3 public questions tagged with this topic.
Both amphibians and reptiles are poikilothermic (cold-blooded), meaning their body temperature varies with the environment (NCERT, Chapter 4, page 58). Warm-bloodedness is specific to birds and mammals, mammary glands to mammals, and feathers to birds.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Vertebrata - Aves and Mammalia
Poikilotherms experience substantial fluctuations in body temperature, often because their heat exchange is strongly coupled to ambient conditions. Most are ectothermic and obtain heat from sunlight, warm surfaces, air, or water rather than sustaining high internal heat production. Their metabolic, locomotor, digestive, and developmental rates consequently change with temperature. Many compensate behaviourally by basking, entering shade, burrowing, or shifting activity time, so a fluctuating temperature does not imply absence of all regulation. Energy efficiency can also characterize ectotherms because less food is spent on thermogenesis, but it is not universal and is not the defining meaning of poikilothermy. A constant metabolic rate is unlikely when biochemical reaction rates are temperature sensitive. Environmental niche breadth varies: some poikilotherms tolerate wide ranges, whereas stenothermal species tolerate narrow ones. The distinction from homeothermy concerns temperature variability, while the distinction between ectothermy and endothermy concerns the main heat source. These categories can cross: an ectotherm in stable water may remain nearly homeothermic, and an endotherm in torpor may become temporarily heterothermic. Nevertheless, fluctuating body temperature is the characteristic captured by the term.
Ref: Evolutionary Analysis, Herron & Freeman, 5th Ed., Ch. 10
Poikilotherms show substantial variation in body temperature, usually because environmental heat strongly influences them. Most fishes, amphibians, reptiles, and invertebrates fit this description. “Poikilothermic” is often paired with “ectothermic,” but the terms are not identical: ectothermy refers to the primary source of heat, whereas poikilothermy refers to variability in body temperature. These animals may regulate temperature behaviourally by basking, seeking shade, changing posture, burrowing, or moving between water layers, so saying that they cannot regulate temperature at all is an oversimplification. They generally cannot maintain a narrow, constant core temperature through sustained metabolic heat production in the manner of typical birds and mammals. Homeothermy denotes relatively constant body temperature, endothermy denotes reliance on internally generated metabolic heat, and thermogenesis is the process of heat production rather than a category for animals lacking regulation. Some ectotherms can remain nearly homeothermic in stable environments, and some endotherms become heterothermic during torpor. Among the supplied terms, poikilothermic best captures animals whose body temperature varies with external conditions, provided this physiological nuance is retained.
Ref: Evolutionary Analysis, Herron & Freeman, 5th Ed., Ch. 10
