A poikilotherm is an animal Animals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also whose internal temperature varies along with that of the ambient environmental temperature. Most, but not all, ectotherms Ectothermic, from the Greek ectos, "outside" and therme, "heat," refers to organisms that control body temperature through external means. As a result, organisms are dependent on environmental heat sources and have relatively low metabolic rates. For example, many reptiles regulate their body temperature by basking in the sun are poikilothermic. The opposite of poikilothermy is homeothermy 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 level, regardless of the ambient temperature. This involves the ability to cool down or produce more body heat. Warm-blooded animals mainly control their body temperature by regulating their, referring to animals that maintain a constant body temperature.[1] The term is used as a more exact description of the vernacular "cold-blooded".
Contents |
Etymology
The term derives from Ancient Greek Ancient Greek is the historical stage in the development of the Greek language spanning the Archaic , Classical (c. 5th–4th centuries BC), and Hellenistic (c. 3rd century BC–6th century AD) periods of ancient Greece and the ancient world. It is predated in the 2nd millennium BC by Mycenaean Greek. Its Hellenistic phase is known as Koine (", poikilos (ποικίλος), meaning "varied"; and thermos (θερμός), meaning "warm".[2]
Physiology
For an important chemical reaction, poikilotherms may have four to ten enzyme Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their systems that operate at different temperatures. As a result, poikilotherms often have larger, more complex genomes In modern molecular biology, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA than homeotherms in the same ecological niche In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different school if the members of these schools utilize significantly different food resources and foraging methods. A shorthand. Frogs Frogs are amphibians in the order Anura , formerly referred to as Salientia (Latin salere (salio), "to jump"). Most frogs are characterized by long hind legs, a short body, webbed digits (fingers or toes), protruding eyes and the absence of a tail. Frogs are widely known as exceptional jumpers, and many of the anatomical characteristics are a notable example of this effect.
Because their metabolism is so variable, poikilothermic animals do not easily support complex, high-energy organ systems such as brains The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all. In vertebrates, the brain is located in the head, protected by the skull and close to the primary or wings A wing is a surface used to produce lift for flight through the air or another gaseous or fluid medium. The wing shape is usually an airfoil. The word originally referred only to the foremost limbs of birds, but has been extended to include the wings of insects , bats, pterosaurs, and aircraft.[citation needed] Poikilothermic animals do not use their metabolisms Metabolism is the set of chemical reactions that happen in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular to heat or cool themselves. For the same body weight, poikilotherms need half to 1/10 of the energy of homeotherms, and thus eat half to 1/10 of the biomass.
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.[citation needed]
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 An ecoregion , sometimes called a bioregion, is an ecologically and geographically defined area that is smaller than an ecozone and larger than an ecosystem. Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural communities and species. The biodiversity of flora, fauna (such as the small bioregions of the Amazon basin The Amazon Basin is the part of South America drained by the Amazon River and its tributaries. The basin is located mainly in Brazil, but also stretches into Peru and several other countries. The South American rain forest of the Amazon is the largest in the world, covering about 8,235,430 km2 with dense tropical forest. For centuries, this has). These often do not have enough food to support a viable breeding population of homeothermic animals. In these niches, poikilotherms such as large lizards Lizards are a very large and widespread group of squamate reptiles, with nearly 3,800 species, ranging across all continents except Antarctica as well as most oceanic island chains. The group, traditionally recognized as the suborder Lacertilia, is defined as all extant members of the Lepidosauria which are neither sphenodonts (i.e., Tuatara) nor, crabs Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax. They are generally covered with a thick exoskeleton, and armed with a single pair of chelae (claws). 6,793 species are known. Crabs are found in all of the and frogs Frogs are amphibians in the order Anura , formerly referred to as Salientia (Latin salere (salio), "to jump"). Most frogs are characterized by long hind legs, a short body, webbed digits (fingers or toes), protruding eyes and the absence of a tail. Frogs are widely known as exceptional jumpers, and many of the anatomical characteristics supplant homeotherms such as birds Birds are winged, bipedal, endothermic (warm-blooded), vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the 5 cm (2 in) Bee Hummingbird to the 3 m (10 ft) Ostrich. The and mammals Mammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.
In medicine
In medicine, loss of normal thermoregulation in humans is referred to as "poikilothermia". This is usually seen with sedative and hypnotic drugs. For example, barbiturates, ethanol, and chloral hydrate may precipitate this effect.
See also
- Ecothermy
- Ectotherm Ectothermic, from the Greek ectos, "outside" and therme, "heat," refers to organisms that control body temperature through external means. As a result, organisms are dependent on environmental heat sources and have relatively low metabolic rates. For example, many reptiles regulate their body temperature by basking in the sun
- Endotherm
- Homeotherm
Notes
- ^ Milton Hildebrand; G. E. Goslow, Jr. Pprincipal ill. Viola Hildebrand. (2001). Analysis of vertebrate structure. New York: Wiley. p. 429. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0471295051.
- ^ (Greek) Triantafyllidis Online Lexicon, ποικιλόθερμος, Retrieved on 2007-01-12
Categories: Animal physiology
|
