Ecology of populations - demecology

Think of what species is.  Species - is a group of organisms that are similar in morphology. Any type of animal, plant, microorganism establishes itself in the environment, masters the arena of life, adapts to the constantly changing conditions, not as a group of individuals, but as a whole, which is the population.

In ecology a population is called a group of individuals of the same species which interact with each other and share a common living area.

The word "population" comes from the Latin "Populus" - people, population. Thus, ecological population can be determined as the population of one species in a particular area.

Populations as group associations have a number of specific properties that are not inherent to each single individual. Members of one population have no less impact on each other than physical factors of the environment, or other types of organisms living together. To some extent, all forms of communications which are specific for interspecies relationships show up in populations, but most common are mutually beneficial and competitive relations. Specific intra-species relations - this is relationship associated with reproduction: between individuals of different sexes and between parent and child generations.

General changes in population size are formed by four phenomena, birth, death, moving in and out of individuals (migration).

Birth rate - the number of new individuals appearing per unit of time as a result of breeding. Fertility depends on the ratio of the breeding season, and overall length of life, as well as the fertility of individuals.  Average fertility of each species is defined historically as a mechanism allowing for recovery of the loss of populations, in favorable conditions fertility is usually low, and in unfavorable conditions is high.   The nature of fertility depends on the rate of sexual maturation and the ratio of males and females in the population, the number of generations per season, on the degree of parental care or provision of eggs with nutrition.  Species which nurse and guard their offspring have a very low fertility.  High fertility is usual for species with high mortality, especially when they are pressured by predators.

Population size and density depend not only on fertility but also on the population mortality. Mortality is the number of individuals who died in the given period. Mortality varies depending on the genetic and physiological usefulness of animals, environmental conditions, age, state of the population, and is expressed as % to initial or average population size.

Population dynamics is greatly influenced by the migration of individuals, that is, exchange of populations. Going of individuals out of the population or its replenishment by strangers (immigration) - is a phenomenon that is based on one of the most important features - its expansive ability. Balanced intensity of fertility and mortality (1-1) forms a stable population in which mortality is compensated by the growth, and its size and habitat are maintained at the same level. However, in nature there are virtually no stable populations, as there is no permanently stable state of the environment and relations within the population. More often it is observed an excess of births over deaths and populations grow up to such an extent that an outbreak of mass reproduction can occur which is especially true for small animals. These populations are called growing.

When population develops excessively, its living conditions worsen, and overcrowding of the population occurs, reserves of food and energy decrease. This leads to a sharp increase in mortality as a result the population begins to shrink. If the death rate exceeds the birth rate, the population is declining. But it can't shrink endlessly.  Under certain conditions, mortality begins to fall, and the fertility increases, and gradually a population transforms into a stable population.

In nature, the population size is regulated by immigration and emigration - this process is called dispersion of the population. Expansive dispersion is a means of communication between populations. It increases with increasing density of the population, and during the depression in size, by contrast, the flow of strangers into the population grows. For example, it is known that residential animals with distinct territorial instincts, show low aggressive behavior towards strangers in a period of low population and invaders occupy vacant lands.

Often, the excessive increase of population density causes cannibalism.

During emigration, penetration of dispersing individuals to unoccupied by the species territory, their population and forming of new populations is called invasion.

Each population is characterized by the age structure, and the ratio of age groups characterizes the ability of a population to reproduce. In population there are individuals of different age, and among these are individuals of different sex. The duration of life and time of sexual maturation is not the same for different species.

Growth in the number and density of the population of any species in nature cannot be endless. Sooner or later population is faced with limitations. These limitations are resources thanks to which species exist: food, shelter, breeding sites. They do not allow the population to expand further. These limits are called the environmental capacity for specific populations. For example, spruce forest is more capacious environment for squirrel than the mixed forest, as the main food for squirrel is seeds of conifers.

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$$$003-013-001$3.3.13.1 Методические указания к практическому занятию №13

{Цель занятия, методические указания к выполнению практического задания, примеры расчетов и задач}

Questions for self-control

 

1.       What determines the size and density of the population?

2.       How does a population adjust its size?

3.       What is the effect of living in groups?

4.        What is polymorphism of the population?

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$$$003-013-002$3.3.13.2 Задания или тестовые вопросы для контроля к занятию №13

{Задания или тесты (при необходимости указать ключ для выбора варианта)}

Find word combinations in the previous exercise and explain about it.

1. environmental capacity

2. birth, death, moving in and out of individuals (migration).

3. Specific intra-species relations

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$$$003-014-000$3.3.14 Практическое занятие №14

{Тема, план занятия}