Cold-blooded
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Cold-blooded organisms, are animals that have no internal metabolic mechanism for regulating their body temperatures. Some (usually smaller) animals have unregulated temperatures, but most have sophisticated physiological and behavioral techniques for obtaining their desired core body temeprature from the environment. Cold-blooded animals are often referred to as ectotherms.
Ectotherms depend largely on external sources of heat, such as solar radiation. As the environmental temperature increases, the animal's metabolic rate will increase. Lizards, fish, and amphibians are examples of ectotherms. Whereas an endotherm, or warm-blooded animal will use up to 98% of its energy for heat production, an ectotherm has all this energy available for activity, growth, repair and reproduction.
Types of temperature control
Examples of this temperature control include:
- Snakes and lizards sunning themselves on rocks.
- Fish changing depths in the water column to find a suitable temperature.
- Desert animals burrowing beneath the sand during the day.
- Insects that warm their flight muscles by vibrating them in place.
- Dilating or constricting peripheral blood vessels to adapt more or less quickly to the ambient temperature.
Many warm-blooded, animals also make use of these techniques at times. For example, all animals are at risk of overheating on hot days in the desert sun, and most homeothermic animals can shiver.
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 generations 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). 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.
See also
- Warm-blooded for organisms that fall in between both catagories.
da:Ectotherm de:Wechselwarmes Tier ja:変温動物 nl:Poikilotherm zh:冷血动物