The 5 Differences Between Ectothermic And Endothermic Animals

Animals are, regardless of gender 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 beings have more control over their own internal environment than others, with the associated costs that this entails.

It is estimated that, on Earth, there are 8.7 million species of living beings, although to date just over 2 million of them have been discovered. With such overwhelming diversity, we only need to look at a few examples to realize that, in the natural world, the condition of human beings 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 Key differences between endotherms and ectotherms

What are the differences between endothermy and ectothermy in animals?

The terms “endothermy” and “ectothermy” refer to the ability of a living being (or lack thereof) to modulate its body heat. In any case, in nature not everything is black or white: as you will discover in later lines, neither endotherm animals are immune to temperature changes, nor are ectotherms incapable of generating heat at all. Let’s see the clearest differences between both biological strategies.

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

We start by laying the foundation. 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 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 putting yourself in the sun to receive energy or in the shade to slow your 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.

The exceptions that call into question 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 species of ophidian Python bivittatus significantly increases your body temperature through spasmodic contractions of your muscles It does this when it is wrapped around its eggs, in order to transmit heat and protect them from the elements. Sea turtles of the species Dermochelys coriacea also maintain a much higher internal temperature than the marine aquatic environment, as they generate heat with their constant muscle 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 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 series 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 ectotherms Mitochondria are the energy generators of organisms, since cellular respiration occurs here, or in other words, the conversion of organic matter into energy.

As homeotherms have more mitochondria, they can generate more metabolic heat, enough to not constantly depend on environmental impositions. In any case, this energy does not come from anywhere: it is obtained from the diet, specifically from organic compounds such as carbohydrates, fats and proteins. Because the homeotherm’s metabolism is much more demanding, it must consume more food in larger quantities compared to the ectotherm.

3. Endotherms can hibernate, while ectotherms cannot.

At an informative level, the term “hibernation” is usually 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 able to hibernate

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 drops and, consequently, the metabolism drops to its possible minimum.

In this state, the animal is deeply asleep and does not get up until the adverse conditions end Hibernating mammals must eat a lot 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 reptile that mists is not completely asleep, as it must activate itself to drink water and respond to stimuli, for example. Additionally, a lizard may eat during its brumation, although it may not search for prey as hard as before. In other words, “metabolic depression” is less drastic in brumation.

4. Endotherms are less dependent on external temperature

The biggest evolutionary disadvantage of ectothermy is the dependence on the external environment. As a general rule, reptiles, fish, and amphibians are clumsier in the mornings and at night , since it is colder (due to the lack of sunlight) and, therefore, your metabolism drops irremediably. As an advantage associated with this state, at least they need much less food to maintain their body, so this exchange “pays off for them.”

Endotherms are less dependent on the environment to maintain their body temperature, but this does not mean that they are immune to environmental variations Without going any further, when a human being is exposed to -30 °C, he freezes and dies in less than a minute.

The heat dissipation and generation mechanisms are very effective in endotherms, but not infallible: below 30 °C body temperature, a person loses consciousness, tension decreases drastically and their heart beats imperceptibly. As you can imagine, in these cases the outcome without treatment is death.

5. Ectotherms have lower metabolic rates

We have already demonstrated this reality at multiple points throughout 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 life strategy of the sit and wait: They wait for prey to pass in front of them, since chasing it is too energetically costly.

Furthermore, 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 overall, and only run for short 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 the rules self-imposed by humans are broken much more than it seems. The determinism of our thinking has made us believe for decades that ectotherms are incapable of generating heat, but this is not the case. From insects to reptiles, there are many examples of supposedly ectothermic animals that thermoregulate, even if not constantly.