E2+Responses+to+Temperature

•  In **ectotherms**- an organism that is dependant on external sources of body heat, cold blooded. Metabolic rates tend to be slower at low temperatures and faster at higher ones. This lizard is an example of an ectotherm

• **Endotherms**-an organism that can generate an internal source of body heat, a warm blooded organism. They do not experience the temperature fluctuations of ectotherms because their internal organs are buffered against such fluctuations. This dog is an example of an endotherm

• The consequence of this is that ectotherms cannot be said to require a //certain length of time// for development. • Ectotherms require **physiological time-** a combination of time and temperature. • It is difficult to determine an organism’s physiological time scale due to the effects of the fluctuating temperatures. • Temperature can act as a stimulus; Ex. in some plants chilling or freezing is necessary before germination. (Winter wheat will only flower if it has been pre-chilled) • This process is called **Vernalization-** the induction of flowe ring by low temperatures. • Ectotherms respond to changes in temperature that they have experienced in the past. • If an ectotherm responds to a temperature, it will be classified as one of the following: • **Acclimation**- several days temperature exposure to (high/low) temperatures can shift the organism's temperature response (up/down). THESE CHANGES IN ACCLIMATION ARE LABORATORY INDUCED • **Acclimatization**- above occurs if the changes ACCLIMATIZATION OCCURS NATURALLY.

• Variations that occur within species are usually slight. Some species have a higher temperature tolerance (lichen, some bacteria). • Different populations can react differently from genetic differences as well as acclimatization. • Geographic differentiation is usually limited enabling species to be designed as have one temperature response. • In some species such as the cabbage white butterfly, an increase in temperature can benefit the development rate.

The Graph Below (from the book) shows the relationship between temperature and growth with the white cabbage butterfly.