Population Characteristics: 5 Important Characteristics of Population (2023)


The population has the following characteristics:

1. Population Size and Density:

Total size is generally expressed as the number of indi­viduals in a population.


Population density is defined as the numbers of individuals per unit area or per unit volume of environment. Larger organisms as trees may be expressed as 100 trees per hectare, whereas smaller ones like phytoplanktons (as algae) as 1 million cells per cubic metre of water.

In terms of weight it may be 50 kilograms of fish per hectare of water surface. Density may be numerical density (number of individuals per unit area or volume) when the size of individuals in the population is relatively uniform, as mammals, birds or insects or biomass density (biomass per unit area or volume) when the size of individuals is variable such as trees.

Since, the patterns of dispersion of organisms in nature are different population density is also differentiated into crude density and ecological density.


a. Crude density:

It is the density (number or biomass) per unit total space.

b. Ecological density or specific or economic density:

It is the density (number or biomass) per unit of habitat space i.e., available area or volume that can actually be colonized by the population.


This distinction becomes important due to the fact that organisms in nature grow generally clumped into groups and rarely as uniformly distributed. For example, in plant species like Cassia tora, Oplismemis burmanni, etc, individuals are found more crowded in shady patches and few in other parts of some area. Thus, density calculated in total area (shady as well as exposed) would be crude density, whereas the density value for only shady area (where the plants actually grow) would be ecological density.

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2. Population dispersion or spatial distribution:

Dispersion is the spatial pattern of in­dividuals in a population relative to one another. In nature, due to various biotic interactions and influence of abiotic factors, the following three basic population distributions can be observed:

(a) Regular dispersion:

Here the individuals are more or less spaced at equal distance from one another. This is rare in nature but in common is cropland. Animals with territorial behaviour tend towards this dispersion.

(b) Random dispersion:

Here the position of one individual is unrelated to the positions of its neighbours. This is also relatively rare in nature.

(c) Clumped dispersion:

Most populations exhibit this dispersion to some extent, with individuals aggregated into patches interspersed with no or few individuals. Such aggregations may result from social aggregations, such as family groups or may be due to certain patches of the environment being more favourable for the population concerned.

3. Age structure:


In most types of populations, individuals are of different age. The pro­portion of individuals in each age group is called age structure of that population. The ratio of the various age groups in a population determines the current reproductive status of the popu­lation, thus anticipating its future. From an ecological view point there are three major ecological ages in any population. These are, pre-reproductive, reproductive and post reproductive. The relative duration of these age groups in proportion to the life span varies greatly with different organisms.

Age pyramid:

The model representing geometrically the proportions of different age groups in the population of any organism is called age pyramid. According to Bodenheimer (1938), there are following three basic types of age pyramids.

(a) A pyramids with a broad base (or triangular structure):


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It indicates a high percentage of young individuals. In rapidly growing young populations birth rate is high and population growth may be exponential as in yeasty house fly, Paramecium, etc. Under such conditions, each successive generation will be more numerous than the preceding one, and thus a pyramid with a broad base would result (Fig. A).

(b) Bell-Shaped Polygon:

It indicates a stationary population having an equal number of young and middle aged individuals. As the growth rate becomes slow and stable, i.e., the pre-
reproductive and reproductive age groups become more or less equal in size, post-reproductive group remaining as the smallest (Fig. B).

(c) An urn-shaped structure:


It indicates a low percentage of young individuals and shows a declining population. Such an un-shaped figure is obtained when the birth rate is drastically reduced the pre-reproductive group dwindles in proportion to the other two age groups of the population. (Fig. C).

4. Natality (birth rate):

Population increase because of natality. It is simply a broader term covering the production of new individuals by birth, hatching, by fission, etc. The natality rate may be expressed as the number of organisms born per female per unit time. In human population, the natality rate is equivalent to the birth-rate. There are distinguished two types of natality.

(a) Maximum natality:

Also called as absolute or potential or physiological natality, it is the theoretical maximum production of new individuals under ideal conditions which means that there are no ecological limiting factors and that reproduction is limited only by physiological factors. It is a constant for a given population. This is also called fecundity rate.

(b) Ecological natality:


Also called realized natality or simply natality, it is the population increase under an actual, existing specific condition. Thus it takes into account all possible existing environmental conditions. This is also designated as fertility rate.

Natality is expressed as

∆Nn/∆ t = Absolute Natality rate (B)

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∆Nn/N ∆ t = Specific natality rate (b) (i.e., natality rate per unit of population).

Where N = initial number of organisms.

n = new individuals in the population.


t = time.

Further, the rate at which females produce offsprings is determined by the following three population characteristics:

(a) Clutch size or the number of young produced on each occasion.

(b) The time between one reproductive event and the next and

(c) The age of first reproduction.

Thus, natality usually increase with the period of maturity and then falls again as the organism gets older.

5. Mortality (death rate):


Mortality means the rate of death of individuals in the population. Like natality, mortality may be of following types:

(a) Minimum mortality:

Also called specific or potential mortality, it represents the theo­retical minimum loss under ideal or non-limiting conditions. It is a constant for a population.

(b) Ecological or realised mortality:

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It is the actual loss of individuals under a given environmental condition. Ecological mortality is not constant for a population and varies with population and environmental conditions, such as predation, disease and other ecological haz­ards.

Vital index and survivorship curves:

A birth-death ratio (100 x births/deaths) is called vital index. For a population, the surviving individuals are more significant for a population than the dead ones. The survival rates are generally expressed by survivorship curves.

Biotic Potential:


Each population has the inherent power to grow. When the environment is unlimited, the specific growth rate (i.e., the population growth rate per individual) becomes constant and maximum for the existing conditions. The value of the growth rate under these favourable conditions is maximal, is characteristics of a particular population age structure, and is a single index of the inherent power of a population to grow.

It may be designated by the symbol r which is the exponent in the differential equation for population growth in an unlimited environment under specific physical conditions. The index r is actually the difference between the instantaneous specific natality rate and the instantaneous specific death rate and may thus be expressed

r = b – d

The Overall population growth rate under unlimited environmental conditions (r) depends on the age composition and the specific growth rates due to reproduction of component age groups. Thus, there may be several values of r for a species depending upon population structure. When a stationary and stable age distribution exists, the specific growth rate is called the intrinsic rate of natural increase or r max. The maximum value of r is often called by the less specific but widely used expression biotic potential or reproductive potential.

Chapman (1928) coined the term biotic potential to designate maximum reproductive power. He defined it as “the inherent property of an organism to reproduce to survive, i.e., to increase in numbers. It is a sort of algebraic sum of the number of young produced at each reproduction, the number of reproduction in a given period of time, the sex ratio and their general ability to survive under given physical conditions.” Thus with the term of biotic potential, one is able to put together natality, mortality and age distribution.

But under natural conditions, this is a rare phenomenon, since environmental conditions do not permit unlimited growth of any population. It size is kept under natural check.

Life tables:


Species differ widely in the number of young produced each year, in the average age to which they live and in their average rate of mortality. When sufficient facts about a species are known, a life table that tabulates the vital statistics of mortality and life expectancy for each group in the population may be formulated.

In each table there are columns for age of individuals; numbers surviving to each age; the number is dying in each age group; the proportion dying from the previous age category; fertility rate; and the number of young born by each age group. The information obtained from these figures provides the net reproductive rate of the population i.e., offspring left by each individual.

Related Articles:

  1. Population Density: Processes of Regulation of Population Density
  2. Population: Notes on Population Growth Rate and How to Control it

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