Seasonal periodicity is one of the most common phenomena in living nature. It is especially pronounced in temperate and northern latitudes. Based on outwardly simple and familiar to us seasonal phenomena In the world of organisms lie complex adaptive reactions of a rhythmic nature, which have been elucidated relatively recently.
Animals living in mountainous areas can use high altitude flights. Instead of traveling long distances, they move to lower altitudes when the snow reaches the mountain tops. Some painted owls, and other animals of the same species that do not live in the mountains, follow differentiated migration patterns. Abrupt changes in the environment or climate can lead to migration when removed. If a species' habitat becomes permanently unsuitable for it, such as when human development depletes a swamp or kills off a forest entirely, the species will attempt to move to another area and will not return to its original home.
Seasonality in nature
As an example, let us consider the seasonal periodicity in the central regions of our country. Here, the annual temperature variation is of leading importance for plants and animals. The period favorable for life lasts about six months.
Signs of spring appear as soon as the snow begins to melt. Some willows, alders, and hazels begin to bloom before their leaves have bloomed; in the thawed areas, even through the snow, the sprouts of the first spring plants are breaking through; are arriving migratory birds; Overwintered insects appear.
These animals are transported by man to serve as food or to be tamed and secret; they have established themselves in places far from their country of origin, causing benefits and harm in many ecosystems. So-called sporadic migrations lead to an expansion of the range of the species concerned, but most often end in disaster for the animals taking part in this escape. The most common reasons for these migrations in large groups are overcrowding of the region or the accelerated reproduction of these species.
However, such migrations provide animals better conditions life, eliminating useless mouths, this is natural selection acting on these people. We read them from Norway, these rodents in the intermediate periods, reproduce at an accelerated rate and their habitats are overpopulated; they then begin to descend the slopes towards the valleys, weasels, hawks and foxes, always pursuing them along the route, many dying along the way, but not a single lemo returns to its place of origin in the mountains.
In mid-summer, despite favorable temperatures and plenty of precipitation, the growth of many plants slows down or stops completely. The quantity is decreasing flowering plants. Bird breeding ends. The second half of summer and early autumn is the period of ripening of fruits and seeds in most plants and accumulation of nutrients in their tissues. At this time, signs of preparation for winter are already visible. Autumn molting begins in birds and mammals, and migratory birds gather in flocks.
The main motivation for all these different forms of migration is the instinct of survival. Most migrations allow breeding, leaving an area with insufficient food to support its population. They also prevent the area's food sources from becoming depleted in the long term. These periodic movements mean that each individual specimen is more likely to find enough food in a particular location.
Although food migration can occur very regularly, there are several variables that can affect food availability, including climate and population levels of other species in the same area. For this reason, some species use irregular migration patterns that are constantly changing, adapting to new conditions. The midge travels across the African plains in search of water. When their normal water sources are depleted, they head to the savannahs for grass and more water.
Even before the arrival of stable frosts, a period of winter dormancy begins in nature.
State of winter dormancy
Winter dormancy is not simply a cessation of development caused by low temperature, but a very complex physiological adaptation. In each species, the state of winter dormancy occurs only at a certain stage of development. Thus, in plants (depending on the species), seeds, aboveground and underground parts with dormant buds overwinter, and in some herbaceous plants, basal leaves overwinter. At different stages of development, winter dormancy occurs in insects. Malaria mosquito and urticaria butterflies overwinter in the adult insect stage, cabbage butterflies - in the pupal stage, and gypsy moth - in the egg stage.
Dry season migrations can be altered by the sound of thunderstorms and rain clouds that the animals see. Migration patterns also benefit mating and reproduction, allowing young animals to be born in regions with richer food sources or further away from dangerous predators.
Later in their lives, the rivers rise again to mate and they lay their eggs in the place where they were born. Young salmon would be too vulnerable to ocean predators and, by returning to their place of origin, would provide storage for eggs in breeding areas. When the rivers in which they breed are dammed, salmon face serious problems and, as a result, populations of the species plummet. Some migrations are driven by both food needs and reproduction.
The overwintering stages of plants and animals have many similar physiological features. The metabolic rate is significantly reduced. The tissues of organisms in a state of winter dormancy contain many reserve nutrients, especially fats and carbohydrates, due to which reduced metabolic processes are maintained during wintering. Usually the amount of water in tissues decreases, especially in seeds and winter buds of plants. Thanks to all these features, the resting stages are able to survive harsh wintering conditions for a long time.
In the cold waters of the Pole he finds a huge amount of his favorite food, krill - a tiny shrimp-like creature. But young whales don't have enough blubber to protect them from the cold, so they return to tropical waters every summer to breed. Migration routes vary from species to species, but many are thousands of kilometers long.
The migration of gray whales reaches up to nine thousand kilometers from the starting point. Some depend on the period of the photo. As the days get shorter, the animals' instincts inform them that winter is coming and so it is time to head south. And for animals that cannot see the sun, as in the case of those sleeping in caves? Some animals react to temperature. They can also respond to internal signals, such as the amount of fat reserves available in their bodies. Some migration patterns follow a strict balance - when fat reserves are reduced due to falling food supply, it is time to seek more generous winter shelter.
Causes of biological rhythms. Photoperiodism
In the process of evolution, each species has developed a characteristic annual cycle of intensive growth and development, reproduction, preparation for winter and wintering. This phenomenon is called biological rhythm. The coincidence of each period of the life cycle with the corresponding time of year is crucial for the existence of the species.
But animals must retain a certain amount of fat to have the energy to travel. Evolution has organized these processes in such a way that, with the exception of outside interference, the required instincts work perfectly. In the absence of external stimuli, many animals still know when to migrate and when to return home. Circadian rhythms and annual rhythms are internal calendars that are part of nervous system animals. We don't fully understand these rhythms, but they are associated with patterns of brain activity that vary with time of day, photoperiods, and seasons.
The most noticeable connection of all physiological phenomena in the body is with the seasonal variation of temperature. But although it influences the speed of life processes, it still does not serve as the main regulator of seasonal phenomena in nature. Biological processes of preparation for winter begin in the summer, when the temperature is high. At high temperatures, insects still fall into a hibernating state, birds begin to molt and the desire to migrate appears. Consequently, some other conditions, and not temperature, influence the seasonal state of the body.
Humans also have them, although they do not use them for migration. Migration instincts developed in different types for various reasons, but most often they respond to population pressure. Most migrations follow the pattern of leaving a cool spot for a hot spot and then returning in the summer. So why did the species live in a place that was too cold for part of the year? The first hypothesis would be that the animals originally lived in areas that were hot all year round and therefore did not need to migrate.
As the population grew, resources were scarce. During the warmer months, northern latitudes were relatively hospitable, and so some members of the species expanded their range to live in these areas. When winter came, food became scarce and the cold was too intense, so the animals temporarily moved to warmer latitudes. The second hypothesis is that climate change is responsible for the phenomenon. Species living in the north may have lived in this area all along when the weather was warmer.
The main factor in the regulation of seasonal cycles in most plants and animals is the change in day length. The response of organisms to day length is called photoperiodism. The importance of photoperiodism can be seen from the experiment shown in Figure 3
Under artificial 24-hour lighting or a day length of more than 15 hours, birch seedlings grow continuously without shedding their leaves. But when illuminated for 10 or 12 hours a day, the growth of seedlings stops even in summer, soon the leaves are shed and winter dormancy sets in, as if under the influence of a short autumn day. Many of our deciduous tree species: willow, white acacia, oak, hornbeam, beech - become evergreen with long days.
Over the course of tens of thousands of years, the climate gradually changed, winters became too cold, and species were forced to travel south every year. The truth about migration may involve a combination of two hypotheses and likely differs from species to species. However, the first theory is more likely - population pressure is the force that drives most migrations and indeed most evolution. Climate change may have influenced the formation or process of migration patterns, but they do not represent a primary force.
Some of his navigation methods are so strange that we can't even understand them. The sun - it seems very simple. In general terms, one can determine in which direction it is moving based on the position of the sun. But if we consider issues such as observation time, time of year and the possible presence of clouds, being driven by the sun is a complex issue. However, ants and starlings are guided by the sun. Some birds can even be guided by the sun at night - theories suggest that they "read" the position in which the sun sets and use it to determine its course.
The length of the day determines not only the onset of winter dormancy, but also other seasonal phenomena in plants. Thus, long days promote the formation of flowers in most of our wild plants. Such plants are called long-day plants. Among the cultivated ones, these include rye, oats, most varieties of wheat and barley, and flax. However, some plants, mainly of southern origin, for example chrysanthemums, dahlias, require short day. Therefore, they bloom here only at the end of summer or autumn. Plants of this type are called short-day plants.
Others believe that polarization of sunlight is part of the process. Visual frames are another very primitive navigation system. Fly towards these mountains, turn slightly left when you see the first and new trees, seeing the ocean and the nest. The whales that travel the Pacific Ocean from the west coast of North America use this method - the navigational landmark they use is hard to miss because the entire continent serves this purpose. They keep the mainland to their left as they sail south and to the right as they sail north.
The influence of the length of the DNR also has a strong effect on animals. In insects and mites, the length of the day determines the onset of winter dormancy. Thus, when keeping cabbage butterfly caterpillars under conditions have a long day(more than 15 hours) butterflies soon emerge from the pupae and a successive series of generations develop without interruption. But if the caterpillars are kept at a day shorter than 14 hours, then even in spring and summer they get overwintering pupae that do not develop for several months, despite a fairly high temperature. This type of reaction explains why in nature, in the summer, while the days are long, insects can develop several generations, and in the fall, development always stops at the wintering stage.
Moon and Stars - Planetarium experiments have shown that many birds rely on star clues to discover the direction of their migration. You can even tell which star they are using for orientation. Faro - When an animal arrives in its general destination area, it can find specific beacon points. The lighthouse won't lead the Saskatchewan animal to Mexico, but it likely helps salmon find good spawning spots, for example. And the smell of rain can determine the fate of wildebeest migrations.
Climate - Wind conditions are plentiful, often used as a navigational aid by birds. When deprived of other cues such as the sun or stars, birds prefer to fly towards the wind in dough. In cases where they could see the sun and stars, they flew in the right direction, regardless of the prevailing wind.
In most birds, the lengthening days of spring cause the development of gonads and the manifestation of nesting instincts. The shortening of days in autumn causes molting, accumulation of reserve fats and the desire to migrate.
Day length is a signaling factor that determines the direction of biological processes. Why have seasonal changes in day length become so important in the life of living organisms?
Magnetic Field - The Earth has a magnetic field that usually cannot be detected by people without a compass. However, some species of animals are able to detect this field and can use it in their migrations. Bats and sea turtles use magnetic information to find their way. Some species of bacteria may even depend only on a magnetic field for orientation. We're not 100% sure how animals detect magnetic fields, but small particles of a magnetic mineral called magnetite have been located in the brains of some species.
Changes in day length are always closely related to the annual temperature variation. Day length therefore serves as an accurate astronomical predictor of seasonal changes in temperature and other conditions. This explains why most different groups Organisms of temperate latitudes, under the influence of the driving forces of evolution, have formed special photoperiodic reactions - adaptations to climatic changes at different times of the year.
These particles can respond to a magnetic field and activate nerves to send targeted information to the animal's brain. Sea Turtle: Baby sea turtles can find their way along a migration route of nearly 13,000 kilometers the first time they wander. Scientists diverted some of the turtles from their course, but they managed to get back on their way without much difficulty. Suspecting that there was some kind of magnetic bias in use, the next experiment exposed the animals to various magnetic fields that differed from the Earth's natural field.
Photoperiodism is a general, important adaptation that regulates seasonal phenomena in a wide variety of organisms.
Biological clock
The study of photoperiodism in plants and animals has shown that the reaction of organisms to light is based on alternating periods of light and darkness of a certain duration during the day. The reaction of organisms to the length of day and night shows that they are able to measure time, that is, they have some " biological clock"All types of living beings have this ability, from single-celled organisms to humans.
The turtles involved lost their way. Exposure to a magnet that mimics the Earth's magnetic field put them back on the road - proof that turtles are able to detect the Earth's magnetic field and use it to navigate. At one point, fewer than 20 specimens of the bird remained. The entire Krana population in the eastern part of the country disappeared. Western cranes have recovered to some extent, but biologists wanted to restore the species' presence in the eastern United States. This creates a bigger problem than just moving some crane families.
“Biological clocks,” in addition to seasonal cycles, control many other biological phenomena, the nature of which until recently remained mysterious. They determine the correct daily rhythm of both the activity of entire organisms and processes occurring even at the cellular level, in particular cell division.
Management of seasonal development of animals and plants.
Clarifying the role of day length and the regulation of seasonal phenomena opens up great opportunities for controlling the development of organisms.
Various development control techniques are used for year-round cultivation of vegetable crops and ornamental plants in artificial light, for winter and early forcing of flowers, and for accelerated production of seedlings. Pre-sowing cold treatment of seeds achieves heading of winter crops during spring sowing, as well as flowering and fruiting already in the first year of many biennial plants. By increasing the length of the day, it is possible to increase the egg production of birds on poultry farms.
Reasons for seasonal changes. Seasonal changes in nature are periodic phenomena that repeat annually in the same sequence. The seasons are characterized by different light and temperature conditions that determine the course of changes in the life processes of plants and animals. Each of the periods of the seasons is determined by geographical location and climatic conditions.
The change of seasons occurs due to the annual revolution of the Earth around the Sun while the inclination of the Earth's axis to the orbital plane remains unchanged. The position of the Earth in its orbit determines the onset of astronomical seasons. The brightness and duration of daily solar radiation at different times of the year affects the temperature of the air and soil, humidity, which entails changes in the life of plants and animals. But due to the instability of periodic weather changes, the astronomical beginnings of the seasons do not coincide with the timing of the onset of periodic phenomena in living nature. For example, astronomical spring begins on the day of the vernal equinox (March 21); naturalists consider March 19 to be the beginning of spring― average term arrival of rooks.
The timing of the onset of seasonal phenomena and their duration are relative; for example, the arrival date of rooks varies between March 7 and March 31.
Study of seasonal.
phenomena. The science of phenology studies the patterns of periodic seasonal changes in the life of plants and animals; observations of the onset of these phenomena are called phenological. The essence of these observations is to monitor the progress of seasonal phenomena and record the dates of their onset, and in some cases, their end. Based on long-term phenological observations, local history organizations compile nature calendars that reflect the time of onset of seasonal phenomena in a particular area.
The importance of studying seasonal phenomena. The need to study seasonal phenomena arose in humans a long time ago in connection with the development of agriculture, fishing, and hunting.
By annually determining the dates of the onset of seasonal changes and comparing them with the time of agricultural work, it is possible to establish the best timing for cultivating the soil and sowing seeds, thereby increasing the yield. For example, according to the agrobiological station named after K. A. Timiryazev, the largest harvest of cucumbers is obtained when they are sown during the flowering of purple lilac and yellow acacia. The best time to sow turnips is when aspen blooms.
Parallel observations of the development of plants and the insects that feed on them make it easier to establish the timing of pest control of cultivated plants.
Phenological observations provide rich factual material that serves as proof of Charles Darwin’s doctrine of natural selection and helps to understand the essence of the basic law of biology - the unity of the organism and its necessary living conditions. Observations broaden a person’s horizons, increase his interest and love for nature. At the same time, they do not require complex equipment and are accessible to anyone.
Nature calendar
Every teacher kindergarten must learn to conduct phenological observations and compile a nature calendar. Only in this case will he be able to correctly outline the timing of observations available to children and teach them to see and hear what is happening in nature.
The calendar of nature and agriculture of the central zone of the European part of Russia can serve a short guide when organizing phenological observations almost throughout the country, with the exception of places with different vegetation.
