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Chapter 3
Organisation at
Population Level
3.1 POPULATION AND ECOSYSTEM
The study of the living elements of an ecosystem could theoretically mean the
examination of the actions of all organisms, which are extremely numerous.
Therefore, for practical reasons, organisms should be grouped, and individuals of the same species that live in the same space should be examined as
a whole. Thus the concept of population results, which constitutes a basic
ecological unit. A significant part of the phenomena observed at a population
or ecosystem level can be explained through the interactions of populations.
Populations are formed by groups of individuals of the same species that
live in a certain place so that they can breed with one another. The total of
populations living in one place is called biological community. Important
issues concerning population ecology are the prediction of:
• Population change over time
• Population distribution in space
• The abundance of each population within the biological community
• The distribution of the individuals of a population by age and sex
Population is a characteristic case of a system. Even though population is
nothing more than the total of individuals comprising it, it can be described
by parameters and variables, such as population size, natality, mortality,
immigration, age distribution etc. that have no meaning for each one of the
individuals but only for the population itself. These parameters determine
in any given moment the state of the population, its temporal change and
the manner in which external circumstances affect it.
The ecological niche is an important concept of theoretical ecology. It
represents the space of a population’s ecological activity, i.e. the natural
space where it lives, its trophic and other relationships with the rest of the
organisms, its place in relation to the environmental grading of the physicochemical factors, and the modifications it causes to the environmental
DOI: 10.1201/b14609-3
Chapter 3
Organisation at
Population Level
3.1 POPULATION AND ECOSYSTEM
The study of the living elements of an ecosystem could theoretically mean the
examination of the actions of all organisms, which are extremely numerous.
Therefore, for practical reasons, organisms should be grouped, and individuals of the same species that live in the same space should be examined as
a whole. Thus the concept of population results, which constitutes a basic
ecological unit. A significant part of the phenomena observed at a population
or ecosystem level can be explained through the interactions of populations.
Populations are formed by groups of individuals of the same species that
live in a certain place so that they can breed with one another. The total of
populations living in one place is called biological community. Important
issues concerning population ecology are the prediction of:
• Population change over time
• Population distribution in space
• The abundance of each population within the biological community
• The distribution of the individuals of a population by age and sex
Population is a characteristic case of a system. Even though population is
nothing more than the total of individuals comprising it, it can be described
by parameters and variables, such as population size, natality, mortality,
immigration, age distribution etc. that have no meaning for each one of the
individuals but only for the population itself. These parameters determine
in any given moment the state of the population, its temporal change and
the manner in which external circumstances affect it.
The ecological niche is an important concept of theoretical ecology. It
represents the space of a population’s ecological activity, i.e. the natural
space where it lives, its trophic and other relationships with the rest of the
organisms, its place in relation to the environmental grading of the physicochemical factors, and the modifications it causes to the environmental
DOI: 10.1201/b14609-3