Reptiles can be found on almost every part of the planet. Antarctica is the only continent that does not have any native reptiles. There are also very few reptiles in the Arctic and the few that do live there are restricted to the outer edges of the Arctic Circle.
The absence of reptiles in these regions is due to the frigid temperatures. Reptiles can’t produce their own body heat and rely on the temperature around them to maintain body heat, this is known as thermoregulation.
Tropical and warm temperate climates are home to the most diverse range of reptiles. This is because these regions allow for optimal thermoregulation in reptiles. Reptiles have thrived in these climates for millions of years, allowing many subspecies to diverge from their ancient ancestors.
Why do Reptiles need to Thermoregulate?
Reptiles need to thermoregulate because they cannot maintain their body temperature by producing metabolic heat. They rely on external conditions to regulate the temperature of their bodies.
Mammals and birds are endothermic, meaning they maintain body temperature through metabolic heat while reptiles are ectothermic meaning they rely on environmental conditions to regulate their body temperature. It is important to note that reptiles do produce metabolic heat, but they produce it at a rate far too low to maintain their optimal body temperature.
Thermoregulation in reptiles is probably the most defining aspect of their lives and their activity levels and behaviour is dictated by this process. However, it does come with some benefits.
Mammals and birds have to eat frequently as they rely on metabolic heat to maintain their optimal body temperature. This is a taxing process with as much as 90% of energy consumption going to this process.
Reptiles on the other hand, consume most of their energy through growth and movement. This is the reason why snakes don’t need to feed very often. They generally don’t move around a lot and don’t produce metabolic heat, so the majority of their energy consumption goes to growth.
Reptiles thermoregulate using the heat from the sun to warm themselves. This can be done directly by basking in the sun or indirectly by soaking up the heat from a hot surface such as a rock. When a reptile needs to cool down, they can retreat into the shade.
How does a Reptile Thermoregulate?
Reptiles rely on external factors to regulate their body temperature. It is often perceived that reptiles have no control over their body temperature as they are cold blooded. This isn’t necessarily true. They are very much in control; they just rely on external factors to thermoregulate rather than an internal process.
For example, a snake can control how much heat it absorbs from the sun by coiling or straightening its body. A stretched-out snake has more surface area to absorb heat while a coiled snake will have less surface area exposed.
The three ways a reptile can gain or lose heat with its surrounding environment is through conduction, convection and radiation. We will explain these in more detail.
Conduction is a process where heat is transferred from one ‘material’ to another through direct contact when there is a difference in temperature between the two materials.
For example, if you were to place your hand on a hot cooker, the heat from the hob would be transferred to your hand, making it hot. Likewise, if you were to touch a metal railing on a cold morning, the heat from your hand would be transferred to the colder railing. This would take heat away from your warm hand, making it cold.
Belly heat is a perfect example of how reptiles thermoregulate using conduction. It is not uncommon in some places to see snakes basking on roads. The black road will attract heat from the sun. As a cool snake lies on the heated road, this heat will be transferred to the snake, raising their body temperature.
Convection is a process where a liquid or gas tends to rise as it is heated. This is because the material becomes less dense as it heats up causing it to rise while the colder denser material sinks due to gravity.
For Example, when a hot air balloon is heated, the air inside the balloon rises. This causes the balloon to rise as the density of the surrounding air is cooler. When the heat is removed, the air inside the balloon cools down and the balloon begins to descend.
An example of this would be an arboreal reptile in a farmhouse barn. As the air in the barn heats up it will rise while the colder air will remain at the bottom. The reptile can move higher or lower in the barn to make use of the temperature variations.
Electromagnetic radiation is emitted from a material as it heats up. This reaction occurs due to the motion of particles as the material is heated. This radiation is dispersed in all directions and travels directly to the material that absorbs it.
For example, if you stand near a fire you will feel the thermal radiation from the heated coals.
An example of radiation can be seen in an arboreal snake lying on branch. Radiated heat from the sun will warm the snake. If the branch is perched over a rock, the rock will also reflect some of this radiation. This reflected radiation can be absorbed by the snake to provide it with more heat.
Can Reptiles Produce Heat
Heat production in reptiles isn’t common. As discussed above, these animals rely on external factors to thermoregulate. However, there are exceptions and reptiles can in fact produce a small amount of heat.
Like mammals and birds, reptiles do in fact produce metabolic heat. The problem is they can’t produce enough of it to maintain their body temperature.
Some reptiles also produce heat by a process known as shivering thermogenesis. This is primarily seen in snakes incubating their eggs. While some species of snake are coiled around their eggs, they shiver to raise the temperature of the eggs. This is an insufficient process and it wouldn’t produce enough heat to allow the snake to maintain its body temperature internally.
What effect does Thermoregulation have on Reptiles
The most noticeable process in a reptile affected by thermoregulation is their behaviour. The need to thermoregulate dictates a reptile’s behaviour. While every species is different, each individual of a specific species will follow a similar routine when thermoregulating.
Many species in tropical regions will be most active at dusk and dawn while the temperature is at an optimal level for them. While they may not be nocturnal, many species are usually inactive during the heat of the day.
Other species Hibernate/Brumate during the harsher winter months. The temperature is too cold for them to function properly, so they retreat to a warm area to keep their body temperature up until the temperatures rise again.
‘Thermoregulation’ and ‘Cold Blooded’ are often terms people associate with the need for a reptile to gain heat from their environment. While this is true, it is probably even more important for a reptile to lose heat through thermoregulation. The majority of reptiles gain heat quicker than they lose it so if a reptile cannot cool down, their body temperatures can rise to dangerous levels.
Thermoregulation in reptiles affects a wide range of processes in the animal. A cold reptile moves slower than a warm one. This puts them at a distinct disadvantage when being hunted. It also affects internal processes such as digestion.
Another very important process affected by thermoregulation in reptiles is their ability to fight off disease. If a reptile cannot maintain correct body temperature, they could be more prone to illness.
Incorrect body temperature can also be critical in reptiles. If their body temperature varies outside the ‘safe range’, it can be lethal for the animal. This ‘lethal limit’ will vary between species. Some will be able to tolerate short fluctuations outside of this range while others will quickly perish.
It is unlikely this will happen naturally in the wild as these reptiles can adjust their behavior to thermoregulate. However, in captivity reptiles do not have the same ability and are at the mercy of the temperatures within their enclosure.