4.1. Aquatic habitat. Specifics of adaptation of aquatic organisms
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 areas also differ in salt regime, speed of horizontal movements (currents) , 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 adaptation to the general properties of the aquatic environment, its inhabitants must also be adapted to a variety of particular conditions. The inhabitants of the aquatic environment received a common name in ecology hydrobionts. They inhabit the World Ocean, continental reservoirs and groundwater. In any body of water, zones with different conditions can be distinguished.
4.1.1. Ecological zones of the World Ocean
In the ocean and its seas, there are primarily two ecological areas: the water column - pelagic and the bottom - benthal (Fig. 38). Depending on the depth, benthal is divided into sublittoral zone - an area of gradual decline of land to a depth of approximately 200 m, bathyal– area of steep slope and abyssal zone– an area of the ocean floor with an average depth of 3–6 km. Even deeper benthic regions, corresponding to the depressions of the ocean floor, are called ultraabyssal. The edge of the shore that is flooded during high tides is called littoral Above the tide level, the part of the coast moistened by the spray of the surf is called supralittoral.
Rice. 38. Ecological zones of the World Ocean
Naturally, for example, the inhabitants of the sublittoral zone 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 monstrous pressure of several hundred, and sometimes about a thousand atmospheres. Therefore, just an indication of the benthic zone in which a particular species of organism lives 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 pelagic zone, are classified as Pelagos. The pelagic zone is also divided into vertical zones corresponding in depth to the benthic zones: epipelagic, bathypelagic, abyssopelagic. 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. In the twilight bathyal and dark abyssal depths, only microorganisms and animals live. Different ecological zones are also distinguished in all other types of reservoirs: lakes, swamps, ponds, rivers, etc. The diversity of aquatic organisms that have mastered all these habitats is very great.
4.1.2. Basic properties of the aquatic environment
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/cm 3 at 4 °C. The density of natural waters containing dissolved salts can be greater, up to 1.35 g/cm 3 . Pressure increases with depth by an average of 1 × 10 5 Pa (1 atm) for every 10 m.
Due to the sharp pressure gradient in water bodies, aquatic organisms are generally much more eurybathic compared to land organisms. Some species, distributed at different depths, tolerate pressure from several to hundreds of atmospheres. For example, holothurians of the genus Elpidia and worms Priapulus caudatus live from the coastal zone to the ultra-abyssal zone. Even freshwater inhabitants, such as slipper ciliates, suvoikas, swimming beetles, etc., can withstand up to 6 × 10 7 Pa (600 atm) in experiments.
However, many inhabitants of the seas and oceans are relatively stenobatic and confined to certain depths. Stenobacy is most often characteristic of shallow- and deep-sea species. Only the littoral zone is inhabited by the annelids Arenicola and limpet mollusks (Patella). Many fish, for example from the group of anglers, cephalopods, crustaceans, pogonophora, 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 provides the ability to lean on it, which is especially important for non-skeletal forms. The density of the environment serves as a condition for floating in water, and many aquatic organisms are adapted specifically to this way of life. Suspended organisms floating in water are combined into a special ecological group of aquatic organisms - plankton (“planktos” – soaring).
Rice. 39. Increase in the relative body surface of planktonic organisms (according to S. A. Zernov, 1949):
A – rod-shaped:
1 – diatom Synedra;
2 – cyanobacterium Aphanizomenon;
3 – peridine alga Amphisolenia;
4 – Euglena acus;
5 – cephalopod Doratopsis vermicularis;
6 – copepod Setella;
7 – Porcellana larva (Decapoda)
B – dissected forms:
1 – mollusk Glaucus atlanticus;
2 – worm Tomopetris euchaeta;
3 – larva of Palinurus crayfish;
4 – larval fish of the monkfish Lophius;
5 – copepod Calocalanus pavo
The plankton includes unicellular and colonial algae, protozoa, jellyfish, siphonophores, ctenophores, pteropods and keelfoot 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. Such adaptations include: 1) a general increase in the relative surface of the body due to reduction in size, flattening, elongation, development of numerous projections or bristles, which increases friction with water; 2) a decrease in density due to the reduction of the skeleton, the accumulation of fats, gas bubbles, etc. in the body. 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 has the appearance of strands that merge only around the nucleus. Siphonophores, a number of jellyfish, planktonic gastropods, etc. also have air chambers.
Seaweed (phytoplankton) They float in water passively, but 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 types 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 type of plankton is an ecological group Neuston (“nein” - swim) - inhabitants of the surface film of water at the border with the air.
The density and viscosity of water greatly influence the possibility of active swimming. Animals capable of fast swimming and overcoming the force of currents are united in an ecological group nekton (“nektos” – floating). Representatives of nekton are fish, squid, and dolphins. Rapid movement in the water column is possible only if you have a streamlined body shape and highly developed muscles. The torpedo-shaped shape is developed in all good swimmers, regardless of their systematic affiliation and method of movement in the water: reactive, due to bending of the body, with the help of limbs.
Oxygen regime. 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 breathing conditions of aquatic organisms are significantly complicated. Oxygen enters water mainly through the photosynthetic activity of algae and diffusion from the air. Therefore, the upper layers of the water column are, as a rule, richer in this gas than the lower ones. As the temperature and salinity of water increase, 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, life-rich depths 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. Conditions near the bottom of reservoirs can be close to anaerobic.
Among aquatic inhabitants there are many species that can tolerate wide fluctuations in oxygen content in water, up to its almost complete absence (euryoxybionts – “oxy” – oxygen, “biont” – inhabitant). These include, for example, the freshwater oligochaete Tubifex tubifex and the gastropod Viviparus viviparus. Among fish, carp, tench, and crucian carp can withstand very low oxygen saturation of water. However, a number of types stenoxybiont – they can exist only with sufficiently high oxygen saturation of the water (rainbow trout, brown trout, minnow, eyelash worm Planaria alpina, larvae of mayflies, stoneflies, etc.). Many species are capable of falling into an inactive state when there is a lack of oxygen - anoxybiosis - and thus experience an unfavorable period.
Respiration of aquatic organisms occurs either through the surface of the body or through specialized organs - gills, lungs, trachea. In this case, the integument can serve as an additional respiratory organ. For example, the loach fish consumes an average of 63% of oxygen through its skin. If gas exchange occurs through the integuments of the body, they are very thin. Breathing is also made easier by increasing the surface area. This is achieved during the evolution of species by the formation of various outgrowths, flattening, elongation, and a general decrease in body size. Some species, when there is a lack of oxygen, actively change the size of the respiratory surface. Tubifex tubifex worms greatly elongate their body; hydra and sea anemone - tentacles; echinoderms - ambulacral legs. Many sessile and sedentary animals renew the water around them, either by creating a directed current or by oscillating movements, promoting its mixing. Bivalve mollusks use cilia lining the walls of the mantle cavity for this purpose; crustaceans - the work of the abdominal or thoracic legs. Leeches, bell mosquito larvae (bloodworms), and many oligochaetes sway their bodies, sticking out of the ground.
In some species, a combination of water and air respiration occurs. These include lungfishes, siphonophores discophants, many pulmonary mollusks, crustaceans Gammarus lacustris, etc. Secondary aquatic animals usually retain the atmospheric type of respiration as it is more energetically favorable and therefore require contact with the air, for example, pinnipeds, cetaceans, water beetles, mosquito larvae, etc.
Lack of oxygen in water sometimes leads to catastrophic phenomena - I'm dying, accompanied by the death of many aquatic organisms. Winter freezes often caused by the formation of ice on the surface of bodies of water and the cessation of contact with air; summer– an increase in water temperature and a resulting decrease in oxygen solubility.
Frequent death of fish and many invertebrates in winter is characteristic, for example, of the lower part of the Ob River basin, the waters of which, flowing from the wetlands of the West Siberian Lowland, are extremely poor in dissolved oxygen. Sometimes death occurs in the seas.
In addition to a lack of oxygen, death 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 regime. Maintaining the water balance of aquatic organisms 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 there is an excess of it in the environment. Excessive amount of water in cells leads to changes in osmotic pressure and disruption 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, and marine forms cannot tolerate desalination. If the salinity of water is subject to changes, animals move in search of a favorable environment. For example, when the surface layers of the sea are desalinated after heavy rains, radiolarians, sea crustaceans Calanus and others descend to a depth of 100 m. Vertebrates, higher crustaceans, insects and their larvae living in water belong to homoiosmotic species, maintaining constant osmotic pressure in the body regardless of the concentration of salts in the water.
In freshwater species, body juices are hypertonic in relation to the surrounding water. They are at risk of excessive watering if the flow of water is not prevented or excess water is not removed from the body. In protozoa this is achieved by the work of excretory vacuoles, in multicellular organisms - by removing water through the excretory system. Some ciliates secrete an amount of water equal to their body volume every 2–2.5 minutes. The cell expends a lot of energy to “pump out” excess water. With increasing salinity, the work of vacuoles slows down. Thus, in Paramecium slippers, at a water salinity of 2.5%o, the vacuole pulsates at intervals 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 water is hypertonic in relation to the body fluids of aquatic organisms, they are at risk of dehydration as a result of osmotic losses. Protection against dehydration is achieved by increasing the concentration of salts also in the body of aquatic organisms. Dehydration is prevented by the water-impermeable integument of homoiosmotic organisms - mammals, fish, higher crayfish, aquatic insects and their larvae.
Many poikilosmotic species transition to an inactive state - suspended animation as a result of a lack of water in the body with increasing salinity. This is characteristic of species living in pools of sea water and in the littoral zone: rotifers, flagellates, ciliates, some crustaceans, the Black Sea polychaete Nereis divesicolor, etc. Salt suspended animation– a means to survive unfavorable periods in conditions of variable salinity of water.
Truly euryhaline There are not many species among aquatic inhabitants that can live in an active state in both fresh and salt water. These are mainly species inhabiting river estuaries, estuaries and other brackish water bodies.
Temperature reservoirs are more stable than on land. This is due to the physical properties of water, primarily its high specific heat capacity, due to which the receipt or release of a significant amount of heat does not cause too sudden changes in temperature. The 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 waters – 30–35 °C. Deep layers of water are characterized by constant temperature. In equatorial waters, the average annual temperature of surface layers is +(26–27) °C, in polar waters it is about 0 °C and below. In hot land-based springs, the water temperature can approach +100 °C, and in underwater geysers, at high pressure on the ocean floor, temperatures of +380 °C have been recorded.
Thus, there is a fairly significant variety of temperature conditions in reservoirs. 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 external and deep waters is greater.
Due to the more stable temperature regime of water, stenothermy is common among aquatic organisms to a much greater extent than among the land population. Eurythermic species are found mainly in shallow continental reservoirs and in the littoral zone of 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. Some of the rays incident on the surface of a reservoir are 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 - 5 hours, and at a depth of 40 m only 15 minutes. The rapid decrease in the amount of light with depth is associated with its absorption by water. Rays of different wavelengths are absorbed differently: red ones disappear close to the surface, while blue-green ones penetrate much deeper. The twilight in the ocean, which deepens with depth, is first green, then blue, indigo and blue-violet, finally giving way to constant darkness. Accordingly, green, brown and red algae, specialized in capturing light with different wavelengths, replace each other with depth.
The color of animals changes with depth just as naturally. The inhabitants of the littoral and sublittoral zones are most brightly and variedly colored. Many deep organisms, like cave organisms, do not have pigments. In the twilight zone, red coloration is widespread, which is complementary to the blue-violet light at these depths. Rays of additional color are most completely absorbed by the body. This allows animals to hide from enemies, since their red color in blue-violet rays is visually perceived as black. Red coloring is characteristic of twilight zone animals such 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 abilities to refract rays. One half of the eye sees in the air, the other in water. Such “four-eyedness” is characteristic of whirling beetles, the American fish Anableps tetraphthalmus, and one of the tropical species of blenny Dialommus fuscus. During low tides, this fish sits in recesses, exposing part of its head from the water (see Fig. 26).
The absorption of light is stronger, the lower the transparency of the 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 clearest 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 muddiest rivers, for example in the Central Asian Amu Darya and Syr Darya, only a few centimeters. The boundary of the photosynthetic zone therefore varies greatly in different bodies of water. In the clearest waters euphotic zone, or zone of photosynthesis, extends to depths not exceeding 200 m, crepuscular, or dysphotic, the zone occupies depths of 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 reservoirs varies greatly depending on the latitude of the area and the time of year. Long polar nights severely limit the time available for photosynthesis in Arctic and Antarctic basins, and ice cover makes it difficult for light to reach all frozen bodies of water in winter.
In the dark depths of the ocean, organisms use light emitted by living things 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 arisen multiple times in different groups at different stages of evolution.
The chemistry of bioluminescence is now quite 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.
Glow may not play a special ecological role in the life of a species, but may be a by-product of the vital activity of cells, as, for example, in bacteria or lower plants. It acquires ecological significance only in animals that have a sufficiently developed nervous system and visual organs. In many species, the luminescent organs acquire a very complex structure with a system of reflectors and lenses that enhance radiation (Fig. 40). A number of fish and cephalopods, unable to generate light, use symbiotic bacteria that multiply in the special organs of these animals.
Rice. 40. Luminescence organs of aquatic animals (according to S. A. Zernov, 1949):
1 – a deep-sea anglerfish with a flashlight over its toothed mouth;
2 – distribution of luminous organs in fish of the family. Mystophidae;
3 – luminous organ of the fish Argyropelecus affinis:
a – pigment, b – reflector, c – luminous body, d – lens
Bioluminescence has mainly a signaling value in the life of animals. Light signals can serve for orientation in a flock, attracting individuals of the opposite sex, luring victims, for camouflage or distraction. A flash of light can act as a defense against a predator by blinding or disorienting it. For example, deep-sea cuttlefish, fleeing from an enemy, release a cloud of luminous secretion, while species living in illuminated waters use dark liquid for this purpose. In some bottom worms - polychaetes - luminous organs develop during the period of maturation of reproductive products, and females glow brighter, and the eyes are better developed in males. In predatory deep-sea fish from the order of anglerfish, 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 blood flow to the gland and, therefore, the supply of oxygen to the bacterium, the fish can voluntarily cause the “bait” to glow, imitating the movements of the worm and luring in prey.
In a terrestrial environment, bioluminescence is developed only in a few species, most strongly in beetles from the family of fireflies, which use light signaling to attract individuals of the opposite sex during twilight or night time.
4.1.3. Some specific adaptations of aquatic organisms
Methods of orientation of animals in the aquatic environment. Living in constant twilight or darkness greatly limits your options visual orientation hydrobionts. Due to the rapid attenuation of light rays in water, even those with well-developed visual organs can only use them to navigate at close range.
Sound travels faster in water than in air. Focus on sound In hydrobionts it is generally better developed than the visual one. A number of species detect even very low frequency vibrations (infrasounds), arising when the rhythm of waves changes, and descends from the surface layers to deeper ones in advance of the storm (for example, jellyfish). Many inhabitants of water bodies - mammals, fish, mollusks, crustaceans - make sounds themselves. Crustaceans do this by rubbing various body parts against each other; fish - using the swim bladder, pharyngeal teeth, jaws, pectoral fin rays and other means. Sound signaling most often serves for intraspecific relationships, for example, for orientation in a school, attracting individuals of the opposite sex, etc., and is especially developed among inhabitants of turbid waters and great depths, living in the dark.
A number of hydrobionts find food and navigate using echolocation– perception of reflected sound waves (cetaceans). Many perceive reflected electrical impulses, producing discharges of different frequencies while swimming. About 300 species of fish are known to generate electricity and use it for orientation and signaling. The freshwater elephant fish (Mormyrus kannume) sends out up to 30 pulses per second, detecting invertebrates that it forages in liquid mud without the aid of vision. The discharge frequency of some marine fish reaches 2000 pulses per second. A number of fish also use electric fields for defense and attack (electric stingray, electric eel, etc.).
For orientation in depth it is used perception of hydrostatic pressure. It is carried out using statocysts, gas chambers and other organs.
The most ancient method 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 navigate mainly by smell, finding spawning or feeding grounds with amazing accuracy. It has been experimentally proven, for example, that salmon artificially deprived of their sense of smell do not find the mouth of their river when returning to spawn, but they are never mistaken if they can perceive odors. The subtlety of the sense of smell is extremely high in fish that make especially long migrations.
Specifics of adaptations to life in drying up water bodies. On Earth, there are many temporary, shallow reservoirs that appear after river floods, heavy rains, snow melting, etc. In these reservoirs, despite the brevity of their existence, a variety of aquatic organisms settle.
Common features of the inhabitants of drying up pools are the ability to give birth to numerous offspring in a short time and endure long periods without water. Representatives of many species bury themselves in the silt, going into a state of reduced vital activity - hypobiosis. This is how scale insects, cladocerans, planarians, oligochaete worms, mollusks and even fish behave like loaches, African protopterus and the South American lepidosiren from lungfishes. Many small species form cysts that can withstand drought, such as sunflowers, ciliates, rhizopods, a number of copepods, turbellarians, and nematodes of the genus Rhabditis. Others experience an unfavorable period in the highly resistant egg stage. Finally, some small inhabitants of drying up reservoirs have a unique ability to dry out to a film state, and when moistened, resume growth and development. The ability to tolerate complete dehydration of the body has been revealed 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 the cushions of mosses and lichens and are adapted to sudden changes in humidity conditions.
Filtration as a type of nutrition. Many hydrobionts have a special feeding pattern - this is the filtering or sedimentation of particles of organic origin suspended in water and numerous small organisms (Fig. 41).
Rice. 41. Composition of planktonic food of ascidians from the Barents Sea (according to S. A. Zernov, 1949)
This method of feeding, which does not require large amounts of energy to search for prey, is characteristic of elasmobranch mollusks, sessile echinoderms, polychaetes, bryozoans, ascidians, planktonic crustaceans, etc. (Fig. 42). Filter-feeding animals play a vital role in the biological purification of water bodies. Mussels living on an area of 1 m2 can drive 150–280 m3 of water through the mantle cavity per day, precipitating suspended particles. Freshwater daphnia, cyclops, or the most abundant crustacean in the ocean, Calanus finmarchicus, filter up to 1.5 liters of water per individual per day. The littoral zone of the ocean, especially rich in accumulations of filter-feeding organisms, works as an effective purification system.
Rice. 42. Filtering devices of hydrobionts (according to S. A. Zernov, 1949):
1 – Simulium midge larvae on the stone (a) and their filter appendages (b);
2 – filter leg of the crustacean Diaphanosoma brachyurum;
3 – gill slits of the ascidian Phasullia;
4 – Bosmina crustacean with filtered intestinal contents;
5 – food current of the ciliate Bursaria
The properties of the environment largely determine the ways of adaptation of its inhabitants, their lifestyle and methods of using resources, creating chains of cause-and-effect dependencies. Thus, the high density of water makes the existence of plankton possible, and the presence of organisms floating in 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 for self-purification of water bodies of biosphere significance is formed. It involves a huge number of hydrobionts, both benthic and pelagic, from single-celled 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 dozens of times during the growing season, and the entire volume of the World Ocean is filtered within a few days. Disruption of the activity of filter feeders by various anthropogenic influences poses a serious threat to maintaining water purity.
4.2. Ground-air environment of life
The ground-air environment is the most complex in terms of environmental conditions. Life on land required adaptations that turned out to be possible only with a sufficiently high level of organization of plants and animals.
4.2.1. Air as an environmental factor for terrestrial organisms
The low density of air determines its low lifting force and low air mobility. Inhabitants of the air must have their own support system that supports the body: plants - with a variety of mechanical tissues, animals - with a solid or, much less frequently, hydrostatic skeleton. In addition, all inhabitants of the air are closely connected with the surface of the earth, which serves them for attachment and support. Life suspended 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, but 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, staying in the air is associated only with settling or searching for prey.
Rice. 43. Distribution of aerial plankton arthropods by height (according to Dajo, 1975)
Low air density causes low resistance to movement. Therefore, during the course of evolution, many terrestrial animals 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 efforts, but some can also glide using air currents.
Thanks to the mobility of air and 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 - the oldest method 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, goosefoot, sedge, cereals, palms 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 dispersal occurs with its help. Such a double dependence is observed in spruce, pine, poplar, birch, elm, ash, cotton grass, cattail, saxaul, dzhuzgun, etc.
Many species have developed anemochory– settlement using 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 by analogy with 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 dismemberment, a large relative surface of the wings, the use of a web, etc. (Fig. 44). Anemochorous seeds and fruits of plants also have either very small sizes (for example, orchid seeds) or a variety of wing-like and parachute-like appendages that increase their ability to plan (Fig. 45).
Rice. 44. Adaptations for transport by air currents in insects:
1 – mosquito Cardiocrepis brevirostris;
2 – gall midge Porrycordila sp.;
3 – Hymenoptera Anargus fuscus;
4 – Hermes Dreyfusia nordmannianae;
5 – gypsy moth larva Lymantria dispar
Rice. 45. Adaptations to wind transfer in fruits and seeds of plants:
1 – linden Tilia intermedia;
2 – maple Acer monspessulanum;
3 – birch Betula pendula;
4 – cotton grass Eriophorum;
5 – dandelion Taraxacum officinale;
6 – cattail Typha scuttbeworhii
In the dispersal 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.
Low air density causes relatively low pressure on land. Normally it is 760 mmHg. 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 respiration rate. The limits of advancement of higher plants into the mountains are approximately the same. Somewhat more hardy are arthropods (springtails, mites, spiders), which can be found on glaciers above the vegetation line.
In general, all terrestrial organisms are much more stenobatic than aquatic ones, since normal pressure fluctuations in their environment amount to fractions of the atmosphere and, even for birds rising to great heights, do not exceed 1/3 of normal.
Gas composition of air. In addition to the physical properties of the air, its chemical properties 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 diffusivity of gases and constant mixing convection and wind currents. However, various impurities of gaseous, droplet-liquid and solid (dust) particles entering the atmosphere from local sources can have significant environmental significance.
The high oxygen content contributed to an increase in metabolism in terrestrial organisms compared to primary aquatic ones. It was in a terrestrial environment, on the basis of the high efficiency of oxidative processes in the body, that animal homeothermy 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 deficiency created, for example in accumulations of decomposing plant residues, reserves of grain, flour, etc.
The carbon dioxide content 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 tens of times. There are regular daily changes in the carbon dioxide content in the surface layers associated with the rhythm of plant photosynthesis. Seasonal are caused by changes in the intensity of respiration of living organisms, mainly the microscopic population of soils. Increased saturation of air with carbon dioxide occurs in areas 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 breathe very intensively. Carbon dioxide diffuses from the soil into the atmosphere, especially vigorously during rain. It is abundant in soils that are moderately moist, well heated, and 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 emits only 2 kg/ha.
In modern conditions, human activity in burning fossil fuel reserves has become a powerful source of additional amounts of CO 2 entering the atmosphere.
Air nitrogen is an inert gas for most inhabitants of the terrestrial environment, 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. A mountainside with destroyed vegetation due to sulfur dioxide emissions from surrounding industrial enterprises
Local pollutants entering the air can also significantly affect living organisms. This especially applies to toxic gaseous substances - methane, sulfur oxide, carbon monoxide, nitrogen oxide, hydrogen sulfide, chlorine compounds, as well as dust particles, soot, etc., that pollute 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 forests around large cities indicates high air purity. The resistance of plants to impurities in the air is taken into account when selecting species for landscaping in populated areas. Sensitive to smoke, for example, common spruce and pine, maple, linden, birch. The most resistant are thuja, Canadian poplar, American maple, elderberry and some others.
4.2.2. Soil and relief. Weather and climatic features of the ground-air environment
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 collectively called edaphic environmental factors (from the Greek “edaphos” - foundation, soil).
The nature of the plant root system 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 shallow depths and spread out wide. Where there is no permafrost, the root systems of these same plants are less widespread and penetrate deeper. In many steppe plants, the roots can reach water from great depths; at the same time, they also have many surface roots in the humus-rich soil horizon, from where the plants absorb elements of mineral nutrition. 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 soil acidity, they distinguish: 1) acidophilic species - grow on acidic soils with a pH less than 6.7 (plants of sphagnum bogs, white grass); 2) neutrophilic – gravitate towards soils with a pH of 6.7–7.0 (most cultivated plants); 3) basophilic– 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 that are content with a small amount of ash elements (Scots pine); 2) eutrophic, those that need a large amount of ash elements (oak, common gooseberry, perennial woodweed); 3) mesotrophic, requiring a moderate amount of ash elements (common spruce).
Nitrophils– plants that prefer nitrogen-rich soils (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 shifting sands.
The terrain and the nature of the soil affect the specific movement of animals. For example, ungulates, ostriches, and bustards living in open spaces need hard ground to enhance repulsion when running fast. In lizards that live on shifting sands, the toes are fringed with a fringe of horny scales, which increases the support surface (Fig. 47). For terrestrial inhabitants that dig holes, dense soils are unfavorable. The nature of the soil in some cases influences the distribution of terrestrial animals that dig burrows, burrow into the soil to escape heat or predators, or lay eggs in the soil, etc.
Rice. 47. Fan-toed gecko - 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 at the earth's surface up to an altitude of approximately 20 km (the boundary of the troposphere). Weather variability is manifested in constant variations in the combination of environmental factors such as temperature and humidity, cloudiness, precipitation, wind strength and direction, etc. Weather changes, along with their natural alternation in the annual cycle, are characterized by non-periodic fluctuations, which significantly complicates the conditions of 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.
Climate of the area. The long-term weather regime characterizes climate of the area. The concept of climate includes not only the average values of meteorological phenomena, but also their annual and daily cycle, 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 zonation, much similar to the change of zones from low latitudes to high latitudes. All this creates an extraordinary diversity 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 as the conditions of their immediate habitat. Very often, local environmental elements (relief, exposure, vegetation, etc.) change the regime of temperature, humidity, light, air movement in a particular area in such a way that it differs significantly from the climatic conditions of the area. Such local climate modifications that develop in the surface layer of air are called microclimate. Each zone has very diverse microclimates. Microclimates of arbitrarily small areas can be identified. For example, a special regime is created in the corollas of flowers, which is used by the insects living there. Differences in temperature, air humidity and wind strength are widely known in open space and in forests, in grass stands and over bare areas of soil, on slopes of 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 other ecological roles. Thus, heavy rainfall 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 depth only up to 25 cm; deeper the temperature remains almost unchanged. With 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 renewal buds and protects green parts of plants from freezing; many species go under the snow without shedding their foliage, for example, hairy grass, Veronica officinalis, hoofed grass, etc.
Rice. 48. Scheme of telemetric study of the temperature regime of hazel grouse located in a snow hole (according to A.V. Andreev, A.V. Krechmar, 1976)
Small land animals also lead an active lifestyle in winter, creating entire galleries of tunnels under the snow and in its thickness. A number of species that feed on snow-covered vegetation are even characterized by winter reproduction, 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 partridge - burrow in the snow for the night ( Fig. 48).
Winter snow cover makes it difficult for large animals to obtain food. Many ungulates (reindeer, wild boars, musk oxen) feed exclusively on snow-covered vegetation in winter, and deep snow cover, and especially the hard crust on its surface that occurs during icy conditions, doom them to starvation. During nomadic cattle breeding in pre-revolutionary Russia, a huge disaster in the southern regions was jute – mass mortality of livestock as a result of icy conditions, 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 spruce trees, where the layer of snow is thinner, and almost never go out into open glades and forest edges. Snow depth may limit the geographic distribution of species. For example, real deer do not penetrate north into those areas where the snow thickness in winter is more than 40–50 cm.
The whiteness of the snow cover reveals dark animals. Selection for camouflage to match the background color apparently played a major role in the occurrence of seasonal color changes in the ptarmigan 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 stay mainly near dark rocks and ice-free surf strips, while the white ones prefer areas with snow cover.
4.3. Soil as a habitat
4.3.1. Soil Features
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 vital 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 develop in it, favorable for the life of many micro- and macroorganisms (Fig. 49). In the soil, temperature fluctuations are smoothed out compared to the surface layer of air, and the presence of groundwater and the penetration of precipitation create moisture reserves and provide a humidity 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 greater saturation of the soil with life.
The root systems of terrestrial plants are concentrated in the soil (Fig. 50).
Rice. 49. Underground passages of the Brandt's vole: A – top view; B – side view
Rice. 50. Placement of roots in steppe chernozem soil (according to M. S. Shalyt, 1950)
On average, per 1 m 2 of soil layer there are more than 100 billion protozoan cells, millions of rotifers and tardigrades, tens of millions of nematodes, tens and hundreds of thousands of mites and springtails, thousands of other arthropods, tens of thousands of enchytraeids, tens and hundreds of earthworms, mollusks and other invertebrates . In addition, 1 cm 2 of soil contains tens and hundreds of millions of bacteria, microscopic fungi, actinomycetes and other microorganisms. The illuminated surface layers contain hundreds of thousands of photosynthetic cells of green, yellow-green, diatoms and blue-green algae in every gram. Living organisms are just as characteristic of the soil as its nonliving components. Therefore, V.I. Vernadsky classified the soil as a bio-inert body of nature, emphasizing its saturation with life and its inextricable connection with it.
The heterogeneity of soil conditions is most pronounced in the vertical direction. With depth, a number of the most important environmental factors affecting the life of soil inhabitants change dramatically. First of all, this relates to the structure of the soil. It contains three main horizons, differing in morphological and chemical properties: 1) the upper humus-accumulative horizon A, in which organic matter accumulates and is transformed and from which some of the compounds are carried down by washing waters; 2) the inwash 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 subdivided layers are distinguished, which also differ greatly in properties. For example, in a temperate climate zone under coniferous or mixed forests the horizon A consists of litter (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 ones, and a podzolic layer (A 2)– ash-gray in color, in which silicon compounds predominate, and all soluble substances are washed into the depths of the soil profile. Both the structure and chemistry of these layers are very different, and therefore plant roots and soil inhabitants, moving just a few centimeters up or down, find themselves in 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, at 1–2 cm – 2 mm, and at a depth of 2–3 cm – only 1 mm; deeper the soil pores are even smaller. Soil density also changes with depth. The loosest layers are those containing organic matter. The porosity of these layers is determined by the fact that organic substances glue mineral particles into larger aggregates, the volume of cavities between which increases. The illuvial horizon is usually the densest IN, cemented by colloidal particles washed into it.
Moisture in the soil is present in various states: 1) bound (hygroscopic and film) firmly held by the surface of soil particles; 2) capillary occupies small pores and can move along them in different directions; 3) gravitational fills larger voids and slowly seeps down under the influence of gravity; 4) vaporous is contained in the soil air.
Water content varies in different soils and at different times. If there is too much gravitational moisture, then the soil regime is close to the regime of reservoirs. In dry soil, only bound water remains and conditions approach those found on land. However, even in the driest soils, the air is moister than the ground air, 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 in it decreases greatly and the concentration of carbon dioxide increases. Due to the presence of decomposing organic substances in the soil, the soil air may contain a high concentration of toxic gases such as ammonia, hydrogen sulfide, methane, etc. When the soil is flooded or intensive rotting of plant residues, completely anaerobic conditions may occur in some places.
Fluctuations in cutting temperature only on the soil surface. Here they can be even stronger than in the surface layer of air. However, with each centimeter in depth, daily and seasonal temperature changes become less and less and at a depth of 1–1.5 m they are practically no longer traceable (Fig. 51).
Rice. 51. Decrease in annual fluctuations in soil temperature with depth (according to K. Schmidt-Nilsson, 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. The steep gradient of temperature and humidity in the soil profile allows soil animals to provide themselves with a suitable ecological environment through minor movements.
4.3.2. Soil inhabitants
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 overwhelming majority of the microbial population is adsorbed on them. The complexity of the soil environment creates a wide variety of conditions for a wide variety of functional groups: aerobes and anaerobes, consumers of organic and mineral compounds. The distribution of microorganisms in the soil is characterized by fine focality, since even within a few millimeters different ecological zones can change.
For small soil animals (Fig. 52, 53), which are combined under the name microfauna (protozoa, rotifers, tardigrades, nematodes, etc.), soil is a system of micro-reservoirs. Essentially, these 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 also live in ordinary bodies of water. However, soil forms are much smaller than freshwater ones and, in addition, are distinguished by their ability to remain in an encysted state for a long time, waiting out unfavorable periods. While freshwater amoebas are 50-100 microns in size, soil amoebas 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 their body shape.
Rice. 52. Testate amoebas feeding on bacteria on decaying leaves of the forest floor
Rice. 53. Soil microfauna (according to W. Dunger, 1974):
1–4 – flagella; 5–8 – naked amoebas; 9-10 – testate amoebas; 11–13 – ciliates; 14–16 – roundworms; 17–18 – rotifers; 19–20 – tardigrades
To slightly larger air-breathing animals, the soil appears as a system of small caves. Such animals are grouped under the name mesofauna (Fig. 54). The sizes of soil mesofauna representatives range from tenths to 2–3 mm. This group includes mainly arthropods: numerous groups of mites, primary wingless insects (collembolas, proturus, two-tailed insects), small species of winged insects, symphila centipedes, etc. They do not have special adaptations for digging. They crawl along the walls of soil cavities using their limbs or wriggling like a worm. Soil air saturated with water vapor allows breathing through the covers. Many species do not have a tracheal system. Such animals are very sensitive to drying out. The main means of escape from fluctuations in air humidity is to move deeper. But the possibility of deep migration through soil cavities is limited by a rapid decrease in pore diameter, so movement through soil holes is accessible only to the smallest species. Larger representatives of the mesofauna have some adaptations that allow them to tolerate 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 ensures respiration.
Rice. 54. Soil mesofauna (no W. Danger, 1974):
1 – false scorion; 2 – gama new bell-bottom; 3–4 oribatid mites; 5 – centipede pauroioda; 6 – chironomid mosquito larva; 7 - beetle from this family. Ptiliidae; 8–9 springtails
Representatives of the mesofauna survive periods of soil flooding in air bubbles. Air is retained around the body of animals due to their non-wettable integument, which is also equipped with hairs, scales, etc. The air bubble serves as a kind of “physical gill” for a small animal. Respiration 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 move down from layers exposed to negative temperatures.
Larger soil animals, with body sizes from 2 to 20 mm, are called representatives macrofauna (Fig. 55). These are insect larvae, centipedes, enchytraeids, 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 tunnels. Both methods of movement leave an imprint on the external structure of animals.
Rice. 55. Soil macrofauna (no W. Danger, 1974):
1 - earthworm; 2 – woodlice; 3 – centipede; 4 – two-legged centipede; 5 – ground beetle larva; 6 – click beetle larva; 7 – mole cricket; 8 - Khrushchev larva
The ability to move through thin holes, almost without resorting to digging, is inherent only in species that have a body with a small cross-section, capable of bending strongly in winding passages (centipedes - drupes and geophiles). By pushing apart soil particles due to the pressure of the body walls, earthworms, larvae of long-legged mosquitoes, etc. move. Having fixed the rear end, they thin and lengthen the front, penetrating into narrow soil crevices, then secure the front part of the body and increase its diameter. In this case, in the expanded area, due to the work of the muscles, a strong hydraulic pressure of the non-compressible intracavitary fluid is created: in worms - the contents of the coelomic sacs, and in tipulids - the hemolymph. Pressure is transmitted through the body walls to the soil, and thus the animal expands the well. At the same time, the rear passage remains open, which threatens to increase evaporation and persecution of predators. Many species have developed adaptations to an ecologically more advantageous type of movement in the soil - digging and blocking the passage behind them. Digging is carried out by loosening and raking away soil particles. The larvae of various insects use for this the anterior end of the head, mandibles and forelimbs, expanded and strengthened by a thick layer of chitin, spines and outgrowths. At the rear 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 and in bark beetles, which also use them to clog the passages with drill flour. Closing the passage behind them, the animals that inhabit the soil are constantly in a closed chamber, saturated with the vapors of their own bodies.
Gas exchange of most species of this ecological group is carried out with the help of specialized respiratory organs, but at the same time it is supplemented by gas exchange through the integument. It is even possible that exclusively cutaneous respiration is possible, for example in earthworms and enchytraeids.
Burrowing animals can move away from layers where an unfavorable environment occurs. During drought and winter, they concentrate in deeper layers, usually several tens of centimeters from the surface.
Megafauna soils are large shrews, mainly mammals. A number of species spend their entire lives in the soil (mole rats, mole rats, zokora, Eurasian moles, golden moles
Africa, marsupial moles of Australia, etc.). They create entire systems of passages and burrows 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, ridged body with a short neck, short thick fur, strong digging limbs with strong claws. Mole rats and mole rats loosen the ground with their incisors. Soil megafauna also includes large oligochaetes, especially representatives of the family Megascolecidae, living in the tropics and the Southern Hemisphere. 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 inhabitants (gophers, marmots, jerboas, rabbits, badgers, etc.). They feed on the surface, but reproduce, 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. Burrowers have structural features characteristic of terrestrial animals, but have a number of adaptations associated with the burrowing lifestyle. For example, badgers have long claws and strong muscles on the forelimbs, a narrow head, and small ears. Compared to hares that do not dig holes, rabbits have noticeably shortened ears and hind legs, a more durable skull, more developed bones and muscles of the forearms, etc.
For a number of ecological features, soil is a medium intermediate between aquatic and terrestrial. The soil is similar to the aquatic environment due to its temperature regime, low 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 soil is brought closer to the air environment by the presence of soil air, the threat of drying out in the upper horizons, and rather sharp changes in the temperature regime of the surface layers.
The intermediate ecological properties of soil as a habitat for animals suggest that soil played a special role in the evolution of the animal world. For many groups, in particular arthropods, soil served as a medium through which initially aquatic inhabitants were able to transition to a terrestrial lifestyle and conquer land. This path of arthropod evolution was proven by the works of M. S. Gilyarov (1912–1985).
4.4. Living organisms as habitat
Many types of heterotrophic organisms, throughout their entire life or part of their life cycle, live in other living beings, whose bodies serve as an environment for them, significantly different in properties from the external one.
Rice. 56. Aphids infecting aphids
Rice. 57. Cut gall on a beech leaf with a larva of the gall midge Mikiola fagi
There are several main living environments on planet Earth:
water
ground-air
soil
living organism.
Aquatic living environment.
Organisms living in water have adaptations determined by the physical properties of water (density, thermal conductivity, ability to dissolve salts).
Due to the buoyant force of water, many small inhabitants of the aquatic environment are suspended and are not able to resist currents. The collection of such small aquatic inhabitants is called plankton. Plankton includes microscopic algae, small crustaceans, fish eggs and larvae, jellyfish and many other species.
Plankton
Planktonic organisms are carried by currents and are unable to resist them. The presence of plankton in the water makes a filtration type of nutrition possible, i.e., straining, using various devices, small organisms and food particles suspended in water. It is developed in both floating and sessile bottom animals, such as crinoids, mussels, oysters and others. A sedentary life would be impossible for aquatic inhabitants if there were no plankton, and this, in turn, is possible only in an environment with sufficient density.
The density of water makes active movement in it difficult, so fast-swimming animals, such as fish, dolphins, squids, must have strong muscles and a streamlined body shape.
Mako shark
Due to the high density of water, pressure increases greatly with depth. Deep-sea inhabitants are able to withstand pressure that is thousands of times higher than on the land surface.
Light penetrates water only to a shallow depth, so plant organisms can only exist in the upper horizons of the water column. Even in the cleanest seas, photosynthesis is possible only to depths of 100-200 m. At greater depths, there are no plants, and deep-water animals live in complete darkness.
The temperature regime in reservoirs is milder than on land. Due to the high heat capacity of water, temperature fluctuations in it are smoothed out, and aquatic inhabitants do not face the need to adapt to severe frosts or forty-degree heat. Only in hot springs can the water temperature approach the boiling point.
One of the difficulties in the life of aquatic inhabitants is the limited amount of oxygen. Its solubility is not very high and, moreover, decreases greatly when the water is polluted or heated. Therefore, in reservoirs there are sometimes starvation - mass death of inhabitants due to a lack of oxygen, which occurs for various reasons.
Fish kill
The salt composition of the environment is also very important for aquatic organisms. Marine species cannot live in fresh waters, and freshwater species cannot live in seas due to disruption of cell function.
Ground-air environment of life.
This environment has a different set of features. It is generally more complex and varied than aquatic. It has a lot of oxygen, a lot of light, sharper changes in temperature in time and space, significantly weaker pressure drops, and moisture deficiency often occurs. Although many species can fly, and small insects, spiders, microorganisms, seeds and plant spores are carried by air currents, feeding and reproduction of organisms occurs on the surface of the ground or plants. In such a low-density environment as air, organisms need support. Therefore, terrestrial plants have developed mechanical tissues, and terrestrial animals have a more pronounced internal or external skeleton than aquatic animals. The low density of air makes it easier to move around in it. About two-thirds of land inhabitants have mastered active and passive flight. Most of them are insects and birds.
Black kite
Caligo butterfly
Air is a poor conductor of heat. This makes it easier to conserve heat generated inside organisms and maintain a constant temperature in warm-blooded animals. The very development of warm-bloodedness became possible in a terrestrial environment. The ancestors of modern aquatic mammals - whales, dolphins, walruses, seals - once lived on land.
Land dwellers have a wide variety of adaptations related to providing themselves with water, especially in dry conditions. In plants, this is a powerful root system, a waterproof layer on the surface of leaves and stems, and the ability to regulate water evaporation through stomata. In animals, these are also different structural features of the body and integument, but, in addition, appropriate behavior also contributes to maintaining water balance. They can, for example, migrate to watering holes or actively avoid particularly drying conditions. Some animals can live their entire lives on dry food, such as jerboas or the well-known clothes moth. In this case, the water needed by the body arises due to the oxidation of food components.
Camel thorn root
Many other environmental factors also play an important role in the life of terrestrial organisms, such as air composition, winds, and the topography of the earth's surface. Weather and climate are especially important. The inhabitants of the land-air environment must be adapted to the climate of the part of the Earth where they live and tolerate variability in weather conditions.
Soil as a living environment.
Soil is a thin layer of land surface, processed by the activity of living beings. Solid particles are permeated in the soil with pores and cavities, filled partly with water and partly with air, so small aquatic organisms can also inhabit the soil. The volume of small cavities in the soil is a very important characteristic of it. In loose soils it can be up to 70%, and in dense soils - about 20%. In these pores and cavities or on the surface of solid particles live a huge variety of microscopic creatures: bacteria, fungi, protozoa, roundworms, arthropods. Larger animals make passages in the soil themselves.
Soil inhabitants
The entire soil is penetrated by plant roots. Soil depth is determined by the depth of root penetration and the activity of burrowing animals. It is no more than 1.5-2 m.
The air in soil cavities is always saturated with water vapor, its composition is enriched in carbon dioxide and depleted in oxygen. In this way, the living conditions in the soil resemble the aquatic environment. On the other hand, the ratio of water and air in soils is constantly changing depending on weather conditions. Temperature fluctuations are very sharp at the surface, but quickly smooth out with depth.
The main feature of the soil environment is the constant supply of organic matter, mainly due to dying plant roots and falling leaves. It is a valuable source of energy for bacteria, fungi and many animals, so soil is the most life-rich environment. Her hidden world is very rich and diverse.
Living organisms as a living environment.
Wide tapeworm
Read also:
|
General characteristics. In the course of evolution, the land-air environment was mastered much later than the aquatic environment. Life on land required adaptations that became possible only with a relatively high level of organization in 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, and high oxygen content. Typically, animals in this environment move on the soil (hard 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 compared to 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 land-air environment have developed characteristic anatomical, morphological, physiological, behavioral and other adaptations. For example, organs have appeared that provide direct absorption of atmospheric oxygen during respiration (the lungs and trachea of animals, the stomata of plants). Skeletal formations (animal skeleton, mechanical and supporting tissues of plants) that support the body have received strong development
in conditions of low density of the environment. Adaptations have been developed to protect against unfavorable factors, such as the periodicity and rhythm of life cycles, the complex structure of the integument, mechanisms of thermoregulation, etc. A close connection with the soil has formed (animal limbs, plant roots), the mobility of animals in search of food has developed, and air currents have appeared. seeds, fruits and pollen of plants, flying animals.
Low air density determines its low lifting force and insignificant support. All inhabitants of the air are closely connected with the surface of the earth, which serves them for attachment and support. The density of the air environment does not provide high resistance to organisms when they move along the surface of the earth, but it makes it difficult to move vertically. For most organisms, staying in the air is associated only with settling or searching for prey.
The low lifting force of air determines the maximum 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 mass of a modern whale) could not live on land, since they were crushed by their own weight.
Low air density creates little resistance to movement. 75% of all species of land animals are capable of active flight.
Winds increase the release of moisture and heat from animals and plants. When there is wind, heat is easier to bear and frost is more severe, and desiccation and cooling of organisms occurs faster. Wind causes changes in the intensity of transpiration in plants and 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 helps increase metabolism in 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, and plant crops shade the area and create a special microclimate, weakening radiation.
Thus, in different habitats, not only the intensity of radiation differs, but also its spectral composition, the duration of illumination of plants, the spatial and temporal distribution of light of different intensities, etc. Accordingly, the adaptations of organisms to life in a terrestrial environment under one or another light regime are also varied. . In relation to light, there are three main groups of plants: 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 light conditions:
An example of anatomical and morphological adaptations is a change in external appearance in different light conditions, for example, the unequal size of leaf blades in plants related in systematic position, living under different lighting (meadow bell Cumpanula patula and forest - C. trachelium, field violet - Viola arvensis, growing in fields, meadows, forest edges, and forest violets - V. mirabilis).
In heliophyte plants, the leaves are oriented to reduce the influx of radiation during the most “dangerous” daytime hours. The leaf blades are located vertically or at a large angle to the horizontal plane, so during the day the leaves receive mostly sliding 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 during a sharp lack of light is the loss of the plant’s ability to photosynthesize and 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), orchids (Monotropa hypopitys).
Physiological adaptations of animals. For the vast majority of terrestrial animals with day and night activity, vision is one of the methods of orientation and is important for searching for prey. Many animal species also have color vision. In this regard, animals, especially victims, developed adaptive features. These include protective, camouflage and warning coloring, protective similarity, 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 mode. Moisture deficiency is one of the most significant features of the land-air environment of life. The evolution of terrestrial organisms took place through adaptation to obtaining and preserving 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, the water quickly flows 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. Agricultural crops in individual fields are sometimes completely destroyed by this natural disaster.
The ecological role of snow cover is diverse; for plants whose renewal buds are located in the soil or near its surface, and for many small animals, snow plays the role of a heat-insulating cover, protecting them from low winter temperatures. Winter snow cover often prevents large animals from obtaining food and moving, especially when an ice crust forms on the surface. Often during snowy winters, the death of roe deer and wild boars is observed.
Large amounts of snow also have a negative impact on plants. In addition to mechanical damage in the form of snow chips or snow blowers, a thick layer of snow can lead to damping off of plants, and when the snow melts, especially in a long spring, to soaking of plants.
Temperature. A distinctive feature of the land-air environment is the large range of temperature fluctuations. In most land areas, daily and annual temperature ranges 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 occurs, 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 there is strong cooling due to radiation. Therefore, the surface layer of air experiences the sharpest daily temperature fluctuations, which are most pronounced over bare soil.
In the ground-air environment, living conditions are complicated by the existence of weather changes. Weather is the continuously changing state of the atmosphere at the earth's surface, up to approximately 20 km altitude. Weather variability is manifested in the constant variation of environmental factors: temperature, air humidity, cloudiness, precipitation, wind strength, 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, that is, the climate of the ground layer of air, or ecoclimate.
Geographical zonality and zonality. The distribution of living organisms on Earth is closely related to geographic zones and zones. There are 13 geographic zones on the surface of the globe, which change from the equator to the poles and from the oceans to the interior of the continents. Within the belts, latitudinal and meridial or longitudinal natural zones are distinguished. The former stretch from west to east, the latter from north to south. Each climate zone is characterized by its own unique vegetation and animal population. The richest in life and most productive are tropical forests, floodplains, prairies and forests of the subtropics and transition zone. 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 evident in the terrestrial environment. The vegetation of mountainous countries is richer than on the adjacent plains. Adaptations to life in the mountains: plants are dominated by a cushion-shaped life form, perennials, which have developed adaptation to strong ultraviolet radiation and reduced transpiration. In animals, the relative volume of the heart increases and the hemoglobin content in the blood increases. Animals: mountain turkeys, mountain finches, larks, vultures, rams, goats, chamois, yaks, bears, lynxes.
Features of the ground-air habitat. There is enough light and air in the ground-air environment. But air humidity and temperature vary greatly. In swampy areas there is an excessive amount of moisture, in the steppes it is much less. Daily and seasonal temperature fluctuations are also noticeable.
Adaptation of organisms to life in conditions of different temperatures and humidity. A large number of adaptations of organisms in the ground-air environment are associated with air temperature and humidity. Animals of the steppe (scorpions, tarantula and karakurt spiders, gophers, voles) hide from the heat in burrows. Increased evaporation of water from the leaves protects the plant from the hot rays of the sun. In animals, such an adaptation is the secretion of sweat.
With the onset of cold weather, birds fly away to warmer regions in order to return in the spring to the place where they were born and where they will give birth. A feature of the ground-air environment in the southern regions of Ukraine or Crimea is an insufficient amount of moisture.
Check out Fig. 151 with plants that have adapted to similar conditions.
Adaptation of organisms to movement in the ground-air environment. For many animals of the land-air environment, movement on the earth's surface or in the air is important. To do this, they have developed certain adaptations, and their limbs have different structures. Some have adapted to running (wolf, horse), others to jumping (kangaroo, jerboa, grasshopper), and others to flight (birds, bats, insects) (Fig. 152). Snakes and vipers have no limbs. They move by bending their body.
Significantly fewer organisms have adapted to life high in the mountains, since there is little soil, moisture and air for plants, and animals have difficulty moving. But some animals, for example mouflon mountain goats (Fig. 154), are capable of moving almost vertically up and down if there are at least slight unevenness. Therefore, they can live high in the mountains. Material from the site
Adaptation of organisms to different lighting conditions. One of the adaptations of plants to different lighting is the direction of the leaves towards the light. In the shade, the leaves are arranged horizontally: this way they receive more light rays. Light-loving snowdrops and ryast develop and bloom in early spring. During this period, they have enough light, since leaves have not yet appeared on the trees in the forest.
The adaptation of animals to the specified factor of the ground-air habitat is the structure and size of the eyes. Most animals in this environment have well-developed organs of vision. For example, a hawk from the height of its flight sees a mouse running across a field.
Over many centuries of development, organisms of the land-air environment have adapted to the influence of its factors.
Didn't find what you were looking for? Use the search
On this page there is material on the following topics:
- report on the topic habitat of a living organism, grade 6
- adaptability of the snowy owl to its environment
- terms on the topic of air
- report on land-air habitat
- adaptation of birds of prey to their environment
By “environment” we mean everything that surrounds the body and influences it in one way or another. In other words, the living environment is characterized by a certain set of environmental factors. Wednesday- living environment - aquatic environment - ground-air environment - soil environment - organism as a living environment - key concepts.
Generally accepted definition environment is the definition of Nikolai Pavlovich Naumov: " Wednesday- everything that surrounds organisms directly or indirectly affects their condition, development, survival and reproduction." On Earth, there are four qualitatively different living environments that have a set of specific environmental factors: -ground-aquatic (land); - water; - the soil; - other organisms.
Ground-air The environment is characterized by a huge variety of living conditions, ecological niches and the organisms inhabiting them. Organisms play a primary role in shaping the conditions of the land-air environment of life, and above all, the gas composition of the atmosphere. Almost all the oxygen in the earth's atmosphere is of biogenic origin. The main features of the ground-air environment are
Large changes in environmental factors,
Heterogeneity of the environment,
The action of the forces of gravity,
Low air density.
A complex of physical-geographical and climatic factors related to a certain natural zone leads to the adaptation of organisms to life in these conditions and the diversity of life forms. The high oxygen content in the atmosphere (about 21%) determines the possibility of forming a high (energy) level of metabolism. The atmospheric air is characterized by low and variable humidity. This circumstance largely limited the possibilities of developing the ground-air environment.
Atmosphere(from the Greek atmos - steam and sphaira - ball), the gaseous shell of the earth. It is impossible to indicate the exact upper limit of the earth's atmosphere. The atmosphere has a pronounced layered structure. Main layers of the atmosphere:
1)Troposphere- height 8 - 17 km. all water vapor and 4/5 of the mass of the atmosphere are concentrated in it and all weather phenomena develop.
2)Stratosphere- layer above the troposphere up to 40 km. It is characterized by almost complete constant temperature with altitude. In the upper part of the stratosphere there is a maximum concentration of ozone, which absorbs a large amount of ultraviolet radiation from the Sun.
3) Mesosphere- layer between 40 and 80 km; in its lower half the temperature rises from +20 to +30 degrees, in the upper half it drops to almost -100 degrees.
4) Thermosphere(ionosphere) - a layer between 80 - 1000 km, which has increased ionization of gas molecules (under the influence of unhindered penetrating cosmic radiation).
5) Exosphere(scattering sphere) - a layer above 800 - 1000 km, from which gas molecules are scattered into outer space. The atmosphere transmits 3/4 of solar radiation, thereby increasing the total amount of heat used for the development of natural processes on Earth.
Aquatic life environment. Hydrosphere (from hydro... and sphere), the discontinuous water shell of the Earth, located between the atmosphere and the solid crust (lithosphere). Represents the totality of oceans, seas, lakes, rivers, swamps, as well as groundwater. The hydrosphere covers about 71% of the earth's surface. The chemical composition of the hydrosphere approaches the average composition of sea water.
The amount of fresh water makes up 2.5% of all water on the planet; 85% - sea water. Fresh water reserves are distributed extremely unevenly: 72.2% - ice; 22.4% - groundwater; 0.35% - atmosphere; 5.05% - stable river flow and lake water. The water we can use accounts for only 10-12% of all fresh water on Earth.
Primary environment life was precisely the aquatic environment. First of all, most organisms are not capable of active life without water entering the body or without maintaining a certain fluid content inside the body. The main feature of the aquatic environment is daily and seasonal temperature fluctuations. Huge ecological significance, have a high density and viscosity of water. The specific gravity of water is comparable to that of the body of living organisms. The density of water is approximately 1000 times higher than the density of air. Therefore, aquatic organisms (especially actively moving ones) encounter a greater force of hydrodynamic resistance. The high density of water is the reason that mechanical vibrations (vibrations) propagate well in the aquatic environment. This is very important for the senses, orientation in space and between aquatic inhabitants. The speed of sound in the aquatic environment has a higher frequency of echolocation signals. Four times larger than in the air. Therefore, there is a whole group of aquatic organisms (both plants and animals) that exist without an obligatory connection with the bottom or other substrate, “floating” in the water column.