Ecological Energetics IV full slide set

Ecological Energetics IV full slide set - Ecological...

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Unformatted text preview: Ecological Energetics IV Ecological Temporal and regional heterothermy Benefits of endothermy Operative environmental temperature (Te) Ectothermic behavioral thermoregulation Endotherms in the heat Energetic cost of transport Regional and Temporal Heterothermy Heterothermy (5 slides) Regional Heterothermy in a Duck REVIEW FROM PREVIOUS LECTURE Ducks restrict blood flow to their feet in the cold. At and below 0 C, pulses of blood flow 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 To conserve energy, small mammals and birds relax their endothermic thermoregulation at night and in the cold. Diurnal variation in body temperature for the willow tit (a European chickadee (bird)) during the night at three different ambient temperatures. The degree of temporal heterothermy depends on species and environment. Temporal Heterothermy – Controlled Hypothermia In torpid and hibernating birds and mammals, body temperature is allowed to drop close to Ta, resulting in substantial energy savings. At 15 C, energy expenditure of a torpid bat is ~40-fold less than an active bat. Controlled Hypothermia Temperature regulation during torpor is not abandoned. Control of body temperature during torpor is relaxed and regulated in a manner that varies among species. The West Indian hummingbird readily enters torpor, but it will not allow its body temperature to drop below 18-20 C. Heat production is increased below Ta of 18 C. Benefits of Endothermy: Endothermy Indepence from from Ambient Environmental Temperature Temperature Benefits of Endothermy: Endothermy Activity Capacity And Behavioral Repertoire (5 slides) TREADMILL Maximum rate of aerobic metabolism sets a limit on maximum aerobic speed, thus highest level of sustainable activity. Maximum Maximum rate of O2 consumption Lactate Maximum aerobic speed Maximum rate of O2 consumption Endotherm ● VO2 TREADMILL Maximum aerobic speed is much higher in endotherms than in ectotherms. Endotherms are able to sustain much more vigorous levels of activity than ectotherms. Ectotherm Maximum Aerobic Speed Running Speed Maximum rate of O2 consumption Endotherm ● VO2 Sustainable activity is limited by the maximum rate of aerobic metabolism. Endotherms are more active than ectotherms. Endotherms have a broader “behavioral repertoire” than ectotherms. Ectotherm Maximum Aerobic Speed Running Speed Benefits: Maximum rate of O2 consumption Endotherm ● VO2 Endotherms have some independence from the thermal environment as well as a larger “behavioral repertoire” than ectotherms. This behavioral advantage is the basis for the “aerobic capacity hypothesis” for the evolution of endothermy. Ectotherm Maximum Aerobic Speed Running Speed Standard (or basal) and maximal rates of oxygen consumption scale on body mass with very similar mass exponents (~0.75). exponents VO l ma i ax M VO2, ml O2 / h ● ● 2 ● VO 2 l asa B or a rd d tan S Body Mass, g Maximal rates of oxygen Maximal consumption are about 10X greater than standard (or basal). basal). This is true of ectotherms, This ectotherms and it is true of endotherms. endotherms Thus, both standard and Thus, maximal rates of oxygen consumption are about 10X higher in endotherms than in endotherms than ectotherms. ectotherms Heat Exchange Heat And Operative Operative Environmental Temperature (Te) Temperature (5 slides) Heat Exchange Heat Between an Organism and its Environment is Complicated Heat Exchange Between an Heat Between Organism and its Environment Organism No single measurement of environmental No temperature adequately characterizes the thermal temperature environment of a terrestrial organism. environment Operative environmental temperature = Te Te provides a measure of the effective thermal provides environment of an organism. environment Te is the temperature of an isothermal black body in an identical conductive, convective, and radiative environment as that of the animal. Heat Exchange Between an Organism Heat Between and its Environment is Complicated is Ecological physiologists don’t usually try to measure usually all of the pathways of heat exchange. all Instead, they make models to serve as isothermal Instead, black bodies that are identical to the organisms they study in terms of conductive, convective, and radiative heat exchange. They put these models into the environment and let the models do the hard work. Voilà! let Voil Operative environmental temperature = Te Quantifying thermoregulation in nature Quantifying Quantifying thermoregulation in nature Quantifying Behavioral Thermoregulation in Ectotherms Behavioral Thermoregulation in Ectotherms Lizards and some other ectotherms use behavioral thermoregulation to achieve some level of control of their body temperature. Lizards shuttle between a heat source (usually sunlight) and a heat sink (shade) to absorb and release heat, thus maintaining their body temperature within a limited range of variation while they are active. The range of body temperatures achieved through behavioral thermoregulation is the range of “preferred body temperatures” of a species. Endotherms Endotherms in the Heat (7 slides) Heat Balance Heat Review from Previous Lecture 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. HEAT BALANCE HEAT Cape Ground Squirrel Kalahari Desert Heat balance on the desert surface is dominated by Solar Thermal Radiation. HEAT BALANCE HEAT Kalahari Desert Kalahari Border of South Africa and Botswana HEAT BALANCE Cape Ground Squirrel Tail Down Salivation ↑ Tb Tail Up HEAT BALANCE By shading itself with its tail, the cape ground squirrel By extends its daily activity period by about 5 hours. extends Cape Ground Squirrel Salivation ↑ Tb Behavior is almost always the first and most Behavior flexible line of defense. Most desert rodents are nocturnal – they behaviorally avoid the extreme heat of day. Cape ground squirrels are diurnal. They use their tails to shade themselves from the sun. By using the tail as a parasol, they increase their diurnal activity period by 5 hours. Energetics of Activity Energetics Cost of Transport (8 slides) Measurement of the maximal Measurement rate of oxygen consumption Measurement of the maximal Measurement rate of oxygen consumption TREADMILL Rate of Oxygen Consumption as a Function of Running Speed TREADMILL Rate of Oxygen Consumption as a Function of Running Speed Cost of Transport (energy cost per unit distance traveled) How much energy is required to transport a unit mass over a unit distance? Metabolic Rate ÷ Velocity (ml O2 / (g ● h)) ÷ (km / h) = ml O2 / (g ● km) Cost of transport predicts most economical speed for long-distance travel. Cost of Transport (or cost of locomotion) Insects Runners Fliers Swimming Fish Birds & Mammals Lizards, Birds & Mammals Cost of Transport Cost of locomotion depends mainly on mode of locomotion, not phylogenetic position. Runners Fliers Swimming Fish Cost of Transport Cost of locomotion depends mainly on mode of locomotion, not phylogenetic position. Runners Fliers Migratory Line Swimming Fish Most migratory species are found below the migratory line. Natural selection favors longdistance migration only when the cost of transport is relatively low. ...
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