Introductions of Organisms and Population
The basic key to the survival of living beings on Earth is the interaction between each other and with nonliving components of the ecosystem. Ecology is the study of how organisms communicate with one another within their environment. These interactions of living beings with nonliving components and interspecies interactions in a given area within an environment are studied under Ecology. These interactions are the basis of continuity of life on Earth. No ecosystem or habitat in the environment is composed of just one type of species. Each of the species grows as a population in the ecosystem. Within the ecosystem, they live as a group and share or compete for the available resources. The summaries describing the characteristics of the population are known as Population Attributes.
Organisms and Population
The population can be defined as the group of the same species who are capable of interbreeding, present in the same geographical region. It’s a community of animals, plants, humans, or any species of living organisms, among whose members, interbreeding occurs. Both types of reproduction, sexual and asexual, may contribute to the population.
Examples of the population are: Number of people living in a particular state or nation is the population of that particular state or nation. The total number of live mites in an abandoned place or rats in a place is population. A population can be anything from rats in an abandoned house to teak wood trees in a forest tract to bacteria in a culture plate.
The environment is not always habitable for all species, and a lot of times, it is very harsh and opposes the factors that provide for easy survival of organisms. In such cases, the population of organisms adapts to living in such harsh conditions. Natural selection, as well as evolution, played a role in forming the populations.
Population Attributes
There is a basic line of difference between being a part of a population and an individual. An individual organism does not have the attributes that the population has. Different attributes of the population are as follows:
Natality Rate
Mortality Rate
Population density
Sex ratio
Age pyramid
Natality or Birth Rate
Natality or birth rate is the rate at which new individuals are born in a population per unit of time. It can be statistically measured only for a population and not for an individual. An individual can only have birth but not a birth rate. The birth rate is calculated by dividing the total number of offspring produced or births by the total population in a given time. Example - If a rose garden has 20 rose plants in a year and it has produced 8 more offspring plants in the next year to give the total population of 28, then the birth rate is 8/20= 0.4 individuals per rose plant per year.
Mortality Rate
The mortality rate or death rate is the number of individuals of a population loss due to death per unit of time. The death rate is also influenced by environmental factors that lead to a rise in deaths by predation, competition for resources, etc. Example - If 4 individuals in a rat population of 40 died in a specified time interval, then the death rate will be given as 4/40, that is, 0.1 individuals per rat per week.
Population Density
Population density refers to the size of the population in a given area in a given time. It is also measured to look at the conditions of the habitat. This is because higher population density indicates that the habitat is healthy and provides more favorable living conditions.
Population density is given by the formula:
Population Density (PD) = (Number of Individuals in a Region (N))/(Number of Unit Area in the Region (S)) = PD = N/S
Sex Ratio
The sex ratio is the number of males to females in a population. A population has, for example, 60 % of males to 40 % of females among the total individuals of the population.
Age Pyramid or Age Distribution
The age distribution is also an important feature of the population. A population consists of individuals of different age groups. The different age groups of the population include individuals in pre-reproductive, reproductive, and post-reproductive stages, respectively. When the percentage of individuals of a given age is plotted on a graph, it is called the age pyramid. Age pyramid is a measure to check if the population is growing, stable, or declining.
Thus, different features of the population or the population attributes give the data about the population and ecology of the population.
FAQs on Organisms and Population Attributes
1. What are the main attributes of a population as per the Class 12 syllabus?
A population, which is a group of individuals of the same species in a specific area, has several unique characteristics that an individual organism does not. The key population attributes are:
- Natality (Birth Rate): The rate at which new individuals are added to the population through reproduction.
- Mortality (Death Rate): The rate at which individuals are lost from the population due to death.
- Sex Ratio: The proportion of males to females in the population.
- Age Distribution: The proportion of individuals in different age groups (pre-reproductive, reproductive, and post-reproductive), often visualised as an age pyramid.
- Population Density: The number of individuals per unit area or volume.
2. How is population density calculated and what does it indicate?
Population density is a measure of how crowded a population is within its habitat. It is calculated by dividing the total number of individuals (N) by the total unit of space (S). The formula is PD = N/S. A higher population density can indicate a habitat with favourable conditions and abundant resources, while a very low density might suggest a harsh environment or a population in decline.
3. What is an age pyramid and what do its different shapes signify?
An age pyramid is a graphical representation of the age distribution of a population, showing the percentage of individuals in pre-reproductive, reproductive, and post-reproductive age groups. The shape of the pyramid indicates the population's growth status:
- Expanding (Triangular): A broad base indicates a high percentage of young individuals and a high birth rate, signifying future population growth.
- Stable (Bell-shaped): The number of individuals in pre-reproductive and reproductive groups is roughly equal, indicating a stable population.
- Declining (Urn-shaped): A narrow base indicates a lower number of young individuals than older ones, suggesting a future decline in the population.
4. What is the difference between birth/death in an individual and natality/mortality in a population?
This is a key distinction in ecology. An individual organism experiences birth and death as singular life events. In contrast, a population exhibits a natality rate (births per individual per unit time) and a mortality rate (deaths per individual per unit time). These are statistical rates that describe the collective dynamics of the group and cannot be applied to a single individual. For example, an individual is born only once, but a population has a birth rate, such as 0.4 offspring per individual per year.
5. Provide a real-world example for each key population attribute.
Here are some examples illustrating population attributes:
- Natality: If 20 new lotus plants grow in a pond that initially had 200, the natality rate is 0.1 offspring per lotus per year.
- Mortality: If 40 out of 500 tigers in a reserve die in a year, the mortality rate is 0.08 individuals per tiger per year.
- Sex Ratio: In a hive of 1,000 bees, if there are 100 males (drones) and 900 females (workers/queen), the sex ratio is 1:9.
- Age Pyramid: A country like Nigeria has an expanding, triangular age pyramid, indicating a rapidly growing population.
- Population Density: The density of teak trees in a forest tract might be 150 trees per hectare.
6. How do attributes like age distribution and sex ratio help ecologists predict a population's future?
Population attributes provide crucial data for ecological forecasting. A high natality rate combined with a low mortality rate suggests population growth. The sex ratio influences reproductive potential; a skewed ratio can limit growth. Most importantly, the age pyramid (age distribution) acts as a predictive tool. A pyramid with a broad base (many young individuals) predicts a future population boom, while a pyramid with a narrow base predicts a future decline. These insights are vital for wildlife management and conservation efforts.
7. What is the primary difference between exponential and logistic population growth?
The primary difference lies in the concept of environmental limits.
- Exponential Growth: This occurs when resources like food and space are assumed to be unlimited. The population grows at its maximum potential, resulting in a J-shaped curve. This is rarely sustained in nature.
- Logistic Growth: This is a more realistic model where resources are limited. The population's growth slows as it approaches the habitat's carrying capacity (K)—the maximum size the environment can sustain. This results in an S-shaped (sigmoid) growth curve.
8. Why is carrying capacity a crucial concept in understanding population dynamics?
Carrying capacity (K) is crucial because it represents the environmental resistance that prevents indefinite exponential growth. In any real-world ecosystem, resources are finite. As a population grows, it consumes more resources, leading to increased competition. Carrying capacity defines the point at which the birth rate equals the death rate, and population growth stabilises. Understanding K is essential for managing natural resources, predicting population crashes, and implementing effective conservation strategies.
