· A natural ecosystem is an assemblage of plants and animals which functions as a unit and is capable of maintaining its identity such as forest, grassland, an estuary.
· There are two main categories of ecosystems.
(1) Terrestrial ecosystem:
· Ecosystems found on land e.g. forest, grasslands, deserts, tundra.
(2) Aquatic ecosystem:
· Plants and animal community found in water bodies.
· These can be further classified into two sub groups.
(i) Fresh water ecosystems, such as rivers, lakes and ponds.
(ii) Marine ecosystems, such as oceans, estuary.
TERRESTRIAL ECOSYSTEMS :
Terrestrial ecosystems are
(c) deserts and
(a) Forests :
· Forests are large areas supporting rich growth of trees.
· Depending on the climate and type of trees they are generally grouped into:
(i) Tropical rain forests
(ii) Temperate deciduous forests
(iii) Boreal or north coniferous forests
(i) Tropical rain forest :
· These are found in the high rain fall areas on either side of the equator.
· Such forests are found in the western coast of India, scattered in south east Asia, some parts of Africa and south America.
Flora and fauna:
· Tropical rainforests occur in areas by having high temperature and
high humidity and receives above 200 cm of rainfall per year.
· Soil is rich in humus.
· These forests have a very rich biodiversity e.g. Brazilian tropical rain. forests have more than 300 species of trees in an area of 200 skm.
· Trees are tall growing upto 50 to 60 m.
· These forests also support epiphytes, like vines, creepers, woody creepers and orchid etc.
· These forests are rich in tree dwelling animals such as monkeys, flying squirrels, snails, centipedes, millipedes, and many insect species are common on the forest floor.
(ii) Temperate deciduous forests :
• They occur mostly in northwest, central and eastern Europe, eastern north America, north China, Korea, Japan, far eastern Russia and Australia.
• Trees of deciduous forests shed their leaves in autumn and a new foliage grows in spring.
• areas of moderate climatic conditions.
• temperature ranging b/t 10 to 20oC with a 6 month long winter annual
• rainfall between 75 to 150 cm.
• They have its brown soils which are rich in nutrients.
Flora and fauna:
· Common trees are oak, beach, heath, chest nut, birch, pine.
· These forests also show stratification and have a under storey of saplings shrubs and tall herbs.
· Prominent grazers include deer, bison and rodents.
· Rodents play a very important role in these forests.
· They feed on seeds, fruits and tree leaves. Black bear, raccoons, wild cat, wolves, fox and skunks are the omnivores found in these forests.
· Hibernation or winter sleep during winter is a common feature of animals found in these forests.
· Invertebrate fauna comprises green flies, aphids, certain moths and butterflies.
(iii) Boreal or north coniferous forests:
• Coniferous forests are also known as ‘Taiga’.
• They extend as a continuous belt across north America and north Eurasia below the arctic tundra.
• There is no counterpart of these forests in southern hemisphere as there is no land at this latitude.
• Climate is cold with long, harsh winter, with mean annual temperature below 00C.
• The soils are acidic and poor in nutrients.
Flora and fauna:
• Coniferous forests are characterized by evergreen, drought resistant and woody.
• Conifers (gymnosprerms) e.g. spruce, fir and pine trees which bear naked seeds in cones.
• The animals found in these forests, are red squirrel, deer, goat, mule, moose etc.
• The carnivores which feed upon them are timber wolves, lynxes, bear.
• Some common birds are crossbill, thrushes, warblers, flycatchers, robin and sparrow.
• Grasslands are areas dominated by grasses.
• They occupy about 20% of the land on the earth surface.
• Grasslands occur in both in tropical and temperate regions where rainfall is not enough to support the growth of trees.
• Grasslands are known by various names in different parts of the world.
Place Name of the grassland :
• North America - Prairies
• Eurasia (Europe and Asia) - Steppes
• Africa - Savanna
• South America - Pampas
• India Grassland - Savanna
• Grasslands are found in areas having well defined hot and dry, warm and rainy seasons.
• Tropical grasslands are commonly called Savannas.
• They occur in eastern Africa, South America, Australia and India.
Flora and fauna:
• Grasses are the dominating plants with scattered drought resistant thorny trees in the tropical grasslands.
• Badgers, fox, ass, zebra, antelope are found grazing on grasslands support the dairy and leather industries.
• Grasslands also support large population of rodents, reptiles and insects.
(c) Deserts :
• Deserts are hot and low rain areas suffering from water shortage and high wind velocity.
• They show extremes of temperature.
• Globally deserts occupy about 1/7th of the earth’s surface.
Flora and fauna:
• common desert plants- Cacti, Acacia, Euphorbia and prickly pears
• Desert animals - shrew, fox, wood rats, rabbits, camels and goat are common mammals in desert.
• Other prominent desert animals are, reptiles, and burrowing rodents insects.
Desert plants are hot and dry conditions.
(i) These plants conserve water by following methods:
• They are mostly shrubs.
• Leaves absent or reduced in size.
• Leaves and stem are succulent and water storing.
• In some plants even the stem contains chlorophyll for photosynthesis.
• Root system well developed spread over large area.
(ii) The animals are physiologically and behaviorally adapted to desert conditions.
• They are fast runners.
• They are nocturnal in habit to avoid the sun’s heat during day time.
• They conserve water by excreting concentrated urine.
• Animals and birds usually have long legs to keep the body away from the hot ground.
• Lizards are mostly insectivorous and can live without drinking water for several days.
• Herbivorous animals get sufficient water from the seeds which they eat.
• Camel is known as the ship of the desert as it can travel long distances without drinking water for several days.
(d) Tundra :
• The word tundra means a “barren land”.
• environmental conditions are very severe.
• There are two types of tundra- arctic and alpine.
• it extends as a continuous belt below the polar ice cap and above the tree line in the northern hemisphere.
• It occupies the northern fringe of Canada, Alaska, European Russia, Siberia and island group of arctic ocean.
• On the south pole Anatarctica tundra in the south pole is very small since most of it is covered by ocean .
• it occurs at high mountains above the tree line.
• Since mountains are found at all latitudes therefore alpine tundra shows day and night temperature variations.
Flora and fauna:
• Typical vegetation of arctic tundra is cotton grass, sedges, dwarf heath, willows, birches and lichens.
• Animals of tundra are reindeer, musk ox, arctic hare, caribous, lemmings and squirrel.
• Most of them have long life e.g. Salix arctica that is arctic willow has a life span of 150 to 300 years.
• They are protected from chill by the presence of thick cuticle and epidermal hair.
• Mammals of the tundra region have large body size and small tail and ear to avoid the loss of heat from the surface.
• The body is covered with fur for insulation.
• Insects have short life cycles which are completed during favourable period of the year.
AQUATIC ECOSYSTEMS :
• Aquatic ecosystems refers to plant and animal communities ocuring in water bodies.
• Aquatic ecosystems are classified on the basis of salinity into following two types:
(i) Fresh water ecosystem
• Water on land which is continuously cycling and has low salt content is known as fresh water and its study is called limnology.
(i) Static or still water (Lentic) e.g. pond, lake, bogs and swamps.
(ii) Running water (Lotic) e.g. springs, mountain brooks, streams and rivers.
• Fresh waters have a low concentration of dissolved salts.
• The temperature shows diurnal and seasonal variations.
• In tropical lakes, surface temperature never goes below 400C,
• in polar lakes never above 40C.
• In temperate regions, the surface layer of water freezes but the organisms survive below the frozen surface.
• Light has a great influence on fresh water ecosystems.
• A large number of suspended materials obstruct penetration of light in water.
• Certain animals float upto water surface to take up oxygen for respiration.
• Aquatic plants use carbon dioxide dissolved in water for photosynthesis.
• Lakes and ponds are inland depressions containing standing water.
• The largest lake in the world is lake Superior in North America.
• Lake Baikal in Siberia is the deepest.
• Chilka lake of Orissa is largest lake in India.
Three main zones can be differentiated in a lake:
• Peripheral zone (littoral zone) with shallow water.
• Open water beyond the littoral zone where water is quite deep.
• Bentic zone (bottom) or the floor of the lake.
• Aquatic organisms can be floating in water or free swimming or sedentary (fixed), depending on their size and habit.
• Microscopic floating organisms such as algae, diatoms, protozoans
and larval forms are called plankton.
• Rooted aquatic plants, fish, mollusk and echinoderms are bottom dwellers.
• Wetlands are areas that periodically get inundated with water and support a flourishing community of aquatic organisms including frog and other amphibians. Swamps, marshes and mangroves are examples of wetlands.
(ii) Marine ecosystem:
• Pertains to the seas and oceans including marine organisms.
• Marine ecosystem covers nearly 71% of the earth’s surface with an
average depth of about 4000 m.
• Fresh water rivers eventually empty into ocean.
• Different kinds of organisms live at different depths of the sea or ocean.
• Salinity of open sea is 3.6% and is quite constant.
• The range of temperature variation is much less in the sea than on the land.
• Hydrostatic pressure due to water column increases with depth in oceans.
• It is 1 atm near the surface and 1000 atm at greatest depth.
• Animals in the deeper layers are adapted to the high pressure.
• Some marine organisms such as sperm whales and certain seals can dive to the great depths and swim back to the surface without difficulty.
• Tides, due to gravitational pull of the moon and sun are a common feature of marine ecosystems.
Flora and fauna:
• Biodiversity of the marine ecosystems is very high as compared to terrestrial ecosystems.
• Almost every major group of animals occurs in the sea.
• Insects and vascular plant are completely absent in marine ecosystem.
• Maximum diversity of marine organisms is found in the tidal zone that is near the shore.
• Diatoms, algae, dinoflagellates and jelly fishes are some of the free floating life forms in oceans.
• Bottom dwellers are generally sessile (fixed) organisms like sponges, corals, crabs and starfish.
• Light weight animals and plants float in water and move with the water currents.
• Animals and plants in ocean are tolerant to high concentration of salts (osmoregulation).
• Osmoregulation is the process by which a constant osmotic pressure is maintained in blood.
• Swimming animals have streamlined body.
• Their body is laterally compressed.
• Deep sea forms show bioluminescence (they emit light).
• They are dependent for their food on the upper sea zones.