Biome

Biome Definition

Biome can be defined as a group of organisms that shares common characteristics, and these characteristics can be correlated to the environment in which they exist. A biome consists of both plants and animals. Biomes can be found on almost all continents. The characteristics of the organisms living inside a biome have developed in response to the environmental conditions. 

There is a subtle difference between a biome and a habitat. A habitat is the place of living of a type of organism. However, a biome is considered on a broader scale and is considered as a collection of different types of habitats.


What is Biome?

The definition of a biome is best explained as a collection of all the plants and animals living in an environment that shares common characteristics. Biomes, however, not only include only plants and animals. They can also be defined in terms of microorganisms as well. The term used for microorganisms is the microbiome. For microorganisms, the area considered need not be as large as that considered for plants and animals. They can be defined on a much lesser scale. For example, the term 'human microbiome' refers to all bacteria, viruses, parasites, fungi, and other microorganisms living inside the human body. 

A biota is defined as the complete collection of all the organisms living in a geographical region or a defined time scale. The scale of the region or the time considered can be as small as a local region or instantaneous time scales. It can also be as large as the whole planet or complete span of life on earth. All the biotas living on the earth build up the earth's biosphere.


Whittaker's Classification of Earth's Biomes 

Eminent American plant ecologist, R. H. Whittaker classified biomes on the basis of two abiotic factors: temperature and precipitation. There are important terminologies needed to be understood regarding Whittaker's classification schemes:

  • Physiognomy: physiognomy is the outward features, apparent characteristics, and appearance of species.

  • Formation: formation is based on the major population of the plant typically found in a given environment.

  • Biome-Type: biome type is defined by the grouping of several convergent biomes and the formation of different continents, based on physiognomy.

  • Formation Type: formation type is defined by the grouping of a number of convergent formations. 

Whittaker used the term 'formation' for plant species only, while 'biome' is used to refer to both plants and animals.

The Parameters used by Whittaker for his classification are:

  • Intertidal levels

  • Climatic moisture gradient

  • Temperature gradient defined by latitude.

  • Temperature gradient defined by altitude.


The Biome types defined in Whittaker's classification are:

  • Tropical rainforest

  • Temperate giant rainforest

  • Tropical seasonal rainforest which can be deciduous or semi-deciduous

  • Montane rainforest.

  • Temperate evergreen forest- needle-leaved and sclerophyll

  • Temperate deciduous forest.

  • Subarctic- subalpine needle-leaved forests, better known as taiga

  • Tundra

  • Elfin woodland

  • Thorn scrub

  • Woodlands and thorn forests

  • Temperate shrublands- heath, deciduous, sclerophyll, subalpine needle-leaved, or broad-leaved.

  • Temperate woodland

  • Temperate grassland

  • Savannah

  • Alpine grassland

  • Tropical desert

  • Warm temperate desert

  • Arctic-alpine desert

  • Cool temperate desert

  • Bog

  • Temperate freshwater swamp forest

  • Tropical freshwater swamp forest

  • Saltmarsh

  • Mangrove swamp

  • Wetlands 


Olson and Dinerstein's Classification of Biome

According to Olson and Dinerstein's classification of the biome, the following groups are enlisted:

Terrestrial Biome

  • Tropical and subtropical forests with dry broadleaf (found in semi-humid conditions)

  • Tropical and subtropical forests with moist broadleaf (found in humid conditions)

  • Tropical and subtropical conifers (found in semi-humid conditions)

  • Temperate conifers (found in humid to semi-humid conditions)

  • Temperate mixed forests with broadleaf (found in humid conditions)

  • Taiga (found in subarctic, humid conditions)

  • Tropical and subtropical savannahs, grasslands and shrublands (found in semi-arid regions)

  • Temperate savannahs, grasslands, and shrublands (found in semi-arid regions)

  • Flooded savannahs and grassland (found near fresh or brackish water)

  • Tundra (found in arctic regions)

  • Montane shrublands and grasslands (montane or alpine climate)

  • Deserts (found in arid regions)

  • Mediterranean forests, scrubs, woodlands and sclerophyll forests (temperate, semi-arid to semi-humid with winter rainfall)

  • Mangroves (found in salty areas)


The freshwater biomes will include

  • Large ponds

  • Large deltas formed at the mouth of the river

  • Freshwater found in the polar regions

  • Freshwater found in the montane region

  • Temperate coastal rivers

  • Wetlands and floodplain rivers found in temperate regions

  • Upland rivers found in the temperate regions.

  • Coastal rivers found in tropical and subtropical regions

  • Wetlands and floodplain rivers found in tropical and subtropical regions

  • Upland rivers found in tropical and subtropical regions

  • Endorheic basins and xeric freshwaters

  • Oceanic islands.


The marine biomes will include the continental shelf and the coastal areas:

  • Polar marine ecosystem

  • Temperate upwelling 

  • Seas and temperate shelves

  • Tropical coral, and

  • Tropical upwelling.


Examples of Biome- Tundra

According to the tundra definition, the biome is best explained as a type where the growth of trees are stunted by short growing seasons and low temperature. The word tundra is derived from a Russian word meaning treeless mountain tract. The tundra vegetation mainly composed of grasses and sedges, dwarf shrubs, lichens, and mosses. Some scattered trees might also be found in the tundra region. Due to the small vegetation found in tundra, the soil found in the tundra region is rich in phosphorus and nitrogen. The tundra region is generally succeeded by forest regions as the temperature increases. The ecotone, defined as the borderline between two biomes, between the tundra and the forests, is known as timberline or tree line. 

Based on their geographical locations, the tundra vegetation can be further subdivided into Arctic tundra, alpine tundra and the Antarctic tundra.


Examples of Biome- Mangrove Forests

Mangrove forests are found in places where the salt content of the soil is high. These regions are mainly found in the delta region, where the river meets the sea. The high content of salt in the soil is mainly due to its deposition from the seawater. Due to the waterlogged condition and high salt content, a unique type of vegetation is found in these regions, known as the mangrove forests. The uniqueness of the mangrove forests is the presence of Rhizophora or breathing roots. These breathing roots move above the surface of the soil and look like horns protruding from the soil. These roots are deprived of enough oxygen in the soil and, therefore, prefer to fix atmospheric oxygen.

According to a recent NASA-led study, mangrove forests can use atmospheric carbon dioxide more than any other forest, making them one of the largest contributors to the prevention of global warming.


Conclusion

Biomes are classified depending on the type of living organisms present in a given space at a given time. Several scientists have tried to classify biomes based on different parameters, and some of the acceptable theories came from Whittaker and Olson and Dinerstein. The biome of an ecosystem contributes to maintaining the harmony of that system. 

FAQ (Frequently Asked Questions)

1. What is described by the term 'Biome'?

A biome is the entire collection of all living organisms found in a given ecosystem at a given time. It not only consists of plants and animals but also microorganisms. However, a separate term microbiome is used to describe the entire collection of microorganisms. The biome of a place is defined by its environmental condition, such as temperature, humidity, rainfall, soil content, food source, altitude, latitude, and many more. A biome generally encompasses a large area comprising of several individual habitats. However, a microbiome can be defined on a much smaller scale. For example, all the microorganisms present in the human body can be defined as the human microbiome.

2. What is the basis of Whittaker's classification?

Plant ecologist R. H. Whittaker studied the pattern of plant and animal growth until 1975 and chose four parameters to demarcate the different biomes. They are intertidal levels, temperature changes by latitude and altitude and climatic moisture gradient. He observes that such gradients change from moderate to extreme, with subsequent changes in the production of different organisms. Not only was the production of species, but the development of physiognomic complexities also defined by the environmental conditions. He also observed that the dominant forms in a particular place might also be the dominant form in another place with similar environmental conditions.

3. What is the type of vegetation found in the tundra region?

The tundra region is characterised by extreme cold and semi-humid to arid conditions. They are sometimes compared to desert conditions. Tundra vegetation mainly consists of grasses, dwarf shrubs, bushes, with occasional trees scattered in a few places. As the temperature increases with a decrease in latitude, the tundra region is succeeded by forests, separating them by the timberline. The tundra soil is rich in nitrogen and phosphorus due to the type of vegetation found in these regions.

4. What is the speciality of mangrove vegetation?

Mangrove vegetation are found in places where the salt content of the soil is high. These are waterlogged areas found mostly in the delta region where the river meets the sea. Due to the waterlogged and salty conditions, the roots of the plants do not get enough oxygen to 'breathe'. As a result, these roots show negative geotropism and move above the surface of the soil, resembling horns jutting out from the ground. These roots are called Rhizophore or 'breathing roots' and are considered to be the special characteristic of mangrove vegetation.