Environmental factors always act on organisms in combination. Moreover, the result is not the sum of the influence of several factors, but is a complex process of their interaction. At the same time, the vitality of the organism changes, specific adaptive properties arise that allow it to survive in certain conditions and tolerate fluctuations in the values of various factors.
The influence of environmental factors on the body can be represented in the form of a diagram (Fig. 94).
The most beneficial intensity for the body environmental factor called optimal or optimum.
Deviation from the optimal action of the factor leads to inhibition of the body’s vital functions.
The limit beyond which the existence of an organism is impossible is called endurance limit.
These boundaries are different for different types and even for different individuals of the same species. For example, the upper layers of the atmosphere, thermal springs, and the ice desert of Antarctica are beyond the limits of endurance for many organisms.
An environmental factor that goes beyond the limits of the body's endurance is called limiting.
It has upper and lower limits. So, for fish the limiting factor is water. Outside the aquatic environment, their life is impossible. A decrease in water temperature below 0 °C is the lower limit, and an increase above 45 °C is the upper limit of endurance.
Rice. 94. Scheme of the action of an environmental factor on the body
Thus, the optimum reflects the characteristics of living conditions various types. According to the level of the most favorable factors organisms are divided into heat- and cold-loving, moisture-loving and drought-resistant, light-loving and shade-tolerant, adapted to life in salt and fresh water, etc. The wider the limit of endurance, the more plastic the organism. Moreover, the limit of endurance in relation to various environmental factors varies among organisms. For example, moisture-loving plants can tolerate large temperature changes, while the lack of moisture is detrimental to them. Narrowly adapted species are less plastic and have a small limit of endurance; widely adapted species are more plastic and have a wide range of fluctuations in environmental factors.
For fish living in the cold seas of Antarctica and the Arctic Ocean, the temperature range is 4-8 °C. As the temperature rises (above 10 °C), they stop moving and fall into thermal stupor. On the other hand, fish from equatorial and temperate latitudes tolerate temperature fluctuations from 10 to 40 °C. Warm-blooded animals have a wider range of endurance. Thus, arctic foxes in the tundra can tolerate temperature changes from -50 to 30 °C.
Temperate plants can withstand temperature fluctuations of 60-80 °C, while tropical plants have a much narrower temperature range: 30-40 °C.
Interaction of environmental factors is that changing the intensity of one of them can narrow the limit of endurance to another factor or, conversely, increase it. For example, optimal temperature increases tolerance to lack of moisture and food. High humidity significantly reduces the body's resistance to high temperatures. The intensity of exposure to environmental factors is directly dependent on the duration of this exposure. Prolonged exposure to high or low temperatures is detrimental to many plants, while plants tolerate short-term changes normally. The limiting factors for plants are the composition of the soil, the presence of nitrogen and other nutrients in it. So, clover grows better in soils poor in nitrogen, and nettle does the opposite. A decrease in nitrogen content in the soil leads to a decrease in the drought resistance of cereals. Plants grow worse on salty soils; many species do not take root at all. Thus, the organism’s adaptability to individual environmental factors is individual and can have both a wide and narrow range of endurance. But if the quantitative change in at least one of the factors goes beyond the limit of endurance, then, despite the fact that other conditions are favorable, the organism dies.
The set of environmental factors (abiotic and biotic) that are necessary for the existence of a species is called ecological niche.
An ecological niche characterizes the way of life of an organism, its living conditions and nutrition. In contrast to a niche, the concept of habitat denotes the territory where an organism lives, i.e. its “address”. For example, the herbivorous inhabitants of the steppes, cows and kangaroos, occupy the same ecological niche, but have different habitats. On the contrary, the inhabitants of the forest - squirrel and elk, also classified as herbivores, occupy different ecological niches. The ecological niche always determines the distribution of an organism and its role in the community.
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§ 67. Impact of certain environmental factors on organisms§ 69. Basic properties of populations
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Adaptations of organisms to the environment are called adaptations. The ability to adapt is one of the main properties of life in general, since it provides the very possibility of its existence, the ability of organisms to survive and reproduce. Adaptations appear on different levels: from the biochemistry of cells and the behavior of individual organisms to the structure and functioning of communities and ecological systems. Adaptations arise and change during the evolution of species.
Individual properties or elements of the environment that affect organisms are called environmental factors. Environmental factors are diverse. They can be necessary or, conversely, harmful to living beings, promote or hinder survival and reproduction. Environmental factors have different natures and specific actions. Ecological factors are divided into abiotic and biotic, anthropogenic.
Abiotic factors - temperature, light, radioactive radiation, pressure, air humidity, salt composition of water, wind, currents, terrain - these are all properties of inanimate nature that directly or indirectly affect living organisms.
Biotic factors are forms of influence of living beings on each other. Each organism constantly experiences the direct or indirect influence of other creatures, enters into contact with representatives of its own species and other species, depends on them and itself influences them. The surrounding organic world - component environment of every living being. Mutual connections between organisms are the basis for the existence of biocenoses and populations; their consideration belongs to the field of synecology.
Anthropogenic factors are forms of activity of human society that lead to changes in nature as the habitat of other species or directly affect their lives. Although humans influence living nature through changes in abiotic factors and biotic relationships of species, anthropogenic activity should be identified as a special force that does not fit into the framework of this classification. The importance of anthropogenic influence on the living world of the planet continues to grow rapidly. The same environmental factor has different meaning in the life of cohabiting organisms of different species. For example, strong winds in winter are unfavorable for large, open-living animals, but have no effect on smaller ones that hide in burrows or under the snow. The salt composition of the soil is important for plant nutrition, but is indifferent to most terrestrial animals, etc.
Changes in environmental factors over time can be: 1) regularly periodic, changing the strength of the impact in connection with the time of day or season of the year or the rhythm of ebbs and flows in the ocean; 2) irregular, without clear periodicity, for example changes weather conditions in different years, catastrophic phenomena - storms, showers, landslides, etc.; 3) directed over certain, sometimes long, periods of time, for example, during cooling or warming of the climate, overgrowing of water bodies, constant grazing of livestock in the same area, etc. Environmental environmental factors have various effects on living organisms, i.e. can act as stimuli causing adaptive changes in physiological and biochemical functions; as limiters that make it impossible to exist in given conditions; as modifiers that cause anatomical and morphological changes in organisms; as signals indicating changes in other environmental factors.
Despite the wide variety of environmental factors, a number of general patterns can be identified in the nature of their impact on organisms and in the responses of living beings.
1.Law of optimum. Each factor has only certain limits of positive influence on organisms. The result of a variable factor depends primarily on the strength of its manifestation. Both insufficient and excessive action of the factor negatively affects the life activity of individuals. The favorable force of influence is called the zone of optimum of the environmental factor or simply the optimum for organisms of a given species. The greater the deviation from the optimum, the more pronounced the inhibitory effect of this factor on organisms (pessimum zone). The maximum and minimum transferable values of a factor are critical points, beyond which existence is no longer possible and death occurs. The endurance limits between critical points are called the ecological valence (range of tolerance) of living beings in relation to a specific environmental factor.
Representatives of different species differ greatly from each other both in the position of the optimum and in ecological valence. For example, arctic foxes in the tundra can tolerate fluctuations in air temperature in the range of about 80°C (from +30° to -55°C), while warm-water crustaceans Copilia mirabilis can withstand changes in water temperature in the range of no more than 6°C (from 23 ° up to 29°C). The emergence of narrow ranges of tolerance in evolution can be considered a form of specialization, as a result of which greater efficiency is achieved at the expense of adaptability and diversity increases in the community.
The same strength of manifestation of a factor can be optimal for one type, pessimal for another, and go beyond the limits of endurance for a third.
The broad ecological valence of a species in relation to abiotic environmental factors is indicated by adding the prefix “eury” to the name of the factor. Eurythermal species - tolerate significant temperature fluctuations, eurybates - a wide range of pressure, euryhaline - varying degrees of salinity of the environment.
The inability to tolerate significant fluctuations in a factor, or narrow ecological valence, is characterized by the prefix “steno” - stenothermic, stenobat, stenohaline species, etc. In a broader sense, species whose existence requires strictly defined environmental conditions are called stenobiont, and those which are able to adapt to different environmental conditions - eurybionts.
2. Ambiguity of the factor’s effect on different functions. Each factor affects different body functions differently. The optimum for some processes may be a pessimum for others. Thus, air temperature from 40° to 45°C in cold-blooded animals greatly increases the rate of metabolic processes in the body, but inhibits motor activity, and the animals fall into thermal stupor. For many fish, the water temperature that is optimal for the maturation of reproductive products is unfavorable for spawning, which occurs in a different temperature range.
The life cycle, in which during certain periods the organism primarily performs certain functions (nutrition, growth, reproduction, settlement, etc.), is always consistent with seasonal changes in a complex of environmental factors. Mobile organisms can also change habitats to successfully carry out all their vital functions. The breeding season is usually critical; During this period, many environmental factors often become limiting. Tolerance limits for reproducing individuals, seeds, eggs, embryos, seedlings and larvae are usually narrower than for non-reproducing adult plants or animals. Thus, an adult cypress can grow both on dry highlands and immersed in water, but it reproduces only where there is moist, but not flooded soil for the development of seedlings. Many marine animals can tolerate brackish or fresh water with high chloride content, so they often enter upstream rivers. But their larvae cannot live in such waters, so the species cannot reproduce in the river and does not settle here permanently.
3. Variability, variability and variety of responses to the action of environmental factors in individual individuals of the species.
The degree of endurance, critical points, optimal and pessimal zones of individual individuals do not coincide. This variability is determined both by the hereditary qualities of individuals and by gender, age and physiological differences. For example, the mill moth, one of the pests of flour and grain products, has a critical minimum temperature for caterpillars of -7°C, for adult forms -22°C, and for eggs -27°C. Frost of 10°C kills caterpillars, but is not dangerous for the adults and eggs of this pest. Consequently, the ecological valency of a species is always broader than the ecological valence of each individual individual.
4. Species adapt to each environmental factor in a relatively independent way. The degree of tolerance to any factor does not mean the corresponding ecological valency of the species in relation to other factors. For example, species that tolerate wide variations in temperature do not necessarily also need to be able to tolerate wide variations in humidity or salinity. Eurythermal species can be stenohaline, stenobatic, or vice versa. The ecological valencies of a species in relation to different factors can be very diverse. This creates an extraordinary variety of adaptations in nature. A set of environmental valences in relation to various environmental factors constitutes the ecological spectrum of a species.
5. Discrepancy in the ecological spectra of individual species. Each species is specific in its ecological capabilities. Even among species that are similar in their methods of adaptation to the environment, there are differences in their attitude to some individual factors.
6. Interaction of factors.
The optimal zone and limits of endurance of organisms in relation to any environmental factor can shift depending on the strength and in what combination other factors act simultaneously. This pattern is called the interaction of factors. For example, heat is easier to bear in dry rather than humid air. The risk of freezing is significantly higher in frosty conditions strong wind than in calm weather. Thus, the same factor in combination with others has different environmental impacts. On the contrary, the same environmental result can be obtained in different ways. For example, plant wilting can be stopped by both increasing the amount of moisture in the soil and lowering the air temperature, which reduces evaporation. The effect of partial substitution of factors is created.
At the same time, mutual compensation of environmental factors has certain limits, and it is impossible to completely replace one of them with another. Complete absence water or at least one of the basic elements of mineral nutrition makes plant life impossible, despite the most favorable combinations of other conditions. The extreme heat deficit in the polar deserts cannot be compensated by either an abundance of moisture or 24-hour illumination.
7. Rule of limiting (limiting) factors. Environmental factors that are furthest from the optimum make it especially difficult for a species to exist under these conditions. If at least one of the environmental factors approaches or goes beyond critical values, then, despite the optimal combination of other conditions, the individuals are threatened with death. Such factors that strongly deviate from the optimum acquire paramount importance in the life of the species or its individual representatives in each specific period of time.
Limiting environmental factors determine the geographic range of a species. The nature of these factors may be different. Thus, the movement of the species to the north may be limited by a lack of heat, and into arid regions by a lack of moisture or too high temperatures. Biotic relationships can also serve as limiting factors for distribution, for example, the occupation of a territory by a stronger competitor or a lack of pollinators for plants.
To determine whether a species can exist in a given geographic area, it is necessary first to determine whether any environmental factors are beyond its ecological valence, especially during its most vulnerable period of development.
Organisms with a wide range of tolerance to all factors are usually the most widespread.
8. The rule of compliance of environmental conditions with the genetic predetermination of the organism. A species of organisms can exist until and to the extent that the natural environment surrounding it corresponds to the genetic capabilities of adapting this species to its fluctuations and changes. Each species of living things arose in a certain environment, adapted to it to one degree or another, and its further existence is possible only in it or a similar environment. A sharp and rapid change in the living environment can lead to the fact that the genetic capabilities of a species will be insufficient to adapt to new conditions.
In this work I will cover in detail the topic “Limiting factors”. I will consider their definition, types, laws and examples.
Different environmental factors have different significance for living organisms.
For organisms to live, a certain combination of conditions is necessary. If all environmental conditions are favorable, with the exception of one, then this condition becomes decisive for the life of the organism in question.
Of the variety of limiting environmental factors, the attention of researchers is primarily attracted to those that inhibit the vital activity of organisms and limit their growth and development.
Main part
In the total environmental pressure, factors are identified that most strongly limit the success of the life of organisms. Such factors are called limiting or limiting.
Limiting factors - This
1) any factors inhibiting population growth in the ecosystem; 2) environmental factors, the value of which greatly deviates from the optimum.
In the presence of optimal combinations of many factors, one limiting factor can lead to oppression and death of organisms. For example, heat-loving plants die at negative air temperatures, despite the optimal content of nutrients in the soil, optimal humidity, light, and so on. Limiting factors are irreplaceable if they do not interact with other factors. For example, a lack of mineral nitrogen in the soil cannot be compensated for by an excess of potassium or phosphorus.
Limiting factors for terrestrial ecosystems:
Temperature;
Nutrients in the soil.
Limiting factors for aquatic ecosystems:
Temperature;
Sunlight;
Salinity.
Typically, these factors interact in such a way that one process is limited simultaneously by several factors, and a change in any of them leads to a new equilibrium. For example, an increase in food availability and a decrease in predation pressure can lead to an increase in population size.
Examples of limiting factors are: outcrops of uneroded rocks, erosion base, valley sides, etc.
Thus, the factor limiting the spread of deer is the depth of the snow cover; moths of the winter armyworm (a pest of vegetable and grain crops) - winter temperature, etc.
The idea of limiting factors is based on two laws of ecology: the law of the minimum and the law of tolerance.
Law of the minimum
In the mid-19th century, the German organic chemist Liebig, studying the effect of various microelements on plant growth, was the first to establish the following: plant growth is limited by an element whose concentration and significance is at a minimum, that is, present in a minimal amount. The so-called “Liebig barrel” helps to represent the law of the minimum figuratively. This is a barrel with wooden slats different heights, as it shown on the picture . It is clear that no matter what the height of the other slats, you can pour exactly as much water into the barrel as the height of the shortest slats. Likewise, a limiting factor limits the life activity of organisms, despite the level (dose) of other factors. For example, if yeast is placed in cold water, low temperature will become a limiting factor in their reproduction. Every housewife knows this, and therefore leaves the yeast to “swell” (and actually multiply) in warm water with a sufficient amount of sugar.
Heat, light, water, oxygen, and other factors can limit or limit the development of organisms, if their movement corresponds to the ecological minimum. For example, the tropical fish angelfish dies if the water temperature drops below 16 °C. And the development of algae in deep-sea ecosystems is limited by the depth of penetration sunlight: There are no algae in the bottom layers.
Later (in 1909), the law of the minimum was interpreted by F. Blackman more broadly, as the action of any ecological factor that is at a minimum: environmental factors that have the worst significance in specific conditions especially limit the possibility of the existence of a species in these conditions in spite of and in spite of optimal combination of other hotel conditions.
In its modern formulation, the law of the minimum sounds like this: the body's endurance is determined by the weakest link in the chain of its environmental needs .
To successfully apply the law of limiting factors in practice, two principles must be observed:
The first is restrictive, that is, the law is strictly applicable only under stationary conditions, when the inflow and outflow of energy and substances are balanced. For example, in a certain body of water, the growth of algae is limited under natural conditions by a lack of phosphates. Nitrogen compounds are found in excess in water. If they start dumping into this reservoir wastewater with a high content of mineral phosphorus, then the reservoir may “bloom”. This process will progress until one of the elements is used up to the restrictive minimum. Now it may be nitrogen if phosphorus continues to be supplied. At the transition moment (when there is still enough nitrogen and enough phosphorus), the minimum effect is not observed, i.e., none of these elements affects the growth of algae.
The second takes into account the interaction of factors and the adaptability of organisms. Sometimes the body is able to replace the deficient element with another, chemically similar one. Thus, in places where there is a lot of strontium, in mollusk shells it can replace calcium when there is a deficiency of the latter. Or, for example, the need for zinc in some plants is reduced if they grow in the shade. Therefore, a low zinc concentration will limit plant growth less in the shade than in bright light. In these cases, the limiting effect even insufficient quantity one or another element may not appear.
Law of Tolerance
The concept that, along with a minimum, a maximum can also be a limiting factor was introduced 70 years later in 1913 after Liebig by the American zoologist W. Shelford. He drew attention to the fact that not only those environmental factors whose values are minimal, but also those that are characterized by an ecological maximum can limit the development of living organisms, and formulated the law of tolerance: “ The limiting factor for the prosperity of a population (organism) can be either a minimum or a maximum of environmental impact, and the range between them determines the amount of endurance (tolerance limit) or the ecological valency of the organism to this factor)" (Fig. 2).
Figure 2 - Dependence of the result of an environmental factor on its intensity
The favorable range of action of an environmental factor is called optimum zone (normal life activity). The more significant the deviation of a factor’s action from the optimum, the more this factor inhibits the vital activity of the population. This range is called zone of oppression or pessimism . The maximum and minimum transferable values of a factor are critical points beyond which the existence of an organism or population is no longer possible. The tolerance limit describes the amplitude of factor fluctuations, which ensures the most fulfilling existence of the population. Individuals may have slightly different tolerance ranges.
Later, tolerance limits for various environmental factors were established for many plants and animals. The laws of J. Liebig and W. Shelford helped to understand many phenomena and the distribution of organisms in nature. Organisms cannot be distributed everywhere because populations have a certain tolerance limit in relation to fluctuations in environmental environmental factors.
Many organisms are capable of changing tolerance to individual factors if conditions change gradually. You can, for example, get used to the high temperature of the water in the bath if you get into warm water, and then gradually add hot. This adaptation to a slow change in factor is a useful protective property. But it can also be dangerous. Unexpectedly, without warning signs, even a small change can be critical. A threshold effect occurs: the last straw could be fatal. For example, a thin twig can cause a camel's already overloaded back to break.
The principle of limiting factors is valid for all types of living organisms - plants, animals, microorganisms and applies to both abiotic and biotic factors. For example, competition from another species may become a limiting factor for the development of organisms of a given species. In agriculture, pests and weeds often become the limiting factor, and for some plants the limiting factor in development is the lack (or absence) of representatives of another species. In accordance with the law of tolerance, any excess of matter or energy turns out to be a source of environmental pollution. Thus, excess water, even in arid areas, is harmful, and water can be considered a common pollutant, although it is essential in optimal quantities. In particular, excess water prevents normal soil formation in the chernozem zone.
The following was found:
· organisms with a wide range of tolerance to all factors are widespread in nature and are often cosmopolitan, for example, many pathogenic bacteria;
· Organisms may have a wide range of tolerance for one factor and a narrow range for another. For example, people are more tolerant to the absence of food than to the lack of water, i.e., the tolerance limit for water is narrower than for food;
· if conditions for one of the environmental factors become suboptimal, then the tolerance limit for other factors may also change. For example, when there is a lack of nitrogen in the soil, cereals require much more water;
· the limits of tolerance in breeding individuals and offspring are less than in adult individuals, i.e. females during the breeding season and their offspring are less hardy than adult organisms. Thus, the geographic distribution of game birds is more often determined by the influence of climate on eggs and chicks, rather than on adult birds. Caring for offspring and careful attitude to motherhood are dictated by the laws of nature. Unfortunately, sometimes social “achievements” contradict these laws;
· extreme (stressful) values of one of the factors lead to a decrease in the tolerance limit for other factors. If heated water is released into a river, fish and other organisms spend almost all their energy coping with stress. They lack energy to obtain food, protect themselves from predators, and reproduce, which leads to gradual extinction. Psychological stress can also cause many somatic (gr. soma- body) diseases not only in humans, but also in some animals (for example, dogs). With stressful values of the factor, adaptation to it becomes more and more “expensive”.
It is possible to identify probable weak links in the environment that may turn out to be critical or limiting. With targeted influence on limiting conditions, it is possible to quickly and effectively increase plant yields and animal productivity. Thus, when growing wheat on acidic soils, no agronomic measures will be effective unless liming is used, which will reduce the limiting effect of acids. Or, if you grow corn in soils with very low phosphorus content, then even with enough water, nitrogen, potassium and other nutrients she stops growing. Phosphorus in this case is the limiting factor. And only phosphorus fertilizers can save the harvest. Plants can die from too much large quantity water or excess fertilizer, which in this case are also limiting factors.
If a change in the value of the limiting factor leads to a much larger (in compared units) change in the output characteristics of the system or other elements, then the limiting factor is called control element in relation to these latter controlled characteristics, or elements.
Often in a good way identifying limiting factors is the study of the distribution and behavior of organisms on the periphery of their range. If we agree with the statement of Andrevarta and Birch (1954) that distribution and abundance are controlled by the same factors, then studying the periphery of the range should be doubly useful. However, many ecologists believe that the abundance in the center of the range and the distribution on its periphery can be controlled by completely different factors, especially since, as geneticists have discovered, individuals in peripheral populations may differ from individuals in central populations at the genotype level.
Conclusion
In this work, I examined in detail the definition, types, laws and examples of limiting factors.
After analyzing the work, I drew conclusions.
Identification of limiting factors is an approximation technique that reveals the roughest, most significant features of the system.
Identification of limiting links allows one to significantly simplify the description, and in some cases, to qualitatively judge the dynamic states of the system.
Knowledge of limiting factors provides the key to ecosystem management, so only skillful regulation of living conditions can give effective management results.
The concept of limiting factors, originating from the classical works of Liebig, is actively used in biochemistry, physiology, agronomy, as well as in quantitative genetics.
A key role in evolution is played by limiting factors of organization that limit the possibilities of certain directions of evolution.
The value of the concept of limiting factors is that it provides a starting point for research difficult situations.
Identifying limiting factors is the key to controlling the life activity of organisms.
Identifying limiting factors is very important for many activities, especially Agriculture.
Bibliography
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2.Ecology. Textbook for universities. Author: Korobkin V.I., Peredelsky L.V. Publisher: Phoenix, 2010
3. Markov M.V. Agrophytocenology. Ed. Kazan University, 1972.
4. Nebel B. Science of environment. M.: Mir, 1993.
5. Ricklefs R. Fundamentals of General Ecology. M.: Mir. 1979.
6. Soviet encyclopedic dictionary. M.: Soviet Encyclopedia, 1988.
7. encyclopedic Dictionary environmental terms. Kazan, 2001.
Environmental factors.
In concept natural environment includes all conditions of living and inanimate nature in which an organism, population, or natural community exists. The natural environment directly or indirectly affects their condition and properties. Components of the natural environment that influence the state and properties of an organism, population, or natural community are called environmental factors. Among them, three different groups of factors are distinguished:
abiotic factors- all components of inanimate nature, among which the most important are light, temperature, humidity and other climate components, as well as the composition of the water, air and soil environment;
biotic factors - interactions between different individuals in populations, between populations in natural communities;
limiting factors - environmental factors that go beyond the boundaries of maximum or minimum endurance, limiting the existence of the species.
anthropogenic factor - all the diverse human activities that lead to changes in nature as the habitat of all living organisms or directly affect their lives.
Various environmental factors, such as temperature, humidity, food, affect each individual. In response to this, organisms develop various adaptations to them through natural selection. The intensity of factors that is most favorable for life activity is called optimal or optimum.
The optimal value of a particular factor is different for each species. Depending on their attitude to one or another factor, species can be heat- and cold-loving (elephant and polar bear), moisture- and dry-loving (linden and saxaul), adapted to high or low salinity of water, etc.
Limiting factor
The body is simultaneously influenced by numerous diverse and multidirectional environmental factors. In nature, the combination of all influences in their optimal, most favorable values is practically impossible. Therefore, even in habitats where all (or leading) environmental factors are most favorably combined, each of them most often deviates somewhat from the optimum. To characterize the effect of environmental factors on animals and plants, it is essential that in relation to some factors, organisms have a wide range of endurance and can withstand significant deviations in the intensity of the factor from the optimal value.
Effective temperature refers to the difference between the ambient temperature and the temperature threshold for development. Thus, the development of trout eggs begins at 0°C, which means that this temperature serves as a development threshold. At a water temperature of 2 C, the fry emerge from the facial shells after 205 days, at 5 ° C - after 82 days, and at 10 ° C - after 41 days. In all cases the work positive temperatures environment for the number of days of development remains constant: 410. This will be the sum of effective temperatures.
Thus, in order to carry out the genetic development program, animals with unstable body temperatures (and plants) need to receive a certain amount of heat.
Both the development thresholds and the sum of effective temperatures are different for each species. They are determined by the historical adaptation of the species to certain living conditions.
The flowering time of plants also depends on the sum of temperatures over a certain period of time. For example, for coltsfoot to bloom, 77 is required, for oxalis - 453, and for strawberries - 500. The sum of effective temperatures that must be reached to complete life cycle, often limits the geographic distribution of the species. Thus, the northern border of tree vegetation coincides with the July isotherms of Yu...12°C. To the north there is no longer enough heat for the development of trees and the forest zone is replaced by tundra. Likewise, if barley grows well in the temperate zone (its sum of temperatures for the entire period from sowing to harvesting is 160-1900°C), then this amount of heat is not enough for rice or cotton (with the sum of temperatures required for them being 2000-4000°C ).
Many factors become limiting during the breeding season. Hardiness limits for seeds, eggs, embryos, and larvae are usually narrower than for adult plants and animals. For example, many crabs can enter a river far upstream, but their larvae cannot develop in river water. The range of game birds is often determined by the effects of climate on eggs or chicks rather than on adults.
Identifying limiting factors is very important in practical terms. Thus, wheat grows poorly in acidic soils, but adding lime to the soil can significantly increase yields. .
LIMITING
The influence of environmental factors on living organisms is diverse, however, we can highlight general patterns their actions. With extremely weak or extremely strong influence of a factor, the vital activity of organisms undergoing these influences is inhibited. The factor acts most favorably at values that are optimal for a given organism. The range of action of an ecological factor within which the existence of a given species is possible is area of tolerance kind. The area of tolerance is limited by the minimum and maximum points; they correspond to the extreme values of a given factor at which the existence of organisms is possible. Factor value corresponding best performance for life certain type, is called optimal, or optimum point(Fig. 3). The optimum, minimum and maximum points determine the “norm of reaction” of the body to a given factor. The extreme points of the curve, which express the state of oppression of organisms with a deficiency or excess of an environmental factor, are called pessimum areas. Beyond these points, i.e. outside the tolerance zone, the value of the environmental factor is lethal (deadly) for living organisms.
Fig.3. The influence of changes in the quantitative expression of an environmental factor on the vital activity of the organism (it is assumed that all other factors operate at their optimum). 1 – the degree of favorability of these doses for the body: 2 – the amount of costs necessary for adaptation
Environmental conditions under which any factor or their combination has a depressing effect on the life activity of organisms are called limiting. Environmental factors that have values that are farthest from optimal in specific environmental conditions make it difficult for the species to exist in these conditions, despite optimal values other factors. Such factors are called limiting factors. Limiting factors become of paramount importance for the life of a species, and ultimately determine the boundaries of the habitat of a given species, its geographical area.
Optimal - the most favorable intensity of the environmental factor for the body - light, temperature, air, soil, humidity, food, etc.
Limiting factors 1) any factors inhibiting population growth in an ecosystem; 2) environmental factors, the value of which greatly deviates from the optimum.
In the presence of optimal combinations of many factors, one limiting factor can lead to oppression and death of organisms. For example, heat-loving plants die at negative air temperatures, despite the optimal content of nutrients in the soil, optimal humidity, light, and so on. Limiting factors are irreplaceable if they do not interact with other factors. For example, a lack of mineral nitrogen in the soil cannot be compensated for by an excess of potassium or phosphorus.