[Biology Class Notes] on Organisms and Population Attributes Pdf for Exam

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.