What is Ecology? 

Ecology contains two words: Eikos means dwelling, and logy means to study, so the combined meaning is studying habitat or living. 

• It plays an important role in human welfare as the living things (biology) interact with the environment (ecology). 
• It is an interdisciplinary stage in the field of biology. 

What is an Ecosystem? 

• An ecosystem is an area that consists of all different organisms/species that live together and interact with each other constituting a population using the available resources like sunlight, nutrient availability, soil, water, air, and several other ecological factors. 
• An ecosystem comprises a biological community (it is an assemblage of wild and domestic species, bacteria, fungi that interact with each other by living together), integrated with its physical environment through the exchange of energy and nutrient recycling. 

Types of Ecosystems 

1. Terrestrial: It includes forest, grassland, desert, and estuaries. 
2. Marine: It includes the ocean. 
3. Freshwater: It includes abiotic systems like rivers and lentic systems like ponds and lakes. 

Functional aspects of the Ecosystem 

• Productivity of an ecosystem. 
• The energy flow of an ecosystem. 
• Stabilization and development. 
• Nutrient cycling. 

Functional steps in the Ecosystem 

• Producers trap energy and synthesize organic compounds. 
• Consumers consume these organic compounds. 
• Decomposers decompose dead bodies or waste. 

Components of the Ecosystem 

The ecosystem has two major components: 

1. Abiotic (non-living) components 
2. Biotic (living) components 

Abiotic (non-living) components 

• The inorganic substances such as chlorophyll and organic materials such as proteins, carbohydrates, lipids are parts of the abiotic ecosystem. The abiotic component also includes the climate of the given region. 
• The chief substances are light, heat, but the basic component is the water itself. 

The abiotic component of the ecosystem consists of the following: 

1. Sunlight: It is needed for the preparation of food in producers, a process called photosynthesis. 
2. Air: The air has the following things to do: 

• It provides a medium of flight to the birds. 
• It serves as a medium of dispersal of seeds and pollen. 
• It allows flora and fauna to respire. Plants use carbon dioxide for photosynthesis, and animals use oxygen for breathing.  

3. Water: It is used for drinking, maintaining the various nutrient cycles, and absorption by the roots for soil-water interaction. 
4. Temperature: The temperature plays an important role in influencing a given region's flora and fauna interaction. 
5. Soil: It is the basic component for almost every ecosystem. It provides a place for dwelling for many terrestrial animals like snakes and earthworms. It also provides nutrients and minerals that are necessary for the survival and interaction of the population. The nutrients are passed through the trophic levels in the food web. The food web serves as an alternate food choice to provide more stability.  

What is meant by a Community? 

A community is defined as a group of species that live in a common space and interact with each other by fulfilling each other's requirements. 

Characteristics of the Community 

1. Species composition: Different species constitute a population that varies greatly. The composition of species depends upon: 

• The size of the area. 
• Diversity of habitats needed for sustaining the given population in that area. 
• The type of soil. 
• The altitude of the particular area. 

2. Growth form and structure: A community has several growth forms. In each growth form, there may be different kinds of organisms. For example, a growth form of tree population may include broad-leaved, narrow-shaped, evergreen trees. Growth factors play an important role in structuring the community in horizontal layering called zonation and vertical layering called stratification. 

3. Dominance: Only a few species' populations will determine the nature of the community known as dominants. Other species are not equally important. 
4. Succession: The development of a community is a result of directional change.  
5. Self-sufficiency: Each community is a group of autotrophic plants and heterotrophic animals, and their balanced assembly maintains the ecological balance. 

Biotic Community 

The assembly of different species that live and interact with each other in an ecological landscape is known as the biotic community. Examples of biotic communities are pond communities and meadow communities. 

The biotic community is formed of three different types of communities: 

1. Producer community: It consists of the mixed population/species that includes climbers and trees of that particular area. 
2. Consumer community: It consists of the mixed population/species that includes all the animal species of that particular area. 
3. Microbial community: It consists of the mixed population/species of the microbes, including bacteria and fungi of that particular area. 

Flora and Fauna Community 

The flora community acts as producers in the community. It serves as a habitat for many species and provides oxygen for respiration. The fauna community is the consumer in the community. It helps in the pollination and dispersal of seeds and also provides carbon dioxide for photosynthesis. The microbial community serves as the decomposers in the community. The different species of flora and fauna living in a forest form the forest community. 

Biotic (living) components 

It contains living organisms that are distinguished based on their nutritional demands.  

The biotic component can be further divided into: 

1. Autotrophic: These organisms fix energy by using very simple inorganic substances. They include mainly green plants and photosynthetic bacteria. The autotrophs are also known as producers. The producers fix radiant energy and manufacture complex organic substances such as carbohydrates and proteins. 

• Macrophytes: They are rooted, larger aquatic plants, including partly or completely submerged floating hydrophytes. The common species are Trapa, Chara, and Utricularia. Other free-floating species are Lemna and Sphirodella. 
• Phytoplanktons: They are minute, lower organisms that can be present as free-floating or in the suspended forms. Common species are Ulothrix, Oedogonium, and Spirogyra. 

2. Heterotrophic: The heterotrophs utilize the products formed by the producers. Some of them occur to perform the decomposition of complex materials. The heterotrophic organisms are also known as consumers. They consume food prepared by the producers. The heterotrophic organisms are distinguished as follows: 

• Primary (herbivore): These organisms directly feed on living plants and plant remains. The herbivores are further differentiated as: 

-Benthos: These organisms feed on the population present at the bottom of the pond, known as detritivores. 

-Zooplanktons: They consume phytoplanktons as their food. 

• Secondary: They are known as carnivores. These heterotrophs feed on the organism that comes under the primary consumer. 
• Tertiary: These organisms (consumers) feed on other consumers. The omnivores that feed on both plants and animals are tertiary consumers.  
• Decomposer: It is also called a micro consumer responsible for breaking down complex organic matter into simpler ones. The decomposers absorb only a small amount of the organic matter present. They recycle the dead organic matter to make rich humus. The organisms like fungi, bacteria, and actinomycetes are considered decomposers. 

The Sequence of Food levels in the Biotic Component  

1. Trophic level 1 (green plants): It consists of trees, grasses. It is the initial stage from where the nourishment chain starts for all life in a particular ecosystem. 
2. Trophic level 2 (plant-eating animals or herbivores): It consists of organisms like grasshoppers, parrots, and deer. 
3. Trophic level 3 (flesh-eating animals or carnivores): It consists of organisms/species that consume herbivores. Organisms like tigers, lizards, snakes occupy this trophic level. 
4. Trophic level 4 (second rank flesh-eaters): The third rank of consumers represents this trophic level. 

A community is a mixture of several populations interacting with each other, and these interactions are reflected in the food chain. 

Types of Interactions 

1. Dependence of animals on the plants 

• Plants act as producers in the ecosystem, and they are self-nourishing. Consumers are directly or indirectly dependent on plants for their food. 
• Plants produce sugars and oxygen during photosynthesis. This oxygen is used in aerobic respiration. 
• Forests act as habitats for wild species. 

2. Dependence of plants on animals 

• The animals produce carbon dioxide during aerobic respiration. This carbon dioxide is used in photosynthesis by plants. 
• Several insects, birds, and bats help in the pollination process. 
• Some species of animals help in seed and fruit dispersal.  

3. Dependence of plants and animals on the microbes 

• The microbes such as bacteria and fungi act as reducers in the biotic ecosystem. 
• These microbes decompose the dead bodies for material cycling in the ecosystem. 

Context and Applications 

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for 

• Bachelors of Science in Biology 
• Master of Science in Zoology 
• Bachelor of Medicine and Bachelor of Surgery (MBBS)