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I have a rough idea: endotherms need more food to keep their temperature stable whilst ectotherms use less of their food in respiration.

  • but that's just me parroting the textbook I don't really understand it.

Could someone help out? Thank you.

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    $\begingroup$ That's basically right. $\endgroup$
    – ChrKoenig
    Commented Feb 8, 2015 at 15:25

3 Answers 3

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Endotherms also called warm blooded animals have the ability to regulate their body temperature by themselves.

  1. If the endotherms are in a cold place their body increases the metabolism and generates more heat. This will compensate for the cold outside.

  2. In a hot region the body metabolism is tuned down (this is not as efficient as the adaptation to cold region - as the metabolism can't be turned down below a certain limit - this will result in death) a little and heat generation is somewhat reduced. The second and more efficient mechanism is the heat dissipation by sweating and through skin (directly).

Ectotherms on the other hand, do not have efficient temperature regulation systems.

  1. In warm regions when the temperature is high, the ectotherms seek shade and low-temperature areas to prevent over-heating

  2. In cool regions they seek sunlight and expose themselves to the sunlight for warmth. For the same reason, they can also search out and stay near fire pits, campfires etc...

So when we calculate the energy demands, the ectotherms need more energy as they regulate their own metabolisms to match the need.

The increase in need for energy in hot condition maybe due to:

  1. The extra-processes that are regulated like sweating, increased peripheral vasodilation - thereby increasing circulatory rate (increased work for heart)
  2. This thermo-regulation inturn affects other processes and systems like electrolyte and water balance, excretory system, endocrine system, thrist, etc...

During the cold season increased metabolism itself is the main cause for increased need for energy.

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    $\begingroup$ At least in cold temperature elevated demand of food fulfils the law of conservation of energy. To raise the body core temperature requires energy, which has to be taken from anywhere. Apart from depots of fat or glycogen the premier source of energy is food. Homeothermy also has advantages, however, since homeothermic animals are able to move, hunt etc. in conditions, where poikilothermic animals are massively restricted by torpor or staying at shady places. $\endgroup$
    – jwdietrich
    Commented Feb 8, 2015 at 18:00
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An ectotherm is an [cold-blooded] organism which is dependent on external sources of body heat. They do not need to regularly consume food to warm their bodies. As a result, they can subsist on lower metabolic rates and varying internal temperatures (poikilothermy). However, physical activity is restricted to certain hours (night) and or habitats; ectotherms tend to be rapidly exhausted.

An endotherm is an [warm-blooded] organism which is dependent on the interal generation of heat. To maintain consistent temperatures (homeothermy), they must regularly consume food for metabolism. This also allows for a greater work capacity than ectotherms. Physical activity is not limited to certain hours and or habitats.

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Here's a (hopefully) simple answer:

Ectotherms eat, and convert most of the energy in their food into new biomass (i.e. producing more tissue and growing). Between meals their metabolism (all the reactions in all their cells) slows right down so they don't use much energy.

Endotherms eat, and convert most of the energy in their food into generating heat, converting a small amount into new biomass. So they need to consume more, as generating heat all the time takes loads of energy, even when resting between meals!

Hope that helps, along with the previous answers.

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  • $\begingroup$ Ben - can you add some links to your answer or other references so others who are less familiar follow your answer? It would help strengthen your answer significantly - thanks for your contributions. $\endgroup$
    – Vance L Albaugh
    Commented Sep 13, 2016 at 18:53

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