Biomes or Terrestrial Ecosystems and Aquatic Ecosystems

• 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.

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.

• 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.