thermoregulation in ectotherms Flashcards
endotherms and ectotherms
Organisms are constantly heating up and cooling down as a result of their surroundings. These changes depend on a number of physical processes. These include:
• Exothermic chemical reactions.
• Latent heat of evaporation - objects cool down as water evaporates from a surface.
• Radiation - the transmission of electromagnetic waves to and from the air, water, or ground.
-Convection - the heating and cooling by currents of air or water, warm air or water rises and cooler air or water sinks setting up convection currents around an organism.
•Conduction - heating as a result of the collision of molecules. Air is not a good conductor of heat but the ground and water are.
In many cases, the balance between heating and cooling determines the core temperature of the organism. Animals can be classified as ectotherms or endotherms depending on how they maintain and control their body temperature.
ectotherms
Most animals are ectotherms and use their surroundings to warm their bodies (ectotherm literally means ‘outside heat’). Their core body temperature is heavily dependent on their environment. Ectotherms include all the invertebrate animals, along with fish, amphibians, and reptiles.
Many ectotherms living in water do not need to thermoregulate.
The high heat capacity of water means that the temperature of their environment does not change much. Ectotherms that live on land have a much bigger problem with temperature regulation. The temperature of the air can vary dramatically both between seasons and even over a 24-hour period from the middle of the day to the end of the night. As a result ectotherms have evolved a range of strategies that enable them to cool down or warm up.
endotherms
Mammals and birds are endotherms. They rely on their metabolic processes to warm up and they usually maintain a very stable core body temperature regardless of the temperature of the environment (endotherm literally means
‘inside heat’). They have adaptations which enable them to maintain their body temperature and to take advantage of warmth from the environment.
As a result, endotherms survive in a wide range of environments. Keeping warm in cold conditions and cooling down in hot conditions are both active processes. The metabolic rate of endotherms is around five times higher than ectotherms, so they need to consume more food to meet their metabolic needs than ectotherms of a similar size.
temperature regulation in ectotherms-behavioural responses
Ectotherms cannot control their body temperature using their metabolism-however, they have evolved a range of behavioural responses that enable them to overcome the limitations imposed by the temperature of their surroundings.
Ectotherms display a number of behaviours which increase or reduce the radiation they absorb from the Sun. Sometimes they need to warm up to reach a temperature at which their metabolic reactions happen fast enough for them to be active. They may bask in the Sun, orientate their bodies so that the maximum surface area is exposed to the Sun, and even extend areas of their body to increase the surface area exposed to the Sun. For example, lizards often bask for long periods of time to get warm enough to move fast and hunt their prey, and insects such as locusts and butterflies orientate themselves for maximum exposure to the Sun and spread their wings to increase the available surface area to get warm enough to fly.
Ectotherms can increase their body temperature through conduction by pressing their bodies against the warm ground. They also get warmer as a result of exothermic metabolic reactions. Galapagos iguanas will contract their muscles and vibrate increasing cellular metabolism to raise their body temperature. Similarly, moths and butterflies may vibrate their wings to warm their muscles before they take flight.
Ectotherms sometimes need to cool down to prevent their core temperature reaching a point where enzymes begin to denature. To cool down, many of the warming processes are reversed. Ectotherms shelter from the sun by seeking shade, hiding in cracks in rocks, or even digging burrows. They will press their bodies against cool, shady earth or stones, or move into available water or mud. They orientate their bodies so that the minimum surface area is exposed to the sun, and minimise their movements to reduce the metabolic heat generated.
physiological responses to warming
Much of the thermoregulation by ectotherms is the result of behavioural responses but some of them have physiological responses as well. Dark colours absorb more radiation than light colours.
Lizards living in colder climates tend to be darker coloured than lizards living in hotter countries so that they get warmer. Some ectotherms also alter their heart rate to increase or decrease the metabolic rate and sometimes to affect the warming or cooling across the body surfaces.
Ectotherms are always more vulnerable to fluctuations in the environment than endotherms. However, by using a variety of behavioural and physiological strategies many of them can maintain relatively stable core temperatures. They need less food than endotherms as they use less energy regulating their temperatures, and so they can survive in some very difficult habitats where food is in short supply.
physiological responses to warming
Much of the thermoregulation by ectotherms is the result of behavioural responses but some of them have physiological responses as well. Dark colours absorb more radiation than light colours.
Lizards living in colder climates tend to be darker coloured than lizards living in hotter countries so that they get warmer. Some ectotherms also alter their heart rate to increase or decrease the metabolic rate and sometimes to affect the warming or cooling across the body surfaces.
Ectotherms are always more vulnerable to fluctuations in the environment than endotherms. However, by using a variety of behavioural and physiological strategies many of them can maintain relatively stable core temperatures. They need less food than endotherms as they use less energy regulating their temperatures, and so they can survive in some very difficult habitats where food is in short supply.
