And directly or indirectly affects its vital activity, growth, development, reproduction.
Every organism lives in a specific habitat. Elements or properties of the environment are called environmental factors. Four environments of life are distinguished on our planet: ground-air, water, soil, and another organism. Living organisms are adapted to exist in certain conditions of life and in a certain environment.
Some organisms live on land, others in soil, and others in water. Some chose the bodies of other organisms as their place of residence. Thus, four living environments are distinguished: ground-air, water, soil, another organism (Fig. 3). Each of the environments of life is characterized by certain properties to which the organisms living in it are adapted.
Ground-air environment
The ground-air environment is characterized by low air density, an abundance of light, a rapid change in temperature, and variable humidity. Therefore, organisms living in the ground-air environment have well-developed supporting structures - the external or internal skeleton in animals, special structures in plants.
Many animals have organs of movement on the ground - limbs or wings for flight. Thanks to the developed organs of vision, they see well. Land organisms have adaptations that protect them from fluctuations in temperature and humidity (for example, special body covers, nests, burrows). Plants have well developed roots, stems, leaves.
Water environment
The aquatic environment is characterized by a higher density compared to air, so water has a buoyancy force. Many organisms "hover" in the water column - small animals, bacteria, protists. Others are actively moving. To do this, they have organs of movement in the form of fins or flippers (fish, whales, seals). Active swimmers tend to have a streamlined body shape.
Many aquatic organisms (coastal plants, algae, coral polyps) lead an attached way of life, others are sedentary (some mollusks, starfish).
Water accumulates and retains heat, so there are no such sharp temperature fluctuations in water as on land. The amount of light in water bodies varies with depth. Therefore, autotrophs inhabit only that part of the reservoir where light penetrates. Heterotrophic organisms have mastered the entire water column.
soil environment
There is no light in the soil environment, there is no sharp change in temperature, high density. Bacteria, protists, fungi, some animals (insects and their larvae, worms, moles, shrews) live in the soil. Soil animals have a compact body. Some of them have digging limbs, organs of vision are absent or underdeveloped (mole).
The totality of the elements of the environment necessary for the organism, without which it cannot exist, is called the conditions of existence or the conditions of life.
On this page, material on the topics:
shrew habitat ground air water soil or other
organism as habitat examples
examples of organisms living in our environment
what properties are characteristic of the aquatic habitat
organisms living in the body of other organisms
Questions for this article:
What is the habitat and conditions of existence?
What are called environmental factors?
What groups of environmental factors are distinguished?
What properties are characteristic of the ground-air environment?
Why is it believed that the terrestrial-air environment of life is more complex than water or soil?
What are the features of organisms living inside other organisms?
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A feature of the ground-air environment is that the organisms living here are surrounded air- a gaseous medium characterized by low humidity, density, pressure and high oxygen content.
Most animals move on a solid substrate - soil, and plants take root in it.
The inhabitants of the ground-air environment have developed adaptations:
1) organs that ensure the assimilation of atmospheric oxygen (stomata in plants, lungs and tracheas in animals);
2) a strong development of skeletal formations that support the body in the air (mechanical tissues in plants, the skeleton in animals);
3) complex adaptations for protection against adverse factors (periodicity and rhythm of life cycles, thermoregulation mechanisms, etc.);
4) a close connection with the soil has been established (roots in plants and limbs in animals);
5) characterized by high mobility of animals in search of food;
6) flying animals (insects, birds) and wind-borne seeds, fruits, pollen appeared.
The environmental factors of the ground-air environment are regulated by the macroclimate (ecoclimate). Ecoclimate (macroclimate)- the climate of large areas, characterized by certain properties of the surface layer of air. Microclimate– climate of individual habitats (tree trunk, animal burrow, etc.).
41. Ecological factors of the ground-air environment.
1) Air:
It is characterized by a constant composition (21% oxygen, 78% nitrogen, 0.03% CO 2 and inert gases). It is an important environmental factor, because without atmospheric oxygen, the existence of most organisms is impossible, CO 2 is used for photosynthesis.
The movement of organisms in the ground-air environment is carried out mainly horizontally, only some insects, birds and mammals move vertically.
Air is of great importance for the life of living organisms through wind- movement of air masses due to uneven heating of the atmosphere by the Sun. Wind influence:
1) dries up the air, causes a decrease in the intensity of water metabolism in plants and animals;
2) participates in the pollination of plants, carries pollen;
3) reduces the diversity of flying animal species (strong wind interferes with flight);
4) causes changes in the structure of the covers (dense covers are formed that protect plants and animals from hypothermia and loss of moisture);
5) participates in the dispersal of animals and plants (carries fruits, seeds, small animals).
2) Atmospheric precipitation:
An important environmental factor, because The water regime of the environment depends on the presence of precipitation:
1) precipitation changes air humidity and soil;
2) provide available water for aquatic nutrition of plants and animals.
a) Rain:
The most important are the timing of the fallout, the frequency of the fallout, and the duration.
Example: the abundance of rain during the cooling period does not provide the plants with the necessary moisture.
The nature of the rain:
- storm- unfavorable, because plants do not have time to absorb water, streams are also formed that wash away the top fertile layer of soil, plants, and small animals.
- drizzling- favorable, because provide soil moisture, plant and animal nutrition.
- protracted- unfavorable, because cause floods, floods and floods.
b) Snow:
It has a beneficial effect on organisms in the winter, because:
a) creates a favorable temperature regime of the soil, protects organisms from hypothermia.
Example: at an air temperature of -15 0 С, the temperature of the soil under a 20 cm layer of snow is not lower than +0.2 0 С.
b) creates an environment for the life of organisms in winter (rodents, chicken birds, etc.)
fixtures animals to winter conditions:
a) the supporting surface of the legs for walking on snow is increased;
b) migration and hibernation (anabiosis);
c) transition to nutrition with certain feeds;
d) change of covers, etc.
Negative effect of snow:
a) the abundance of snow leads to mechanical damage to plants, the damping of plants and their wetting during the snowmelt in spring.
b) the formation of crust and sleet (it makes it difficult for animals and plants to exchange gases under the snow, creates difficulties for obtaining food).
42. Soil moisture.
The main factor for the water supply of primary producers is green plants.
Soil water types:
1) gravity water - occupies wide gaps between soil particles and, under the influence of gravity, goes into deeper layers. Plants easily absorb it when it is in the zone of the root system. Reserves in the soil are replenished by precipitation.
2) capillary water – fills the smallest spaces between soil particles (capillaries). Does not move down, is held by the force of adhesion. Due to evaporation from the soil surface, it forms an upward current of water. Well absorbed by plants.
1) and 2) water available to plants.
3) Chemically bonded water – water of crystallization (gypsum, clay, etc.). not available to plants.
4) Physically bound water - also inaccessible to plants.
a) film(loosely connected) - rows of dipoles, successively enveloping each other. They are held on the surface of soil particles with a force of 1 to 10 atm.
b) hygroscopic(strongly bound) - envelops soil particles with a thin film and is held by a force of 10,000 to 20,000 atm.
If there is only inaccessible water in the soil, the plant withers and dies.
For sand KZ = 0.9%, for clay = 16.3%.
Total amount of water - KZ = the degree of supply of the plant with water.
43. Geographical zonality of the ground-air environment.
The ground-air environment is characterized by vertical and horizontal zonality. Each zone is characterized by a specific ecoclimate, the composition of animals and plants, and the territory.
Climatic zones → climatic subzones → climatic provinces.
Walter's classification:
1) equatorial zone - is located between 10 0 north latitude and 10 0 south latitude. It has 2 rainy seasons corresponding to the position of the Sun at its zenith. Annual rainfall and humidity are high, and monthly temperature fluctuations are negligible.
2) tropical zone - is located north and south of the equatorial, up to 30 0 north and south latitude. Summer rainy period and winter drought are typical. Precipitation and humidity decrease with distance from the equator.
3) Dry subtropics zone - located up to 35 0 latitude. The amount of precipitation and humidity are insignificant, annual and daily temperature fluctuations are very significant. Frosts are rare.
4) transition zone - characterized by winter rainy seasons, hot summers. Freezes are more common. Mediterranean, California, south and southwest Australia, southwest South America.
5) temperate zone - characterized by cyclonic precipitation, the amount of which decreases with distance from the ocean. Annual temperature fluctuations are sharp, summers are hot, winters are frosty. Divided into subzones:
a) warm temperate subzone- the winter period is practically not distinguished, all seasons are more or less wet. South Africa.
b) typical temperate subzone- short cold winter, cool summer. Central Europe.
in) subzone of arid temperate continental type- characterized by sharp temperature contrasts, a small amount of precipitation, low humidity. Central Asia.
G) boreal or cold temperate subzone Summer is cool and humid, winter lasts half of the year. Northern North America and Northern Eurasia.
6) Arctic (Antarctic) zone - characterized by a small amount of precipitation in the form of snow. Summer (polar day) is short and cold. This zone passes into the polar region, in which the existence of plants is impossible.
Belarus is characterized by a temperate continental climate with additional moisture. Negative aspects of the Belarusian climate:
Unstable weather in spring and autumn;
Mild spring with prolonged thaws;
rainy summer;
Late spring and early autumn frosts.
Despite this, about 10,000 species of plants grow in Belarus, 430 species of vertebrates and about 20,000 species of invertebrates live.
Vertical zonation from the lowlands and the bases of the mountains to the tops of the mountains. Similar to horizontal with some deviations.
44. Soil as a medium of life. General characteristics.
The ground-air environment of life is the most difficult in terms of environmental conditions. In the course of evolution, it was mastered much later than water. Life on land required such adaptations, which became possible only with a sufficiently high level of organization of organisms. The ground-air environment is characterized by low air density, large fluctuations in temperature and humidity, a higher intensity of solar radiation in comparison with other media, and the mobility of the atmosphere.
Low air density and mobility determine its low lifting force and insignificant support. Organisms of the terrestrial environment must have a support system that supports the body: plants - mechanical tissues, animals - a solid or hydrostatic skeleton.
The small lifting force of air determines the limiting mass and size of terrestrial organisms. The largest land animals are much smaller than the giants of the aquatic environment - whales. Animals the size and mass of a modern whale could not live on land, as they would be crushed by their own weight.
The low density of air causes low resistance to movement. Therefore, many animals have acquired the ability to fly: birds, insects, some mammals and reptiles.
Due to air mobility, passive flight of some species of organisms, as well as pollen, spores, fruits and seeds of plants, is possible. Settling with the help of air currents is called anemochoria. Passively airborne organisms are called aeroplankton. They are characterized by very small body sizes, the presence of outgrowths and strong dissection, the use of cobwebs, etc. Seeds and fruits of anemochora plants also have very small sizes (seeds of orchids, fireweed, etc.) or various wing-shaped (maple, ash) and parachute-shaped (dandelion, coltsfoot) appendages.
In many plants, the transfer of pollen is carried out with the help of wind, for example, in gymnosperms, beech, birch, elm, cereals, etc. The method of pollinating plants with the help of wind is called anemophilia. Wind pollinated plants have many adaptations to ensure pollination efficiency.
Winds blowing with great force (storms, hurricanes) break trees, often turning them upside down. Winds constantly blowing in the same direction cause various deformations in the growth of trees and cause the formation of flag-shaped crowns.
In areas where strong winds are constantly blowing, as a rule, the species composition of small flying animals is poor, since they are not able to resist powerful air currents. So, on oceanic islands with constant strong winds, birds and insects that have lost the ability to fly predominate. The wind increases the loss of moisture and heat by the organisms, under its influence the drying and cooling of organisms occurs faster.
The low air density causes a relatively low pressure on land (760 mm Hg). With increasing altitude, the pressure decreases, which may limit the distribution of species in the mountains. A decrease in pressure entails a decrease in oxygen supply and dehydration of animals due to an increase in the respiratory rate. Therefore, for most vertebrates and higher plants, the upper limit of life is about 6000 m.
Gas composition of air in the surface layer of the atmosphere is quite homogeneous. It contains nitrogen - 78.1%, oxygen - 21%, argon - 0.9%, carbon dioxide - 0.03%. In addition to these gases, the atmosphere contains negligible amounts of neon, krypton, xenon, hydrogen, helium, as well as a variety of aromatic plant secretions and various impurities: sulfur dioxide, oxides of carbon, nitrogen, and physical impurities. The high oxygen content in the atmosphere contributed to an increase in the metabolism of terrestrial organisms and the appearance of warm-blooded (homeothermic) animals. Oxygen deficiency can occur in accumulations of decaying plant residues, grain stocks, and plant root systems can experience a lack of oxygen on waterlogged or overly compacted soils.
The content of carbon dioxide can vary in certain areas of the surface layer of air within fairly significant limits. In the absence of wind in large cities, its concentration can increase tenfold. Regular daily and seasonal changes in the content of carbon dioxide in the surface layer of air, due to changes in the intensity of photosynthesis and respiration of organisms. At high concentrations, carbon dioxide is toxic, and its low content reduces the rate of photosynthesis.
Air nitrogen for most organisms of the terrestrial environment is an inert gas, but many prokaryotic organisms (nodule bacteria, azotobacter, clostridia, cyanobacteria, etc.) have the ability to bind it and involve it in the biological cycle.
Many pollutants that enter the air mainly as a result of human activities can significantly affect organisms. For example, sulfur oxide is poisonous to plants even in very low concentrations, causes the destruction of chlorophyll, damages the structure of chloroplasts, inhibits the processes of photosynthesis and respiration. Damage to plants by toxic gases varies and depends on their anatomical, morphological, physiological, biological and other characteristics. For example, lichens, spruce, pine, oak, larch are especially sensitive to industrial gases. Canadian poplar, balsam poplar, ash-leaved maple, thuja, red elderberry and some others are most resistant.
Light mode. Solar radiation reaching the Earth's surface is the main source of energy for maintaining the heat balance of the planet, water metabolism of organisms, creation of organic matter by plants, which ultimately makes it possible to form an environment capable of satisfying the vital needs of organisms. The composition of solar radiation reaching the Earth's surface includes ultraviolet rays with a wavelength of 290-380 nm, visible rays - 380-750 nm and infrared rays with a wavelength of 750-4000 nm. Ultraviolet rays are highly reactive and are harmful to organisms in large doses. In moderate doses in the range of 300-380 nm, they stimulate cell division and growth, promote the synthesis of vitamins, antibiotics, pigments (for example, in humans - sunburn, in fish and amphibians - dark caviar), increase plant resistance to diseases. Infrared rays have a thermal effect. Photosynthetic bacteria (green, purple) are able to absorb infrared rays in the range of 800-1100 nm and exist only at their expense. Approximately 50% of solar radiation comes from visible light, which has different ecological significance in the life of autotrophic and heterotrophic organisms. Green plants need light for the process of photosynthesis, the formation of chlorophyll, and the formation of the structure of chloroplasts. It affects gas exchange and transpiration, the structure of organs and tissues, and the growth and development of plants.
For animals, visible light is necessary for orientation in the environment. In some animals, visual perception extends into the ultraviolet and near infrared parts of the spectrum.
The light regime of any habitat is determined by the intensity of direct and scattered light, its amount, spectral composition, as well as the reflectivity of the surface on which the light falls. These elements of the light regime are very variable and depend on the geographic latitude of the area, the height of the sun above the horizon, the length of the day, the state of the atmosphere, the nature of the earth's surface, relief, time of day and season. In this regard, terrestrial organisms have developed various adaptations to the light regime of habitats during a long process of evolution.
Plant adaptations. In relation to lighting conditions, three main ecological groups of plants are distinguished: photophilous (heliophytes); shade-loving (sciophytes); shade-tolerant.
Heliophytes- plants of open well-lit habitats. They do not tolerate shading. An example of them can be steppe and meadow plants of the upper tier of the community, types of deserts, alpine meadows, etc.
Sciophytes- do not tolerate strong lighting in direct sunlight. These are plants of the lower tiers of shady forests, caves, rock crevices, etc.
shade-tolerant Plants have a broad ecological valence with respect to light. They grow better at high light intensity, but they also tolerate shading well, adapting to changing light conditions more easily than other plants.
Each considered group of plants is characterized by certain anatomical, morphological, physiological and seasonal adaptations to the conditions of the light regime.
One of the most obvious differences in the external appearance of light-loving and shade-loving plants is the unequal size of the leaves. In heliophytes, they are usually small or with a dissected leaf blade. This is especially evident when comparing related species growing under different lighting conditions (field violet and forest violets, spreading bluebell growing in meadows, and forest bluebell, etc.). The trend towards an increase in the size of leaves in relation to the entire volume of plants is clearly expressed in herbaceous plants of the spruce forest: common sorrel, double-leaved mullet, crow's eye, etc.
In photophilous plants, in order to reduce the intake of solar radiation, the leaves are arranged vertically or at an acute angle to the horizontal plane. In shade-loving plants, the leaves are located mainly horizontally, which allows them to receive the maximum amount of incident light. The leaf surface of many heliophytes is shiny, contributing to the reflection of rays, covered with a wax coating, thick cuticle or dense pubescence.
The leaves of shade-loving and light-loving plants also differ in anatomical structure. The light leaves have more mechanical tissues, the leaf blade is thicker than the shadow ones. The mesophyll cells are small, densely packed, the chloroplasts in them are small and light, occupying a lean position. The leaf mesophyll is differentiated into columnar and spongy tissues.
In sciophytes, the leaves are thinner, the cuticle is absent or poorly developed. The mesophyll is not differentiated into columnar and spongy tissue. There are fewer elements of mechanical tissues and chloroplasts in shadow leaves, but they are larger than in heliophytes. Shoots of light-loving plants often have short internodes, strongly branched, often rosette.
Physiological adaptations of plants to light are manifested in changes in growth processes, intensity of photosynthesis, respiration, transpiration, composition and quantity of pigments. It is known that in light-loving plants, with a lack of light, stems are stretched. The leaves of shade-loving plants contain more chlorophyll than light-loving ones, so they have a more saturated dark green color. The intensity of photosynthesis in heliophytes is maximum at high illumination (within 500–1000 lux and more), and in sciophytes, at a low amount of light (50–200 lux).
One of the forms of physiological adaptation of plants to a lack of light is the transition of some species to heterotrophic nutrition. An example of such plants are the types of shady spruce forests - creeping gudayera, real nesting, common podelnik. They live on dead organic matter, i.e. are saprophytes.
Seasonal adaptations of plants to light conditions are manifested in habitats where the light regime periodically changes. In this case, plants in different seasons can manifest themselves either as light-loving or shade-tolerant. For example, in the spring in deciduous forests, the shoot leaves of common goutweed have a light structure and are characterized by a high intensity of photosynthesis. The leaves of the summer shoots of goutweed, which develop after leafing of trees and shrubs, have a typical shadow structure. The attitude to the light regime in plants can change in the process of ontogeny and as a result of the complex influence of environmental factors. Seedlings and young plants of many meadow and forest species are more shade tolerant than adults. Requirements for the light regime sometimes change in plants when they find themselves in different climatic and edaphic conditions. For example, forest taiga species - blueberries, double-leaved maize - in the forest-tundra and tundra grow well in open habitats.
One of the factors regulating the seasonal development of organisms is the length of the day. The ability of plants and animals to respond to the length of the day is called photoperiodic reaction(FPR), and the range of phenomena regulated by the length of the day is called photoperiodism. According to the type of photoperiodic reaction, the following main groups of plants are distinguished:
1. short day plants, which require less than 12 hours of light per day to transition to flowering. These are, as a rule, people from the southern regions (chrysanthemums, dahlias, asters, tobacco, etc.).
2. long day plants- for flowering they need a day length of 12 or more hours (flax, oats, potatoes, radishes).
3. Neutral to day length plants. For them, the length of the day is indifferent, flowering occurs at any length (dandelion, tomatoes, mustard, etc.).
The length of the day affects not only the passage of the generative phases by the plant, but also their productivity and resistance to infectious diseases. It also plays an important role in the geographical distribution of plants and the regulation of their seasonal development. Species distributed in northern latitudes are predominantly long-day species, while in the tropics and subtropics they are mainly short-day or neutral. However, this pattern is not absolute. So, in the mountains of the tropical and subtropical zones, long-day species are found. Many varieties of wheat, flax, barley and other cultivated plants originating from the southern regions have a long-day FPR. Studies have shown that when the temperature drops, long-day plants can develop normally under short-day conditions.
Light in animal life. Animals need light for orientation in space, it also affects metabolic processes, behavior, and the life cycle. The completeness of visual perception of the environment depends on the level of evolutionary development. Many invertebrates have only light-sensitive cells surrounded by pigment, while unicellular ones have a light-sensitive area of the cytoplasm. The most perfect eyes of vertebrates, cephalopods and insects. They allow you to perceive the shape and size of objects, color, determine the distance. Three-dimensional vision is characteristic of humans, primates, and some birds (eagles, falcons, owls). The development of vision and its features also depend on the ecological conditions and lifestyle of specific species. In cave dwellers, the eyes can be completely or partially reduced, as, for example, in blind beetles, ground beetles, Proteus, etc.
Different types of animals are able to withstand lighting of a certain spectral composition, duration and strength. Distinguish light-loving and shade-loving, euryphotic and stenophonic kinds. Nocturnal and twilight mammals (voles, mice, etc.) endure direct sunlight for only 5–30 minutes, while daytime mammals survive for several hours. However, in bright sunlight, even desert species of lizards cannot withstand radiation for a long time, since in 5-10 minutes their body temperature rises to + 50-56ºС and the animals die. Illumination of the eggs of many insects accelerates their development, but up to certain limits (not the same for different species), after which development stops. An adaptation to protect against excessive solar radiation is the pigmented integument of some organs: in reptiles - the abdominal cavity, reproductive organs, etc. Animals avoid excessive exposure by going to shelters, hiding in the shade, etc.
Daily and seasonal changes in the light regime determine not only changes in activity, but also periods of reproduction, migration, and molting. The appearance of nocturnal insects and the disappearance of diurnal insects in the morning or evening occur at a certain brightness of illumination for each type. For example, marble beetle appears 5-6 minutes after sunset. The time of awakening of songbirds varies in different seasons. The hunting grounds of the birds change depending on the illumination. So, woodpeckers, tits, flycatchers hunt in the depths of the forest during the day, and in the morning and in the evening - in open places. Animals navigate with the help of vision during flights and migrations. Birds with amazing accuracy choose the direction of flight, guided by the sun and stars. This innate ability of them is created by natural selection as a system of instincts. The ability for such an orientation is also characteristic of other animals, such as bees. The bees that find the nectar relay information to others about where to fly for a bribe, using the sun as a guide.
The light regime limits the geographic distribution of some animals. So, a long day during the summer months in the Arctic and the temperate zone attracts birds and some mammals there, as it allows them to get the right amount of food (tits, nuthatch, waxwings, etc.), and in autumn they migrate to the south. The reverse effect is exerted by the light regime on the distribution of nocturnal animals. In the north they are rare, and in the south they even prevail over diurnal species.
Temperature regime. The intensity of all chemical reactions that make up metabolism depends on temperature conditions. Therefore, the boundaries of the existence of life are the temperatures at which the normal functioning of proteins is possible, on average from 0 to + 50ºС. However, these thresholds are not the same for different types of organisms. Due to the presence of specialized enzyme systems, some organisms have adapted to live at temperatures outside these limits. Species adapted to life in cold conditions belong to the ecological group cryophiles. In the process of evolution, they have evolved biochemical adaptations that allow them to maintain cellular metabolism at low temperatures, as well as resist or increase resistance to freezing. To resist freezing helps the accumulation in the cells of special substances - antifreeze, which prevent the formation of ice crystals in the body. Such adaptations have been found in some arctic fish of the Nototheniidae family, cod, which swim in the waters of the Arctic Ocean, with a body temperature of -1.86ºС.
The extremely low temperature at which cell activity is still possible has been recorded in microorganisms - up to –10–12ºС. Freezing resistance in some species is associated with the accumulation of organic substances in their bodies, such as glycerol, mannitol, sorbitol, which prevent the crystallization of intracellular solutions, which allows them to survive critical frosty periods in an inactive state (stupor, cryptobiosis). So, some insects in this state can withstand in winter up to -47-50ºС. Cryophiles include many bacteria, lichens, fungi, mosses, arthropods, etc.
Species, the optimum life of which is confined to the area of high temperatures, belong to the ecological group thermophiles.
Bacteria are most resistant to high temperatures, many of which can grow and multiply at +60–75ºС. Some bacteria that live in hot springs grow at temperatures of +85-90ºС, and one of the types of archaebacteria was found to be able to grow and divide at temperatures exceeding +110ºС. Spore-forming bacteria can withstand +200ºС in an inactive state for tens of minutes. There are also thermophilic species among fungi, protozoa, plants and animals, but their level of resistance to high temperatures is lower than that of bacteria. Higher plants of steppes and deserts can tolerate short-term heating up to +50–60ºС, but their photosynthesis is already inhibited by temperatures exceeding +40ºС. At a body temperature of +42–43ºС, in most animals, thermal death occurs.
The temperature regime in the terrestrial environment varies widely and depends on many factors: latitude, altitude, proximity to water bodies, time of year and day, atmospheric conditions, vegetation cover, etc. In the course of the evolution of organisms, a variety of adaptations have been developed to regulate metabolism when the ambient temperature changes. This is achieved in two ways: 1) biochemical and physiological rearrangements; 2) maintaining body temperature at a more stable level than the ambient temperature. The vital activity of most species depends on the heat coming from outside, and the body temperature depends on the course of external temperatures. Such organisms are called poikilothermic. These include all microorganisms, plants, fungi, invertebrates and most chordates. Only birds and mammals are able to maintain a constant body temperature regardless of the ambient temperature. They are called homeothermic.
Plant adaptations to temperature. The resistance of plants to changes in environmental temperature is different and depends on the specific habitat where they live. Higher plants of moderately warm and moderately cold zones eurythermal. In the active state, they tolerate temperature fluctuations from -5 to + 55ºС. At the same time, there are species that have a very narrow ecological valence in relation to temperature, i.e. are stenothermic. For example, tropical forest plants cannot even tolerate temperatures of +5–+8ºС. Some algae on snow and ice live only at 0ºС. That is, the need for heat in different plant species is not the same and varies over a fairly wide range.
Species living in places with constantly high temperatures, in the process of evolution, have acquired anatomical, morphological and physiological adaptations aimed at preventing overheating.
The main anatomical and morphological adaptations include: dense pubescence of the leaves, a shiny surface of the leaves, which contributes to the reflection of sunlight; a decrease in the area of leaves, their vertical position, folding into a tube, etc. Some species are able to secrete salts, from which crystals form on the surface of plants, reflecting the rays of the sun falling on them. Under conditions of sufficient moisture, stomatal transpiration is an effective remedy for overheating. Among the thermophilic species, depending on the degree of their resistance to high temperatures, one can distinguish
1) not heat-resistant plants are damaged already at + 30–40ºС;
2) heat-tolerant- tolerate half an hour heating up to + 50–60ºС (plants of deserts, steppes, dry subtropics, etc.).
Plants in savannahs and dry hardwood forests are regularly affected by fires when temperatures can rise to hundreds of degrees. Fire resistant plants are called pyrophytes. They have a thick crust on the trunks, impregnated with refractory substances. Their fruits and seeds have thick, often lignified integuments.
Many plants live at low temperatures. According to the degree of adaptation of plants to conditions of extreme heat deficiency, the following groups can be distinguished:
1) non-cold-resistant plants are severely damaged or die at temperatures below the freezing point of water. These include plants of tropical regions;
2) non-frost resistant plants - tolerate low temperatures, but die as soon as ice begins to form in the tissues (some evergreen subtropical plants).
3) frost-resistant plants grow in areas with cold winters.
Such morphological adaptations of plants as short stature and special forms of growth - creeping, cushion-shaped, which allow using the microclimate of the surface air layer in summer and being protected by snow cover in winter increase resistance to low temperatures.
More important for plants are physiological mechanisms of adaptation that increase their resistance to cold: leaf fall, death of above-ground shoots, accumulation of antifreezes in cells, a decrease in the water content in cells, etc. In frost-resistant plants, in the process of preparing for winter, sugars, proteins, oil, the water content in the cytoplasm decreases and its viscosity increases. All these changes lower the freezing point of tissues.
Many plants are able to remain viable in a frozen state, for example, alpine violet, arctic horseradish, wood lice, daisy, early spring ephemeroids in the forest zone, etc.
Mosses and lichens are able to tolerate prolonged freezing in a state of suspended animation. Of great importance in the adaptation of plants to low temperatures is the possibility of maintaining normal vital activity by reducing the temperature optimums of physiological processes and the lower temperature limits at which these processes are possible.
In temperate and high latitudes, due to seasonal changes in climatic conditions, plants in the annual cycle of development alternate active and dormant phases. Annual plants after the end of the growing season survive the winter in the form of seeds, and perennials go into a dormant state. Distinguish deep and compelled peace. Plants that are in a state of deep dormancy do not respond to favorable thermal conditions. After the end of deep dormancy, the plants are ready for the resumption of development, but in nature in winter it is impossible due to low temperatures. Therefore, this phase is called forced rest.
Animal adaptations to temperature. Compared to plants, animals have a wider range of ways to regulate their body temperature due to their ability to move around in space and generate much more of their own internal heat.
The main ways of adaptation of animals:
1) chemical thermoregulation- this is a reflex increase in heat production in response to a decrease in the temperature of the environment, based on a high level of metabolism;
2) physical thermoregulation- carried out due to the ability to retain heat due to the special features of the structure (the presence of hair and feather cover, the distribution of fat reserves, etc.) and changes in the level of heat transfer;
3) behavioral thermoregulation- this is a search for favorable habitats, a change in posture, the construction of shelters, nests, etc.
For poikilothermic animals, the main way to regulate body temperature is behavioral. In extreme heat, animals hide in the shade, burrows. As winter approaches, they seek shelter, build nests, and reduce their activity. Some species are able to maintain optimal body temperature due to the work of muscles. For example, bumblebees warm up the body with special muscle contractions, which makes it possible for them to feed in cool weather. Some poikilothermic animals avoid overheating by increasing heat loss through evaporation. For example, frogs, lizards in hot weather begin to breathe heavily or keep their mouths open, increasing the evaporation of water through the mucous membranes.
Homeothermic animals are characterized by very efficient regulation of heat input and output, which allows them to maintain a constant optimal body temperature. Their mechanisms of thermoregulation are very diverse. They tend to chemical thermoregulation, characterized by a high metabolic rate and the production of a large amount of heat. Unlike poikilothermic animals, in warm-blooded animals, under the action of cold, oxidative processes do not weaken, but intensify. In many animals, additional heat is generated due to muscle and adipose tissue. Mammals have a specialized brown adipose tissue, in which all the released energy is used to heat the body. It is most developed in animals of a cold climate. Maintaining body temperature by increasing heat production requires a large expenditure of energy, so animals with increased chemical regulation need a large amount of food or spend a lot of fat reserves. Therefore, the strengthening of chemical regulation has limits due to the possibility of obtaining food. With a lack of food in winter, this way of thermoregulation is ecologically unfavorable.
Physical thermoregulation environmentally more beneficial, since adaptation to cold is carried out by maintaining heat in the body of the animal. Its factors are the skin, thick fur of mammals, feather and down cover of birds, body fat, evaporation of water through sweating or through the mucous membranes of the oral cavity and upper respiratory tract, the size and shape of the animal's body. To reduce heat transfer, large body sizes are more beneficial (the larger the body, the smaller its surface per unit mass, and, consequently, heat transfer, and vice versa). For this reason, individuals of closely related species of warm-blooded animals that live in cold conditions are larger than those that are common in warm climates. This pattern has been named Bergman's rules. Temperature regulation is also carried out through the protruding parts of the body - auricles, limbs, tails, organs of smell. In cold regions, they tend to be smaller than in warmer regions ( Allen's rule). For homoiothermic organisms, it is also important behavioral methods of thermoregulation, which are very diverse - from changing the posture and searching for shelters to the construction of complex shelters, nests, and the implementation of near and far migrations. Some warm-blooded animals use group behavior. For example, penguins in severe frost huddle together in a dense pile. Inside such a cluster, the temperature is maintained at about + 37ºС even in the most severe frosts. Camels in the desert in extreme heat also huddle, but this is achieved by preventing strong heating of the surface of the body.
The combination of various methods of chemical, physical and behavioral thermoregulation allows warm-blooded animals to maintain a constant body temperature in a wide range of environmental temperature fluctuations.
water regime. The normal functioning of the body is possible only with sufficient water supply. The modes of humidity in the ground-air environment are very diverse - from the complete saturation of the air with water vapor in the humid tropics to the almost complete absence of moisture in the air and in the desert soil. For example, in the Sinai desert, the annual rainfall is 10-15 mm, and in the Libyan desert (in Aswan) they do not happen at all. The water supply of terrestrial organisms depends on the mode of precipitation, the availability of soil moisture reserves, reservoirs, the level of groundwater, terrain, features of atmospheric circulation, etc. This has led to the development of many adaptations in terrestrial organisms to various habitat humidity regimes.
Plant adaptations to the water regime. Lower land plants absorb water from the substrate by parts of the thallus or rhizoids immersed in it, and moisture from the atmosphere - by the entire surface of the body.
Among higher plants, mosses absorb water from the soil with rhizoids or the lower part of the stem (sphagnum mosses), and most others with roots. The flow of water into the plant depends on the magnitude of the sucking power of the root cells, the degree of branching of the root system and the depth of penetration of the roots into the soil. Root systems are very plastic and react to changing conditions, primarily moisture.
With a lack of moisture in the surface horizons of the soil, many plants have root systems that penetrate deep into the soil, but branch weakly, as, for example, in saxaul, camel's thorn, Scots pine, rough cornflower, etc. In many cereals, on the contrary, root systems strongly branch and grow in the surface layers of the soil (in rye, wheat, feather grass, etc.). The water that enters the plant is carried through the xylem to all organs where it is spent on life processes. On average, 0.5% goes to photosynthesis, and the rest - to replenish losses from evaporation and maintain turgor. The water balance of the plant remains balanced if the absorption of water, its conduction and expenditure are harmoniously coordinated with each other. Depending on the ability to regulate the water balance of their body, land plants are divided into poikilohydride and homoiohydride.
poikilohydrid plants unable to actively regulate their water balance. They do not have devices that help retain water in the tissues. The water content in cells is determined by air humidity and depends on its fluctuations. Poikilohydrid plants include terrestrial algae, lichens, some mosses, and rainforest ferns. During the dry period, these plants dry up almost to an air-dry state, but after the rain they “come to life” again and turn green.
Homoyohydrid plants able to maintain a relatively constant level of water content in the cells. These include most of the higher land plants. They have a large central vacuole in their cells, so there is always a supply of water. In addition, transpiration is regulated by the stomatal apparatus, and the shoots are covered with an epidermis with a cuticle that is not permeable to water.
However, the ability of plants to regulate their water metabolism is not the same. Depending on their adaptability to the humidity conditions of habitats, three main ecological groups are distinguished: hygrophytes, xerophytes and mesophytes.
Hygrophytes- these are plants of wet habitats: swamps, damp meadows and forests, banks of reservoirs. They cannot stand water deficiency, they react to a decrease in soil and air moisture by rapid wilting or growth inhibition. Their leaf blades are wide, without a thick cuticle. Mesophyll cells are located loosely, between them there are large intercellular spaces. The stomata of hygrophytes are usually widely open and often located on both sides of the leaf blade. As a result, their transpiration rate is very high. In some plants in highly humid habitats, excess water is removed through hydathodes (water stomata) located along the edge of the leaf. Excessive soil moisture leads to a decrease in the oxygen content in it, which makes breathing and the suction function of the roots difficult. Therefore, the roots of hygrophytes are located in the surface horizons of the soil, they branch weakly, and there are few root hairs on them. The organs of many herbaceous hygrophytes have a well-developed system of intercellular spaces through which atmospheric air enters. In plants that live on heavily waterlogged soils, periodically flooded with water, special respiratory roots are formed, as, for example, in swamp cypress, or supporting ones, as in mangrove woody plants.
Xerophytes able to tolerate significant prolonged dryness of air and soil in an active state. They are widely distributed in steppes, deserts, dry subtropics, etc. In the temperate climate zone, they settle on dry sandy and sandy loamy soils, in elevated areas of the relief. The ability of xerophytes to tolerate a lack of moisture is due to their anatomical, morphological and physiological features. On these grounds, they are divided into two groups: succulents and sclerophytes.
succulents- perennial plants with succulent fleshy leaves or stems, in which water storage tissue is highly developed. There are leaf succulents - aloe, agave, stonecrop, young and stem, in which the leaves are reduced, and the ground parts are represented by fleshy stems (cacti, some spurges). A distinctive feature of succulents is the ability to store a large amount of water and use it extremely sparingly. Their rate of transpiration is very low, since there are very few stomata, they are often immersed in leaf or stem tissue and are usually closed during the day, which helps them limit water consumption. Closing the stomata during the day leads to difficulty in the processes of photosynthesis and gas exchange, therefore, succulents have developed a special way of photosynthesis, in which carbon dioxide released during respiration is partially used. In this regard, the intensity of photosynthesis in them is low, which is associated with slow growth and rather low competitiveness. Succulents are characterized by low osmotic pressure of cell sap, with the exception of those that grow on saline soils. Their root systems are superficial, highly branched and fast growing.
Sclerophytes are hard, dry-looking plants due to a large amount of mechanical tissue and low watering of leaves and stems. The leaves of many species are small, narrow or reduced to scales, spines; often have dense pubescence (cat's paw, silver cinquefoil, many wormwood, etc.) or waxy coating (Russian cornflower, etc.). Their root systems are well developed and often many times larger in total mass than the above-ground parts of plants. A variety of physiological adaptations also help sclerophytes successfully withstand the lack of moisture: high osmotic pressure of cell sap, resistance to tissue dehydration, high water-holding capacity of tissues and cells, due to the high viscosity of the cytoplasm. Many sclerophytes use the most favorable periods of the year for vegetation, and when drought sets in, they sharply reduce vital processes. All of the above properties of xerophytes contribute to their drought tolerance.
Mesophytes grow in medium moisture conditions. They are more demanding on moisture than xerophytes, and less than hygrophytes. Mesophyte leaf tissues are differentiated into columnar and spongy parenchyma. Integumentary tissues may have some xeromorphic features (sparse pubescence, thickened cuticle layer). But they are less pronounced than in xerophytes. Root systems can penetrate deep into the soil or be located in the surface horizons. in terms of their ecological needs, mesophytes are a very diverse group. Thus, among meadow and forest mesophytes, there are species with increased moisture love, which are characterized by a high water content in tissues and a rather weak water-retaining capacity. These are meadow foxtail, marsh bluegrass, soddy meadow, Linnaeus's golokuchnik and many others.
In habitats with periodic or constant (slight) lack of moisture, mesophytes have signs of xeromorphic organization and increased physiological resistance to drought. Examples of such plants are pedunculate oak, mountain clover, medium plantain, crescent alfalfa, etc.
Animal adaptations. In relation to the water regime among animals, hygrophiles (moisture-loving), xerophiles (dry-loving) and mesophiles (preferring average moisture conditions) can be distinguished. An example of hygrophiles are wood lice, mosquitoes, springtails, dragonflies, etc. All of them do not tolerate a significant water deficit and do not tolerate even a short-term drought. Monitor lizards, camels, desert locusts, black beetles, etc. are xerophilous. They inhabit the most arid habitats.
Animals obtain water through drinking, food, and through the oxidation of organic matter. Many mammals and birds (elephants, lions, hyenas, swallows, swifts, etc.) need drinking water. Desert species such as jerboas, African gerbils, and the American kangaroo rat can do without drinking water. Caterpillars of clothes moth, barn and rice weevils and many others live solely due to metabolic water.
Animals are characterized by ways of regulating the water balance: morphological, physiological, behavioral.
To morphological methods of maintaining water balance include formations that help retain water in the body: shells of land snails, keratinized integuments of reptiles, poor water permeability of integuments in insects, etc. It is shown that the permeability of integuments of insects does not depend on the structure of chitin, but is determined by the thinnest wax layer covering its surface . The destruction of this layer dramatically increases evaporation through the covers.
To physiological adaptations of the regulation of water metabolism include the ability to form metabolic moisture, save water when excreting urine and feces, endurance to dehydration, changes in sweating and water loss through the mucous membranes. Conservation of water in the digestive tract is achieved by the absorption of water by the intestines and the formation of almost dehydrated feces. In birds and reptiles, the end product of nitrogen metabolism is uric acid, for the removal of which practically no water is consumed. Active regulation of sweating and evaporation of moisture from the surface of the respiratory tract is widely used by homeothermic animals. For example, in a camel, in the most extreme cases of moisture deficiency, sweating stops and evaporation from the respiratory tract is sharply reduced, which leads to water retention in the body. Evaporation associated with the need for thermoregulation can cause dehydration of the body, so many small warm-blooded animals in dry and hot climates avoid exposure to heat and conserve moisture by hiding underground.
In poikilothermic animals, an increase in body temperature following air heating avoids excessive water loss, but they cannot completely avoid evaporative losses. Therefore, for cold-blooded animals, the main way to maintain the water balance during life in arid conditions is to avoid excessive heat loads. Therefore, in the complex of adaptations to the water regime of the terrestrial environment, behavioral ways regulation of water balance. These include special forms of behavior: digging holes, searching for water bodies, choosing habitats, etc. This is especially important for herbivorous and granivorous animals. For many of them, the presence of water bodies is a prerequisite for settling in arid regions. For example, the distribution in the desert of species such as the Cape buffalo, waterbuck, and some antelope is completely dependent on the availability of watering places. Many reptiles and small mammals live in burrows where relatively low temperatures and high humidity promote water exchange. Birds often use hollows, shady tree crowns, etc.
A distinctive feature of the ground-air environment is the presence of air (a mixture of various gases) in it.
Air has a low density, so it cannot act as a support for organisms (with the exception of flying ones). It is the low density of air that determines its insignificant resistance when organisms move along the soil surface. At the same time, it makes it difficult to move them in the vertical direction. The low air density also determines the low pressure on land (760 mm Hg = 1 atm). Air, smaller than water, blocks the penetration of sunlight. It has a higher transparency than water.
The gas composition of the air is constant (you know about this from the geography course). Oxygen and carbon dioxide, as a rule, are not limiting factors. Water vapor and various pollutants are present as impurities in the air.
Over the past century, as a result of human activities in the atmosphere, the content of various pollutants has sharply increased. Among them, the most dangerous are: nitrogen and sulfur oxides, ammonia, formaldehyde, heavy metals, hydrocarbons, etc. Living organisms are practically not adapted to them. For this reason, air pollution is a serious global environmental problem. Its solution requires the implementation of environmental measures at the level of all states of the Earth.
Air masses move in horizontal and vertical directions. This leads to the emergence of such an environmental factor as wind. Wind can cause shifting of sands in deserts (sandstorms). It is able to blow out soil particles on any terrain, reducing land fertility (wind erosion). Wind has a mechanical effect on plants. It is capable of causing windblows (reversing of trees with roots), windbreaks (fractures of tree trunks), deformation of the tree crown. The movement of air masses significantly affects the distribution of precipitation and the temperature regime in the ground-air environment.
Water regime of the ground-air environment
From the course of geography, you know that the ground-air environment can be both extremely saturated with moisture (tropics) and very poor in it (deserts). Precipitation is unevenly distributed both seasonally and geographically. Humidity in the environment fluctuates over a wide range. It is the main limiting factor for living organisms.
Temperature regime of the ground-air environment
The temperature in the ground-air environment has a daily and seasonal periodicity. Organisms have adapted to it since the emergence of life on land. Therefore, temperature is less likely than humidity to act as a limiting factor.
Adaptations of plants and animals to life in the ground-air environment
With the release of plants on land, they developed tissues. You studied the structure of plant tissues in the 7th grade biology course. Due to the fact that air cannot serve as a reliable support, mechanical tissues (wood and bast fibers) arose in plants. A wide range of changes in climatic factors caused the formation of dense integumentary tissues - periderm, crust. Due to the mobility of air (wind), plants have developed adaptations for pollination, the spread of spores, fruits and seeds.
The life of animals in suspension in the air is impossible due to its low density. Many of the species (insects, birds) have adapted to active flight and can stay in the air for a long time. But their reproduction occurs on the surface of the soil.
The movement of air masses in horizontal and vertical directions is used by some small organisms for passive settlement. In this way, protists, spiders, and insects settle. The low air density caused the improvement in animals in the process of evolution of the external (arthropods) and internal (vertebral) skeletons. For the same reason, there is a limitation of the maximum mass and size of the body of terrestrial animals. The largest land animal, the elephant (weight up to 5 tons), is much smaller than the sea giant, the blue whale (up to 150 tons). Thanks to the appearance of different types of limbs, mammals were able to populate areas of land with a variety of relief patterns.
General characteristics of the soil as a living environment
Soil is the top layer of the earth's crust that is fertile. It was formed as a result of the interaction of climatic and biological factors with the underlying rock (sand, clay, etc.). The soil is in contact with the air and acts as a support for terrestrial organisms. It is also a source of mineral nutrition for plants. At the same time, soil is a living environment for many types of organisms. The soil is characterized by the following properties: density, humidity, temperature, aeration (air supply), environmental reaction (pH), salinity.
Soil density increases with depth. Humidity, temperature and soil aeration are closely interconnected and interdependent. Temperature fluctuations in the soil are smoothed compared to the surface air and are no longer traced at a depth of 1-1.5 m. Well-moistened soils warm up slowly and cool down slowly. An increase in soil moisture and temperature worsens its aeration, and vice versa. The hydrothermal regime of the soil and its aeration depend on the structure of the soil. Clay soils are more water-retaining than sandy soils. But they are less aerated and warm up worse. According to the reaction of the environment, soils are divided into three types: acidic (pH< 7,0), нейтральные (рН ≈ 7,0) и щелочные (рН > 7,0).
Adaptations of plants and animals to life in the soil
The soil in the life of plants performs the functions of fixing, water supply, and a source of mineral nutrition. The concentration of nutrients in the soil has led to the development of root systems and conductive tissues in plants.
Animals living in the soil have a number of adaptations. They are characterized by different ways of moving in the soil. It can be digging moves and holes, like a bear and a mole. Earthworms can push apart soil particles and make passages. Insect larvae are able to crawl among soil particles. In this regard, in the process of evolution, appropriate adaptations have been developed. Digging organisms developed digging limbs. Annelids have a hydrostatic skeleton, while insects and centipedes have claws.
Soil animals have a short compact body with non-wetting covers (mammals) or covered with mucus. Life in the soil as a habitat has led to atrophy or underdevelopment of the organs of vision. The mole has tiny, underdeveloped eyes often hidden under a fold of skin. To facilitate movement in narrow soil passages, mole wool acquired the ability to fit in two directions.
In the ground-air environment, organisms are surrounded by air. It has low humidity, density and pressure, high transparency and oxygen content. Humidity is the main limiting factor. The soil as a living environment is characterized by high density, a certain hydrothermal regime, and aeration. Plants and animals have developed a variety of adaptations to life in the ground-air and soil environments.
LECTURE 4
ENVIRONMENTS OF LIFE AND ADAPTATION OF ORGANISMS TO THEM.
Water environment.
This is the oldest environment in which life originated and evolved for a long time even before the first organisms appeared on land. According to the composition of the aquatic environment of life, two of its main variants are distinguished: freshwater and marine environments.
More than 70% of the planet's surface is covered with water. However, due to the comparative evenness of the conditions of this environment (“water is always wet”), the diversity of organisms in the aquatic environment is much less than on land. Only every tenth species of the plant kingdom is associated with the aquatic environment, the diversity of aquatic animals is somewhat higher. The general ratio of the number of land/water species is about 1:5.
The density of water is 800 times higher than the density of air. And the pressure on the organisms inhabiting it is also much higher than in terrestrial conditions: for every 10 m of depth, it increases by 1 atm. One of the main directions of adaptation of organisms to life in the aquatic environment is to increase buoyancy by increasing the surface of the body and the formation of tissues and organs containing air. Organisms can float in the water (as representatives of plankton - algae, protozoa, bacteria) or actively move, like fish that form nekton. A significant part of the organisms is attached to the bottom surface or moves along it. As already noted, an important factor in the aquatic environment is the current.
Table 1 - Comparative characteristics of habitats and adaptation of living organisms to them
The basis of the production of most aquatic ecosystems are autotrophs, using sunlight that breaks through the water column. The possibility of "piercing" this thickness is determined by the transparency of the water. In the clear water of the ocean, depending on the angle of incidence of sunlight, autotrophic life is possible up to a depth of 200 m in the tropics and 50 m in high latitudes (for example, in the seas of the Arctic Ocean). In strongly disturbed freshwater reservoirs, a layer inhabited by autotrophs (it is called photic), may be only a few tens of centimeters.
The red part of the light spectrum is most actively absorbed by water, therefore, as noted, the deep waters of the seas are inhabited by red algae, which are capable of assimilating green light due to additional pigments. The transparency of water is determined by a simple device - the Secchi disk, which is a white-colored circle with a diameter of 20 cm. The degree of water transparency is judged by the depth at which the disk becomes indistinguishable.
The most important characteristic of water is its chemical composition - the content of salts (including nutrients), gases, hydrogen ions (pH). According to the concentration of nutrients, especially phosphorus and nitrogen, water bodies are divided into oligotrophic, mesotrophic and eutrophic. With an increase in the content of nutrients, for example, when a reservoir is polluted with wastewater, the process of eutrophication of aquatic ecosystems occurs.
The oxygen content in water is about 20 times lower than in the atmosphere, and is 6-8 ml/l. It decreases with increasing temperature, as well as in stagnant water bodies in winter, when the water is isolated from the atmosphere by a layer of ice. A decrease in oxygen concentration can cause the death of many inhabitants of aquatic ecosystems, excluding species that are especially resistant to oxygen deficiency, such as crucian carp or tench, which can live even when the oxygen content drops to 0.5 ml/l. The content of carbon dioxide in water, on the contrary, is higher than in the atmosphere. In sea water, it can contain up to 40-50 ml / l, which is about 150 times higher than in the atmosphere. Consumption of carbon dioxide by phytoplankton during intensive photosynthesis does not exceed 0.5 ml/l per day.
The concentration of hydrogen ions in water (pH) can vary within 3.7-7.8. Waters with a pH of 6.45 to 7.3 are considered neutral. As already noted, with a decrease in pH, the biodiversity of organisms inhabiting the aquatic environment rapidly decreases. Crayfish, many types of mollusks die at pH below 6, perch and pike can withstand pH up to 5, eel and char survive when the pH drops to 5-4.4. In more acidic waters, only some species of zooplankton and phytoplankton survive. Acid rains associated with the release of large amounts of sulfur and nitrogen oxides into the atmosphere by industrial enterprises have become the cause of acidification of the waters of lakes in Europe and the United States and a sharp depletion of their biological diversity. Oxygen is often the limiting factor. Its content usually does not exceed 1% by volume. With an increase in temperature, enrichment with organic matter and weak mixing, the oxygen content in water decreases. The low availability of oxygen for organisms is also associated with its weak diffusion (it is thousands of times less in water than in air). The second limiting factor is light. Illumination decreases rapidly with depth. In perfectly clean waters, light can penetrate to a depth of 50-60 m, in heavily polluted waters - only a few centimeters.
This environment is the most homogeneous among others. It varies little in space, there are no clear boundaries between individual ecosystems. The amplitudes of the factor values are also small. The difference between the maximum and minimum temperatures here usually does not exceed 50°C (while in the ground-air environment it is up to 100°C). The medium has a high density. For oceanic waters it is equal to 1.3 g/cm 3 , for fresh waters it is close to unity. The pressure only changes with depth: each 10-meter layer of water increases the pressure by 1 atmosphere.
There are few warm-blooded animals in the water, or homoiothermic(Greek homa - the same, thermo - heat), organisms. This is the result of two causes: a small temperature fluctuation and a lack of oxygen. The main adaptive mechanism of homoiothermia is resistance to unfavorable temperatures. In water, such temperatures are unlikely, and in the deep layers the temperature is almost constant (+4°C). Maintaining a constant body temperature is necessarily associated with intensive metabolic processes, which is possible only with a good supply of oxygen. There are no such conditions in water. Warm-blooded animals of the aquatic environment (whales, seals, fur seals, etc.) are former inhabitants of the land. Their existence is impossible without periodic communication with the air environment.
Typical inhabitants of the aquatic environment have a variable body temperature and belong to the group poikiothermal(Greek poikios - varied). To some extent, they compensate for the lack of oxygen by increasing the contact of the respiratory organs with water. Many water dwellers (hydrobionts) consume oxygen through all the integuments of the body. Often, breathing is combined with a filtration type of nutrition, in which a large amount of water is passed through the body. Some organisms during periods of acute lack of oxygen are able to drastically slow down their vital activity, up to the state suspended animation(almost complete cessation of metabolism).
Organisms adapt to high water density mainly in two ways. Some use it as a support and are in a state of free soaring. The density (specific gravity) of such organisms usually differs little from the density of water. This is facilitated by the complete or almost complete absence of the skeleton, the presence of outgrowths, droplets of fat in the body or air cavities. Such organisms are grouped plankton(Greek planktos - wandering). There are plant (phyto-) and animal (zoo-) plankton. The size of planktonic organisms is usually small. But they account for the bulk of aquatic life.
Actively moving organisms (swimmers) adapt to overcome the high density of water. They are characterized by an elongated body shape, well-developed muscles, and the presence of friction-reducing structures (mucus, scales). In general, the high density of water results in a decrease in the proportion of the skeleton in the total body mass of hydrobionts compared to terrestrial organisms. In conditions of lack of light or its absence, organisms use sound for orientation. It spreads much faster in water than in air. To detect various obstacles, reflected sound is used by the type of echolocation. Odor phenomena are also used for orientation (odors are felt much better in water than in air). In the depths of the waters, many organisms have the property of self-luminescence (bioluminescence).
Plants that live in the water column use the most deeply penetrating blue, blue and blue-violet rays in the process of photosynthesis. Accordingly, the color of plants changes with depth from green to brown and red.
The following groups of aquatic organisms are distinguished adequately to adaptive mechanisms: plankton- free floating nekton(Greek nektos - floating) - actively moving, benthos(Greek benthos - depth) - inhabitants of the bottom, pelagos(Greek pelagos - open sea) - inhabitants of the water column, neuston- inhabitants of the upper film of water (part of the body can be in the water, part - in the air).
Human impact on the aquatic environment is manifested in a decrease in transparency, a change in the chemical composition (pollution) and temperature (thermal pollution). The consequence of these and other impacts is oxygen depletion, reduced productivity, changes in species composition, and other deviations from the norm.
Ground-air environment.
Air has a much lower density than water. For this reason, the development of the air environment, which took place much later than the origin of life and its development in the aquatic environment, was accompanied by an increase in the development of mechanical tissues, which allowed organisms to resist the action of the law of universal gravitation and wind (the skeleton in vertebrates, chitinous shells in insects, sclerenchyma in plants). Not a single organism can live permanently in the conditions of only an air environment, and therefore even the best "flyers" (birds and insects) must periodically descend to the ground. The movement of organisms through the air is possible due to special devices - wings in birds, insects, some species of mammals and even fish, parachutes and wings in seeds, air sacs in coniferous pollen, etc.
Air is a poor conductor of heat, and therefore it was in the air environment on land that endothermic (warm-blooded) animals arose, which are easier to keep warm than ectothermic inhabitants of the aquatic environment. For warm-blooded aquatic animals, including giant whales, the aquatic environment is secondary; the ancestors of these animals once lived on land.
Life in the air required more complex reproductive mechanisms that would eliminate the risk of germ cells drying out (multicellular antheridia and archegonia, and then ovules and ovaries in plants, internal fertilization in animals, eggs with a dense shell in birds, reptiles, amphibians, etc. ).
In general, there are many more opportunities for the formation of various combinations of factors in the ground-air environment than in water. It is in this environment that differences in the climate of different regions (and at different heights above sea level within the same region) are most clearly manifested. Therefore, the diversity of terrestrial organisms is much higher than that of aquatic ones.
This environment is one of the most complex both in terms of properties and diversity in space. It is characterized by low air density, large temperature fluctuations (annual amplitudes up to 100°C), high atmospheric mobility. Limiting factors are most often a lack or excess of heat and moisture. In some cases, for example, under the canopy of the forest, there is a lack of light.
Large fluctuations in temperature over time and its significant variability in space, as well as a good supply of oxygen, were the motives for the appearance of organisms with a constant body temperature (homeothermic). Homeothermy allowed land dwellers to significantly expand their habitat (species ranges), but this is inevitably associated with increased energy expenditure.
For organisms of the ground-air environment, three mechanisms of adaptation to the temperature factor are typical: physical, chemical, behavioral. Physical controlled by heat transfer. Its factors are skin, body fat, water evaporation (sweating in animals, transpiration in plants). This pathway is characteristic of poikyothermic and homeothermic organisms. Chemical adaptations based on maintaining a certain body temperature. It requires an intense metabolism. Such adaptations are characteristic of homoiothermic and only partially poikyothermic organisms. behavioral path it is carried out by means of the choice of preferred positions by organisms (open to the sun or shaded places, various types of shelter, etc.). It is characteristic of both groups of organisms, but poikyothermic to a greater extent. Plants adapt to the temperature factor mainly through physical mechanisms (covers, evaporation of water) and only partially through behavioral ones (rotation of leaf blades relative to the sun's rays, use of the heat of the earth and the warming role of snow cover).
Adaptations to temperature are also carried out through the size and shape of the body of organisms. For heat transfer, large sizes are more advantageous (than the larger the body, the smaller its surface area per unit mass, and hence heat transfer, and vice versa). For this reason, the same species found in colder environments (in the north) tend to be larger than those found in warmer climates. This pattern is called Bergman's rule. Temperature regulation is also carried out through the protruding parts of the body (ears, limbs, olfactory organs). They tend to be smaller in colder regions than in warmer regions. (Allen's rule).
The dependence of heat transfer on body size can be judged by the amount of oxygen consumed during respiration per unit mass by various organisms. It is the larger, the smaller the size of the animals. So, per 1 kg of weight, oxygen consumption (cm 3 / hour) was: horse - 220, rabbit - 480, rat -1800, mouse - 4100.
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