The 5 differences between ectothermic and endothermic animals

These are the biological characteristics that help distinguish between ectotherms and endotherms.

Animals are, regardless of genus and species, open systems. As such, we are in constant relationship with the environment, obtaining energy in the form of organic matter, receiving and dissipating heat, exchanging gaseous substances with the environment and excreting potentially toxic compounds, among other things.

In the midst of this maelstrom of dynamism, some living things have more control over their own internal environment than others, with the associated costs that this entails.

It is estimated that there are 8.7 million species of living beings on Earth, although only a little more than 2 million have been discovered to date. With such overwhelming diversity, it is enough to look for just a few examples to realize that, in the natural world, the human condition is almost anecdotal. For example, the vast majority of living beings on the planet are incapable of regulating their internal temperature with metabolic mechanisms, although our species can do so.

Based on this premise (and perhaps with the intention of breaking some anthropocentric preconceptions), today we present to you the key differences between endothermic and ectothermic animals..

What are the differences between endothermy and ectothermy in animals?

The terms "endothermy" and "ectothermy" refer to a living being's ability (or lack thereof) to modulate its body heat. However, in nature not everything is black and white: as you will discover in later lines, neither endothermic animals are immune to temperature changes, nor ectotherms are unable to generate heat at all. Let's look at the clearest differences between the two biological strategies.

1. Endotherms generate metabolic heat to maintain their temperature, and ectotherms not so much.

Let's start by laying the groundwork. From a biological point of view an endothermic animal is one that is capable of producing heat in relevant quantities and, therefore, can maintain its internal temperature within a favorable range, regardless of the expected environmental conditions.regardless of the environmental conditions expected for the ecosystem in which it lives. The classic endotherms are mammals and birds.

On the other hand, an ectothermic animal is one that generates very little metabolic heat and therefore must regulate its internal temperature through behavioral activities, such as basking in the sun to receive energy or in the shade to lower its metabolic rate.such as basking in the sun to receive energy or in the shade to decrease its metabolic rate. Within this group are all invertebrates, fish, reptiles and amphibians. Since 53% of the world's fauna are insects, it can be assumed that the vast majority of living beings are ectotherms.

Exceptions that cast doubt on the rule

The reality is that this classification criterion, however widespread it may be, is reductionist. Ectothermic animals generate less metabolic heat than endotherms, but this does not mean that they completely lack thermogenesis mechanisms.

For example, the ophidian species Python bivittatus significantly increases its body temperature through spasmodic contractions of its musculature.. It does this when it is wrapped around its eggs, in order to transmit heat and protect them from the harsh environment. Sea turtles of the Dermochelys coriacea species also maintain a much higher internal temperature than the marine aquatic environment, as they generate heat with their constant muscular activity.

Even more interesting is to know that, in insects, moths and other flying invertebrates also defy this rule.. For example, while flying, they can direct the hemolymph from the thorax to the abdomen in a directional manner, in order to dissipate excess heat produced during movement. As you can see, some ectotherms can modulate their internal temperature, although it is often said that they cannot.

2. A different mitochondrial load

In any case, these generalizations do have a number of biological bases, although they are increasingly being questioned. For example, it has been shown that endotherms, on average, have more mitochondria per cell than do it has been shown that endotherms have, on average, more mitochondria per cell than ectotherms.. Mitochondria are the energy generators of organisms, since this is where cellular respiration takes place, i.e., the conversion of organic matter into energy.

Since homeotherms have more mitochondria, they can generate more metabolic heat, enough to avoid constant dependence on environmental constraints. However, this energy does not come from nowhere: it is obtained from the diet, specifically from organic compounds such as carbohydrates, fats and proteins. Because the metabolism of the homeotherm is much more demanding, it must consume more food in larger quantities compared to the ectotherm.

3. Endotherms can hibernate, while ectotherms cannot.

The term "hibernation" is often used to designate any decrease in the activity of a living being in the face of adverse conditions. Again, this generality is reductionist, since the reality is that ectotherms are not capable of hibernating in the face of adverse conditions. ectotherms are not capable of hibernation..

Hibernation is a state of minimal activity and metabolic depression, usually associated only with mammals (for birds it is more correct to use the term "torpor"). In this state of vital reserve, homeothermic animals reduce their internal temperature to a minimum, the heart rate decreases, the respiratory rate falls and, consequently, metabolism drops to its lowest possible levels.

In this state, the animal is deeply asleep and does not wake up until the adverse conditions are over.. Hibernating mammals must eat a great deal before this stage begins, as they must rely on their energy reserves in the form of adipose tissue to survive.

In the case of ectotherms (especially reptiles), the appropriate term is "brumation.". A mumbling reptile is not quite asleep, as it must become active to drink water and respond to stimuli, for example. Also, a lizard may eat during its haze, although it may not seek prey as vigorously as before. In other words, "metabolic depression" is less drastic in brumation.

4. Endotherms are less dependent on external temperature.

The major evolutionary disadvantage of ectothermy is the dependence on the external environment. As a general rule, reptiles, fish and amphibians are more torpid in the morning and at night.The advantage of this state is that they need much less food to maintain their organism, so this exchange "pays off" for them. As an advantage associated with this state, at least they need much less food to maintain their organism, so this exchange "pays off".

Endotherms are less dependent on the environment to maintain their body temperature, but this does not mean that they are immune to environmental variation.. For example, when a human being is exposed to -30 °C, it freezes and dies in less than a minute.

Heat dissipation and heat generation mechanisms are very effective in endotherms, but not infallible: below 30 °C body temperature, a person loses consciousness, Blood Pressure drops dramatically and his heart beats imperceptibly. As you can imagine, the untreated outcome in such cases is death.

5. Ectotherms have lower metabolic rates

We have already evidenced this reality at multiple points throughout the space, but it does not hurt to highlight it again. By "relying" on the environment to generate heat, ectotherms do not have to obtain as much energy in the form of organic matter and therefore tend to move less. Many predatory ectotherms follow the vital strategy of sit and waitThey wait for prey to pass them by, because chasing it is too energetically costly.

Moreover, if you think about a scorpion, a tarantula, a snake or a lizard, you will see that their life strategy is not even comparable to that of a bird. Ectotherms move less, are less active on a general level, and only run for small intervals of time when they feel in danger. In general, ectothermy results in a lower average activity rate (although there are exceptions).

Summary

As you can see, nature shows us, once again, that human self-imposed rules are broken much more than it seems. The determinism of our thinking has led us to believe for decades that ectotherms are incapable of generating heat, but this is not so. From insects to reptiles, there are many examples of supposedly ectothermic animals that thermoregulate, even if not constantly.