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Name: Gregory
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Question:
IS it better for organisms to be warm blooded or cold blooded, and why?



Replies:
Correct terminaology:
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.

Steve Sample


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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