Cold-blooded organisms (called poikilotherms - "of varying temperature"^[1]) maintain their body temperatures in ways different from mammals and birds. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. The term is now outdated in scientific contexts. Cold-blooded creatures were, initially, presumed to be incapable of maintaining their body temperatures at all. Cold-blooded animals are now called ectotherms, a term which signifies that their heat (therm) comes from outside (ecto) of them; the term cold-blooded is misleading.

Advances in the study of how creatures maintain their internal temperatures (termed: Thermophysiology) have shown that many of the earlier notions of what the terms "warm-blooded" and "cold-blooded" mean, were far from accurate (see below: Definitions). Thermoregulation is the ability of an Organism to keep its body temperature within certain boundaries even when temperature surrounding is very different In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant Today scientists realize that body temperature types are not a simple matter of black and white. Most creatures fit more in line with a graded spectrum from one extreme (cold-blooded) to another (warm-blooded). In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant

Definitions

Thermal image of a cold-blooded tarantula on a warm-blooded human hand

Cold-bloodedness generally refers to three separate areas of thermoregulation. Tarantula is the common name for a group of hairy and often very large Spiders belonging to the family Theraphosidae, of which approximately 900 species Thermoregulation is the ability of an Organism to keep its body temperature within certain boundaries even when temperature surrounding is very different

1. Ectothermy - This refers to creatures that control body temperature through external means , such as the sun, or flowing air/water. For more on this, see below.
2. Poikilothermy - This refers to creatures whose internal temperatures vary, often matching the ambient temperature of the immediate environment (Greek: "poikilos" ποικίλος = "varied," "thermia" θερμία = "heat"). (In medicine, loss of normal thermoregulation in humans is referred to as poikilothermia. )
3. Bradymetabolism - This term refers to creatures with a high active metabolism and a considerably slower resting metabolism (Greek: "brady" βραδύ = "slow," "metabolia" μεταβολία = "to change"). Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Bradymetabolic animals can often undergo dramatic changes in metabolic speed, according to food availability and temperature. Many bradymetabolic creatures in deserts and in areas that experience extreme winters are capable of "shutting down" their metabolisms to approach near-death states, until favourable conditions return (see hibernation and estivation). For the ability of certain operating systems see Hibernate (OS feature Hibernation is a state of inactivity and metabolic depression Estivation or aestivation (from Latin aestas, summer also known as "summer sleep" is a state of Dormancy somewhat similar

Few creatures actually fit all three of the above criteria. Most animals use a combination of these three aspects of thermophysiology, along with their counterparts (endothermy, homeothermy & tachymetabolism) to create a broad spectrum of body temperature types. In Thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs Energy in the form of Heat. In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant Most of the time, creatures that use any one of the previously defined aspects are usually pigeon-holed into the term cold-blooded.

Physiologists also coined the term heterothermy for creatures that exhibit a unique case of poikilothermy. Heterothermic (from Greek hetero = "other" thermy = "heat

Types of temperature control

Examples of temperature control include:

• Snakes and lizards sunning themselves on rocks. A snake is an elongate Reptile of the suborder Serpentes Like all reptiles snakes are covered in scales. Lizards are a large and widespread group of Reptiles of the order Squamata, with nearly 5000 species and ranging across all continents except
• Fish changing depths in the water column to find a suitable temperature. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two
• Desert animals burrowing beneath the sand during the day. A desert is a Landscape or region that receives very little precipitation.
• Insects that warm their flight muscles by vibrating them in place. Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described
• Dilating or constricting peripheral blood vessels to adapt more or less quickly to the ambient temperature. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body

Many homeothermic, or warm-blooded, animals also make use of these techniques at times. In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant For example, all animals are at risk of hypothermia on cold days, and most homeothermic animals can shiver to get warmer.

Poikilotherms often have more complex metabolisms than homeotherms (homopathics). For an important chemical reaction, poikilotherms may have four to ten enzyme systems that operate at different temperatures. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins As a result, poikilotherms often have larger, more complex genomes than homeotherms in the same ecological niche. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby In Ecology, a niche (pronounced nich nēsh or nish A shorthand definition of niche is how an organism makes a living Frogs are a notable example of this effect. This article is about the block cipher algorithm For the ultrafast laser pulse measurement technique see Frequency-resolved optical gating.

Because their metabolism is so variable, poikilothermic animals do not easily support complex, high-energy organ systems such as brains or wings. Some of the most complex adaptations known involve poikilotherms with such organ systems. One example is the swimming muscles of Tuna, which are warmed by a heat exchanger. Tuna, are several Species of ocean-dwelling Fish in the family Scombridae, mostly in the genus Thunnus. A heat exchanger is a device built for efficient Heat transfer from one medium to another whether the media are separated by a solid wall so that they never mix or the media In general, poikilothermic animals do not use their metabolisms to heat or cool themselves. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. For the same body weight poikilotherms need ⅓ to 1/10 of the energy of homeotherms. They therefore eat only ⅓ to 1/10 of the food needed by homeothermic animals.

Some larger poikilotherms, by virtue of their substantial volume to surface area ratio, are able to maintain relatively high body temperatures and high metabolic rates. The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically Surface area is the measure of how much exposed Area an object has Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. This phenomenon, known as gigantothermy (inertial homeothermy), has been observed in sea turtles and great white sharks, and was most likely present in many dinosaurs and ancient sea reptiles (such as ichthyosaurs and plesiosaurs). Gigantothermy is a phenomenon with significance in Biology and Paleontology, whereby large bulky ectothermic (cold-blooded animals are more easily able Sea turtles ( Superfamily Chelonioidea) are Turtles found in all the world's oceans except the Arctic Ocean. The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform Ichthyosaurs ( Greek for 'fish lizard' - ιχθυς / ichthyos meaning 'fish' and σαυρος / sauros meaning 'lizard' were giant Plesiosaurs (ˈpliːziəˌsɔɹ ( Greek: plesios/πλησιος meaning 'near' or 'close to' and sauros/σαυρος meaning For example, some species of sea turtles are homeothermic some of the time. They float on the surface of the ocean to absorb heat and then, after submerging again, stay homeothermic for periods of time because of their sheer size. During long periods of time underwater their body temperature may decrease, depending on the temperature of the surrounding water. Their body temperature may also decrease when they float on the surface of the ocean at night, depending on the surrounding temperature.

However, large dinosaurs were probably not poikilotherms, but homeotherms (homeothermic all the time) due to the overwhelming mass of their bodies.

Ecological niches

It is comparatively easy for a poikilotherm to accumulate enough energy to reproduce. Poikilotherms in the same ecological niche often have much shorter lifetimes than homeotherms: weeks rather than years.

This energy difference also means that a given niche of a given ecology can support three to ten times the number of poikilothermic animals as homeothermic animals. However, in a given niche, homeotherms often drive poikilothermic competitors to extinction because homeotherms can gather food for a greater fraction of each day.

Poikilotherms succeed in some niches, such as islands, or distinct bioregions (such as the small bioregions of the Amazon basin). An ecoregion ( ecological region) sometimes called a bioregion, is an ecologically and geographically defined area smaller than a "realm" or " These often do not have enough food to support a viable breeding population of homeothermic animals. In these niches, poikilotherms such as large lizards, crabs and frogs supplant homeotherms such as birds and mammals.

References

See also

• Warm-blooded for organisms that fall in between both categories. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 475 - Basiliscus becomes Byzantine Emperor, with a coronation ceremony in the Hebdomon palace in Constantinople In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant

External links

• Dinosauria.com: What is Warm-bloodedness anyway?
• The Reptipage: What is cold-blooded?