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Kim Dej

September 24 , 2012 Biology 2F03: Fundamental and Applied Ecology Water Essentials Water Essentials - gradients of water potential - terrestrial plants and animals balance water loss against water intake - marine and freshwater animals regulate water and salt diffusion depending on osmotic pressure - precipitation and its timing, and humidity define biomes in N. America The cicada puzzle - Sonoran desert: air temp = 46C (deadly) ground = 70C - Cicada singing actively, no predator actively, no predator active, sits on branches, in shade - How can it do it and not dry up or overheat Question - how much water is needed to saturate the air Physics again - water vapour in air can be measured either as grams of vapour per cubic meter of air or by the pressure exerted by the water vapour in air - measured by grams of H O in2air or pressure of H O vapo2r - recall water precipitation in ait circulation cells (when it cools) - evaporation cools (energy used) - H 2 is lost as vapour, must be replenished (drinking, absorption) - In 100% relative humidity, evaporation cannot take place and thus no cooling - To cool cicada must loose H O…b2t which water Cicada answers - the cicada can remain active when environmental temperatures exceed its lethal maximum because it uses evaporative cooling to reduce body temperature - evaporative cooling allows cicada to function in hot air; water gained from plant - it compensates for high evaporative water loss by high rate of drinking - the insect gets the water it needs for evaporative cooling by tapping into water that its host plant draws from deep below the surface of the ground - also varying humidity enables or disables H O r2gulation Some adaptations - desert beetles: lives on sand in very hot area, gets water on legs which he drinks, they gather for water on their bodies (morning) and let it drip to the moth - fog-laden winds blow across dune crest - moisture in fog condenses on abdomen - beetles gather on dune crests, face into the fog-laden wind, and tip their abdomen upward - grooves in the abdomen collect condensed water and direct it toward the head - beetles drink from the water droplet that collects around their mouths - whatever water there is in the sand gets picked up by the winds due to the drop in temperature from day to night Beetle water budget - water is important to be
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