Coldblooded/warmblooded. Turns out that these are lousy terms. Wrong and simplistic.
Interested in 2 aspects of regulation
Where energy comes from to warm body
Ectothermy – Outside Heat
Sit in sun, or in some other way absorb heat from environment
Endothermy – Inside heat
Convert food they heat into energy through biochemical reactions
ATP powers all bodily mechanics, and in the process, generate heat – but endotherms do this to a greater
extent than ectotherms. Biochemical processes are the same, just at a much lower level. There is a cost to
this, though. Endotherms do more, but it’s not for free.
Second differentiating factor: endotherms are producing all of this heat, but they have to keep it in their
bodies, need some covering, some insulation, so most, particularly the small ones, have some kind of
insulation (fur, feathers, some insects like bees). When they get big enough, problem lost – produce so
much energy that aren’t loosing it rapidly enough, and sometimes have opposite problem, too much heat,
By contrast, ectotherms sit in warm places. Bask in sun. Behavioral thermoregulation – ectotherms can
achieve very high temperatures.
Lizard can warm body temp above air temperature. Or, can move in shade to keep temperature lower as air
Animal can lose heat in a number of ways – evaporation, convection (heat exchange with wind)
Other factors: some can change colors a little bit, from pale colors to dark to impact rate at which it
increases temperature. Or, change orientation, turn into sun when wants to warm up, or perpendicular to
sun when don’t want to warm, and can also pant
They can also alter where the blood flows in their body.
How variable an animal’s temperature is over the course of a day and a year
Poikilotherm – “Varying temperature”
Homiotherm – “Same Temperature”
Most endotherms keep body temperature more or less the same. But this is not true of all endotherms –
bears hibernating allow temp to drop very low, so bears are poikilotherm in seasonal context. Many small
endotherms living in cool places will allow body temps to drop at night – bats and birds, go into torpor.
However, even behavioral thermoregulators are poikilotherms even if body temperature is relatively stable
throughout the day. But there is another way: If take a small lizard, double it in size, area increases at a much slower rate than volume. If double it in size,
surface area increases 4 times, but volume up 8 times. Heat exchange goes through surface but heating
volume – so ability to get heat in or radiate it is cut in half.
What is the biological significance of body temperature?
1. Most biological molecules function best at high temperatures
Another example, most species run faster at higher temperatures
2. Biological function enhanced when organisms have a stable body temperature.
Cost of endothermy/homiothermy? We have to eat a LOT more food! A mouse has to eat 10x as much as
Even within ectotherms, though, there are costs and beneftis to poikilothermy and homothermy. Maintaining
high constant body temperature is that is gained through behavior means – the need to move is a cost
because more open to predators, opportunity cost needed for hunting, energy cost of moving.
When costs are low and thermoregulation is easy, lizards will do it, when costs are high (in forest) they just
For the most part, amphibians do not engage in behavioral thermoregulation. This is because they cant
stay in sun for too long because have to balance water. Also, they don’t really gain heat in sun because
they evaporate, and body temp stays the same. So amphibians can often sit in the sun I places where