Explanation

Organism, which present in tropical regions are called megatherms. Temperature gradient over the earth’s surface is 6.4-$6.5℃$ per 1000m altitude or $10{^\circ}$ latitude. Therefore, there is lowering of mean temperature from equator to poles. Tropical, sub-tropical, temperate and arctic organisms living in these zones are respectively called Megatherms, mesotherms, microtherms and hekistotherms [table] Zone | Latitude | Mean Annual Temperature | Winter | Vegetation ; Tropical Sub-tropical Temperature Arctic and Antarctic | $0{^\circ} - 20{^\circ}$ $20{^\circ} - 40{^\circ}$ $40{^\circ} - 60{^\circ}$ $60 - 80{^\circ}$ | Above-$24℃$ $17{^\circ} - 24℃$ $7{^\circ} - 17℃$ Below-$7℃$ | Nil Mild winter Winter with occasional show Severe prolonged winter with abundant show | Tropical forests Sub-tropical deciduous forest Mixed coniferous forest Arctic forest [/table]