Difference Between Homeothermic and Poikilothermic

The key difference between homeothermic and poikilothermic is that homeothermic is a living organism that maintains a stable internal body temperature irrespective of external influence, while poikilothermic is a living organism whose body temperature varies considerably.

Thermoregulation is the ability of organisms to keep their body temperature within certain limits even when the temperature of the surrounding environment is different. Most animals need to maintain their core body temperature within a narrow range. Some organisms tend to use internally generated heat to maintain body temperature. Their body temperature stays steady regardless of the environment. On the other hand, some organisms depend on external heat sources and their body temperature changes with the environment. Therefore, depending on how stable an organism’s deep-body temperature is, we can divide organisms into two types: Homeothermic and poikilothermic.

CONTENTS

1. Overview and Key Difference
2. What is Homeothermic 
3. What is Poikilothermic
4. Similarities – Homeothermic and Poikilothermic
5. Homeothermic vs Poikilothermic in Tabular Form
6. Summary – Homeothermic vs Poikilothermic

What is Homeothermic?

Homeothermic is a living organism that maintains a stable internal body temperature regardless of external influence. This internal body temperature is usually higher than the immediate environment.  Homeothermy is one of the three types of thermoregulation in warm blooded animal species.

Homeothermic organisms are not necessarily endothermic in nature. This is because some homeothermic organisms may maintain a constant body temperature through behavioural mechanisms. Many reptiles, such as desert lizards, use this strategy. There are lots of advantages in the mechanism of homeothermy. The enzymes have a relatively narrow temperature range. Therefore, the activity of enzymes is optimal in this narrow temperature range. Temperatures outside this range can reduce the rate of a reaction due to the inefficiency of enzymes. Hence, homeothermic organisms with a fairly constant body temperature can specialize in enzymes that are efficient at that particular temperature. This is an enormous advantage. On the other hand, the disadvantage of homeothermy is that when many homeothermic animals use enzymes that are specialized for a narrow range of body temperatures, a condition like hypothermia may rapidly lead to a state of decreased physiological activity in these animals. Additionally, another disadvantage in homeothermy has high energy expenditure.

What is Poikilothermic?

Poikilothermic is a living organism whose body temperature varies considerably. Poikilothermic organisms have to survive and adapt to environmental stress. One of the most common stresses is temperature change. This can lead to alterations in membrane lipid order. It can also cause protein unfolding and denaturation at elevated temperatures.

Many terrestrial ectotherms are poikilothermic in nature. This term is often applied to animals and mostly to vertebrates though it can apply principally to all organisms. Poikilothermic animals include vertebrate animals such as fish, amphibians, and reptiles, as well as many invertebrate animals also are poikilothermic. The naked mole-rat and sloth are rare mammals that are poikilothermic. Furthermore, in medicine, the loss of normal thermoregulation in humans is referred to as “poikilothermia”. This is usually due to sedative and hypnotic drugs such as barbiturates, ethanol, and chloral hydrate.

What are the Similarities Between Homeothermic and Poikilothermic?

• These terms are based on internal body temperature.
• Both terms refer to animals.
• These groups maintain their core body temperature within a narrow range using different strategies.
• Both groups contain mammals and reptiles.

What is the Difference Between Homeothermic and Poikilothermic?

Homeothermic is a living organism that maintains a stable internal body temperature regardless of external influence while poikilothermic is a living organism whose body temperature varies considerably. So, this is the key difference between homeothermic and poikilothermic. Moreover, the temperature of habitat or environment has no effect on the body temperature of homeothermic, whereas the temperature of habitat or environment affects the body temperature of poikilothermic.

The following infographic presents the differences between homeothermic and poikilothermic in tabular form.

Summary – Homeothermic vs Poikilothermic

Body temperature is determined by the balance between heat production and heat loss. Organisms that maintain a fairly constant internal body temperature are called homeothermic. On the other hand, those that have variable internal body temperature are called poikilothermic. Thus, this is the summary of the difference between homeothermic and poikilothermic.

Reference:

1. “Thermoregulation in Homeothermic and Poikilothermic Organisms.” EPA, Environmental Protection Agency.
2. “Homeostatic Processes for Thermoregulation” Nature News, Nature Publishing Group.

Image Courtesy:

1. “Homeothermy-poikilothermy” By Petter Bøckman – Own work (Public Domain) via Commons Wikimedia
2. “Bgbo frosch ies” By – Ies assumed (based on copyright claims). – No machine-readable source provided. Own work assumed (CC BY-SA 3.0) via Commons Wikimedia