INDIA AS A MEGA DIVERSITY NATION

The term megadiverse country refers to any nation that harbours the majority of Earth's species and high numbers of endemic species.The UNEP (United Nations Environment Programme) has recognised 17 Megadiversity Nations across the world. India is one among them due to its commendable diversity of organisms. 

India has 4 out of 34 globally identified  Biodiversity Hotspots (Himalaya, Western Ghats, Indo-Burma, and Srinlanka- Sundaland). India has wide range of habitats- The varied edaphic, climatic and topographic conditions and years of geological stability have resulted in a wide range of ecosystems and habitats such as forests, grasslands, wetlands, deserts, and coastal and marine ecosystems. Arid, semi- arid and desert regions occupy 38.8% of India's land mass with 682 species of which 6% is endemic. This area is also rich with cat type predators- Lion, Leopard and Tiger. The Great Indian Bustard is a threatened bird living in this habitat. 

The cold Himalayan region covers 5.8% of the geographical area. The cold desert also harbors endangered species such as snow leopard, yak and Asiatic ibex.  

India has a good collection of wetland habitats as well with about 4500 square kilometers of Mangrove ecosystem. The fish and bird diversity is high in such regions.  We have 783 fresh water fishes, of which 223 are endemic. India has good fish diversity and the country is one of the largest fish producers of the world. 

India has a lengthy coastal habitat of 7500 kilometers, with diverse habitats like estuaries, lagoons, backwaters, salt marshes and coral reefs. These habitats are also rich in species diversity.

India has diverse forest habitats, consisting of 23.5% of total land mass of which 75% are located in North East states India. India has 16 major forest types. The mountain ecosystem of India consists of forest ecosystems. Western Ghats and Eastern Himalayas are rich in diversity of species with 40% of endemism. 

Considering the major categories of life forms, India has the following diversity:

Animals

1. Protists- 2577 (out of 31,200 in the world)
2. Mollusca- 5070 (out of 81,000)
3. Arthropoda - 68300 ( out of 9,90,000)
4. Fishes- 2546 (out of 30,000)
5. Amphibia- 209 (out of 6200)
6. Reptiles- 456 (out of 8200)
7. Birds- 1232 (out of 9900)
8. Mammals- 390 (out of 5490)

Plants (As per 2007 data)

1. Algae- 6500 (out of 40,000)
2. Bryophytes - 2825 (out of 17000)
3. Pteridophytes- 1200 (out of 13000)
4. Gymnosperms- 48 (out of 980)
5. Angiosperms- 18000 (out of 2,50,000)

Microbes

1. Bacteria- 850 (out of 8500)
2. Fungi- 14500 (out of 72000)
3. Virus- 1200 (out of ????? not estimated) as per 2019 data
4. Lichens - 2000 (out of 35000)

 

ECOSYSTEMS: AN INTRODUCTION

 Ecosystem is a broad term which includes all organisms and the environment they live, i.e. it includes all living and non living things, and their interactions. In other words it is a community of organisms along with their physical environment. The study of ecosystems is called Ecology. It was Sir A G Tansley, who was an English Botanist, who introduced the concept of 'Ecosystem". The living and non-living components of the ecosystems are interlinked by means of energy transfer and biogeochemical cycles. Ecosystem can be defined as 'the living community of plants, animals and microbes in an area and their surrounding environment such as soil, air and water.' The basic living components of the ecosystem are producers, consumers and decomposers.

Ecosystems are broadly divided into terrestrial or land based ecosystems, and aquatic ecosystems in water.

1. AQUATIC ECOSYSTEMS

Aquatic ecosystems are water based ecosystems in which water acts as the surrounding environment for the living organisms. Aquatic ecosystems are further classified in to the following categories. - marine ecosystem, estuarine ecosystem and freshwater ecosystem, based on the salinity of water.

Marine ecosystem: When the salinity of the water is equal or more than 35ppt (parts per thousand), the ecosystem is considered to be marine. 

Freshwater ecosystem: When the salinity is 0.5 ppt or less, it is considered as freshwater ecosystem.

Estuarine ecosystem: When the salinity keeps varying between 0.5 to 30 ppt it is considered to be estuarine.

2. TERRESTRIAL ECOSYSTEMS

All the ecosystems which are seen on the land are called terrestrial ecosystems. They can be further divided based on the the types of plants and animals inhabiting. Some features of terrestrial organisms are the following; they are exposed directly to air, hence developed respiratory system for gaseous exchange; the plants have extensive root system for finding water in the soil and absorbing it; animals have developed mechanisms to combat with heat or cold.

Forest ecosystem: Terrestrial ecosystem in which trees are the dominant vegetation. They can be further subdivided into tropical forests, temperate forests and boreal forests.

Grassland ecosystem: When the vegetation is dominated by grasses, the ecosystem is called grassland ecosystem. They can be further divided into tropical grasslands and temperate grasslands. Tropical grasslands are called savannah and temperate grasslands are called prairies, steppes, pampas, veldts etc. in different places.

Desert ecosystem: Desert is a region which receives very less rainfall, which is usually less than 25 cm per year. There are two types of deserts: hot deserts and cold deserts.

ECOLOGICAL PYRAMIDS

 Ecological pyramids are graphical representations of the trophic structure in an ecosystem. The major trophic levels in an ecosystem are the following;

1. Producers

2. Primary consumers

3. Secondary consumers

4. Tertiary consumers

5. Decomposers

Producers are green plants and algae which have the potential to fix atmospheric carbon dioxide and make glucose through a process called photosynthesis. 

Primary consumers are the animals which eat the green plants and algae. They are called herbivores, for example cow, rabbit, goat, deer.

Secondary consumers are the animals which prey upon herbivores. For example, Fox, dog, cat

Tertiary consumers are those animals which prey upon all animals irrespective of trophic levels, such as lion, tiger and hawk.

Decomposers are organisms which decay the dead organic matter formed by the death of organism, leaf fall etc. For example, fungi and microbes.

The energy trapped by green plants is transferred to primary consumers, then to secondary consumers and then to tertiary consumers. There is an energy loss at each level, which means only 10% of energy from one trophic level is transferred to the next. This is called 10% Rule. 

For example, if a producer has 1000 calories of energy, then the herbivore will get only 100 calories. When the herbivore is eaten by primary carnivores, they get only 10 calories. Finally the top carnivores will get only 1 calorie. At each trophic level, 90% of energy is lost for activities such as respiration, movement etc.

The following diagram explains the concept.

Ecological pyramids are of different types as given below.

1. Pyramid of Number: Graphical representation of number of organisms at each trophic level is called pyramid of number.

2. Pyramid of Energy: When the energy level of each trophic level is represented in an ecological pyramid, it is called pyramid of energy.

3. Pyramid of Biomass: When the biomass of organisms at each trophic level is represented in an ecological pyramid, it is called pyramid of biomass.

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FOOD CHAIN AND FOOD WEB

 The process of life on earth follows a similar pattern for all organisms. All life forms require energy to run its day to day activities such as movement, communication, seeing and hearing. The ultimate source of energy for all living organisms is sun. The solar energy from the sun is trapped by the photosynthesizing plants, which are called as producers. Plants can trap up to 2% of solar energy reaching the earth. The light  energy trapped by plants is converted and stored as chemical energy in the form of biomolecules such as starch, glucose etc. 

SUN--------> LIGHT ENERGY---------> PLANTS---------PHOTOSYNTHEIS--------> CHEMICAL ENERGY

The herbivores eat photosynthesizing plants such as grasses, herbs etc. These herbivores which directly depend upon plants are called primary consumers. For example, grass hopper, rabbit, cow, goat. The herbivores are eaten by carnivores, such as snake, frog and lizard. These carnivores are eaten by large carnivores such as lion, tiger and hawk. Finally when all these organisms die, the dead body is eaten by detrivore animals such as millipedes, dung flies, worms etc or decayed by fungi and bacteria. 

This linear chain of organisms in the ecosystems, which are connected to each other by the process of eating and being eaten is called food chain.

The following are examples;

Maize---> Locust---> Lizard---> Snake

Corn--> Rat--> Owl.

Carrot-->Rabbit-->Fox--> Lion

Food chains are of two types:

1. Grazing food chain- The food chain that starts from  green plants and depend on solar radiation is called grazing food chain. Most of the food chains in the ecosystems are of this type.

2. Detritus food chain- The food chain that starts from a dead organic matter and less dependent on solar energy is termed detritus food chain. This mainly involves microbes, detrivores and their predators.

FOOD WEB 

In nature, we cannot find linear food chains, because organisms eat multiple types of food and eaten by different types of animals. In real, the process of eating and being eaten forms a web or organisms which are interdependent and forms a cluster of different food chains so that an interconnecting food web is formed. 

A food web is a collective representation of all food chains in an ecosystem.

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