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Population Attributes can be defined as the summaries or features that describe the characteristics of the population such as birth rate, death rate, population density, etc. The main basis for the survival of living things in the world is the interaction with each other and with the non-living things in the ecosystem. Ecology is the study of the interactions of living things with non-living things and interactions in the environment. No ecosystem or habitat contains a single species. In an ecosystem, they live in groups and share or compete for available resources. A population can be defined as the collection of organisms from the same species living in close proximity. The terms that describe the characteristics of a population are called demographic characteristics.
Key Terms: Population, Organisms, Population Density, Ecology, Natality, Mortality, Sex Ratio, Age Pyramid, Birth Rate, Death Rate
Organisms and Populations
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A population can be defined as a group of the same species that can reproduce and be found in the same area. It is a living species community of animals, plants, people or its members, interbreeding takes place. Both types of reproduction, sexual and asexual, contribute to the population.
Examples of Population: The population of a state or country is the people living in a state or country. Worms in an abandoned place or rats in a place are all populations. Populations can be anything from mice in an abandoned house to trees in a forest to bacteria in culture.
Organisms and Population
The environment is not the same for all species and many times it is very harsh and against the conditions that facilitate the survival of organisms. In that case, the population of the disease changes in such a severe condition. Natural selection, along with evolution, played a role in the creation of populations.
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Population Attributes
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There is a difference between a segment of a population and an individual. An individual's body does not have the same characteristics as a population. Several attributes of the population are as follows:
- Natality Rate/Birth Rate
- Mortality Rate/Death Rate
- Population Density
- Sex Ratio
- Age Pyramid
Read More: Characteristics Of Organisms
These population attributes are explained in detail below:
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Natality or Birth Rate
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Mortality or Death Rate
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Population Density
Population density refers to the size of the population in an area at a given time. It can also be measured to see the habitat conditions. Because more and more species are surviving indicates that this place is healthier and more healthy. Population density is given by the formula:
Population density (PD) = (Number of individuals in an area (N)) / (Number of the unit area in an area (S)) = PD = N/S
Read More: Population Growth
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Sex Ratio
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Age Pyramid or Age Distribution
Age distribution in the population is also an important component. A group of individuals consists of a population of different ages. The different age groups of the population consist of individuals in the pre-natal, natal and post-natal stages respectively. When the percentage of people in a particular age group is plotted on a graph, it is called an age pyramid. An age pyramid is a measure of whether a population is growing, stable, or declining.
Population Pyramid
Read More: Human Population
Things to Remember
- A population can be defined as a collection of all organisms of the same species present in a geographical area and able to live and reproduce together.
- Both sexual and asexual reproduction contribute to population growth.
- Evolution through natural selection also plays a role in population structure.
- Population attributes are Birth and death rate, Sex ratio, Age distribution, and Population density
- The birth rate is called the natality rate and the death rate is called the mortality rate.
- Gender or sex ratio calculates the ratio of males to females in a population.
- The age pyramid shows whether the population is increasing, stable or decreasing.
- Age distribution in the population is also an important component. A group of individuals consists of a population of different ages.
- Population density refers to the size of the population per unit area.
Previous Year Questions
- Which Of The Following Is A Partial Root Parasite
- Which Of The Following Is Not An Example Of Prey P
- Which Of The Following Options Exemplifies A Behav
- Which Of The Following Options Is Correct
- Which Of The Following Statements Is Incorrect
- Which Type Of Interaction Is Being Shown In The Gi
- Warm Blooded Animals Have Larger Size In Colder Ar
- Very Small Animals Are Rarely Found In Polar Regio
- Two Insect Species Were Used In A Laboratory Exper
- Term Ecology Was Given By
- Read The Following Statements And Select The Corre
- Progestasert And Lng 20 Are
- Lichens Are The Associations Of
- India Population Crossed 1 Billion In
- Increased Imr And Decreased Mmr In A Population Wi
- In A Population Per Capita Birth Rate Is 0 15 And
- In 2005 For Each Of The 14 Million People Present
- If N Population Density At Time T Then Population
- Helophytes Are
- Grasslands Of New Zealand Are Called
Sample Questions
Ques. In a pond, there are 200 frogs. 40 more frogs are born in a year. Calculate the birth rate of the frog population. (2 Marks)
Ans. The birth rate of the frog population is - =40/200 = 0.2 frogs per year or 200 frogs per thousand frogs per annum.
Ques. Give any two significant roles predation plays in nature. (2 Marks)
Ans. Two significant roles played by predators in nature are predators keeping the prey population under control throughout. They also help in maintaining species diversity in a community by reducing the intensity of intraspecific competition.
Ques. Prepare an age pyramid which reflects the expanding growth status of the human population. (3 Marks)
Ans. The age pyramid can geometrically be represented by the proportions of different age groups in the population. The triangular shape of the age pyramid represents the expanding growth status of the human population.
Ques. Explain with an example Verhulst-Pearl Logistic Growth of a population. (3 Marks)
Ans. The population that is growing in a habitat with limited resources initially shows a lag phase, then followed by an exponential phase and finally a declining or stationary lag phase, when the growth or density of the population reaches the carrying capacity, it is called Verhulst-Pearl logistic growth. It can be explained by the following equation where N is Population density at time t. r refers to the Intrinsic rate of natural increase K is the carrying capacity
Ques. Explain any two defence mechanisms that have been involved in prey to avoid the overpopulation of their predator. (3 Marks)
Ans. The two defence mechanisms evolved in prey are:
- To avoid easy detection by predators, some species of insects and frogs are cryptically coloured (camouflaged).
- Some flowering plants have thorns or spines as defence mechanisms, e.g. Acacia, and cactus.
Ques. (i) What is the letter ‘r’ in the population equation given below dN/ dt = rN
(ii) How do the increase and the decrease in the value of ‘r’ affect the population size in an area? (2 Marks)
Ans. (i) ‘r’ refers to an intrinsic factor assessing the impacts of both biotic and abiotic factors on population growth.
(ii) When ‘r’ increases, population size also increases, and vice versa
Ques. Identify the following curves A and B shown in the graph given. List down the conditions responsible for growth patterns A and B. (3 Marks)
Ans. A is the exponential growth curve. When the natural resources are not limited, this form of the curve appears. B is the logistic growth curve, When the natural resources are limited, this form of growth curve appears, where K is the carrying capacity.
Ques. (i) Write the significance of measuring the size of a population in a habitat or an ecosystem.
(ii) Explain with the help of an illustration, how the percentage cover is a more meaningful measure of population size than just numbers? (3 Marks)
Ans. (i) Measurement of any population in a habitat determines the relative abundance of a particular species. Its effect on the available resources of that particular habitat is also indicated.
(ii) The percentage cover of a species is a more meaningful measure of population size than just numbers as the relative abundance of a species is not only determined by several individuals but by both the relative abundance in biological biomass and species number. E.g. in a unit area, the number of some grass species or relative abundance in number is high but not the relative total biomass, if the same unit area has one or two Ficus bengalensis (Banyan) trees, it is deficient in relative abundance but high in the relative abundance of total biomass
Ques. Study the following 3 different age pyramids, for the human population and answer the questions that follow
(i)Write the particular names given to each of these age pyramids.
(ii) Mention the pyramid which is ideal for the human population and why? (3 Marks)
Ans. (i) A – Expanding population B – Stable population C -Declining population
(ii) Stable human population is preferred. It is beneficial for the survival and better living of the entire human population. It helps plan welfare activities also.
Ques. Construct and explain a logistic curve for a population of density (N) at the time (it) whose intrinsic rate of natural increase in population (r) and carrying capacity (K) of population. (5 Marks)
Ans. (i) In the beginning, the population shows a lag phase and then shows a phase of acceleration or exponential growth followed by a phase of deceleration (decline)
(ii) Population can grow exponentially for only a certain period and then gains a steady state, as the natural resource availability becomes limited at some point in time.
(iii) Every natural environment has natural resources to support a particular maximum number of individuals, called its carrying capacity. Beyond that, there is no increase in the size/density of a population of a species.
(iv) A species population showing logistic growth shows a sigmoid curve when the number of individuals of the species is plotted as a function of time (v) Equation can be described as
\(\frac{dN}{dt} = rN (\frac{K-N}{K})\)
Where
- N = Population density at time t,
- r = Intrinsic rate of natural increase,
- K = Carrying capacity
(vi) The above model is more realistic in nature because no population of a species can sustain exponential growth indefinitely.
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