HOMEOSTASIS OVERVIEW o Homeostasis tendency of all living

HOMEOSTASIS OVERVIEW o Homeostasis – tendency of all living things to maintain a constant internal environment

HOMEOSTASIS OVERVIEW Conformers vs. Regulators o REGULATORS – maintain internal environment substantially different from external environment o CONFORMERS – internal environment nearly identical to external environment

HOMEOSTASIS OVERVIEW REALITY? o Regulating and conforming are extremes o Most animals typically conform in some environments and regulate in others because environmental conditions vary over time o Cost of regulation can outweigh benefits of homeostasis n Regulation is energy expensive

ENDOTHERMY VS. ECTOTHERMY o ENDOTHERM – warmed mostly from the heat of metabolism n Mammals, birds, some fish, a few reptiles, numerous insect species o ECTOTHERM – warmed mostly from external sources n Most invertebrates, fish, amphibians, reptiles (not birds)

ENDOTHERMY VS. ECTOTHERMY o ENDOTHERM n High metabolic rate n Large amount of heat generated o ECTOTHERM n Low metabolic rate n Little heat generated

ENDOTHERMY VS. ECTOTHERMY o ENDOTHERM n Capable of sustained, intense activity n High level of aerobic metabolism possible due to high, stable body temperature n Supported by other biochemical & physiological adaptations, i. e. elaborate circulatory and respiratory systems o ECTOTHERM n Capable of intense bursts of activity n Metabolic rate to low to provide energy for extended periods of intense activity

ENDOTHERMY VS. ECTOTHERMY o ENDOTHERM n Can survive in a broader range of environments o Terrestrial temperatures generally fluctuate over a greater range of temperatures than aquatic environments; water conducts heat 50 -100 X better than air o ECTOTHERM n Live only where their adaptations help maintain an internal temperature appropriate for chemical reactions.

ENDOTHERMY VS. ECTOTHERMY o ENDOTHERM n Need large amount of food to maintain high metabolic rate – a serious disadvantage when food is limited o ECTOTHERM n Need less food that similar size endotherm in the same environment n Ex. At 20 o. C, at rest, similar size o Human needs 1300 -1800 kcal/day o American alligator needs only 60 kcal/day

Vocabulary Issues o Warm-blooded and cold-blooded are imprecise and misleading o “cold blooded”? ? A basking lizard may have a higher body temperature than some mammals o “constant”? ? In some aquatic environments the body temperature of fish and invertebrates varies less than that of humans

Vocabulary Issues: 2 STRATEGIES (ADAPTATIONS) FOR MANAGING HEAT BUDGET ECTOTHERMIC “externally heated”/ POIKILOTHERMIC “of variable temperature” n body temperature determined by heat gained from or lost to environment (ectothermy) n body temperature allowed to vary with environmental temperature - at rest their temperature is nearly same as that of environment (poikilothermy) n do not produce enough metabolic heat to have much affect on body temperature

Vocabulary Issues: 2 STRATEGIES (ADAPTATIONS) FOR MANAGING HEAT BUDGET ENDOTHERMIC “internally heated”/ HOMEOTHERMIC “of uniform temperature” n bodies warmed by heat generated by metabolism (endothermy) n maintain high, stable internal temperature regardless of environmental temperature (homeothermy) n can vary metabolic rate in response to changes in environmental temperatures

Figure 44. 4 The relationship between body temperature and ambient (environmental) temperature in an ectotherm and an endotherm

Are all endotherms homeotherms? Are all ectotherms poikilotherms? o There is no fixed relationship! o Some marine fish (ectotherms) live in waters with very stable temperatures so their temperature varies less than many endotherms. o Some endotherms like hummingbirds experience wide variations in internal temperatures as they enter states of inactivity.

QUESTION 11: 20 g reptile vs 20 g mammal o Reptile has lower respiration rate. Reptile is ectothermic – rate of respiration related to environmental temperatures o Mammal is endothermic – internal temperature independent of environmental temperature.

QUESTION 12: mammal at 10 o. C and at 21 o. C o At 10 o. C mammal is losing heat into colder environment. o Mammals can increase respiration rate to produce more heat to maintain body temperature o mammal at 10 o. C would have a higher rate of cellular respiration thus consume oxygen at a higher rate