LIFE ON THE EARTH
Living organisms are found from the poles to the equator, from the bottom of the sea to several km in the air, from freezing waters to dry valleys, from under the sea to underground water lying below the earth’s surface.
Ecology
Ecology is the study of the earth as a ‘household’, of plants, human beings, animals and microorganisms. They all live together as interdependent components.
Ecological Systems : The interactions of a particular group of organisms with abiotic factors with a particular habitat resulting in clearly defined energy flows and material cycles on land, water and air.
Ecological adaptation : Different types of ecosystems exist with varying ranges of environmental conditions where various plants and animal species have got adapted through evolution.
Types of Ecosystems
1. Terrestrial ecosystem : Can be further classified into ‘biomes’. A biome can be defined as the total assemblage of plant and animal species interacting within specific conditions. These include rainfall, temperature, humidity and soil conditions. Some of the major biomes of the world are: forest, grassland, desert and tundra biomes.
2. Aquatic ecosystems : Can be classed as marine and freshwater ecosystems. Marine ecosystem includes the oceans, estuaries and coral reefs. Freshwater ecosystem includes lakes, ponds, streams, marshes and bogs.
Structure and Functions of Ecosystems
The structure of an ecosystem involves a description of the available plant and animal species. From a structural point of view, all ecosystems consist of Abiotic and biotic Factors.
(I). Abiotic factors include rainfall, temperature, sunlight, atmospheric humidity, soil conditions, inorganic substances (carbon dioxide, water, nitrogen, calcium, phosphorus potassium, etc.).
(II). Biotic factors include the producers, the consumers (primary, secondary, tertiary) and the decomposers. Producers include all the green plants, which manufacture their own food through photosynthesis.
The primary consumers include herbivorous animals like deer, goats, mice and all plant eating animals. The carnivores include all the flesh-eating animals like snakes, tigers and lions. Certain carnivores that feed also on carnivores are known as top carnivores like hawks and mongooses.
Decomposers are those that feed on dead organisms (for example, scavengers like vultures and crows), and further breaking down of the dead matter by other decomposing agents like bacteria and various microorganisms
Two types of food chains are recognised :
(i). Grazing food: Chain, the first level starts with plants as producers and ends with carnivores as consumers at the last level, with the herbivores being at the intermediate level. There is a loss of energy at each level which may be through respiration, excretion or decomposition.
(ii). Detritus food: The levels involved in a food- chain range between three to five and energy is lost at each level. Chain is based on autotrophs energy capture initiated by grazing animals and involves the decomposition or breaking down of organic wastes and dead matter derived from the grazing food-chain.
Types Of Biomes
There are five major biomes - forest, desert, grassland, aquatic and altitudinal biomes.
Biomes
1. Forest
Subtypes
A. Tropical
1. Equatorial
2. Deciduous
B . Temperate
C . Boreal
Regions
A1. 10° N-S
A2 . 10° - 25° N-S
B. Eastern North America, N.E. Asia, Western and Central Europe.
C. Broad belt of Eurasia and North America, parts of Siberia, Alaska, Canada and Scandinavia
Climatic characteristics
A1. Temp. 20-25°C, evenly distributed
A2. Temp. 25-30°C, Rainfall, average ann. 1,000mm, seasonal
B. Temp. 20-30° C, Rainfall evenly distributed 750-1,500mm, Well defined seasons and distinct winter.
C. Short moist moderately warm summers and long cold dry winter; very low temperatures. Precipitation mostly snowfall 400 -1,000mm
Soil
A1. Acidic, poor in Nutrients.
A2. Rich in Nutrients.
B. Fertile, enriched with decaying litter.
C. Acidic and poor in nutrients, thin soil cover
Flora and fauna
A1. Multi-layered canopy tall and large trees.
A2. Less dense, trees of medium height; Many varieties coexist. Insects, bats, birds and mammals are common species in both.
B . Moderately dense broad leaved trees. With less diversity of plant species. Oak, Beach, Maple etc. are some common species. Squirrels, rabbits, skunks, birds, black bears, mountain lions etc.
C. Evergreen conifers like pine, fur and spruce etc. Wood peckers, hawks, bears, wolves, deer, hares and bats are common animals.
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Biomes
Desert
Subtypes
A. Hot and Dry Desert
B. Semi arid desert
C. Coastal desert
D. Cold desert
Regions
A. Sahara, Kalahari, Marusthali, Rub-el-Khali
B. Marginal areas of hot deserts.
C. Atacama
D . Tundra climatic regions.
Climatic characteristics
A. Temp. 20 - 45°C.
B. 21 - 38°C.
C. 15 - 35°C.
D. 2 - 25°C
A-D Rainfall is less than 50 mm
Soil
Rich in nutrients with little or no organic matter
Flora and fauna
A-C. Scanty vegetation; few large mammals, insects, reptiles and birds.
D. Rabbits, rats, antelopes and ground squirrels.
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Biomes
Grassland
Subtypes
A. Tropical Savannah
B. Temperate Steppe
Regions
A. Large areas of Africa, Australia, South America and India.
B. Parts of Eurasia and North America.
Climatic characteristics
A. Warm hot climates, Rainfall 500-1,250mm
B. Hot summers and cold winter. Rainfall 500 - 900 mm
Soil
A. Porous with thin layer of humus.
B. Thin flocculated soil, rich in bases
Flora and fauna
A. Grasses; trees and large shrubs absent; giraffes zebras, buffalos, leopards, hyenas, elephants, mice, moles, snakes and worms etc., are common Animals.
B. Grasses; occasional trees such as cottonwoods, oaks and willows; gazelles, zebras, rhinoceros, wild horses, lions, varieties of birds, worms, snakes etc., are common animals.
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Biomes
Aquatic
Subtypes
A . Freshwater
B . Marine
Regions
A . Lakes, streams, rivers and Wetlands.
B. Oceans, coral reefs, lagoons and estuaries
Climatic characteristics
A-B Temperatures vary widely with cooler air temperatures and high humidity.
Soil
A. Water, swamps and marshes
B. Water, tidal swamps and marshes
Flora and fauna
Algal and other aquatic and marine plant communities with varieties of water dwelling animals.
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Biomes
Altitudinal
Subtypes
______
Regions
Slopes of high mountain ranges like the Himalayas, the Andes and the Rockies.
Climatic characteristics
Temperature and precipitation vary depending upon latitudinal zone.
Soil
Re goliath over slopes
Flora and fauna
Deciduous to tundra vegetation varying according to altitude.
Cycles
1. Biogeochemical Cycle
The sun is the basic source of energy on which all life depends. Out of the total solar insolation that reaches the earth’s surface, only a very small fraction (0.1%) is fixed in photosynthesis
The cycle starts by absorbing the chemical elements by the organism and is returned to the air, water and soil through decomposition. These cycles are largely energised by solar insolation.
These cyclic movements of chemical elements of the biosphere between the organism and the environment are referred to as biogeochemical cycles.
There are two types of biogeochemical cycles: the gaseous and the sedimentary cycle.
(i). In the gaseous cycle, the main reservoir of nutrients is the atmosphere and the ocean.
(ii).In the sedimentary cycle, the main reservoir is the soil and the sedimentary and other rocks of the earth’s crust.
2. Water Cycle
All living organisms, the atmosphere and the lithosphere maintain between them a circulation of water in solid, liquid or gaseous form referred to as the water or hydrologic cycle.
3. Carbon Cycle
Carbon basic elements of all living organisms. The carbon cycle is mainly the conversion of carbon dioxide. This conversion is initiated by the fixation of carbon dioxide from the atmosphere through photosynthesis.
Such conversion results in the production of carbohydrate, glucose that may be converted to other organic compounds such as sucrose, starch, cellulose, etc. Here, some of the carbohydrates are utilised directly by the plant itself.
During this process, more carbon dioxide is generated and is released through its leaves or roots during the day. The remaining carbohydrates not being utilised by the plant become part of the plant tissue.
Plant tissues are either being eaten by the herbivorous animals or get decomposed by the micro- organisms.
The herbivores convert some of the consumed carbohydrates into carbon dioxide for release into the air through respiration.
The microorganisms decompose the remaining carbohydrates after the animal dies. The carbohydrates that are decomposed by the microorganisms then get oxidised into carbon dioxide and are returned into the atmosphere.
4. Oxygen Cycle
Oxygen is the main by-product of photosynthesis. It is involved in the oxidation of carbohydrates with the release of energy, carbon dioxide and water.
The cycling of oxygen is a highly complex process. Oxygen occurs in a number of chemical forms and combinations. It combines with nitrogen to form nitrates and with many other minerals and elements to form various oxides such as the iron oxide, aluminium oxide and others.
Much of oxygen is produced from the decomposition of water molecules by sunlight during photosynthesis and is released in the atmosphere through transpiration and respiration process of plants.
5. Nitrogen Cycle
Nitrogen is a major constituent of the atmosphere comprising about 79% of the atmospheric gases.
It is also an essential constituent of different organic compounds such as the amino acids, nucleic acids, proteins, vitamins and pigments.
Only a few types of organisms like certain species of soil bacteria and blue green algae are capable of utilising it directly in its gaseous form.
Generally, nitrogen is usable only after it is fixed. 90% of fixed nitrogen is biological.
The principal source of free nitrogen is the action of soil microorganisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil.
Nitrogen can also be fixed in the atmosphere by lightning and cosmic radiation.
Dead plants and animals, excretion of nitrogenous wastes are converted into nitrites by the action of bacteria present in the soil. Some bacteria can even convert nitrites into nitrates that can be used again by green plants.
There are still other types of bacteria capable of converting nitrates into free nitrogen, a process known as denitrification.
6. Other Mineral Cycles
Phosphorus, sulphur, calcium and potassium. They usually occur as salts dissolved in soil water or lakes, streams and seas. Mineral salts come directly from the earth’s crust by weathering where the soluble salts enter the water cycle, eventually reaching the sea.
Other salts are returned to the earth’s surface through sedimentation, and after weathering, they again enter the cycle.
All living organisms fulfil their mineral requirements from mineral solutions in their environments.
Other animals receive their mineral needs from the plants and animals they consume.
After the death of living organisms, the minerals are returned to the soil and water through decomposition and flow.
Ecological Balance
Ecological balance is a state of dynamic equilibrium within a community of organisms in a habitat or ecosystem. It can happen when the diversity of the living organisms remains relatively stable.
Gradual changes do take place but that happens only through natural succession.
It can also be explained as a stable balance in the numbers of each species in an ecosystem. This occurs through competition and cooperation between different organisms where the population remains stable.
This balance is brought about by the fact that certain species compete with one another determined by the environment in which they grow.
This balance is also attained by species dependent on others for their food and sustenance. Clearing of forest brings changes; change is due to competition and called as succession. Such accounts are encountered in vast grasslands where the herbivorous animals (deer, zebras, buffaloes, etc.) are found in plenty.
Ecological balance can be disturbed by new species, natural hazard and human interference. This can lead to calamities like landslides, disease and floods. Knowledge and understanding of factors provides a base for protection and conservation of ecosystem.
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