FORS2355 Vertebrate Natural History
Final Lecture Exam
Lectures 20-27
Lecture 20 -- Thermoregulation: Ectothermy vs Endothermy (November 3, 2021)
1. Thermoregulation -- regulation of body temperature and is essential for most tetrapods; some climates are too hot; some are too cold. 2. Ectotherms -- animals that gain heat from external sources in order to raise body temperature. Ancestral form; lower metabolic rate. Example -- non-amniotes like turtles, lizards, and crocodilians. 3. Endotherms -- animals that gain heat from metabolic processes in order to raise body temperature. Derived form; higher metabolic rate. Example -- birds and mammals 4. Not mutually exclusive -- for example, pythons heating eggs and roadrunners basking in the sun 5. Thermoregulation by semiaquatic and terrestrial ectotherms -- amphibians, turtles, lizards, snakes, and crocodilians. a. Heat gained by the sun: directly or reflected. i. Conduction ii. Convection b. Heat lost via: i. Conduction ii. Convention ii. Evaporation iv. Breathing 6. Thermoregulation is not a passive activity (constantly regulating). Behavioral control of heat loss, gain yields complex scenarios. Movement, posture, blood flow, evaporative cooling, etc. 7. Thermoregulation by aquatic, semiaquatic, and terrestrial endotherms -- generally same sources of heat exchange as ectotherms, but much higher metabolic heat production. 8. Specific Dynamic Action -- increased heat production associated with digesting food. a. 7-10 times higher than similar-sized ectotherm. b. During metabolism, breakdown of chemical bonds releases energy, heat
taking molecules from diet and a phosphate group -> ADP (powers the cell and generates energy and heat) 9. Mechanisms of Thermoregulation in Endotherms a. Zone of Tolerance -- range of temps over which body temp. can be kept stable. i. Above ZOT, cannot dissipate heat -> die ii. Below ZOT, heat loss > heat production -> die b. Thermoneutral Zone i. Range of temps. Where metabolic rate is standard ii. Regulate by altering rate of heat loss (change in posture, etc.) c. Lower Critical Temperature i. Point where heat production must be increased. ii. Metabolism and/or shivering
d. Lower Lethal Temperature i. Metabolic heat production maximized, but still not able to elevate body temp. ii. As body temp drops, chemical reactions sensitive to temp -> metabolism slows, positive feedback into hypothermia. e. Upper Critical Temperature i. Nonevaporative heat loss maximized ii. Must use evaporative cooling for further heat loss 1. Sweat, pant, etc. f. Upper Lethal Temperature i. Evaporative cooling maximized, but still not able to reduce body temperature. ii. As body temperature increases, positive feedback into hyperthermia. 10. Torpor -- short-term (nights or days) reduction of metabolic activity, body temperature. a. Spurred by air temp and food availability b. Example -- black-capped chickadees i. Daytime body temp: 40-42 degrees Celsius ii. Nighttime body temp: 29-30 degrees Celsius iii. Relies on less fat reserves to maintain lower body temp, if not bird would starve 11. Hibernation -- long-term (week to months) form of torpor. Spurred by photoperiod hormonal changes. Animal can maintain stable body temperature in cold environments via increase in heat production. a. Not practical -> need to i