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Biological Changes

Aug 24, 2022

Key Concepts

  • Interdependent relationship
  • Changes in ecosystem
  • Changes due to human activities
  • Natural changes
  • Ecological Succession


An ecosystem is a community of living organisms in a particular geographic area. It is composed of biotic (living) and abiotic components (non-living). All living organisms in an ecosystem are dependent on each other either directly or indirectly. On the basis of the living environment, ecosystems are classified into different types (Fig No. 1). Over a period of time, an ecosystem may undergo some changes. These changes may affect the ecosystem in different ways. 

Classification of ecosystem 

Changes in Ecosystem 

An ecosystem may change slowly over a period of time. These changes could be broadly classified into two types: 

  1. Natural changes 
  2. Man-made changes  

Natural Changes: 

Changes that occur naturally in an ecosystem over a period of time are referred to as natural changes. These types of changes happen due to natural events that cannot be controlled by humans.  

Example: Earthquakes, landslides, floods, tsunami, droughts, wildfires, volcano eruptions 

Man-made changes:  

In an ecosystem, certain changes may occur as a result of human activities. Such kinds of changes are known as man-made changes.  


Example: Deforestation, introduction of new species in an ecosystem, industrialization, pollution 

Climate Changes: 

Climate change refers to long-term variation in the temperature and weather of a particular geographic region or Earth as a whole. Biotic and abiotic components of an ecosystem interact with each other. In other words, they are interdependent. Abiotic components such as air, water, sunlight, temperature, soil, etc., may undergo changes over a period. Changes in the abiotic factors of an ecosystem would have an impact on organisms living in the ecosystem.  

Example: Sunlight is the basic source of energy on Earth. Plants make use of sunlight to prepare their food. All living organisms on Earth depend on plants for their food either directly or indirectly. In short, plants are producers in a terrestrial ecosystem. A simple example of a forest food chain is shown in fig -2. Any kind of change in the abiotic components such as sunlight or water source would have an impact on the ecosystem. If there is less sunlight or water, then the number of plants grown will be less. If there are less number of plants, the primary consumer population will decrease. This, in turn, would affect the secondary and tertiary consumer populations. Thus, a change in the abiotic component of an ecosystem affects all the living organisms in it.  

Interdependence in forest ecosystem 
Interdependence in an ecosystem


Drought occurs in an area when there is a high temperature, and there is less rainfall. Shortage of water affects plants and animals that live in that ecosystem. Some plants and animals may die due to a lack of water. Some animals may migrate to other places. 

Floods & Tsunami: 

Excess water also affects the living things in the habitat. Flood is an overflow of water that submerges land. Flood washes away soil, plants, and seeds. Some animals may drown in floods. Grassland ecosystem is most commonly affected by floods. 



Wildfire is an uncontrollable fire in a natural ecosystem. Natural occurrences such as lightning or some human activity may cause wildfires. Wildfires are common in forest ecosystems during dry and hot climates. Wildfire would burn many plants and trees. Animals depend on plants for food and shelter. Without plants, many animals die or migrate to other places.  

Climate change and ecosystem 

Human Activities: 

Several human activities create an imbalance in the ecosystem. The following are some examples of such kinds of human activities. 


Humans chase and kill animals for food or as a sport. Therefore, there may be a significant reduction in the population of a certain organism. This, in turn, would affect their predators.  

Example: Overfishing reduces the food available to sharks  


Trees in forests are cut down for several reasons such as industrialization, wood extraction, expansion of agriculture, etc. Such a kind of removal of producers in an ecosystem affects all the consumers in the ecosystem. Without producers, the consumers either die or migrate to some other habitat. 

Introduction of new species:  

Introduction of new species into an ecosystem could cause harm to native organisms of that ecosystem. These invasive species would compete with the native organisms of an ecosystem for their food, water, and shelter. Sometimes, invasive species may become overpopulated and affect the native organisms of that ecosystem. 

Example: Kudzu vine is an invasive plant that grows very fast and affects the growth of native plants.  

Invasive Species – Kudzu 
Destructive effect of Kudzu on ecosystem 

Other human activities: 

Human activities such as construction of dams, highways, industries near forest areas affect the ecosystem. These kinds of human activities affect the food and water sources of the animals living in the surrounding area. Therefore, there is a reduction in the population of animals in such regions. 

Rise in Sea Levels: 

Human activities such as deforestation, industrialization, burning of fuels etc., increase greenhouse gases which results in global warming. As a result of global warming, glaciers, and ice sheets all over the world melt, thereby increasing sea levels. Sea level rise could lead to loss of coastal ecosystem. Rise in sea levels could cause erosion and degradation of shores. Low-lying coastal areas, few islands may be submerged due to sea level increase. As a result, living organisms in these habitats get affected. 

Due to the rise in sea levels, saltwater may get intruded into groundwater and increase the salinity of inland freshwater sources. This in turn affects agriculture and other living organisms such as plants, trees, insects, animals, and birds associated with that ecosystem. 

Impact of sea level rise on ecosystem 


Sucession is defined as the process of change in the structure of a species in an ecosystem over a period of time. Succession can be classified into two types, 

  1. Primary Succession 
  2. Secondary Succession 
Primary Succession 
Secondary Succession 

Primary Succession: 

When living organisms colonize a newly formed land, it is referred to as primary succession. For example, after a volcanic eruption, new land is formed. Following a volcanic eruption, lava flows into the ocean, and new rocks are formed. Over a period of time, several natural forces break down rocks and allow the growth of pioneer species such as lichens. These pioneer species break down the lava into the soil and pave the way for the growth of intermediate species such as grasses, shrubs, and trees. Over a period of time, the area attains an equilibrium state with a new set of organisms that are different from pioneer species. This new community at the equilibrium state is referred to as the climax community.  

Example: Hawaii islands are well known examples of primary succession following a volcanic eruption. 

Secondary Succession: 

Secondary succession occurs when an existing ecosystem is destroyed or disturbed. For example, a large forest area may be destroyed by wildfire or heavy floods. Even after the natural calamity, the soil is retained in the ecosystem. After a few years, pioneer and intermediary species start colonizing the area. Over a period of time, the area reaches an equilibrium state with the climax community.  

Example: Hunza valley landslide resulted in the destruction of forests and human population. The valley was replaced by the Attabad lake (Gojal region – Pakistan), and then it gave rise to freshwater habitats. 

The first species that colonize a new land is called pioneer species.


  • An ecosystem is composed of biotic and abiotic factors.
  • All living organisms in an ecosystem are interdependent.
  • Any change in the biotic factors of an ecosystem affects the producers and all consumers of the ecosystem.
  • Changes taking place in an ecosystem can be natural or man-made.
  • Natural changes – earthquake ,landslide, floods & tsunami, volcanic eruption, wildfire
  • Man-made changes – pollutions, deforestation, industrialization, hunting, introduction of invasive species.
  • Rise in sea levels have a destructive effect on the ecosystem.
  • Succession – primary and secondary
  • Example of primary succession – Hawaii islands
  • Example of secondary succession – Attabad lake


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