the inhabitants of the air environment are closely connected with the surface of the earth, which serves them for attachment and support. Life in suspension in the air is impossible.

True, many microorganisms and animals, spores, seeds, fruits and pollen of plants are regularly present in the air and are carried by air currents (Fig. 43), many animals are capable of active flight, however, in all these species, the main function of their life cycle - reproduction - is carried out on the surface of the earth. For most of them, being in the air is associated only with resettlement or the search for prey.

Rice. 43. Altitude distribution of aerial plankton arthropods (according to Dajot, 1975)

The low density of air causes low resistance to movement. Therefore, many terrestrial animals in the course of evolution used the ecological benefits of this property of the air environment, acquiring the ability to fly. 75% of the species of all terrestrial animals are capable of active flight, mainly insects and birds, but flyers are also found among mammals and reptiles. Land animals fly mainly with the help of muscular effort, but some can also glide due to air currents.

Due to the mobility of air, the vertical and horizontal movements of air masses existing in the lower layers of the atmosphere, passive flight of a number of organisms is possible.

Anemophilia is the oldest way of pollinating plants. All gymnosperms are pollinated by wind, and among angiosperms, anemophilous plants make up approximately 10% of all species.

Anemophily is observed in the families of beech, birch, walnut, elm, hemp, nettle, casuarina, haze, sedge, cereals, palm trees and many others. Wind pollinated plants have a number of adaptations that improve the aerodynamic properties of their pollen, as well as morphological and biological features that ensure pollination efficiency.

The life of many plants is completely dependent on the wind, and resettlement is carried out with its help. Such a double dependence is observed in spruce, pine, poplar, birch, elm, ash, cotton grass, cattail, saxaul, juzgun, etc.

Many species have developed anemochory- settling with the help of air currents. Anemochory is characteristic of spores, seeds and fruits of plants, protozoan cysts, small insects, spiders, etc. Organisms passively carried by air currents are collectively called aeroplankton by analogy with the planktonic inhabitants of the aquatic environment. Special adaptations for passive flight are very small body sizes, an increase in its area due to outgrowths, strong dissection, a large relative surface of the wings, the use of cobwebs, etc. (Fig. 44). Anemochore seeds and fruits of plants also have either very small sizes (for example, orchid seeds) or various pterygoid and parachute-shaped appendages that increase their ability to plan (Fig. 45).

Rice. 44. Adaptations for airborne transport in insects:

1 – mosquito Cardiocrepis brevirostris;

2 – gall midge Porrycordila sp.;

3 – Hymenoptera Anargus fuscus;

4 – Hermes Dreyfusia nordmannianae;

5 - larva of the gypsy moth Lymantria dispar

Rice. 45. Adaptations for wind transport in fruits and seeds of plants:

1 – linden Tilia intermedia;

2 – Acer monspessulanum maple;

3 – birch Betula pendula;

4 – cotton grass Eriophorum;

5 – dandelion Taraxacum officinale;

6 – cattail Typha scuttbeworhii

In the settlement of microorganisms, animals and plants, the main role is played by vertical convection air currents and weak winds. Strong winds, storms and hurricanes also have significant environmental impacts on terrestrial organisms.

The low density of air causes a relatively low pressure on land. Normally, it is equal to 760 mm Hg. Art. As altitude increases, pressure decreases. At an altitude of 5800 m, it is only half normal. Low pressure may limit the distribution of species in the mountains. For most vertebrates, the upper limit of life is about 6000 m. A decrease in pressure entails a decrease in oxygen supply and dehydration of animals due to an increase in the respiratory rate. Approximately the same are the limits of advancement to the mountains of higher plants. Somewhat more hardy are arthropods (springtails, mites, spiders) that can be found on glaciers above the vegetation boundary.

In general, all terrestrial organisms are much more stenobatic than aquatic ones, since the usual fluctuations in pressure in their environment are fractions of the atmosphere, and even for birds rising to great heights do not exceed 1/3 of the normal one.

Gas composition of air. In addition to the physical properties of the air environment, its chemical features are extremely important for the existence of terrestrial organisms. The gas composition of air in the surface layer of the atmosphere is quite homogeneous in terms of the content of the main components (nitrogen - 78.1%, oxygen - 21.0, argon - 0.9, carbon dioxide - 0.035% by volume) due to the high diffusive ability of gases and constant mixing convection and wind currents. However, various admixtures of gaseous, droplet-liquid and solid (dust) particles entering the atmosphere from local sources can be of significant ecological importance.

The high oxygen content contributed to an increase in the metabolism of terrestrial organisms compared to primary aquatic ones. It was in the terrestrial environment, on the basis of the high efficiency of oxidative processes in the body, that animal homoiothermia arose. Oxygen, due to its constantly high content in the air, is not a factor limiting life in the terrestrial environment. Only in places, under specific conditions, is a temporary deficit created, for example, in accumulations of decaying plant residues, stocks of grain, flour, etc.

The content of carbon dioxide can vary in certain areas of the surface layer of air within fairly significant limits. For example, in the absence of wind in the center of large cities, its concentration increases tenfold. Regular daily changes in the carbon dioxide content in the surface layers associated with the rhythm of plant photosynthesis. Seasonal are due to changes in the intensity of respiration of living organisms, mainly the microscopic population of soils. Increased air saturation with carbon dioxide occurs in zones of volcanic activity, near thermal springs and other underground outlets of this gas. In high concentrations, carbon dioxide is toxic. In nature, such concentrations are rare.

In nature, the main source of carbon dioxide is the so-called soil respiration. Soil microorganisms and animals respire very intensively. Carbon dioxide diffuses from the soil into the atmosphere, especially vigorously during rain. A lot of it is emitted by soils that are moderately moist, well warmed up, rich in organic residues. For example, the soil of a beech forest emits CO 2 from 15 to 22 kg/ha per hour, and unfertilized sandy soil is only 2 kg/ha.

In modern conditions, human activity in the combustion of fossil fuels has become a powerful source of additional amounts of CO 2 entering the atmosphere.

Air nitrogen for most inhabitants of the terrestrial environment is an inert gas, but a number of prokaryotic organisms (nodule bacteria, Azotobacter, clostridia, blue-green algae, etc.) have the ability to bind it and involve it in the biological cycle.

Rice. 46. Mountainside with destroyed vegetation due to sulfur dioxide emissions from nearby industries

Local impurities entering the air can also significantly affect living organisms. This is especially true for toxic gaseous substances - methane, sulfur oxide, carbon monoxide, nitrogen oxide, hydrogen sulfide, chlorine compounds, as well as particles of dust, soot, etc., polluting the air in industrial areas. The main modern source of chemical and physical pollution of the atmosphere is anthropogenic: the work of various industrial enterprises and transport, soil erosion, etc. Sulfur oxide (SO 2), for example, is toxic to plants even in concentrations from one fifty-thousandth to one millionth of the volume of air. Around industrial centers that pollute the atmosphere with this gas, almost all vegetation dies (Fig. 46). Some plant species are particularly sensitive to SO 2 and serve as a sensitive indicator of its accumulation in the air. For example, many lichens die even with traces of sulfur oxide in the surrounding atmosphere. Their presence in the forests around large cities testifies to the high purity of the air. The resistance of plants to impurities in the air is taken into account when selecting species for landscaping settlements. Sensitive to smoke, for example, spruce and pine, maple, linden, birch. The most resistant are thuja, Canadian poplar, American maple, elder and some others.

Edaphic environmental factors. Soil properties and terrain also affect the living conditions of terrestrial organisms, primarily plants. The properties of the earth's surface that have an ecological impact on its inhabitants are united by the name edaphic environmental factors (from the Greek "edafos" - foundation, soil).

The nature of the root system of plants depends on the hydrothermal regime, aeration, composition, composition and structure of the soil. For example, the root systems of tree species (birch, larch) in areas with permafrost are located at a shallow depth and spread out in breadth. Where there is no permafrost, the root systems of these same plants are less spread out and penetrate deeper. In many steppe plants, the roots can get water from great depths, while at the same time they have many surface roots in the humus soil horizon, from where the plants absorb mineral nutrients. On waterlogged, poorly aerated soil in mangroves, many species have special respiratory roots - pneumatophores.

A number of ecological groups of plants can be distinguished in relation to different soil properties.

So, according to the reaction to the acidity of the soil, they distinguish: 1) acidophilic species - grow on acidic soils with a pH of less than 6.7 (plants of sphagnum bogs, belous); 2) neutrophilic - gravitate towards soils with a pH of 6.7–7.0 (most cultivated plants); 3) basiphilic- grow at a pH of more than 7.0 (mordovnik, forest anemone); 4) indifferent - can grow on soils with different pH values ​​(lily of the valley, sheep fescue).

In relation to the gross composition of the soil, there are: 1) oligotrophic plants content with a small amount of ash elements (scotch pine); 2) eutrophic, those in need of a large number of ash elements (oak, common goatweed, perennial hawk); 3) mesotrophic, requiring a moderate amount of ash elements (spruce).

Nitrophils- plants that prefer soils rich in nitrogen (dioecious nettle).

Plants of saline soils form a group halophytes(soleros, sarsazan, kokpek).

Some plant species are confined to different substrates: petrophytes grow on rocky soils, and psammophytes inhabit loose sands.

The terrain and the nature of the soil affect the specifics of the movement of animals. For example, ungulates, ostriches, bustards living in open spaces need solid ground to enhance repulsion when running fast. In lizards that live on loose sands, the fingers are bordered with a fringe of horny scales, which increases the support surface (Fig. 47). For terrestrial inhabitants digging holes, dense soils are unfavorable. The nature of the soil in some cases affects the distribution of terrestrial animals that dig holes, burrow into the ground to escape heat or predators, or lay eggs in the soil, etc.

Rice. 47. Fan-toed gecko - an inhabitant of the sands of the Sahara: A - fan-toed gecko; B - gecko leg

weather features. Living conditions in the ground-air environment are complicated, in addition, weather changes. Weather - this is a continuously changing state of the atmosphere near the earth's surface up to a height of about 20 km (the boundary of the troposphere). Weather variability is manifested in the constant variation of the combination of such environmental factors as air temperature and humidity, cloudiness, precipitation, wind strength and direction, etc. Weather changes, along with their regular alternation in the annual cycle, are characterized by non-periodic fluctuations, which significantly complicates the conditions for the existence terrestrial organisms. The weather affects the life of aquatic inhabitants to a much lesser extent and only on the population of the surface layers.

The climate of the area. The long-term weather regime characterizes the climate of the area. The concept of climate includes not only the average values ​​of meteorological phenomena, but also their annual and daily course, deviations from it and their frequency. The climate is determined by the geographical conditions of the area.

The zonal diversity of climates is complicated by the action of monsoon winds, the distribution of cyclones and anticyclones, the influence of mountain ranges on the movement of air masses, the degree of distance from the ocean (continentality), and many other local factors. In the mountains, there is a climatic zonality, in many respects similar to the change of zones from low latitudes to high latitudes. All this creates an extraordinary variety of living conditions on land.

For most terrestrial organisms, especially small ones, it is not so much the climate of the area that is important, but the conditions of their immediate habitat. Very often, local elements of the environment (relief, exposure, vegetation, etc.) in a particular area change the regime of temperature, humidity, light, air movement in such a way that it differs significantly from the climatic conditions of the area. Such local climate modifications that take shape in the surface air layer are called microclimate. In each zone, the microclimates are very diverse. It is possible to single out microclimates of arbitrarily small areas. For example, a special mode is created in the corollas of flowers, which are used by insects living there. Differences in temperature, air humidity and wind strength are widely known in open space and in forests, in herbage and over bare soil areas, on the slopes of the northern and southern exposures, etc. A special stable microclimate occurs in burrows, nests, hollows, caves and other closed places.

Precipitation. In addition to providing water and creating moisture reserves, they can play another ecological role. Thus, heavy rain showers or hail sometimes have a mechanical effect on plants or animals.

The ecological role of snow cover is especially diverse. Daily temperature fluctuations penetrate into the snow thickness only up to 25 cm; deeper, the temperature almost does not change. At frosts of -20-30 ° C, under a layer of snow of 30-40 cm, the temperature is only slightly below zero. Deep snow cover protects the buds of renewal, protects the green parts of plants from freezing; many species go under the snow without shedding foliage, for example, hairy sorrel, Veronica officinalis, hoof, etc.

Rice. 48. Scheme of telemetric study of the temperature regime of a hazel grouse located in a snow hole (according to A. V. Andreev, A. V. Krechmar, 1976)

Small terrestrial animals also lead an active lifestyle in winter, laying entire galleries of passages under the snow and in its thickness. For a number of species that feed on snowy vegetation, even winter breeding is characteristic, which is noted, for example, in lemmings, wood and yellow-throated mice, a number of voles, water rats, etc. Grouse birds - hazel grouse, black grouse, tundra partridges - burrow into the snow for the night ( Fig. 48).

Winter snow cover prevents large animals from foraging. Many ungulates (reindeer, wild boars, musk oxen) feed exclusively on snowy vegetation in winter, and deep snow cover, and especially a hard crust on its surface that occurs in ice, doom them to starvation. During nomadic cattle breeding in pre-revolutionary Russia, a huge disaster in the southern regions was jute - mass loss of livestock as a result of sleet, depriving animals of food. Movement on loose deep snow is also difficult for animals. Foxes, for example, in snowy winters prefer areas in the forest under dense fir trees, where the layer of snow is thinner, and almost do not go out into open glades and edges. The depth of snow cover can limit the geographic distribution of species. For example, true deer do not penetrate north into areas where the snow thickness in winter is more than 40–50 cm.

The whiteness of the snow cover unmasks dark animals. Selection for camouflage to match the background color apparently played a large role in the occurrence of seasonal color changes in the white and tundra partridge, mountain hare, ermine, weasel, and arctic fox. On the Commander Islands, along with white foxes, there are many blue foxes. According to the observations of zoologists, the latter keep mainly near dark rocks and non-freezing surf strip, while whites prefer areas with snow cover.

The soil is a loose, thin surface layer of land in contact with the air. Despite its insignificant thickness, this shell of the Earth plays a crucial role in the spread of life. The soil is not just a solid body, like most rocks of the lithosphere, but a complex three-phase system in which solid particles are surrounded by air and water. It is permeated with cavities filled with a mixture of gases and aqueous solutions, and therefore extremely diverse conditions are formed in it, favorable for the life of many micro- and macro-organisms (Fig. 49). In the soil, temperature fluctuations are smoothed compared to the surface layer of air, and the presence of groundwater and the penetration of precipitation create moisture reserves and provide a moisture regime intermediate between the aquatic and terrestrial environments. The soil concentrates reserves of organic and mineral substances supplied by dying vegetation and animal corpses. All this determines the high saturation of the soil with life.

The root systems of terrestrial plants are concentrated in the soil (Fig. 50).

Rice. 49. Underground passages of Brandt's vole: A - top view; B - side view

Rice. 50. Placement of roots in the steppe chernozem soil (according to M. S. Shalyt, 1950)

On average, there are more than 100 billion cells of protozoa, millions of rotifers and tardigrades, tens of millions of nematodes, tens and hundreds of thousands of ticks and springtails, thousands of other arthropods, tens of thousands of enchitreids, tens and hundreds of earthworms, mollusks and other invertebrates per 1 m 2 of the soil layer. . In addition, 1 cm 2 of soil contains tens and hundreds of millions of bacteria, microscopic fungi, actinomycetes and other microorganisms. In the illuminated surface layers, hundreds of thousands of photosynthetic cells of green, yellow-green, diatoms and blue-green algae live in every gram. Living organisms are as characteristic of the soil as its non-living components. Therefore, V. I. Vernadsky attributed the soil to the bio-inert bodies of nature, emphasizing its saturation with life and inseparable connection with it.

The heterogeneity of conditions in the soil is most pronounced in the vertical direction. With depth, a number of the most important environmental factors that affect the life of the inhabitants of the soil change dramatically. First of all, this refers to the structure of the soil. Three main horizons are distinguished in it, differing in morphological and chemical properties: 1) the upper humus-accumulative horizon A, in which organic matter accumulates and transforms and from which part of the compounds is carried down by washing water; 2) the intrusion horizon, or illuvial B, where the substances washed out from above settle and are transformed, and 3) the parent rock, or horizon C, the material of which is transformed into soil.

Within each horizon, more fractional layers are distinguished, which also differ greatly in properties. For example, in a temperate zone under coniferous or mixed forests, the horizon A consists of pad (A 0)- a layer of loose accumulation of plant residues, a dark-colored humus layer (A 1), in which particles of organic origin are mixed with mineral, and a podzolic layer (A 2)- ash-gray in color, in which silicon compounds predominate, and all soluble substances are washed into the depth of the soil profile. Both the structure and the chemistry of these layers are very different, and therefore the roots of plants and the inhabitants of the soil, moving only a few centimeters up or down, fall into different conditions.

The sizes of cavities between soil particles, suitable for animals to live in, usually decrease rapidly with depth. For example, in meadow soils, the average diameter of cavities at a depth of 0–1 cm is 3 mm, 1–2 cm, 2 mm, and at a depth of 2–3 cm, only 1 mm; deeper soil pores are even finer. Soil density also changes with depth. The loosest layers contain organic matter. The porosity of these layers is determined by the fact that organic substances stick together mineral particles into larger aggregates, the volume of cavities between which increases. The most dense is usually the illuvial horizon IN, cemented by colloidal particles washed into it.

Moisture in the soil is present in various states: 1) bound (hygroscopic and film) is firmly held by the surface of soil particles; 2) capillary occupies small pores and can move along them in various directions; 3) gravity fills larger voids and slowly seeps down under the influence of gravity; 4) vapor is contained in the soil air.

The water content is not the same in different soils and at different times. If there is too much gravitational moisture, then the regime of the soil is close to the regime of water bodies. In dry soil, only bound water remains, and conditions approach those on the ground. However, even in the driest soils, the air is wetter than the ground, so the inhabitants of the soil are much less susceptible to the threat of drying out than on the surface.

The composition of soil air is variable. With depth, the oxygen content decreases sharply and the concentration of carbon dioxide increases. Due to the presence of decomposing organic substances in the soil, the soil air can contain a high concentration of toxic gases such as ammonia, hydrogen sulfide, methane, etc. When the soil is flooded or the plant residues rot intensively, completely anaerobic conditions can occur in places.

Fluctuations in cutting temperature only on the soil surface. Here they can be even stronger than in the ground layer of air. However, with each centimeter deep, daily and seasonal temperature changes become less and less visible at a depth of 1–1.5 m (Fig. 51).

Rice. 51. Decrease in annual fluctuations in soil temperature with depth (according to K. Schmidt-Nilson, 1972). The shaded part is the range of annual temperature fluctuations

All these features lead to the fact that, despite the great heterogeneity of environmental conditions in the soil, it acts as a fairly stable environment, especially for mobile organisms. A steep temperature and humidity gradient in the soil profile allows soil animals to provide themselves with a suitable ecological environment through minor movements.

The heterogeneity of the soil leads to the fact that for organisms of different sizes it acts as a different environment. For microorganisms, the huge total surface of soil particles is of particular importance, since the vast majority of the microbial population is adsorbed on them. The complexity of the soil environment creates a wide variety of conditions for a variety of functional groups: aerobes and anaerobes, consumers of organic and mineral compounds. The distribution of microorganisms in the soil is characterized by small foci, since even over a few millimeters different ecological zones can be replaced.

For small soil animals (Fig. 52, 53), which are combined under the name microfauna (protozoa, rotifers, tardigrades, nematodes, etc.), the soil is a system of micro-reservoirs. Essentially, they are aquatic organisms. They live in soil pores filled with gravitational or capillary water, and part of life can, like microorganisms, be in an adsorbed state on the surface of particles in thin layers of film moisture. Many of these species live in ordinary water bodies. However, soil forms are much smaller than freshwater ones and, in addition, they are distinguished by their ability to stay in an encysted state for a long time, waiting out unfavorable periods. While freshwater amoebas are 50-100 microns in size, soil ones are only 10-15. Representatives of flagellates are especially small, often only 2-5 microns. Soil ciliates also have dwarf sizes and, moreover, can greatly change the shape of the body.

Rice. 52. Testate amoeba feeding on bacteria on decaying forest floor leaves

Rice. 53. Soil microfauna (according to W. Dunger, 1974):

1–4 - flagella; 5–8 - naked amoeba; 9-10 - testate amoeba; 11–13 - ciliates; 14–16 - roundworms; 17–18 - rotifers; 19–20 – tardigrades

For air-breathers of slightly larger animals, the soil appears as a system of shallow caves. Such animals are grouped under the name mesofauna (Fig. 54). The sizes of representatives of the soil mesofauna range from tenths to 2–3 mm. This group mainly includes arthropods: numerous groups of ticks, primary wingless insects (springtails, protura, two-tailed insects), small species of winged insects, centipedes symphyla, etc. They do not have special adaptations for digging. They crawl along the walls of soil cavities with the help of limbs or wriggling like a worm. Soil air saturated with water vapor allows you to breathe through the covers. Many species do not have a tracheal system. Such animals are very sensitive to desiccation. The main means of salvation from fluctuations in air humidity for them is movement inland. But the possibility of migration deep into the soil cavities is limited by the rapid decrease in the diameter of the pores, so only the smallest species can move through the soil wells. Larger representatives of the mesofauna have some adaptations that allow them to endure a temporary decrease in soil air humidity: protective scales on the body, partial impermeability of the integument, a solid thick-walled shell with an epicuticle in combination with a primitive tracheal system that provides breathing.

Rice. 54. Soil mesofauna (no W. Danger, 1974):

1 - false scorion; 2 - Gama new flare; 3–4 shell mites; 5 – centipede pauroioda; 6 – chironomid mosquito larva; 7 - a beetle from the family. Ptiliidae; 8–9 springtails

Representatives of the mesofauna experience periods of flooding of the soil with water in air bubbles. The air is retained around the body of animals due to their non-wetting integuments, which are also equipped with hairs, scales, etc. The air bubble serves as a kind of "physical gill" for a small animal. Breathing is carried out due to oxygen diffusing into the air layer from the surrounding water.

Representatives of micro- and mesofauna are able to tolerate winter freezing of the soil, since most species cannot go down from layers exposed to negative temperatures.

Larger soil animals, with body sizes from 2 to 20 mm, are called representatives macro fauna (Fig. 55). These are insect larvae, centipedes, enchytreids, earthworms, etc. For them, the soil is a dense medium that provides significant mechanical resistance when moving. These relatively large forms move in the soil either by expanding natural wells by pushing apart soil particles, or by digging new passages. Both modes of movement leave an imprint on the external structure of animals.

Rice. 55. Soil macrofauna (no W. Danger, 1974):

1 - earthworm; 2 – woodlice; 3 – labiopod centipede; 4 – bipedal centipede; 5 - beetle larva; 6 – click beetle larva; 7 – bear; 8 - grub larva

The ability to move along thin holes, almost without resorting to digging, is inherent only in species that have a body with a small cross section that can strongly bend in winding passages (millipedes - drupes and geophiles). Pushing soil particles apart due to the pressure of the body walls, earthworms, larvae of centipede mosquitoes, etc. move. Having fixed the posterior end, they thin and lengthen the anterior one, penetrating into narrow soil cracks, then fix the anterior part of the body and increase its diameter. At the same time, strong hydraulic pressure of the incompressible intracavitary fluid is created in the expanded area due to the work of the muscles: in worms, the contents of coelomic sacs, and in tipulids, hemolymph. The pressure is transmitted through the walls of the body to the soil, and thus the animal expands the well. At the same time, an open passage remains behind, which threatens to increase evaporation and the pursuit of predators. Many species have developed adaptations to an ecologically more beneficial type of movement in the soil - digging with clogging the passage behind them. Digging is carried out by loosening and raking soil particles. For this, the larvae of various insects use the anterior end of the head, mandibles and forelimbs, expanded and reinforced with a thick layer of chitin, spines and outgrowths. At the posterior end of the body, devices for strong fixation develop - retractable supports, teeth, hooks. To close the passage on the last segments, a number of species have a special depressed platform, framed by chitinous sides or teeth, a kind of wheelbarrow. Similar areas are formed on the back of the elytra in bark beetles, which also use them to clog passages with drill flour. Closing the passage behind them, the animals - the inhabitants of the soil are constantly in a closed chamber, saturated with the evaporation of their own body.

Gas exchange of most species of this ecological group is carried out with the help of specialized respiratory organs, but along with this, it is supplemented by gas exchange through the integuments. It is even possible exclusively skin respiration, for example, in earthworms, enchitreid.

Burrowing animals can leave layers where unfavorable conditions arise. In drought and winter, they concentrate in deeper layers, usually a few tens of centimeters from the surface.

Megafauna soils are large excavations, mainly from among mammals. A number of species spend their whole lives in the soil (mole rats, mole voles, zokors, moles of Eurasia, golden moles

Africa, marsupial moles of Australia, etc.). They make whole systems of passages and holes in the soil. The appearance and anatomical features of these animals reflect their adaptability to a burrowing underground lifestyle. They have underdeveloped eyes, a compact, valky body with a short neck, short thick fur, strong digging limbs with strong claws. Mole rats and mole voles loosen the ground with their chisels. Large oligochaetes, especially representatives of the Megascolecidae family living in the tropics and the Southern Hemisphere, should also be included in the soil megafauna. The largest of them, the Australian Megascolides australis, reaches a length of 2.5 and even 3 m.

In addition to the permanent inhabitants of the soil, a large ecological group can be distinguished among large animals. burrow dwellers (ground squirrels, marmots, jerboas, rabbits, badgers, etc.). They feed on the surface, but breed, hibernate, rest, and escape danger in the soil. A number of other animals use their burrows, finding in them a favorable microclimate and shelter from enemies. Norniks have structural features characteristic of terrestrial animals, but have a number of adaptations associated with a burrowing lifestyle. For example, badgers have long claws and strong muscles on the forelimbs, a narrow head, and small auricles. Compared to non-burrowing hares, rabbits have noticeably shortened ears and hind legs, a stronger skull, stronger bones and muscles of the forearms, etc.

For a number of ecological features, the soil is an intermediate medium between water and land. The soil is brought closer to the aquatic environment by its temperature regime, the reduced oxygen content in the soil air, its saturation with water vapor and the presence of water in other forms, the presence of salts and organic substances in soil solutions, and the ability to move in three dimensions.

The presence of soil air, the threat of desiccation in the upper horizons, and rather sharp changes in the temperature regime of the surface layers bring the soil closer to the air environment.

The intermediate ecological properties of the soil as a habitat for animals suggest that the soil played a special role in the evolution of the animal world. For many groups, in particular arthropods, the soil served as a medium through which the originally aquatic inhabitants could switch to a terrestrial way of life and conquer the land. This path of evolution of arthropods was proved by the works of M. S. Gilyarov (1912–1985).

Many types of heterotrophic organisms live in other living beings throughout their life or part of their life cycle, whose bodies serve as an environment for them that differs significantly in properties from the external one.

Rice. 56. Aphid infecting rider

Rice. 57. Cut gall on a beech leaf with a larva of the gall midge Mikiola fagi

In the ground-air environment, temperature has a particularly large effect on organisms. Therefore, the inhabitants of the cold and hot regions of the Earth have developed various adaptations to conserve heat or, conversely, to release its excess.

Give some examples.

The temperature of the plant due to heating by the sun's rays may be higher than the temperature of the surrounding air and soil. With strong evaporation, the temperature of the plant becomes lower than the air temperature. Evaporation through stomata is a process regulated by the plant. With an increase in air temperature, it increases if a quick supply of the required amount of water to the leaves is possible. This saves the plant from overheating, lowering its temperature by 4-6, and sometimes by 10-15 ° C.

During muscle contraction, much more thermal energy is released than during the functioning of any other organs and tissues. The more powerful and active the musculature, the more heat the animal can generate. Compared with plants, animals have more diverse possibilities to regulate, permanently or temporarily, their own body temperature.

By changing the posture, the animal can increase or decrease the heating of the body due to solar radiation. For example, the desert locust exposes the wide lateral surface of the body to the sun's rays in the cool morning hours, and the narrow dorsal surface at noon. In extreme heat, animals hide in the shade, hide in burrows. In the desert during the day, for example, some species of lizards and snakes climb the bushes, avoiding contact with the hot surface of the soil. By winter, many animals seek refuge, where the course of temperatures is smoother than in open habitats. The forms of behavior of social insects are even more complex: bees, ants, termites, which build nests with a well-regulated temperature inside them, almost constant during the period of insect activity.

The thick fur of mammals, feathers and especially the down cover of birds make it possible to keep a layer of air around the body with a temperature close to that of the animal's body, and thereby reduce heat radiation to the external environment. Heat transfer is regulated by the slope of the hair and feathers, the seasonal change of fur and plumage. The exceptionally warm winter fur of animals from the Arctic allows them to do without an increase in metabolism in cold weather and reduces the need for food.

Name the inhabitants of the desert known to you.

In the deserts of Central Asia, a small shrub is a saxaul. In America - cacti, in Africa - euphorbia. The animal world is not rich. Reptiles predominate - snakes, monitor lizards. There are scorpions, few mammals (camel).

1. Continue filling out the table "Habitats of living organisms" (see homework for § 42).