Biome

Biome can be defined as a group of organisms that share 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.

The term Biome was first used by Frederic E. Clements to represent plants and animals of a given region or habitat. 

Over time, scientists expanded and refined the definition of biomes and related different concepts in new areas of ecology, and in 1963 Shelford characterized the following biomes: tundra, coniferous forest, Deciduous forests, grasslands, deserts. Later, ecologist Arthur Tansley created another definition of the ecosystem, including biological processes, rather than the definition of  biome.

Common to all biome definitions is that biomes are distinguishable according to the organisms and climate in which they live and that the organisms within the biome share an adaptation to this particular environment. Climate is one of the important factors that determines which organisms can be found in which biome, and the factors that affect climate are Latitude, geographic features, and atmospheric processes that diffuse heat and humidity. 

Whittaker's Classification of Earth's Biomes 

To classify the planet into several ecological zones is challenging, mainly because of the small-scale variances that occur all over the earth and in an account of the slow transition from one biome to the next. Their boundaries must consequently be established randomly and their categorization determined according to the typical circumstances that prevail in them. The overall outcomes from the research were that rain and water consumption led to above-basic production. While the sun irradiation and temperature lead to below-ground primary production (roots). Temperature and water lead to cold and warm season growth habits. The number of classification systems and the range of determinants utilized in those schemes. However, it should be viewed as significant signs that biomes do not fit properly into the categorization schemes produced. 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- health, 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 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 savannas, grasslands and shrublands (found in semi-arid regions)

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

• Flooded savannas 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 are found in 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.

Biome Types 

The number of existing biomes is being discussed by scientists. While some aspects of the definition related to the climate and life of the resident are in close agreement with all, some definitions have been extended to include factors such as biodiversity and human activity. The definition may be inconsistent, but usually, several types of biomes arise from the definition, such as tundra, deserts, grasslands, deciduous forests, coniferous forests, rainforests, and water. And with every new definition, more factors will keep getting added. 

• Tundra Biomes

The tundra is located in the northernmost part of the world and features long, cold winters and cool summers. The flora and fauna that inhabit here have developed adaptations to survive in this cold environment, such as thick fur and hibernation ability. 

• Desert Biomes 

Deserts are found in both cold and warm climates around the world and are characterized by their dryness, and life in these areas adapts to water and nutrient deficiencies.

• Grassland Biomes 

The grassland biomes found on all continents except Antarctica are characterized by grassy, flat and overgrown trees. Large grazing mammals such as elephants and bison live in these areas along with small mammals, birds and predators.

• Deciduous Forest Biomes

These Biomes are located in eastern North America, Western Europe, and Northeast Asia, and feature deciduous trees such as maple and oak that seasonally lose their leaves when temperatures cool down. Overall, these areas are warm, but there are still clear winter seasons. 

• Tropical rainforest biomes 

These equatorial areas are warm and moist, with very diverse vegetation forming leaf canopies. Deciduous leaves on the ground and humidity in the air create a layer of nutrients on poor quality soil and grow a  variety of plants. Rainforests are known to be home to vast amounts of biodiversity.

• Aquatic Biomes 

There are many ways to classify aquatic biomes, and freshwater and saltwater biomes are often defined separately. Factors used for classification include water depth, temperature, and salt content. Terrestrial biota is usually categorized by vegetation type, but this method can be difficult to apply to aquatic environments where the lifespan of visible plants is not very long.

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 is 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 the 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.

Etymology of Biome

The word was introduced in 1916 by Clements, initially as a substitute for the biotic community of Möbius (1877). Eventually, it received its present meaning, relying on older ideas of Phyto-physiognomy, formation, and vegetation (used in contrast to flora). With the inclusion of the animal element and the deletion of the taxonomic aspect of species composition. In 1935, Tansley incorporated the climate and soil characteristics into the theory, naming its ecosystem. The International Biological Program (1964–74) programs established the idea of the biome. Nevertheless, in certain instances, the word biome is utilized in a different manner. In German texts, especially in the Walter terminology, the term is used similarly as a biotope. While the biome used deciduous the is used as an international, non-regional, terminology. It is irrespective of the continent in which an area is present. In Brazilian literature, the word biome is sometimes used as a byword of the biogeographic province. It is described as an area based on species composition. It is a geographic space with subcontinental dimensions, with the primacy of comparable geomorphologic and climatic attributes, and a certain vegetation form. Both include several biomes in reality.

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.