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Lecture 4

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BIOL 1902
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Lecture 4Environmental Stress How do plants and animals cope with extreme temperaturesSubzero temperatures and animals Problem with subzero temperatures Water turns to ice and expands Animals are full of water so this can kill them Ectothermsmost of their heat is derived from the outside environment Examples turtles frogs snakes insects spiders Endothermscontrol their own body temperature able to generate heat internally Examples birds and mammals Main solutions to the cold problem1Escape the cold either by leavingmigration or by going dormant2For animals that stay active and deal with the subzero temperatures Dress for the occasion iMammalsstay warn by growing more hair for the winter guard hairs however hair is more complex than that Mammals have dense underfur that traps body heat iiBirdsgrow bulkier feathers contour feathers on the outside and down feathers underneath Chickadees very effective in trapping body heatAnimals can also add extra layers on the inside Two types of fats iSubcutaneous fat for insulationwarmth iiBrown fat is a high efficiency fuel mammals not birds Birds have subcutaneous fat but the difference is that birds dont maintain that layer all the time for insulation they burn it for heat and they produce that heat but shivering Shivering is important means of thermogenesis Breast muscle of the bird is fat biggest muscle the flight muscles are being worked when they are shivering For birds it is a natural way of generating body heat good for birds bad for mammals Colours can also be used for warmth In certain conditions black would be better if an animal is outside and it is dead calm When wind is combined with cold there is windchill means that your body heat is coming out of your skin and the wind is taking that away from you so your body has to replace more heat to replace the quicker loss of heat If it is windy black is not as good because black will release faster than white will Animals with white fur or feathers have hollow spaces inside of them that help trap the warm air Pale colours retain body heat better snowy owlarctic fox Glogers Rule the farther north you go generally the paler the animals tend to be Snowshoe Hares gain 27 in the coats insulation value by being white What shape is best for the cold Allens Rule The shorter the extremities the better Arctic fox short ears snout and legs but long tail with dense fur
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