In nature, populations fluctuate. Thus, the number of individual populations of insects and small plants can reach hundreds of thousands and a million individuals. In contrast, animal and plant populations can be relatively small in number.
The actuation of regulatory mechanisms can cause fluctuations in the number of populations. Three main types of population dynamics can be distinguished: stable, cyclical, and spasmodic (explosive).
Any population cannot consist of a smaller number of individuals than is necessary to ensure the stable implementation of this environment and the resistance of the population to factors external environment- the principle of the minimum population size.
Minimum population size specific to different types. Going beyond the minimum leads the population to death. So, further crossing of the tiger on Far East, will inevitably lead to extinction due to the fact that the remaining units, not finding breeding partners with sufficient frequency, will die out over a few generations. It also threatens rare plants(orchid "lady's slipper", etc.).
There is also a population maximum. 1975, Odum, - population maximum rule:
Population density regulation occurs when energy and space resources are fully utilized. A further increase in population density leads to a decrease in food supply and, consequently, to a decrease in fertility.
There are non-periodic (rarely observed) and periodic (permanent) fluctuations in the number of natural populations.
The stable type is distinguished by a small range of fluctuations (sometimes the number increases several times). It is characteristic of species with well-defined mechanisms of population homeostasis, high survival rate, low fecundity, long life span, complex age structure, developed care for offspring. A whole complex of efficiently operating regulatory mechanisms keeps such populations within certain density limits.
Periodic (cyclic) fluctuations in the number of populations. They are usually performed within one season or several years. Cyclical changes with an increase in numbers on average after 4 years was registered in animals living in the tundra - lemmings, snowy owl, polar fox. Seasonal fluctuations in abundance are also characteristic of many insects, mouse-like rodents, birds, and small aquatic organisms.
Question 1. What is population dynamics? What factors cause population fluctuations?
Population dynamics is the most important ecological process, characterized by a change in the number of organisms that make up them over time. Population changes are a complex process that ensures the stability of populations, the most efficient use of environmental resources by organisms, and finally, changes in the properties of the organisms themselves in accordance with the changing conditions of their life.
Population dynamics is closely dependent on indicators such as fertility and mortality, which are constantly changing depending on many factors. When the birth rate exceeds the death rate, the population increases, and vice versa: the number decreases when the death rate becomes higher than the birth rate. Constant changes in the living conditions of organisms lead to an increase in one or the other process. As a result, populations fluctuate.
Population fluctuations can be caused by seasonal changes in living conditions - factors: abiotic (temperature, humidity, light, etc.) or biotic (development of parasitic infections, predation, competition). In addition, the population dynamics is affected by the ability of individuals that make up the population to migrate - to fly, roam, etc.
Question 2. What is the significance of population dynamics in nature?
Dynamic population changes ensure the stability of populations, the most efficient use of ecological resources by the organisms that compose them, and finally, changes in the properties of the organisms themselves in accordance with the changing conditions of their life.
Question 3. What is the regulatory mechanisms-we? Give examples.
Populations have the ability to naturally regulate their numbers due to regulatory mechanisms that have the character of behavioral or physiological reactions of organisms to changes in population density. They are triggered automatically when the population density reaches either too high or too low values. material from the site
In some species, they manifest themselves in a severe form, leading to the death of an excess of individuals (self-thinning in plants, cannibalism in some animal species, throwing "extra" chicks out of the nest in birds), and in others - in a softened form. : expressed in a decrease in fertility at the level of conditioned reflexes (various manifestations of stress reactions) or by secreting substances that retard growth (daphnia, tadpoles - amphibian larvae) and development (often found in fish).
Interesting are the cases of limiting the size of the population by such changes in behavior with an increase in density, which ultimately lead to a mass migration of individuals.
For example, with an excessive increase in the population of butterflies of the Siberian silkworm, part of the butterflies (mainly females) scatter over distances of up to 100 km.
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Question 1. What is population dynamics? What factors cause population fluctuations?
Population dynamics is the most important ecological process, characterized by a change in the number of organisms that make up them over time. Population changes are a complex process that ensures the stability of populations, the most efficient use of ecological resources by organisms, and finally, changes in the properties of the organisms themselves in accordance with the changing conditions of their life.
Population dynamics is closely dependent on indicators such as fertility and mortality, which are constantly changing depending on many factors. When the birth rate exceeds the death rate, the population increases, and vice versa: the number decreases when the death rate becomes higher than the birth rate. Constant changes in the living conditions of organisms lead to an increase in one or the other process. As a result, populations fluctuate.
Question 2. What is the significance of population dynamics in nature?
Dynamic population changes ensure the stability of populations, the most efficient use of ecological resources by the organisms that compose them, and finally, changes in the properties of the organisms themselves in accordance with the changing conditions of their life.
Question 3. What are regulatory mechanisms? Give examples.
Populations have the ability to naturally regulate their numbers due to regulatory mechanisms that have the character of behavioral or physiological reactions of organisms to changes in population density. They are triggered automatically when the population density reaches either too high or too low values.
In some species, they manifest themselves in a severe form, leading to the death of an excess of individuals (self-thinning in plants, cannibalism in some animal species, throwing "extra" chicks out of the nest in birds), and in others - in a milder form: they are expressed in a decrease in fertility at the level of conditional reflexes (various manifestations of stress reactions) or by secreting substances that retard growth (daphnia, tadpoles - amphibian larvae) and development (often found in fish).
Of interest are the cases of limiting the size of the population by such changes in behavior with increasing density, which ultimately lead to mass migration of individuals.
For example, with an excessive increase in the population of butterflies Siberian silkworm part of the butterflies (mainly females) spread over distances of up to 100 km.
lesson type - combined
Methods: partially exploratory, problem presentation, reproductive, explanatory-illustrative.
Target:
Students' awareness of the importance of all the issues discussed, the ability to build their relationship with nature and society based on respect for life, for all living things as a unique and priceless part of the biosphere;
Tasks:
Educational: to show the multiplicity of factors acting on organisms in nature, the relativity of the concept of "harmful and beneficial factors", the diversity of life on planet Earth and the options for adapting living beings to the whole range of environmental conditions.
Developing: develop communication skills, the ability to independently acquire knowledge and stimulate their cognitive activity; the ability to analyze information, highlight the main thing in the studied material.
Educational:
To cultivate a culture of behavior in nature, the qualities of a tolerant person, to instill interest and love for wildlife, to form a stable positive attitude towards every living organism on Earth, to form the ability to see beauty.
Personal: cognitive interest to ecology. Understanding the need to obtain knowledge about the diversity of biotic relationships in natural communities in order to preserve natural biocenoses. The ability to choose the target and semantic settings in their actions and deeds in relation to wildlife. The need for fair evaluation of one's own work and the work of classmates
cognitive: the ability to work with various sources of information, convert it from one form to another, compare and analyze information, draw conclusions, prepare messages and presentations.
Regulatory: the ability to organize independently the execution of tasks, evaluate the correctness of the work, reflection of their activities.
Communicative: participate in the dialogue in the classroom; answer the questions of the teacher, classmates, speak to the audience using multimedia equipment or other means of demonstration
Planned results
Subject: know - the concepts of "habitat", "ecology", "environmental factors" their influence on living organisms, "connections of living and non-living";. Be able to - define the concept of "biotic factors"; characterize biotic factors, give examples.
Personal: make judgments, search and select information; analyze connections, compare, find an answer to a problematic question
Metasubject: connections with such academic disciplines as biology, chemistry, physics, geography. Plan actions with a set goal; find the necessary information in the textbook and reference literature; to carry out the analysis of objects of nature; draw conclusions; formulate your own opinion.
Form of organization learning activities - individual, group
Teaching methods: visual and illustrative, explanatory and illustrative, partially exploratory, independent work with additional literature and textbook, with DER.
Receptions: analysis, synthesis, conclusion, transfer of information from one type to another, generalization.
Learning new material
Population dynamics
The population size is determined mainly by two phenomena - fertility and mortality
In the process of reproduction, the number of individuals in a population increases, theoretically it is capable of an unlimited increase in numbers (curve 1 in the figure), however, the factors environment limit this growth, and the real curve (curve 2) of population growth approaches the value of the limiting number. The space enclosed between the theoretical curve and the real one characterizes the resistance of the medium.
Total population populations are subject to seasonal, long-term periodic fluctuations in numbers, as well as non-periodic ones (for example, outbreaks of mass reproduction of pests). These changes in numbers are the dynamics of the number of populations.
There are conditional reasons for fluctuations in the number of populations.
In the presence of available food, the population size grows, but at its maximum value, food becomes a limiting factor, and its lack leads to a decrease in the number.
Population ups and downs can occur in the process of competition between several populations for one ecological niche.
Abiotic factors ( temperature regime, humidity, chemical composition of the environment, etc.) have a strong influence on the size of the population and often cause significant fluctuations.
Population density usually has a certain optimum. With any deviation of the number from this optimum, the mechanisms of its intrapopulation regulation come into effect.
An increase in the population density of many insects is accompanied by a decrease in the size of individuals, a decrease in their fertility, an increase in the mortality of larvae and pupae, a change in the rate of development and sex ratio, which sharply reduces the active part of the population. An excessive increase in population density often stimulates cannibalism(from French cannibal - cannibal). A striking example is the phenomenon of eating their own eggs by flour beetles. Cannibalism is observed in some species of fish, amphibians and other animals. Cannibalism is known in more than 1300 animal species.
One of the important mechanisms of intrapopulation regulation of abundance is emigration- eviction, relocation of part of the population to less preferred habitats of the same range. In some species of aphids, an increase in population density is accompanied by the appearance of winged individuals capable of
settle down. During overcrowding, emigration occurs in a number of mammals (especially in murine rodents) and birds.
Drop in population density below the optimal level
(for example, with increased extermination of rats) causes an increase in fertility and stimulates their earlier puberty.
Some mechanisms of population size regulation can simultaneously prevent intraspecific competition. So, if a bird marks its nesting area by singing, then another pair of the same species nests outside it. Marks left by many mammals limit their hunting
site and prevent the introduction of other individuals. All this removes intraspecific competition and prevents excessive population compaction.
As I. I. Shmalgauzen (1884-1963) notes, all biologists
logical systems are characterized by a greater or lesser ability to self-regulate, i.e. Homeostasis is the ability of a living system (including a population) to maintain a stable dynamic balance in changing environmental conditions. Dynamic equilibrium is the fluctuation of the population size within some average value.
The first attempt to identify the mechanisms of homeostasis in wildlife was made by K. Linnaeus
(1760). The generalized concept of homeostasis and the term itself were proposed by W. Kennon (1929).
The homeostatic system is, first of all, each individual, and beyond
the already population.
An important mechanism for regulating abundance is the stress response.
For a person, the phenomenon of stress was first described in 1936 by G. Selye. In response to the negative impact of any factors, two types of reactions occur in the body: specific, depending on the nature of the damaging agent
(for example, an increase in heat production under the influence of cold), and a non-specific stress reaction (stress) as a general effort of the body to adapt to changing conditions in nature, there are many forms of stress:
anthropogenic (occurs in animals under the influence of
human activities);
neuropsychiatric (manifested with incompatibility in-
individuals in a group or as a result of population overcrowding);
thermal, noise, etc.
Questions and tasks
1. What is called the resistance of the environment? What is the ecological meaning of this concept?
2. What are the main reasons for population fluctuations.
3. Give a description of the population as a self-regulating system. What is called population homeostasis?
/ Chapter 9. Organism and environment Task: §9.6. Fluctuations in the number of organisms. Environmental regulation
Answer to Chapter 9. Organism and environment Task: §9.6. Fluctuations in the number of organisms. Environmental regulation
Ready-made homework assignments (GDZ) Biology Pasechnik, Kamensky Grade 9
Biology
Grade 9
Publisher: Bustard
Year: 2007 - 2014
Question 1. What is population dynamics? What factors cause population fluctuations?
Population dynamics is the most important ecological process, characterized by a change in the number of organisms that make up them over time. Population changes are a complex process that ensures the stability of populations, the most efficient use of ecological resources by organisms, and finally, changes in the properties of the organisms themselves in accordance with the changing conditions of their life.
Population dynamics is closely dependent on indicators such as fertility and mortality, which are constantly changing depending on many factors. When the birth rate exceeds the death rate, the population increases, and vice versa: the number decreases when the death rate becomes higher than the birth rate. Constant changes in the living conditions of organisms lead to an increase in one or the other process. As a result, populations fluctuate.
Population fluctuations can be caused by seasonal changes in living conditions - factors: abiotic (temperature, humidity, illumination, etc.) or biotic (development of parasitic infections, predation, competition). In addition, the population dynamics is affected by the ability of individuals that make up the population to migrate - to fly, roam, etc.
Question 2. What is the significance of population dynamics in nature?
Dynamic population changes ensure the stability of populations, the most efficient use of ecological resources by the organisms that compose them, and finally, changes in the properties of the organisms themselves in accordance with the changing conditions of their life.
Question 3. What are regulatory mechanisms? Give examples.
Populations have the ability to naturally regulate their numbers due to regulatory mechanisms that have the character of behavioral or physiological reactions of organisms to changes in population density. They are triggered automatically when the population density reaches either too high or too low values.
In some species, they manifest themselves in a severe form, leading to the death of an excess of individuals (self-thinning in plants, cannibalism in some animal species, throwing "extra" chicks out of the nest in birds), and in others - in a milder form: they are expressed in a decrease in fertility at the level of conditional reflexes (various manifestations of stress reactions) or by secreting substances that retard growth (daphnia, tadpoles - amphibian larvae) and development (often found in fish).
Of interest are the cases of limiting the size of the population by such changes in behavior with increasing density, which ultimately lead to mass migration of individuals.
For example, with an excessive increase in the population of Siberian silkworm butterflies, part of the butterflies (mainly females) fly apart over distances of up to 100 km.
