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Population Dynamics – Definition and Examples

Grade 10
Aug 23, 2022

Population Dynamics 


What is meant by interdependent relationship in an ecosystem

Living beings in an ecosystem rely on one another for existence and growth. This is referred to as interdependence. All living things, from small microorganisms to massive predators, rely on one another for energy and other fundamental needs. 

The link between a predator and its prey is critical in an ecosystem. In an ecosystem, the number of predators balances the population of prey. 

Relationships in Ecosystem 

Population dynamics 

Population dynamics is the field of life sciences that investigates population size and age as driving systems, because the biological and environmental mechanisms that drive them (for example birth rates and death rates, and by immigration and emigration). 

Population Dynamics 


Population density or size 

The concentration of individuals within a species in a certain geographic location is referred to as population density. Data on population density may be used to quantify demographic information as well as to evaluate relationships with ecosystems, human health, and infrastructure. 

The number of people in a population is referred to as its population size. The average number of people in a population per unit of area or volume is referred to as population density.  

Population Density 

To calculate the population density the following formula is being used: 


Formula of Population Density 

Population dispersion or spatial distribution 

A population’s dispersion pattern (distribution pattern) reflects the arrangement of individuals within a habitat at a certain moment in time, and broad patterns are used to characterize them. The three patterns of dispersion are clumped, random, and uniform.  

Different Kinds of Population Distribution 

  • Clumped distribution: – Individuals clustered into patches have a clumped distribution. This can happen if resources are not dispersed evenly.  
  • Random distribution: – Randomly distributed populations are not organized in any specific way. Some people may be quite near to one another, while others may be very far apart. 
  • Uniform distribution: – Individuals who are evenly distributed in the environment have a uniform distribution. Uniform distributions can occur because of interference competition, which occurs when individuals take proactive attempts to avoid competing for resources. 

Age structure 

The distribution of persons of various ages is the age structure of a population. The proportions of people of various ages in a population, shown as a bar graph with younger people at the bottom and men and women on either side. The impact of age structure on population dynamics is most visible in population productivity, which is affected by individual fertility, fecundity, and the likelihood of rearing a juvenile to weaning or recruitment. 

Age Pyramids 

Demography commonly divides the population into three basic age groups: 

  1. Adolescents and children (under 15 years old) 
  1. The population of working age (15-64 years)  
  1. The elderly people (65 years and older) 
Comparison of Different Age Groups 

The term “age pyramid” refers to a model that represents geometrically the proportions of different age groups in a population of any organism. 

  1. A pyramid with a broad base (or triangular structure): It signifies a large proportion of youthful people. Birth rates are high in quickly increasing young populations, and population expansion can be exponential, as shown in yeasty house flies, Paramecium, and other organisms. 
  1. Bell-Shaped Polygon: It indicates a steady population with an equal number of youthful and middle-aged people. As the growth rate slows and becomes more stable, the pre-reproductive and reproductive age groups become more or less equal in size, with the post-reproductive age group staying the smallest. 
  1. An urn-shaped structure: It displays a low percentage of young people and a shrinking population. When the birth rate is dramatically lowered, the pre-reproductive group shrinks in proportion to the other two age groups of the population, resulting in an un-shaped figure. 

Natality [birth rate] 

Natality is defined as the rate of births per unit area of people per unit time. It is simply known as the birth rate. The birthrate is the ratio of total live births to total population in a given place over a certain time period, represented as childbirths per 1000 people (or population) every year. Natality is computed by dividing the number of births during the period of the risk of birth by the total population. 

Formula for Finding Natality 

Natality criteria are as follows:  

  • When the birth rate exceeds 30, it is termed high. 
  • When the birth rate is between 20 and 30, it is deemed moderate. 
  • A birth rate of fewer than 20 is considered low. 

There are two distinct forms of natality: 

  1. Maximum natality: It is the theoretical maximum generation of new people under perfect conditions, which means that there are no ecological limiting constraints and that reproduction is restricted solely by physiological reasons. It is also known as absolute, potential, or physiological natality. It is a constant for a particular population. This is also known as the fecundity rate. 
  2. Ecological natality: It is the population growth caused by an actual, existent particular circumstance. It is also known as actual natality or just natality. As a result, it takes into consideration all current environmental factors. This is also known as the fertility rate. 

Mortality [death rate] 

The mortality rate, often known as the death rate, is a measure of the number of deaths (in general or due to a specific cause) in a given population, scaled to the population’s size / unit of time.  

The mortality rate is often represented in terms of deaths per 1,000 people per year. 

Formula for Finding Mortality 

The rate of death in a population is referred to as mortality. Mortality can be classified into the following categories: 

  1. Minimum mortality: It is the theoretical minimum loss under ideal or non-limiting conditions. It is also known as specific or potential mortality. It is a population’s constant. 
  1. Ecological or realized mortality: It is the real loss of people because of a certain environmental situation. Ecological mortality for a population is not constant and changes with population and environmental factors such as predation, illness, and other ecological hazards. 

Factors that are dependent or independent of population density govern population size. 

  • Population size may be influenced by both biological and non-biological forces. Interspecific interactions such as predation, competition, parasitism, and mutualism, as well as illness, are examples of biological variables. Environmental variables like temperature, precipitation, disturbance, pollution, salinity, and pH are examples of non-biological influences. Only the biological elements have the ability to modify population size. 
  • The biological mechanisms that govern population increase, such as competition, predation, and so on, influence dense vs sparse populations differently. For example, infectious disease cannot spread fast in a sparsely packed community, but disease can spread swiftly through interaction between individuals in a dense group, such as persons living in a college residence hall. 
Population Dynamics


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