A population refers to a group of freely interbreeding individuals of the same species living in a specific area at a given time. For example, when we say that the population of a city is 50,000, it implies that there are 50,000 human beings residing in that city. However, all human populations across the world together constitute the species Homo sapiens.

• A population possesses certain characteristics that are distinct from those of the individual organisms that comprise it. While an individual is born and dies, a population continues over time. The size of a population may change depending on its birth and death rates. Furthermore, individuals are either male or female, young or old, whereas a population is described in terms of its sex ratio, i.e., the proportion of males to females, and its age structure, i.e., the distribution of individuals among different age groups.
• The characteristics of a population are influenced by several factors such as its density, natality (birth rate), mortality (death rate), dispersal, biotic potential, age distribution, dispersion pattern, and growth form. Of these, population density is one of the most important parameters. It is defined as the number of individuals per unit area at a given time. Population density is not constant; it varies with time and place. For instance, one may observe a greater number of plant and animal species in a garden during the monsoon season compared to other times of the year.
• For plants and small or immobile organisms, density is usually determined by selecting random sample areas called quadrats and counting individuals within them. In the case of large, mobile animals like tigers, lions, leopards, and deer, population density is estimated by direct counting or by analyzing their pugmarks (foot imprints) in a defined area.
• Pugmarks are unique to each individual and can provide valuable information if interpreted carefully. They help in determining the presence of different species in the area, identifying individual animals, estimating the population of large cats, and assessing the sex ratio and age (young or adult) of these animals.