Endotherm vs Ectotherm

Human beings can survive in a wide range of temperatures due to our body's ability to adapt. Other mammals, such as polar bears, lions, cheetahs, and dogs, are also able to survive temperature changes. Have you ever wondered why mammals can survive in high heat or extreme cold? This is because all mammals are endotherms. Being an endotherm means that your body can adapt to environmental changes in temperature to promote your survival. While mammals are endothermic species, most reptiles, amphibians, and insects are ectotherms. An ectothermic organism is unable to adapt to extreme changes in temperature due to its poor regulation of body temperature. Let's discuss this phenomenon in more detail.

Endotherm vs ectotherm metabolic rate

Animals need to obtain energy from the food they eat. The nutrients that animals take in through food are digested, absorbed, and converted into adenosine triphosphate (ATP) for cellular use.¹ Some animals are capable of storing energy for longer periods of time in the form of glycogen, while other animals store energy for even longer periods of time in the form of triglycerides within adipose tissue.

An animal's metabolic process produces waste energy in the form of heat. Endothermic and exothermic animals each respond to their environment; however, they differ in their ability to regulate body temperature.¹ If an animal is able to conserve heat and maintain a relatively constant body temperature, it is classified as a warm-blooded animal, also known as an endotherm. Endothermic organisms may use fur, fat, or feathers to keep themselves warm.¹ Animals that are not able to regulate their body temperatures are classified as ectothermic animals. These animals have an increased dependence on their environment to regulate their body temperatures.

Difference between ectotherm and endotherm

The more active an animal is, the more energy the animal needs to maintain their activity and the higher its BMR or SMR becomes. Because most animals are active, the average daily rate of energy consumption is about two to four times the animal's BMR or SMR. Humans have evolved into more sedentary animals, which is why we only have an average daily rate of 1.5 times our BMR. An endothermic animal's diet is determined by its BMR.¹ Let's look at herbivores, for example. The type of food a herbivore eats determines how many calories it will receive from that food. For example, if an animal eats a berry, it will have more energy than if it ate a piece of grass.

Animals are able to adapt to extreme temperatures or lack of food through torpor, which is a process that allows animals to decrease their activity and their metabolic rate in order for them to conserve their energy and survive. Torpor is used by animals for long periods of time, such as entering hibernation. During hibernation, an animal can maintain its body temperature using torpor.¹

If torpor is used During the extremely hot summer with little available water, it is known as estivation.¹ Desert animals use estivation to survive the boiling heat and lack of available water.

Ectothermic animals do not have body temperature regulators in place, which is why they depend on the consistency of temperature from their environment to maintain their body temperature.

Examples of endotherms and ectotherms

Examples of endotherms include mammals. Mammals such as humans, dogs, cats, birds, and rodents are capable of regulating their body temperature despite their climate. This allows these animals to survive in harsh temperatures. See Figure 1 for examples of endotherms.

Ectotherms, on the other hand, do not have internal regulations in place which is why they cannot regulate their body temperatures internally. Examples of ectothermic animals include reptiles, amphibians, and insects. Ectothermic animals may be flies, mosquitos, lizards, frogs, and snakes. These animals can only survive in climates that do not have drastic fluctuations in temperatures. See Figure 2 for some examples of ectotherms.

Ectotherm vs endotherm and energy

The amount of energy that an animal expends over a specific amount of time is called its metabolic rate. An animal's metabolic rate has various units of measurement, such as joules, calories, or kilocalories. If you walk down a grocery store aisle and pick up a box of cereal, you will see the number of calories you will receive if you eat a serving-size portion of the cereal. The calorie amount on the box is actually a measure of kilocalories. So if you see that you will receive 100 Calories per serving, you are actually receiving 100,000 calories. Usually, carbohydrates and proteins contain about 4.5 to 5 kcal per gram, while fat contains 9 kcal per gram.¹

An animal's metabolic rate is estimated as the basal metabolic rate (BMR) in endothermic animals that are at rest while an ectothermic animal's metabolic rate is measured as the standard metabolic rate (SMR).¹ It is estimated that human males have a BMR of 1600 to 1800 kcal per day while human females have a BMR of 1300 to 1500 kcal per day. This is significantly lower than an ectothermic animal's SMR. An alligator is estimated to only have an SMR of 60 kcal per day. This means that even with insulation, endothermic animals require a great deal of energy to maintain a constant body temperature.

Smaller endothermic animals have a greater surface area for their mass compared to larger animals which is why smaller animals lose body heat must faster than larger animals. As a result, smaller animals require more energy to maintain a constant internal temperature causing smaller animals to have a higher BMR than larger animals.

Endothermic vs ectothermic animals

As previously mentioned, endothermic animals are able to regulate their body temperature, while ectothermic animals cannot. So how exactly do endothermic animals accomplish this task? This is done via the hypothalamus. When an endothermic animal experiences a slight drop in temperature, the hypothalamus recognizes the temperature drop and makes an effort to restore the body's initial temperature. The hypothalamus is able to measure the body's temperature via the bloodstream and decides if the body is too hot or too cold.

If you are too hot, the hypothalamus triggers signals to cool you down. The nervous system can send signals to your skin to stimulate sweat glands to secrete sweat onto the surface of the skin. Sweat cools you down because your body uses its heat to evaporate the sweat, which reduces the amount of heat inside your body and lowers your body's internal temperature. Another way that your body reduces heat is vasodilation. When you are too hot, your blood vessels expand, allowing heat to escape your bloodstream.

If you are too cold, your vessels will constrict in order to keep your blood away from the surface of the skin. This concept is known as vasodilation. Another way that your body warms itself is by closing your pores. Closing your pore creates goosebumps that cause your hairs to stick up. Goosebumps not only keep warm air inside your skin, but it also traps a layer of air around the skin by making your hairs stick up. The methods that your body uses to regulate your body temperature are all examples of negative feedback mechanisms. See Figure 3 for a visual illustration of the body's efforts to regulate its temperature.