An individual and a population has certa | Class 12 Biology Chapter Organisms and Population, Organisms and Population NCERT Solutions

Population is defined as the group of individuals of the same species which lives together at the particular region. Population contains several characteristics or attributes that are functions of whole group not of an single individual:

1. Population density: When the size of population is defined by its fundamental properties is known as Density which is expressed as the number of individuals or biomass per unit area or volume. Population size is determined on the basis of density which is expressed as number of individuals per unit area (on land) or per unit volume (in aquatic system). Population size or density can be calculated by various methods: Complete counts/ Total counts, Incomplete counts, Indirect counts and Mark- recapture method (widely used method). Population size formula (mark- recapture method):

N = Total individuals marked in first sample x size of second sample                                                                                                                            Number of marked individuals recaptured in second sample

2. Natality: This is also known as the birth rate of the individuals in the population. It is defined as the number of individuals produced per female per unit time (at specific interval of time). 

3. Mortality: This is also known as the death rate of the individuals in the population. It is defined as the number of individuals died during a given period. 

4. Age structure and age pyramid: Different age groups are present in the population. Then age structure is defined as the relative numbers of young and old individuals in a population which influences the behaviour of birth and death rate; so this relative proportion of individuals in each different age group is age structure. And, an age pyramid is a graphical representation which shows the number and the proportion of the individuals that belongs to various age classes in a population of an individual at the given time. There are three types of age pyramid: Upright broad based pyramid, Bell shaped pyramid and Urn shaped pyramid.

Diagram:

5. Dispersion: It is defined as the spatial or temporal distribution pattern of the individuals of a population within the boundaries of the population. It is divided into three major patters: Regular (even distribution), Random (unrelated or scattered distribution) and Clumped (aggregated or contagious distribution).

Diagram: