Evolution of Homeothermy
Vocabulary
Poikilotherms – “cold-blooded” animals
Body temp tracks environmental temp
Homeotherms – “warm-blooded” animals
Heat production/loss is controlled: Set Point
Poikilotherm
Homeotherm
Body
Temperature
Set Point
Environmental Temperature
More Vocabulary
Endotherm
* Uses metabolism to generate much heat
* Uses body “wall” to retard heat loss
Ectotherm
* Uses ambient sources of heat (small metabolic output)
* Poor insulation of “wall” (sensible?)
Q: What animals are endothermic homeotherms?
Q: What animals are ectothermic poikilotherms??
C
O
R
E
S
34-35
40-41
37-38
Basal Metabolic Rates
Temptation: Assume homeothermy is a superior way
of life.
Fact:
1,500,000 named animal species
- 9000 bird species
- 4500 mammals
1,486,500 poikilotherms (99.1 %)
Cost-Benefit Analysis ??
Benefits of being an ectothermic poikilotherms
• No worries about heat production
I=P+E+R
• Poikilotherms can be small
Smallest Poikilotherm??
Smallest Homeotherm??
ciliate
Least shrew
Bee
hummingbird
SA:VOL
Little animal
Big animal
Costs of being an ectothermic poikilotherms
* Limited by cold
* Latitude
* Elevation
* Season
STRATEGY:
BEHAVIORALLY THERMOREGULATE
STRATEGY: BEHAVIORALLY
THERMOREGULATE
ARCHITECTURE
Heat-trapping Silk Web
Not regulating body temperature …
but not freezing in a freezing environment
Overwintering
Forms
Tolerate Freezing
CLAIM
• Ectotherms have low capacity for aerobic metabolism ...
limited ability for sustained vigorous activity.
TRUE??
Migrating butterflies and salmon
CLAIM
• Ectotherms have low capacity for aerobic metabolism ...
Limited to smallish body sizes
TRUE??
Poikilotherm?
Homeotherm?
BULK HOMEOTHERM ??
Endothermic Homeotherms
Fluxes
Endothermic Homeotherms
Heat production = Heat lost
Loss is through the body wall
Body “Wall” Adaptations of Endotherms
Mammalian Walls
Arctic Fox
WALRUS
Skin
Blubber
Body Wall Thickness ??
Core ~ 37o C
Core ~ 37o C
*
*
CCE !!
PAW
Small and Homeothermic??
STRATEGY: HIBERNATION
Arctic Ground Squirrel
Metabolic Savings While Hibernating
STRATEGY: MIGRATION
STRATEGY: LIVE UNDERGROUND
Poikilothermic
Mammal !!
Naked
Mole
Rat
CCE !!
New Vocabulary Terms
Spatial Heterothermy … EXAMPLE: Tuna
Temporal Heterothermy …. EXAMPLE: Hummingbird
Groundhogs