Ecological Energetics III full slide set

Ecological Energetics III full slide set - Ecological...

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Unformatted text preview: Ecological Energetics III Ecological Energetics of thermoregulatory strategy Endothermy vs. Ectothermy Homeothermy vs. Poikilothermy Heat exchange and organismal heat budgets MR = a(Mass)b “a” varies “b” is constant; ~0.75 Metabolic Rate And Thermoregulatory Strategy Thermoregulatory Terminology Thermoregulatory Non-Scientific Cold blooded Warm blooded Regarding the Stability of Body Temperature Poikilothermic Homeothermic Regarding the Predominant Source of Heat Ectothermic Endothermic Endothermic Endothermic Homeotherms Ectothermic Poikilotherms Endothermic Endothermic Homeotherms Ectothermic Poikilotherms Controlling for body size and body temperature, metabolic rate is about 10X higher in endotherms than in ectotherms. A Conceptual Energy Budget Endotherms use metabolic heat production to regulate their body temperatures. They have to allocate a large fraction of ingested energy for heat production. The requirement for energy to produce heat is traded off against other possible uses of ingested energy. Ectotherms can use more of their ingested energy for growth and reproduction than endotherms. Ectotherms live on a smaller total energy budget than endotherms. In any ecosystem, ectotherms outnumber endotherms at the same trophic level. Homeothermy versus Poikilothermy Endothermy versus Ectothermy Endothermic homeothermy Thermal physiology is inseparable from ecological energetics. Balanced Heat Budget energy in + energy generated = energy out + energy stored “Energy in” is dominant in ectotherms. “Energy generated” is dominant in endotherms. The sum total of heat exchange between an organism and its environment determines the body temperature of the organism. Balanced Heat Budget heat in + heat generated = heat out + heat stored “Heat in” is dominant in ectotherms. “Heat generated” is dominant in endotherms. The sum total of heat exchange between an organism and its environment determines the body temperature of the organism. ● Heat + C + S + R + LE Heat Balance M + s = 0 +G ● Heat + C + S + R + LE Heat Balance M + s = 0 +G Don’t worry about the details of this equation. It’s complicated, and that’s the point. Later, I will show you a simple way to determine the heat load encountered by an animal in its environment. Heat Balance Heat ● S + R + LE + G + C + M + s = 0 S = solar radiation R = thermal radiation to and from substrate L = latent heat of evaporation ● E = rate of evaporation G = conduction to and from the ground C = convectional exchange with the air M = metabolic heat production s = storage (or loss) of heat Heat Balance Heat ● S + R + LE + G + C + M + s = 0 Rearrange. ● (S + Ri) + M = (G + C + Re + LE) + s Translate into plain language. heat in + heat generated = heat out + heat stored Heat Balance Heat ● S + R + LE + G + C + M + s = 0 ● (S + Ri) + M = (G + C + Re + LE) + s Think about what this means. Endotherms: M normally >> (S + Ri) ● M = G + C + Re + LE At constant body temperature, heat generated = heat lost Heat Balance Heat ● S + R + LE + G + C + M + s = 0 ● (S + Ri) + M = (G + C + Re + LE) + s Think about what this means. Ectotherms: M is usually negligible. ● S + Ri = G + C + Re + LE Heat Balance Heat In general, the distinction between endothermy and ectothermy depends on the relative magnitudes of M versus other terms in the heat balance equation. In extreme cases, heat balance in endotherms can be dominated by heat gain from solar radiation, leading to storage of heat and an increase in Tb. This phenomenon has been noted in diurnal rodents, including antelope ground squirrels and cape ground squirrels. TEMPERATURE AND ENERGY METABOLISM ENERGY TEMPERATURE AND METABOLISM: ECTOTHERMS Thermal Relations in Ectotherms As Tb increases, energy cost of maintenance (SMR) increases. ENDOTHERMS: IN THE COLD ENDOTHERMS: Thermal Neutral Zone Range of ambient environmental temperatures within which an endotherm can thermoregulate at constant Tb with no energetic cost simply by varying its rate of heat transfer to the environment. Upper and lower critical temperatures: environmental temperatures at the upper and lower ends of the TNZ. Above and below TNZ, thermoregulation requires an energy cost above BMR. Above the TNZ, thermoregulation usually requires evaporative heat loss. ENDOTHERMS: IN THE COLD ENDOTHERMS: Thermal Conductance (C) specifies net rate of heat transfer of an organism per degree centigrade difference between Tb and Ta. At constant Tb in cool environment: heat gain = heat production = heat loss Heat production = metabolic rate (MR) Heat loss = MR = C(Tb-Ta) Rate of Heat Loss Wearing heavy jackets, the guys on the right have lower thermal conductance than the nude guy in the water. Energy Requirement ENDOTHERMS: IN THE COLD ENDOTHERMS: Thermal Neutral Zone Range of ambient environmental temperatures within which there is no energetic cost to varying thermal conductance. Heat loss = MR = C(Tb-Ta) Within the thermal neutral zone, MR is constant. Tb is constant; Ta varies Thus, (Tb - Ta), which is the gradient that drives heat exchange, becomes larger as Ta decreases. Within the thermal neutral zone, thermal conductance decreases as Ta decreases. ENDOTHERMS: IN THE COLD ENDOTHERMS: Thermal Neutral Zone Range of ambient environmental temperatures within which there is no energetic cost to varying thermal conductance. Heat loss = MR = C(Tb-Ta) Lower critical temperature is the temperature at which thermal conductance is at its minimum and insulation, the inverse of conductance, is at its maximum. At temperatures below Tlc, thermal conductance cannot be reduced, and an animal must increase its metabolic heat production to maintain a constant Tb. ENDOTHERMS: IN THE COLD ENDOTHERMS: Thermal conductance is usually lower in Thermal larger animals and at higher latitudes. larger Endothermic Homeothermy Summer versus winter acclimatization. Costs and Benefits Costs Of Endothermy Costs: Endothermy is Energetically Expensive Endothermic Endothermic Homeotherms The “fire of life” burns 10X “hotter” in endotherms than in ectotherms. Ectothermic Poikilotherms Regional Heterothermy in a Duck To conserve heat and thus to conserve energy, ducks restrict blood flow to their feet in the cold. At and below 0 C, intermittent pulses of blood flow are used to prevent freezing and tissue damage to the feet . Temporal Heterothermy Hibernation, Estivation, and Torpor allow animals to escape energetic costs of endothermy. Hibernation (long), torpor (short), and estivation (summer) are distinguished by differences in duration and season Golden-mantled ground squirrel ...
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This note was uploaded on 08/18/2011 for the course ECOLOGY 351 taught by Professor Staff during the Spring '11 term at Rutgers.

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