Population Attributes – Overview Notes- Class 12

Population Attributes are the characteristics used to define a population. Population attributes play an essential role in understanding the dynamics and characteristics of a population. These attributes are measured for a population, not for an organism. There are five important attributes of a population, namely, Natality Rate, Mortality Rate, Sex ratio, Age distribution, and Population Density.

Organism and Population

Organism: An organism refers to a living individual of any species. It is a basic unit of life that exhibits various characteristics such as growth, reproduction, and response to stimuli. Organisms can be unicellular or multicellular.

Population: A Population refers to a group of individuals of the same species living in common geography, sharing and competing for resources, and potentially interbreeding. Populations interact with their environment, and their size, distribution, and attributes can be studied to understand ecological dynamics and patterns.

Population Attributes

Population Attributes are the parameters that help us to study the population. These attributes are measured for a population, not for an organism. There are five essential attributes of a population, namely, Natality Rate, Mortality Rate, Sex ratio, Age distribution, and Population Density

Natality Rate

The Natality Rate can be defined as the number of births per capita per unit of time. Factors such as access to healthcare, socio-economic conditions, and cultural norms influence the birth rate.

Example: There were 20 lotuses in a pond initially, after a year the number of lotuses increased to 24. The natality rate is change/initial i.e. 4/20 equals 0.2 individuals per lotus per year. The natality rate is also known as the ‘Birth Rate’. It is defined as a population, not as an individual. Since, individuals show birth, not birth rate.

Mortality Rate

The Mortality Rate can be defined as the number of deaths per capita per unit of time. Factors like healthcare facilities, disease prevalence, and overall socio-economic conditions contribute to the death rate.

Example: In a lab, there are 40 fruit flies initially, after a week the number of fruit flies reduces to 36. The mortality rate is change/initial i.e. 4/40 equals 0.1 individuals per fruit fly per week. The mortality rate is also known as the ‘Death Rate’. It is also defined as a population, not as an individual. Since, individuals show death, not death rate.

Sex Ratio

Individuals can be either male or female but the population has a sex ratio. ​The sex ratio is defined as the number of males to females in a population. It provides insights into gender composition and can indicate social and cultural factors that influence the population. Example- In India, the sex ratio is 934 which means 934 females per 1000 males.

Age Distribution

Age distribution refers to the proportion of individuals in different age groups within a population. It helps in understanding the dependency ratio, workforce distribution, and potential social and economic implications. We can divide a population into certain categories by taking age as a criterion. A population consists of different age groups like

• Pre-reproductive age group contains individuals 0 to 14 years of age.
• The reproductive age group contains individuals having age between 14 to 50 years who are reproductively active.
• Post-reproductive age group- contains individuals aged more than 50 years.

This age distribution is represented by an age pyramid. There are three types of age pyramids indicating whether a population is expanding, stable, or declining.

• Expanding population pyramid:  This pyramid belongs to poor, less developed countries where health facilities are not good and family planning programs are not implemented. In an expanding population, the number of individuals in pre-reproductive age is more than that in reproductive age. And the number of individuals of reproductive age is more than that of post-reproductive age. The shape of the Expandi​ng population pyramid does not change with time whereas the size of the pyramid increases with time.
• Stabilizing population pyramid: This pyramid belongs to developing countries. In a stabilizing population, the number of individuals in pre-reproductive age is equal to that in reproductive age. And the number of individuals of reproductive age is more than that of post-reproductive age. The pyramid is urn-shaped. The shape and size of the Stabilising population pyramid do not change with time.
• Declining population pyramid: This pyramid belongs to highly developed countries. In a declining population, the number of individuals in pre-reproductive age and post-reproductive age is less than that in reproductive age. The pyramid is spindle-shaped.

Population Density

Population density can be defined as the number of individuals per unit area in a given time. Population density helps in understanding the intensity of human presence and resource utilization within a given area It is represented by ‘N’. It can be calculated by counting numbers per unit area. In most cases, it is the best method to calculate population density. But this method is not useful in every case.

For example

• To calculate the population density of fish in the ocean, the number of fish in a single catch is counted.
• To calculate the population density of bacteria, the number of colonies is counted.
• To calculate the population density of tigers, the number of pug marks and fecal pellets are counted
• To calculate the population density of large trees like the Banyan tree, biomass or area covered is measured.

FAQs on Population Attributes

Q: What is the definition of population in ecology?

Answer:

In ecology, population refers to a group of individuals of the same species that live in a common geographical area, share and compete for resources, and have the potential to interbreed.

Q: What is the difference between an organism and a population?

Answer:

An organism refers to a living individual of any species, exhibiting characteristics such as growth and reproduction. In contrast, a population refers to a group of individuals of the same species living in a specific area, sharing resources and potentially interbreeding

Q: What are the five important attributes of a population?

Answer:

The five important attributes of a population are natality rate, mortality rate, sex ratio, age distribution, and population density.

Q: How is population density calculated?

Answer:

Population density is calculated by counting the number of individuals per unit area in a given time. This can be achieved through various methods, such as counting the number of individuals, colonies, pug marks, and faecal pellets, or measuring biomass or area covered, depending on the organism being studied.

Q: How is the natality rate defined, and what factors can influence it?

Answer:

The natality rate, also known as birth rate, is defined as the number of births per capita per unit of time. Factors such as access to healthcare facilities, socio-economic conditions, and cultural norms can influence the birth rate.

Q: Why is population-level ecology significant?

Answer:

Population-level ecology is important because no habitat consists of just a single individual. Instead, a group of individuals inhabits an area. Natural selection, a powerful force for evolution, acts on populations rather than on individual organisms.