What parameters are used for tiger census in our country's national parks and sanctuaries? (a) Pug marks only

NCERT Exemplar · Q4

Q. What parameters are used for tiger census in our country's national parks and sanctuaries?

(a) Pug marks only

(b) Pug marks and faecal pellets

(d) Actual head counts

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Concept understanding — Population Level Properties

Population Level Properties: A First Look

Think about a single person. You can describe them: tall, short, speaks Hindi, works as a teacher, has two children. Now think about a whole village or a whole country. You cannot describe every single person one by one — but you can still say something meaningful about the group as a whole. That is what population level properties are: characteristics that belong to the collection of individuals, not to any one individual.

The Everyday Intuition

Imagine you are looking at a crowd at a railway station. You cannot know each person's name, age, or destination. But you can say: "About 60% of the people here are men" or "The average age seems to be around 30 years." These statements are true of the crowd, not of any single person in it. That is a population level property.

Now take a more personal example. Your family has three generations living together. No single member of your family is "the average" of the family — the grandmother is old, the child is young, the parents are middle-aged. Yet the average age of the family is a real, useful number that describes the family as a whole. That number is a population level property.

The Precise Meaning

In the NCERT textbook for Class 12 Biology (Chapter 11: Organisms and Populations), population level properties are defined as attributes that emerge only when individuals come together to form a population. They do not exist at the level of the individual organism.

Important

Population level properties are emergent properties — they arise from the group, not from any single member. You cannot observe them by studying one individual alone.

The textbook gives a clear example: birth rate. An individual is born or not born — that is a binary event. But a population has a birth rate: the number of births per thousand individuals per year. That rate is a property of the population, not of any one person. Similarly, death rate, sex ratio, and age distribution are all population level properties.

Why This Matters

Understanding population level properties is essential because:

They allow comparison. You can compare the birth rate of India with that of Japan, even though no two individuals in either country are identical.
They reveal trends. A population with many young individuals will grow differently from one with many elderly individuals. This tells you about future needs — schools, hospitals, jobs.
They are the basis of policy. Governments do not make policies for "the average person" — they make policies based on population level data like literacy rate, infant mortality rate, and dependency ratio.

Key Population Level Properties (as per NCERT)

The textbook lists four main properties that every population has:

Birth rate (natality): The number of new individuals added per unit time per existing individual. It is always a rate, not a count.
Death rate (mortality): The number of deaths per unit time per existing individual. Again, a rate.
Sex ratio: The number of females per thousand males (or vice versa). This is a ratio, not a count.
Age distribution: The proportion of individuals in different age groups — pre-reproductive, reproductive, and post-reproductive. This is often shown as an age pyramid. …

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Tiger census in India primarily relies on indirect methods like analyzing pug marks and faecal pellets to estimate population size.

Understanding the size and health of a population is fundamental to ecology and conservation, especially for endangered species like the tiger. When we talk about "population level properties," we refer to characteristics that emerge only when individuals are grouped together, such as birth rates, death rates, sex ratios, and, crucially, population density or size. For many species, especially those that are large, elusive, and inhabit dense, vast areas, directly counting every individual is practically impossible. This challenge necessitates the use of indirect methods to estimate their numbers.

In India's national parks and sanctuaries, the tiger census, a critical exercise for conservation, has historically relied on such indirect indicators. One of the oldest and most widely used parameters involves the study of pug marks. These are the footprints left by tigers. Each tiger's pug marks are considered unique in terms of size, shape, and stride pattern, much like human fingerprints. Forest officials meticulously track and measure these pug marks, creating plaster casts or tracings to identify individual tigers and estimate their presence and movement within a given area. By systematically mapping these unique prints, it's possible to avoid double-counting and arrive at an estimated population figure.

Note

While pug mark analysis has been a cornerstone of tiger census for decades, its accuracy can be affected by environmental factors like rain washing away prints, varying soil conditions, and the skill of the trackers.

More recently, and with increasing sophistication, the analysis of faecal pellets (scat) has become an invaluable parameter for tiger census. Faecal samples contain genetic material (DNA) from the individual tiger that deposited them. By collecting these pellets from the forest floor, scientists can extract and analyze the DNA. This allows for the identification of individual tigers, their sex, and even their genetic lineage. This method provides a more robust and scientifically verifiable way to count tigers, as DNA analysis offers a unique genetic signature for each animal, significantly reducing the chances of misidentification or overestimation.

Important

The use of faecal pellets for DNA analysis represents a significant advancement in tiger census methodology, offering higher accuracy and reliability compared to traditional methods alone. …

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Immigration is one of the four basic factors that regulate population density, adding new individuals from outside into a population.

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Natality and immigration are the two processes that add individuals to a population, thereby driving its growth.

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The study of human populations and their attributes is demography.

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Sex ratio is one of the key population attributes, expressing the relative number of males and females.

A population is characterised by attributes such as birth rate (natality), death rate (mortality), age distribution, population density and sex ratio. Sex ratio specifically describes the ratio of the number of males to females (or females to males) within the population at a given time, which affects the population's reproductive potential. Birth …

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CBSE 2025Set ANNUAL1 mark
$Q. Write one factor which increases population density.$
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Population density increases when the rate of addition of new individuals (through births or immigration) exceeds the rate of loss.

A population's density can grow due to natality (the birth rate — the number of new individuals born per unit time) and/or immigration (individuals of the same species entering the habitat from elsewhere). Of the four factors governing population density (natality, mortality, immigration, emigration …

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CBSE 2025Set ANNUAL1 markMCQ
$Q. Natality refers to$
(a) birthrate
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Natality is one of the two processes (along with immigration) that increase a population's size, referring specifically to birth rate.

A population's size changes through four basic processes: natality (births, increasing density), mortality (deaths, decreasing density), immigration (individuals entering from outside, increasing density), and emigration (individuals leaving, decreasing density). Natality specifically refers to births wit …

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A stable (zero-growth) population has a bell-shaped age pyramid.

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Triangular (broad-based) pyramid - an expanding, rapidly growing population with many young individuals. …
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CBSE 2024Set A11 markMCQ
$Q. Population density increases as$
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Population density rises when more individuals are added — through births (natality) and immigration.

Population density changes through four processes: natality (births) and immigration add individuals, while mortality (deaths) and emigration remove them. Density therefore increases only when the additive processes — natality and immigration — increase. Options (a) and (b) in …
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$Q. Correct set of processes which decreases the population density are-$
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Population density increases due to natality and immigration, and decreases due to mortality and emigration.

A population's density changes due to four basic processes: natality (births) and immigration (individuals entering from outside) increase population density, while mortality (deaths) an …

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CBSE 2024Set ANNUAL1 mark
$Q. Define population.$
›Reveal solutionSolution

A population comprises all the interbreeding members of a single species that occupy a shared, defined area at a particular time.

A population is defined, in ecology, as a group of organisms of the same species that occupy a particular geographic area at a given time and are (potentially) capable of interbreeding with one another. Populations have characteristic group-level attributes not applicable to individuals, such as population density, birth and death rates, age distribution, and sex ratio, whi …

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CBSE 2023Set A1 mark
$Q. The number of deaths in the population during the given period. What does it called?$
›Reveal solutionSolution

Mortality is one of the four basic parameters (along with natality, immigration, and emigration) that determine changes in population density.

Population density (N) changes over time due to four processes: natality (births), mortality (deaths), immigration (individuals entering), and emigration (individuals leaving). If N is the population density at time t, then Nt+1 = Nt + [(B + I) − (D + E)]. Here, D — …

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Q.What parameters are used for tiger census in our country's national parks and sanctuaries?

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