Microbiology is one of the Biology Topics that involves the study of microorganisms, including bacteria, viruses, and fungi.
The Major Biomes of the World – Terrestrial and Aquatic Biomes
Biomes are climatically and geographically defined as contiguous areas with similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a large area, creating a typical ecosystem over that area. Such major ecosystems are termed biomes. Biomes are defined by factors such as plant structures (such as trees, shrubs, and grasses), leaf types (such as broadleaf and needleleaf), plant spacing (forest, woodland, savanna), and climate.
Unlike ecozones, biomes are not defined by genetic, taxonomic, or historical similarities. Biomes are often identified with particular patterns of ecological succession and climax vegetation (quasi-equilibrium state of the local ecosystem). An ecosystem has many biotopes and a biome is a major habitat type. A major habitat type, however, is a compromise, as it has an intrinsic homogeneity. Some examples of habitats are ponds, trees, streams, creeks, under rocks, and burrows in the sand or soil. The biodiversity is characteristic of each extinction, especially the diversity of fauna and subdominant plant forms, and is a function of abiotic factors and the biomass productivity of the dominant vegetation. In terrestrial biomes, species diversity tends to correlate positively with net primary productivity, moisture availability, and temperature.
Ecoregions are grouped into both biomes and ecozones. [Holdridge (1947, 1964) classified climates based on the biological effects of temperature and rainfall on vegetation under the assumption that these two abiotic factors are the largest determinants of the types of vegetation found in a habitat. Whittaker (1962, 1970, 1975) classified biomes using two abiotic factors – Precipitation and Temperature]. A fundamental classification of biomes is:
- Terrestrial (land) biomes.
- Aquatic biomes (including freshwater biomes and marine biomes).
Biomes are often known in English by local names. For example, a temperate grassland or shrubland biome is known commonly as ‘steppe’ in Central Asia, ’prairie’ in North America, and ‘pampas’ in South America. Tropical grasslands are known as ‘Savana’ in Australia, whereas in Southern Africa it is known as certain kinds of Veld (from Africans). Sometimes an entire biome may be targeted for protection, especially under and individual nation’s biodiversity action plan.
The importance of biomes cannot be overestimated. Biomes have changed and moved many times during the history of life on Earth. More recently, human activities have drastically altered these communities. Thus conservation and preservation of biomes should be a major concern to all. Climate is a major factor determining the distribution of terrestrial biomes. Among the important climatic factors are:
- Latitude: Arctic, boreal, temperate, subtropical, tropical.
- Humidity: Humid, semi-humid, semi-arid, and arid.
Rainfall may be distributed evenly throughout the year or be marked by seasonal variations.
Dry Summer, Wet Winter:
Most regions of the earth receive most of their rainfall during the summer months; Mediterranean climate regions receive their rainfall during the winter months.
Increasing elevation causes a distribution of habitat types similar to that of increasing latitude. The most widely used systems of classifying biomes correspond to latitude (or temperature zoning) and humidity. Biodiversity generally increases away from the poles towards the equator and increases with humidity. There are several types of biomes – Tropical forest, Deciduous forest, Coniferous forest, Temperate forest, Desert, Grassland, Arctic, and Alpine Tundra.
Main Five Types of Biomes:
|Biome||Geographical Distribution||Climate||Plants and Animals|
|1. Forest Biome|
|A. Tropical Forest Biome||Tropical regions, the Amazon basin of South America, New Guinea island of Northern Australia, Congo basin of Africa, Central America, Indonesia, and Srilanka.||Rainfall is throughout the year. Average rainfall (200-400) cm, Average temperature 27°C.||The forest is called evergreen forest. Mahogany, rubber, rosewood, plum, and climbers are found. In the case of animals, tigers, lions, foxes, deer, elephants, hornbills, parrots, woodpeckers and snails, spiders, and aneater are found.|
|B. Coniferous Forest||Switzerland, Canada, Sweden, and hilly regions of tropical areas.||Prolonged winter, the temperature in winter is – 30°C to 10°C and 2-4 months in summer.||The main plants are pine, willow, birch, fir, cedar, poplar, etc. The main animals are deer, wolves, porcupines, beer, woodpeckers, kingfishers, etc.|
|C. Tropical Deciduous Forest||Eastern, South-Eastern, Southern countries of Asia, Eastern region of North America, Brazil, Colombia, some countries of Australia and Africa.||Average rainfall 100-200 cm. Dry in 1-2 months in a year. Rainfall in a particular season. The average temperature in a year is 18°-30°C.||Sal, Teak, Palas, Mohua, Sissoo, Shimul, Jarul, Ficus, Neem etc. The main animals are wolves, deer, bears, some wild mammals, birds, etc.|
|2. Grassland Biome||35°-55° latitude of Asia and North America, 40°-60° of east Europe, Africa, 35°-50° Latitude of South America and Oceania.||25-75 cm. rainfall average in a year. Rainfall in a particular season.||Different types of grasses. In savanna grassland, palm and babla trees with some long grass. Animals are cows, buffalo, horses, many snakes, spiders, etc.|
|3. Tundra Biome||North America, Northern part of Eurasia, Greenland.||Prolonged winter duration 9 months, temperature -40°C, average rainfall less than 25 cm. Snowfall in winter.||Birch, willow, juniper, and many lichens in winter. Animals are snow leopards, whales, seals, penguins, etc.|
|4. Taiga Biome||From North America to New Found land.||Prolonged frozen winter, temperature below 6°C for six months, heavy snowfall.||Fir, Pine coniferous tree and arctic fox, polar bear are found.|
|5. Desert Biome||Rajasthan desert, Sahara desert.||Scorching heat during the day and biting cold at night. Rainfall is less than 50 cm in a year.||Babla, Euphorbia, cactus, some orchids, etc. Animals are camel, rattlesnake, desert rat, lizard, spider, gazelle, antelope, small foxes etc.|
1. Tropical Forest
A tropical rainforest is an ecosystem type that occurs roughly within the latitudes 28° north or south of the equator (in the equation zone between the Tropic of Cancer and Tropic of Capricorn). This ecosystem experiences high average temperatures and a significant amount of rainfall. Rainforests can be found in Asia, Australia, Africa, South America, Central America, Mexico, and on many of the Pacific, Caribbean, and Indian Ocean islands. Within the World Wildlife Fund’s biome classification, tropical rainforests are thought to be a type of tropical wet forest (or tropical moist broadleaf forest) and may also be referred to as lowland equatorial evergreen rainforests.
Tropical rainforests can be characterized in two words: warm and wet. Mean monthly temperatures exceed 18°C (64°F) during all months of the year. Average annual rainfall is no less than 168 cm (66 inches) and can exceed 1,000 cm (390 inches) although it typically lies between 175 cm (69 inches) and 200 cm (79 inches). This high level of precipitation often results in poor soils due to leaching of soluble nutrients.
Tropical rainforests exhibit high levels of biodiversity. Around 40% to 75% of all biotic species are indigenous to the rainforests. Rain forests are home to half of all the living animal and plant species on the planet. Two-thirds of all flowering plants can be found in rainforests. A single hectare of rainforest may contain 42,000 different species of insect, upto 807 trees of 313 species and 1,500 species of higher plants. Tropical rain forests have been called the “world’s largest pharmacy”, because over one-quarter of natural medicines have been discovered within them. It is likely that there may be many millions of species of plants, insects, and microorganisms still undiscovered in tropical rainforests.
Tropical rainforests are among the most threatened ecosystems globally due to large-scale fragmentation due to human activity. Habitat fragmentation caused by geological processes such as volcanism and climate change occurred in the past, and have been identified as important drives of speciation. However, fast human-driven habitat destruction is suspected to be one of the major causes of species extinction. Tropical rainforests have been subjected to heavy logging and agricultural clearance throughout the 20th century and the area covered by rainforests around the world is rapidly shrinking.
In Southern India, some important plants of rain forest are Dipterocarpus grandiflorus, D. pilosa, D. indicus, Hopea odorata, H. parviflora, Artocarpus hirsuta, A. chaplasha, Mesua ferrea, etc. 2nd and 3rd storied species of forests are Mangifera indica, Emblica officinalis, Michelia sp., Syzygium sp., Ervatamia heyneana, Lagerstromia speciosa, Strobilanthes sp., Ixora sp., etc. Some climbers are Ventrilago sp., Jasminum sp., Calamus sp., Smilax sp., Pathos sp., Caesalpinia sp., Rubia sp., Gnetum sp., etc. Some animals are ants, bees, crows, Naja sp., hornbills, termites, chameleons, tigers, etc.
Types of Tropical Rainforest:
Several types of forest comprise the general tropical rainforest biome: Lowland equatorial evergreen rainforests are forests that receive high rainfall (more than 2000 mm, or 80 inches, annually) throughout the year. These forests occur in a belt around the equator, with the largest areas in the Amazon Basin of South America, the Congo Basin of Central Africa, Indonesia, and New Guinea.
Moist deciduous and semi-evergreen seasonal forests receive high overall rainfall with a warm summer wet season and a cooler winter dry season. Some trees in these forests drop some or all of their leaves during the winter dry season. These forests are found in parts of South America, Central America, and around the Caribbean, in coastal West Africa, parts of the Indian subcontinent, and across much of Indo-China. The moist semi-evergreen forest of India is dominated by Artocarpus sp., Michelia sp., Eugenia sp., and some deciduous trees like Terminalia sp., Tetrameles sp., Shorea sp., etc. Odina wordier, Dillenia pentagyna, Sterospermum sp., Amoora rohituka, etc. are also found.
In South India, main trees of moist deciduons forest are Terminalia crenulata grewia sp., Garuga pinnata, Salmalia malabarica, Tectona grandis, Pterocarpus marsupium, Adina cordifolia, Lannea grandis. Mountain rainforests, some of which are known as cloud forests, are found in cooler-climate mountain areas. Depending on latitude, the lower limit of montane rainforests on large mountains is generally between 1500 and 2500 m while the upper limit is usually from 2400 to 3300 m.
Flooded forests, seven types of flooded forests are recognized for Tambopata Reserve in Amazonian Peru:
- Permanently waterlogged swamp forest – Former oxbow lakes still flooded but covered in forest.
- Seasonally waterlogged swamp forest – Oxbow lakes in the process of filling in.
- Lower floodplain forest – Lowest floodplain locations with a recognizable forest.
- Middle floodplain forest – Tall forest, flooded occasionally.
- Upper floodplain forest – Tall forest, rarely flooded
- Old floodplain forest – Subjected to flooding within the last two hundred years.
- Previous floodplain – Now terrafirma, but historically ancient floodplain of Tambopata River.
2. Deciduous Forest
Deciduous means “falling off at maturity” or “tending to fall off”, and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe. In a more general sense, deciduous means the dropping of a part that is no longer needed, or falling away after its purpose is finished. In plants, it is the result of natural processes.
These deciduous forests characterized as are evergreen as here foliage is shed on a different schedule from deciduous trees, therefore appearing to remain green year-round. Plants that are intermediate may be called semi-deciduous; they lose old foliage as new growth begins. Other plants are semi-evergreen and lose their leaves before the next growing season, retaining some during winter or dry periods. Some trees, including a few species of oak, have desiccated leaves that remain on the tree throughout winter; these dry persistent leaves are called marcescent leaves and are dropped in the spring as new growth begins.
Many deciduous plants flower during the period when they are leafless, as this increases the effectiveness of pollination. The absence of leaves improves wind transmission of pollen or wind-pollinated plants and increases the visibility of the flowers to insects in insect-pollinated plants. This strategy is not without risks, as the flowers can be damaged by frost or, in dry seasons, result in water stress on the plant. Nevertheless, there is much less branch and trunk breakage from glaze ice storms when they are leafless, and plants can reduce water loss due to the reduction in the availability of liquid water during cold winter days.
Leaf drop or abscission involves complex physiological signals and changes within plants. The process of photosynthesis steadily degrades the supply of chlorophylls in foliage; plants normally replenish chlorophylls during the summer months. When autumn arrives and the days are shorter or when plants are drought-stressed, deciduous trees decrease chlorophyll pigment production, allowing other pigments present in the leaf to become apparent, resulting in non-green coloured foliage. The brightest leaf colours are produced when days grow short and nights are cool but remain above freezing. These other pigments include carotenoids that are yellow, brown, and orange.
Anthocyanin pigments produce red and purple colours, though they are not always present in the leaves. Rather, they are produced in the foliage in late summer, when sugars are trapped in the leaves after the process of abscission begins. Parts of the world that have showy displays of bright autumn colours are limited to locations where days become short and nights are cool. In other parts of the world, the leaves of deciduous trees simply fall off without the bright colours produced by the accumulation of anthocyanin pigments.
The beginnings of leaf drop start when an abscission layer is formed between the leaf petiole and the stem. This layer is formed in the spring with active new growth of the leaf. It consists of layers of cells that can separate from each other. The cells are sensitive to a plant hormone called auxin that is produced by the leaf and other parts of the plant. When auxin coming from the leaf is produced at a rate consistent with that from the body of the plant, the cells of the abscission layer remain connected; in autumn, or when under stress, the auxin flow from the leaf decreases or stops, triggering cellular elongation within the abscission layer. The elongation of these cells breaks the connection between the different cell layers, allowing the leaf to break away from the plant. It also forms a layer that seals the break, so the plant does not lose sap.
In west Uttar Pradesh and Punjab Anogeissus latifolin, Acacia catechu, Terminalia tomentosa, Boswellia serrata are dominant and Dendrocalamus strictus, Emblica officinalis, Woodfordia floribunda are relatively less. In UP and Bihar Shorea robusta, Terminalia arjuna, Boswellia serrata, Buchanania lanzan, Diospyros melanoxylon are dominant. In southern India, deciduous forest is made up of long grass, deciduous plants, and shrubs. Some deciduous plants are Terminalia sp. Anogeissus latifolia, Pterocarpus marsupium, Tectona grandis, Ougeinia dalbergiodes, Boswellia sp. etc. Grasses are Andropogon sp., Panicum sp., Heteropogon sp. etc. Animals are dear, bear, Opossum, Ambystoma etc.
A number of deciduous plants remove nitrogen and carbon from the foliage before they are shed and store them in the form of proteins in the vacuoles of parenchyma cells in the roots and the inner bark. In the spring, these proteins are used as a nitrogen source during the growth of new leaves or flowers. The deciduous forest is of two types-
A. Temperate deciduous forest:
Biomes are plant communities distributed in North and South America, Asia, the Southern slopes of the Himalayas, Europe, and for cultivation purposes in Oceania. They have formed under climatic conditions which have great seasonable temperature variability with growth occurring during warm summers leaf drop in autumn and dormancy during cold winters. These seasonally distinctive communities have diverse life forms that are impacted greatly by the seasonality of their climate, mainly temperature and precipitation rates. These varying and regionally different ecological conditions produce distinctive forest plant communities in different regions.
B. Tropical and subtropical deciduous forest:
Biomes have developed in response not to seasonal temperature variations but to seasonal rainfall patterns. During prolonged dry periods the foliage is dropped to conserve water and prevent death from drought. Leaf drop is not seasonally dependent as it is in temperate climates, and can occur any time of year and varies by region of the world. Even within a small local area there can be variations in the timing and duration of leaf drop; different sides of the same mountain and areas that have high water tables or areas along streams and rivers can produce a patchwork of leafy and leafless trees.
3. Coniferous Forest
It is a terrestrial biome found in temperate regions of the world with warm summers and cool and adequate rainfall to sustain a forest. In most temperate coniferous forests, evergreen conifers predominate, while some are a mix of conifers and broadleaf evergreen trees and/or broadleaf deciduous trees. Temperate evergreen forests are common in the coastal areas of regions that have mild winters and heavy rainfall, or inland in drier climates or mountain areas. Coniferous forests can be found in the United States, Canada, Europe, and Asia. Many species of trees inhabit these forests including cedar, cypress, Douglas fir, fir, juniper, kauri, pine, podocarpus, spruce, redwood, and yew. The undershrubs also contain a wide variety of herbaceous and shrub species.
Structurally, these forests are rather simple, generally consisting of two layers: an over-story and an understory. Some forests may support an intermediate layer of shrubs. Pine forests support a herbaceous understory that is generally dominated by grasses and herbaceous perennials and are often subject to ecologically important wildfires.
Temperate rain forests occur only in seven regions around the world: the Pacific temperate rain forests of the Pacific Northwest, the Valdivian temperate rain forests of southwestern South America, the rain forests of New Zealand and Tasmania, Northwest Europe (small pockets in Ireland, Scotland, Wales, Iceland and a somewhat larger area in Norway), Southern japan and the Eastern Black Sea-Caspian sea region of Turkey and Georgia to northern Iran. The moist conditions of temperate rainforests generally support an understory of mosses, ferns, and some shrubs. Temperate rainforests can be temperate coniferous forests or temperate broadleaf and mixed forests. In southern India plants are Eugenia sp„ Ficus sp., Actinodophne sp., Canthium sp., Memecylon sp., Mangifera sp., etc., climbers are Piper trichostachyon, Gnetum scandens, Smilax macrophylla, Vitis elongata. The main animals are white bears, squirrels, rats, Indian civets, beavers, etc.
4. Temperate Forest
Temperate forests correspond to forest concentrations formed in the Northern and Southern hemispheres, or in temperate regions. Main characteristics include wide leaves, large and tall trees, and non-seasonal vegetation. Temperate forests can be further distinguished by weather patterns and geographical features that favour the predominance of certain kinds of trees. In temperate coniferous forests, evergreen conifers predominate, while in temperate broadleaf and mixed forests, a more even distribution exists between evergreen and deciduous trees.
Temperate deciduous forests, a subgroup of temperate broadleaf forests, consist of trees that lose their leaves every year. Finally, temperate rainforests typically have heavy rainfall and dense humidity. Most temperate forests are located in the Eastern United States, Canada, Europe, China, Japan, and parts of Russia. Temperate forests are areas with high levels of precipitation and humidity. These forests also contain a variety of deciduous trees.
In the temperate region, winters are mild and rainfall is moderate. The forests have trees, shrubs, and bushes. There is less undergrowth. Most of the trees are deciduous, which shed their leaves during the autumn. In some areas, the deciduous trees are replaced by coniferous trees. The main trees found in these forests are oak, ash, maple, birch, beech, poplar, elm, and pine. In many areas, forests have been cleared to make way for cultivation. Hardwood evergreen trees which are widely spaced and are found in the Mediterranean region are olive, cork, oak, and stone pine.
Main plants of Nilgiri hills in India are Balanocarpus utilis, Hopea parviflora, Artocarpus hirsutus, Salma- lia malabarica, Hardwickia pinnata etc. Some climbers are Piper nigrum, Hoya sp., Jasminum sp., Dioscorea sp., Thunbergia sp., etc. Deer, bears, and Opossum are also found.
The local and regional variations of the biome tend to the formation of a large variety of habitats. On earth, life is not properly stable or life exists not just in a few favorable habitats, but even in extreme heat scorching, dry, and mostly harsh habitats. For example: the Rajasthan Desert, the African Desert, etc. This desert biome lacks rain due to either being present in a rain shadow. Here the ground is sandy and rocky. In this biome cacti, deep-rooted shrubs or other xerophytic plants are present, and desert rats, rattlesnakes, lizards, spiders, and camel present as important animals.
Some desert plants are Carex indica, Ipomoea pes-caprae, Convolvulus arvensis, Opuntia dillenii, Euphorbia an-tiquorum, Acacia sphaerocephala, and Aloe vera. Shrubs found in the desert are Acacia arabica, Prosopis juliflora, Salvadora persica, Tamarix dioca, Capparis aphylla, and Ziziphus nummularia. In Mt. Abu Boswellia, serrata, Sterculia urens, Anogeissus pendula are present. In dry environments Acacia catechu, Buta monosperma, and Acacia senegale are dominant.
Grasslands are areas where the vegetation is dominated by grasses (Poaceae), however, sedge (Cyperaceae) and rush (Juncaceae) families can also be found. Grasslands occur naturally on all continents except Antarctica. Grasslands are found in most ecoregions of the Earth. For example, there are five terrestrial ecoregion classifications (subdivisions) of the temperate grasslands, savannas, and shrublands biome (‘ecosystem’), which is one of eight terrestrial ecozones of the earth’s surface.
Grassland vegetation can vary in height from very short, as in chalk where the vegetation may be less than 30 cm (12 inches) high, to quite tall, as in the case of North American tallgrass prairie, South American grasslands, and African savanna.
Woody plants, shrubs or trees, may occur on some grasslands forming savannas, scrubby grassland, or semi-wooded grassland, such as the African savannas or the Iberian dehesa. Such grasslands are sometimes referred to as wood pasture or woodland.
As flowering plants, grasses grow in great concentrations in climates where annual rainfall ranges between 500 and 900 mm. The root systems of perennial grasses and forbs form complex mats that hold the soil in place. Schima dichanthium, Mimosa rubicaulis, Acacia catechu, Acacia Senegal, Calotropis gigantea, Salvadora persica, Butea monosperma, Cynodon dactylon, Ziziphus nummularia, Dichanthium annulatum are found in grassland ecosystem.
7. Arctic and Alpine Tundra
The Tundra biome is divided into two Arctic and Alpine Tundra.
It is located in the far north of Greenland, Asia, Alaska, Canada, Europe and Russia. It is a frozen, windy, desert-like plain with scattering bogs and ponds. The average winter temperature is -30°C and the summer temperature is 37-54°C. There are about 1,700 kinds of plants in the arctic and sub-arctic and these include low shrubs, sedges, reindeer mosses, liverworts, grasses, around 400 varieties of flowers, and also presence of crustose and foliose lichen. In arctic tundra, there are several types of animals like Mammals (arctic foxes, arctic hares, caribou, lemmings, muskoxen, polar bears, etc.), birds (snowy owl, falcons, gulls, sand pipers, etc.), Insects (blackflies, grasshoppers, moths, mosquitoes, etc.).
It is located high in the mountains above the tree line usually at an altitude of about 10,000 feet or more. There is the presence of well-drained soil. Temperatures vary depending on the altitude. In the alpine tundra, there are several types of animals found, like Mammals (elk, mountain goats, sheep, etc.), birds (house-like birds), and Insects (beetles, grasshoppers, butterflies, etc.).