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| Climatic Factors - Temperature |
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| Temperature is one of the essential and changeable environmental factors. It penetrates into every region of the biosphere and profoundly influences all forms of life by increasing or decreasing some of the vital activities of the organism. It is frequently a limiting factor for the growth or distribution of animals and plants. |
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| The vertical temperature gradient over earth's surface is called Lapse rate. |
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| Normal life activities go on smoothly at a specific temperature or at a specific range of temperatures. This is called the optimum temperature or the optimum range of temperature and it ranges from 5o C - 35o C. Some bacteria and cyanobacteria are known to survive even in hot springs (60o C - 90o C) or permafrost (-30o C to -50o C). But most of the organisms are killed by higher temperatures due to denaturation of enzymes while others are killed by very low temperatures due to freezing of body fluids. |
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| Pond System |
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| Environmental temperatures fluctuate both daily and seasonally. Temperature fluctuations are comparatively less in the aquatic environment than in the terrestrial environment. The increase in depth of aquatic medium often increases the temperature fluctuations. The minimum temperature in the sea is - 3o C, while in fresh water pond it never goes below 0o C. Deep lakes show thermal stratification. It has 3 strata. |
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| Thermal stratification occurs in lakes |
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| The epilimnion - temperatures upto 22oC during summer. |
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| The hypolimnion - temperatures between 5o C to 9o C. |
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| The metalimnion or thermocline which has rapid temperature changes between 9o C to 21o C. |
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| In the terrestrial environment the seasonal and daily fluctuations in temperature are varied and marked. The lowest temperature recorded for any land mass is - 70o C (Siberia). Higher temperatures may like wise go often to 85o C as in certain deserts at noon. |
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| The organisms which can tolerate very large fluctuations in temperature are called eurythermal organisms. For example Cyclops, toads, wall lizard, man. The organisms which can tolerate only a small variation in temperature are termed stenothermal organisms. For example fishes, snails and coral reefs. |
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| Pond (aquatic) ecosystem / habitat |
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| An animal's response to wide ranges in temperature is influenced by its physiology. All invertebrates, lower chordates, cyclostomes, fishes, amphibians and reptiles have no internal mechanism for thermal regulation, and their body temperatures vary with the surrounding environmental temperatures. Such animals are called cold blooded, ectothermic or poikilothermic organisms. |
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| Birds and mammals, in contrast, within limits maintain constant body temperatures regardless of temperature variations of air and water. Such animals are termed warm blooded, homeothermic or endothermic animals. |
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| Plants too can be divided into 3 categories on the basis of their heat tolerating capacity as |
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| Megatherms - occur in warm habitat. E.g., desert plants. |
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| Microtherm - occur in cold habitat. E.g., plants of high altitude. |
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| Mesotherms - habitat is neither very hot or very cold. E.g., aquatic plants. |
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| Hekistotherms include alpine vegetation which tolerate very low temperatures. |
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| Reproduction |
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| The flowering in plants in response to temperatures is called thermoperiodism. Many species of plants require very low temperature treatment for seed germination and flowering. This is known as vernalization. In animals, the maturation of gonads and activity of spermatogenic tissue are also temperature dependent. In some plants, low temperatures of winter stimulate the sprouting of dormant buds. |
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| Growth and Development |
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| Extremely low and high temperatures retard the growth and development of plants. Low temperatures are known to cause dessication, chilling injury and freezing injury to plants. |
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| Morphology |
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| Temperature is known to affect a number of morphological characters. |
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| Different living organisms tide over very low or very high temperature conditions differently. |
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| For E.g., |
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| i) Encystment |
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| It involves the formation of a hard and chitinous protective coat called cyst, around the body. It is commonly seen in amoeba, euglena. |
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| ii) Hibernation (winter sleep) |
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| Some animals undergo hibernation during which body temperature, metabolic rate and energy requirements are greatly reduced. |
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| iii) Aestivation (summer sleep) |
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| It is a period of dormancy during summer months so as to escape the scorching heat of the sun. It is commonly observed in lungfishes. Lady - bird, beetles, certain bugs and snails. In insects, aestivation is characterised by diapause (suspension of morphological growth and development). |
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| iv) Cyclomorphosis |
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| It is characterised by changes in body shape with seasonal temperature changes and has been observed in small aquatic creatures like cladocera and daphnia. |
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| v) Thermal Migration |
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| It involves the short or long journeys undertaken by animals so as to resist the temperature extremes. E.g., nocturnal activity of some desert animals, long trips migration by many birds. E.g., Arctic terns, Siberian crane, American golden plover, Bison and caribou. |
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| vi) Homeothermy |
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| This is achieved through evaporation of sweat in the mammals from their bodies during summer and through insulation action of fur (mammals) feathers (birds) and fat (subcutaneous blubber in whales and seals) during cold weather of winter months. |
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| Maintenance of relatively constant internal environment under under changing external environment is called Homeostasis. Maintaining a constant body temperature is advantages for warm-blooded animals or endotherms. These animals can remain active ever under cold condition by exhibiting different types of adaptations. |
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| vii) Behavior |
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| Temperature changes also induce certain behavioural patterns. |
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| Example: Thermotaxis (orientation towards heat). |
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| viii) Plants protect themselves from extremes of temperatures by development of thick cuticle, thick corky bark, dense hairy coat, thick leaves, mucilage, tannins, etc. |
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| ix) Some animals lay winter eggs to withstand the cold weather and continue the race while the adults die in cold weather. |
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| x) Shivering increases body temperature while perspiration and panting reduce body temperature. |
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