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Unformatted text preview: Lecture 4 – How Animals Survive in Subzero Temperatures PROBLEM: BELOW FREEZING = SUBZERO TEMPERATURES MAKE WATER FREEZE – IT TURNS TO ICE IF WATER IN CELLS OF LIVING ANIMAL, IT FREEZES AND EXPANDS AND CELLS BURST AND ORGANISM DIES. (SO SAD!) TWO DIFFERENT WAYS ANIMALS GENERATE THEIR INTERNAL TEMPERATURES (thermoregulation): • ENDOTHERMS (warm-blooded) GENERATE HEAT INTERNALLY... control body temperature by regulating their metabolic rates (increasing their metabolic rate as the surrounding temperature begins to decrease). Includes muscle shivering, fat burning, and panting. • EXAMPLES: BIRDS (contour feather on outside, then down layer) AND MAMMALS • ECTOTHERMS (cold-blooded) : LARGELY CONTROLLED BY THE TEMPERATURE OF THE EXTERNAL ENVIRONMENT...term which signifies that their heat (therm) comes from outside (ecto) of them...creatures that control body temperature different from most mammals and birds, through external means, such as the sun, or flowing air/water. They go below the frost line , where it is guaranteed not to be frozen (freeze avoidance ). • Example: American toads (amphibians) – dig down in fall, about 1 meter or so, going underground to avoid freezing temperatures • EXAMPLES: FROGS, SNAKES ( go underground also in large numbers together) , TURTLES, INSECTS , AND SPIDERS • Site of many of these is called hibernacula ( plur .)/or hybernaculum ( sing. ) - a form of dormancy • Most of these animals make a natural antifreeze – glycerol is the key to survival for many ectotherms , especially in the insect world. They add this to the water inside their cells, and the internal water temperature can be as cold as -50 degrees Celsius. This is called a cryoprotectant , because it protects their lives ( cryo-). • Prior to becoming dormant, they flush or void their system out, to disallow crystals of ice from forming around other particles. To enhance the effects of the antifreeze, they also tend to choose a very sheltered site to hibernate within, somewhere beneath leaves, below the snow, under bark of a log, where they are less exposed to really cold conditions, beneath the ground level ADAPTATIONS TWO MAIN SOLUTIONS TO THE COLD PROBLEM: • ESCAPE THE COLD EITHER BY RUNNING AWAY (LEAVING = MIGRATING) OR BY GOING DORMANT • STAY ACTIVE AND DEAL WITH THE SUBZERO TEMPERATURES . • Farther North we go, the paler animals become, shape becomes more rotund, extremities may be smaller, smaller surface area (such as birds putting head under wings or animal protecting head with tail) • Chickadees go through torpid period (one of few birds). Torpor is a (short term) for the state of decreased physiological activity in an animal, usually characterized by a reduced body temperature and rate of metabolism. Animals that go through torpor include birds (even tiny hummingbirds) and some small mammals such as bats. During the active part of their day, these animals maintain normal body temperature and activity levels, but their body temperature drops during a portion of the day usually at night to conserve energy. •...
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This note was uploaded on 08/13/2008 for the course BIOL 1902 taught by Professor Runtz during the Winter '08 term at Carleton CA.
- Winter '08