Homeothermic vs Heterothermic Animals
IS it better for organisms to be warm blooded or cold
blooded, and why?
homeothermic is warm blooded
heterothermic is cold blooded.
Each has its advantages and disadvantages.
Warm blooded takes energy to keep the blood warm (constant body temperature) and these organisms must eat a great deal and all the time! However, they do not depend as much on
the external environmental temperature for their activities, can work day
and night, and change easily from water to land to air. Winter may or may
not be a problem.
Cold blooded animals do not have to eat as often [a great deal less than
warm blooded animals] and rely upon the surrounding temperature to
determine their level of activity. Cold weather is a problem, but most
adapt to levels of inactivity and bury themselves to avoid freezing, if
they live in that type of environment. Tropical cold blooded animals are
not often restricted.
Well, I suppose if you're Scarlett O'Hara or Yurii Zhivago it's
better to be warm-blooded, and if you're Columbo or Sam Spade it's
better to be cold-blooded. . .
But I suppose you are talking about lower animals.
The answer is that it depends on your environment. Most of a
warm-blooded animal's energy output goes into maintaining a constant
body temperature. You may use up 1500 calories a day of food energy,
and perhaps 800 to 1000 of that is just to keep your temp at 98.6 F.
A cold-blooded animal, which does not attempt to keep its interior
temperature constant, would use much less fuel. Hence, when food is
scarce and external heat plentiful -- in the desert, for example --
cold-blooded animals might do better. That may be why some of the
principal inhabitants of deserts are tortoises, snakes, and lizards.
On the other hand, if you keep your body temp constant, you can be
sure that your body chemistry will work reliably around the clock, and
you can range widely, look for food in difficult places, and take
active measures against predators whatever the circumstances. Hence
when food is plentiful or external heat is lacking, being warm-blooded
may be good, as in the tropics or the polar regions.
That's all just a guess, however, and it can't be that accurate, as
every environment today sports some cold-blooded and some warm-blooded
animals. Deserts have kangaroo rats in addition to lizards, and polar
seas have fish as well as polar bears. It is possible, therefore,
that neither cold- nor warm-bloodedness has any generic advantage, and
the fact that both exist on the planet is mere biological accident.
Dr. C. Grayce
Both have advantages and disadvantages, which is why both kinds of animals
are still around. If one were clearly superior, the other would not be
able to compete, and would be extinct.
To be cold-blooded has the disadvantage that the speeds of chemical (and
biochemical) reactions change with temperature. The general rule is that
they speed up as the temperature gets higher, but they don't all speed up
to the same degree. A "cold-blooded" animal has to deal with the fact that
it will slow down when the weather is colder, and that it biochemical
reactions will not always be in perfect synchrony. So they must have some
mechanism to deal with this. The advantage of being cold-blooded is that
it does not require much energy. If you feed your snake every month or so,
that's about right. I wouldn't recommend that schedule for your dog.
Teh advantages and disadvantages of being warm-blooded are the opposite
side of the coin. Warm-blooded animals maintain their body temperatures to
the optimum temperatures for their bodily processes, so they don't get
thrown out of whack when the weather changes. The disadvantage is that
this is very expensive. Warm-blooded animals living in cold places need
lots of insulation, otherwise they couldn't possibly generate enough heat
to maintain their temperatures. Cold-blooded animals are much more
efficient that way. Of course, cold-bloded animals can freeze more easily.
But the warm-blooded animals need to get lots more food ( = energy) to stay
alive that cold-blooded animals do.
These conditions have certain other consequences. Since heat is lost
through the surface, and since small things have proportionally more
surface area than large things, warm-blooded animals can't maintain their
body temperatures if they get too small. So, they have to be above a
certain size. The smallest warm-blooded animals (for mammals, it's the
shrew; for birds, it's the hummingbird) have to be extremely active to
maintain their temperatures. Below that size, you pretty much have to be
cold-blooded. So, insects can get much smaller than birds.
Richard Barrans Jr., Ph.D
There are advantages and disadvantages to both lifestyles. A cold blooded
animal doesn't have to spend its energy on keeping a constant body
temperature. However, it can only move in short bursts before it needs to
gain more energy. Since it takes on the temperature of its surroundings,
when it is cool or cold, it can't move as fast and or must hibernate. But on
the other hand, their metabolism slows and they don't need to eat as often.
A warm blooded animal can live in almost any environment because it can keep
a constant body temperature even in very warm or very cold climates. They
also can expend energy (as long as its available) relatively constantly. But
they also need a constant supply of energy and must eat on a regular basis.
Each animal is adapted to its own environment or it would be extinct, so one
lifestyle isn't necessarily better than any other.
k. Van Hoeck
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Update: June 2012