Each population has a definite structure. A population has certain attributes that an individual organism does not.
A population has group attributes like birth rates, death rates, sex ratio, age distribution, population size etc.
Birth rate and death rate: It refers to per capital births and per capita deaths respectively. Hence these rates are expressed in change in numbers with respect to members of the population.
Sex ratio is an important attribute characteristic of a population. An individual has a sex.But population has a sex ratio.
Age distribution: A population at any given time is composed of individuals of different stages. The reproductive status of a population is determined by various age groups. The individuals of a population can be divided into three ecological age groups-Pre reproductive, reproductive and post reproductive.
Population size may be the outcome of competition with another species, the impact of the predator or the effect of a pesticide application. The population size tells us about its status in the habitat. Population size is more technically called population density. It is designated as N.Population density can be defined as the total number of individuals present per unit area or volume at a given time.
Population growth: The growth of a population can be measured as increase in its size over a period of time. The size of population of any species is not a static parameter. It changes every time. The change in the population size gives us some idea about what is happening to the population, whether it is increasing or decreasing. Population growths are of two types-Exponential growth and logistic growth