Poikilo

Poikilo is a term used in biology and ecology to describe organisms that are unable to regulate their internal environment and whose internal conditions vary with the external environment. This means that their body temperature, salinity, or other physiological factors fluctuate in response to changes in their surroundings. Organisms that exhibit poikilothermy are often referred to as "cold-blooded," although this term can be misleading as their body temperature can sometimes be warmer than the ambient temperature, especially during periods of activity.

Poikilothermy is common in many animal groups, including reptiles, amphibians, fish, and invertebrates. These animals rely on external sources of heat to regulate their body temperature. For example, a reptile might bask in the sun to warm up or seek shade to cool down. Their metabolic rate is directly influenced by their body temperature, meaning they are less active in colder conditions and more active when warm. This strategy allows them to conserve energy compared to endothermic animals that generate their own heat.

In contrast, homeothermic or endothermic organisms, such as mammals and birds, maintain a stable internal body temperature regardless of external conditions through physiological processes. The ability to adapt to a wide range of environmental temperatures through behavioral means is a key characteristic of poikilothermic species, enabling them to inhabit diverse ecological niches.