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Poikilotherms: Animals That Rely on External Sources for Heat

Understanding Ectotherms and Poikilotherms

In the animal kingdom, there are two main categories based on body temperature regulation: endotherms and ectotherms. Endotherms, such as humans and mammals, can generate their own body heat to maintain a relatively constant internal temperature. Ectotherms, on the other hand, rely on external sources of heat to regulate their body temperature.

Poikilothermy: A More Precise Term

Poikilothermy is a term often used to describe ectotherms, meaning “variable temperature.” While the term “cold-blooded” is sometimes used to refer to ectotherms, it can be misleading because it suggests that these animals are always cold, which is not always the case. Poikilothermy more accurately reflects the ability of these animals to have body temperatures that vary with the surrounding environment.

Temperature Ranges in Cold Environments

Even in extreme cold environments, such as the arctic seas, ectothermic animals can survive and maintain a limited control over their internal temperature. Water temperatures in these regions can range from below 0°C (32°F) to 10-15°C (50-59°F), allowing ectotherms to adjust their body temperature accordingly.

Behavioral Adaptations for Temperature Regulation

Since poikilotherms cannot generate heat on their own, they rely on behavioral adaptations to regulate their body temperature. For example, a lizard may bask in the sun to warm up or seek shade to cool down. They may also adjust their activity levels based on the temperature, becoming more active in warmer conditions and less active in cooler conditions.