Biomes or Terrestrial Ecosystems and Aquatic Ecosystems

PMF IAS Environment
  • A natural ecosystem is an assemblage of plants and animals which functions as a unit and is capable of maintaining its identity.
  • There are two main categories of ecosystems: 1) Terrestrial ecosystem or Biomes and 2) Aquatic ecosystem

Biomes or Terrestrial Ecosystems

  • The terrestrial part of the biosphere is divisible into enormous regions called biomes.
  • No two biomes are alike. They are characterized, by distinct climate (precipitation and temperature mainly), vegetation, animal life and general soil type.
  • The climate determines the boundaries of a biome and abundance of plants and animals found in each one of them.
Tundra
  • Arctic and Alpine Tundra Biome
Forest
  • Taiga or Boreal Biome (Evergreen Coniferous forests)
  • Temperate Deciduous Biome (North Western Europe – British Type Climate)
  • Temperate Rainforest Biome
  • Sub-Tropical Deciduous Biome in Eastern China, South Eastern USA
  • Temperate Deciduous Biome (Mediterranean Climate)
  • Tropical Deciduous Biome (Monsoon Climate)
  • Savanna or Tropical Wet and Dry Biome
  • Tropical Rain Forest Biome
Grassland
  • Steppe or Temperate Grassland Biome
  • Savanna or Tropical Wet and Dry Biome (Tropical Shrublands and Grasslands)
Desert
  • Tropical and Mid Latitude Desert Biome

For detailed explanation ad maps, you must go through Geography > Climatology > Climatic Regions.

Biomes or Terrestrial Ecosystems

Tundra Biome

  • There are two types of tundra – arctic and alpine.
  • Alpine tundra occurs at high mountains above the tree line. E.g. High ranges of the Himalayas, Andes, Alps etc.
  • There are no trees in the tundra (due to permafrost).
  • The lowest form of vegetation like mosses, lichens are sparsely found on bare rocks.
  • Coastal lowlands reindeer moss which provides the only pasturage for reindeers.
  • In the summer, birds migrate north to prey on the numerous insects which emerge when the snow thaws.
  • Insects have short life cycles which are completed during the favourable period of the year.
  • Animals like the reindeer, arctic fox, wolves, musk-ox, polar bear, lemming, arctic hare, arctic willow live in tundra region.
  • Reptiles and amphibians are almost absent.
  • Most of the animals have long life, e.g. arctic willow has a life span of 150 to 300 years.
  • They are protected from chillness by the presence of thick cuticle and epidermal hair or fur.
  • Mammals have a large body size and small tail and ear to avoid the loss of heat from the surface.

Taiga or Boreal Biome

  • Boreal forest soils are characterized by thin podzols and are rather poor. This is because:
  • The weathering of rocks proceeds slowly in cold environments
  • the litter derived from conifer needle (leaf) is decomposed very slowly and is not rich in nutrients (humus content is low).
  • conifers do not shed their leaves frequently.
Podzols
  • Podzols are the typical soils of a coniferous or boreal biome.
  • The top layer of the soil is very thin and is overlain over sandy or loamy subsurface which has no organic matter (lost due to leaching of nutrients to the bottom layers).

Podzols

  • The soils are characterized by low levels of moisture (excessively drained) and nutrients and are loamy or sandy. Others have shallow rooting zones and poor drainage due to subsoil cementation.
  • A low pH further compounds issue. The low pH (acidic) is due to excessive leaching of alkaline matter which if present would neutralise the organic acids of the accumulating litter.
  • Hence, most Podzols are poor soils for agriculture. They are mostly used for grazing.
  • The predominant vegetation is an evergreen coniferous forest with species such as spruce, fir and pine.
  • The conifers require little moisture are best suited to this type of sub-Arctic climate.
  • The productivity of boreal forest is lower than those of any other forest ecosystem.
  • Animals found in this region include Siberian tiger, wolverine, lynx, wolf, bear, red fox, squirrel, and amphibians like Hyla, Rana, etc.

Temperate Deciduous Biome (North-Western Europe – British Type Climate)

  • Soils of temperate forests are podzolic and fairly deep.
  • The natural vegetation of this climatic type is deciduous.
  • The trees shed their leaves in the cold season.
  • This is an adaptation for protecting themselves against the winter snow and frost.
  • Shedding begins in autumn, the ‘fall’ season. Growth begins in spring.
  • Some of the common species include oak, elm, ash, birch, beech, and poplar.

Temperate Rainforest Biome

  • This is a small biome in terms of area covered. The main stretch of this habitat is along the northwestern coast of North America from northern California through southern Alaska.
  • There are also small areas in southern Chile, New Zealand, Australia and a few other places around the world.
  • Big coniferous trees dominate this habitat, including Douglas fir, Western red cedar, Mountain hemlock, Western hemlock, Sitka spruce and Lodgepole pine.
  • In addition to the trees, mosses and lichens are very common, often growing as epiphytes.
  • Grizzly bears are the common mammals found in Alaska.

Sub-Tropical Deciduous Biome in Eastern China, South Eastern USA

  • Supports luxuriant vegetation.
  • The lowlands carry both evergreen broad-leaved forests and deciduous trees (hardwood).
  • On the highlands, various species of conifers such as pines and cypresses are important.
  • Perennial plant growth is not checked by either a dry season or a cold season.

Steppe or Temperate Grassland Biome

  • They are practically treeless, and the grasses are much shorter.
  • Grasses are fresh and nutritious.
  • Poleward, an increase in precipitation gives rise to a transitional zone of wooded steppes where some conifers gradually appear.
  • Do not have much animal diversity.

Temperate Deciduous Biome (Mediterranean Climate)

  • Trees with small broad leaves are widely spaced and never very tall.
  • Regions with adequate rainfall are inhabited by low, broad-leafed evergreen trees (mostly evergreen oaks).
  • Fire is an important hazardous factor in this ecosystem, and the adaptation of the plants enable them to regenerate quickly after being burnt.
  • Plants are in a continuous struggle against heat, dry air, excessive evaporation and prolonged droughts.
  • They are, in short xerophytic (drought tolerant).

Tropical Deciduous Biome (Monsoon Climate)

  • Tropical Monsoon Forests are also known as a drought-deciduous forest; dry forest; dry-deciduous forest; tropical deciduous forest.
  • Teak, neem, bamboos, sal, shisham, sandalwood, khair, mulberry are some of the important species.

Savanna or Tropical Wet and Dry Biome

  • The savanna landscape is typified by tall grass and short trees.
  • The trees are deciduous, shedding their leaves in the cool, dry season to prevent excessive loss of water through transpiration, e.g. acacias.
  • Trees usually have broad trunks, with water-storing devices to survive through the prolonged drought.
  • Many trees are umbrella shaped, exposing only a narrow edge to the strong winds.
  • Savanna biome is rich in mammal, bird and reptile diversity.

Tropical Rain Forest Biome

  • High temperature and abundant rainfall support a luxuriant tropical rain forest.
  • The equatorial vegetation comprises a multitude of evergreen trees, e.g. mahogany, ebony, dyewoods etc.
  • In the coastal areas and brackish swamps, mangrove forests thrive.
  • All plants struggle upwards (most epiphytes) for sunlight resulting in a peculiar layer arrangement (canopy).
  • Epiphyte (commensalism – epiphyte benefits without troubling the host): An epiphyte is a plant that grows harmlessly upon another plant (such as a tree) and derives its moisture and nutrients from the air, rain, and sometimes from debris accumulating around it.
Q. Which of the following is/are unique characteristic/characteristics of equatorial forests?
  1. Presence of tall, closely set trees with crowns forming a continuous canopy
  2. Coexistence of a large number of species
  3. Presence of numerous varieties of epiphytes

Select the correct answer using the code given below:

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

Answer: d) All

Desert Biome

  • The predominant vegetation of both hot and mid-latitude deserts is xerophytic or drought-resistant.
  • This includes the cacti, thorny bushes, long-rooted wiry grasses and scattered dwarf acacias.
  • Most desert shrubs have long roots and are well spaced out to gather moisture, and search for ground water.
  • Plants have few or no leaves, and the foliage is either waxy, leathery, hairy or needle-shaped to reduce the loss of water through transpiration.
  • The seeds of many species of grasses and herbs have thick, tough skins to protect them while they lie dormant.

Aquatic Ecosystems

  • Aquatic ecosystems refer to plant and animal communities occurring in water bodies.
  • Aquatic ecosystems are classified into two subgroups: 1) Freshwater ecosystems, such as rivers, lakes and ponds; 2) Marine ecosystems, such as oceans, estuary and mangroves.
  • Aquatic ecosystems are classified on the basis of salinity into the following types:
  • Freshwater ecosystems: water on land which is continuously cycling and has low salt content (always less than 5 ppt) is known as fresh water.
  • There are two types of freshwater ecosystems: 1) Static or still water (Lentic) ecosystems, e.g. pond, lake, bogs and swamps. 2) Running water (Lotic) ecosystems, e.g. springs, mountain brooks, streams and rivers.
  • Marine ecosystems: the water bodies containing salt concentration equal to or above that of seawater (i.e., 35 ppt or above). E.g. shallow seas and open ocean.
  • Brackish water ecosystems: these water bodies have salt content in between 5 to 35 ppt. e.g. estuaries, salt marshes, mangrove swamps and forests.

Aquatic Organisms

  • The aquatic organisms are classified on the basis of their zone of occurrence.
  • Neuston: These organisms live at the air-water interface, e.g. floating plants.
  • Periphyton: These are organisms which remain attached to stems and leaves of rooted plants or substances emerging above the bottom mud such as sessile algae.
  • Plankton: Microscopic floating organisms such as algae, diatoms, protozoans and larval forms are called plankton. This group includes both microscopic plants like algae (phytoplankton) and animals like crustaceans and protozoans (zooplankton).
  • The locomotory power of the planktons is limited so that their distribution is controlled, largely, by currents in the aquatic ecosystems.
  • Nekton: This group contains powerful swimmers that can overcome the water currents.
  • Benthos: The benthic organisms are those found living at the bottom of the water mass.

Factors Limiting the Productivity of Aquatic Habitats

  • Sunlight and oxygen are the most important limiting factors of the aquatic ecosystems.

Sunlight

  • Sunlight penetration rapidly diminishes as it passes down the column of water.
  • The depth to which light penetrates a lake determines the extent of plant distribution.
  • Suspended particulate matters such as clay, silt, phytoplankton, etc. make the water turbid.
  • Turbidity limits the extent of light penetration and photosynthetic activity in a significant way.
  • Based on light penetration and plant distribution they are classified as photic and aphotic zones.
Photic zone
  • Photic (or “euphotic”) zone is the portion that extends from the lake surface down to where the light level is 1% of that at the surface. The depth of this zone depends on the transparency of water.
  • Photosynthetic activity is confined to the photic zone.
  • Both photosynthesis and respiration activity takes place.
Aphotic zone
  • The lower layers of the aquatic ecosystems, where light penetration and plant growth are restricted forms the aphotic zone (profundal zone). Only respiration activity takes place in this zone.
  • The aphotic zone extends from the end of the photic zones to bottom of the lake.

Dissolved oxygen

  • In freshwater the average concentration of dissolved oxygen is 10 parts per million by weight.
  • This is 150 times lower than the concentration of oxygen in an equivalent volume of air.
  • Oxygen enters the aquatic ecosystem through the air-water interface and by the photosynthetic activities of aquatic plants.
  • Dissolved oxygen escapes the water body through the air-water interface and respiration of organisms (fish, decomposers, zooplankton, etc.).
  • The amount of dissolved oxygen retained in water is also influenced by temperature.
  • Oxygen is less soluble in warm water. Warm water also enhances decomposer activity. Therefore, increasing the temperature of a water body increases the rate at which oxygen is depleted from the water.
  • When the dissolved oxygen level falls below 3-5 ppm, many aquatic organisms are likely to die.
Winterkill
  • An ice layer on the top of a water body can effectively cut off light. Photosynthesis stops but respiration continues in such water body.
  • If the water body is shallow, the oxygen gets depleted, and the fish die. This condition is known as winterkill.

Temperature

  • Since water temperatures are less subject to change, the aquatic organisms have narrow temperature tolerance limit.
  • As a result, even small changes in water temperature are a great threat to the survival of aquatic organisms when compared to the changes in air temperatures in the terrestrial organisms.
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