Part 2: Physiological Response

Top: (1) thermal safety margins for diurnal lizards
 Bottom:(1) Comparative Ectotherm thermal ranges across latitudes

Relying on external sources of heat ectotherms are very susceptible to changes in temperature. Depending on external sources of heat means basic life functions such as movement and reproduction depend on the temperature. (2)  Endotherms are capable of  internally producing or maintaining heat and so are not as sensitive.Tropical ectotherms are often more sensitive. Having evolved in a stable temperature environment these species have developed narrow thermal tolerances compared to those found in temperate regions which experience seasonal temperature shifts (13). The selective advantage of having a small thermal tolerance in a constant temperature environment is that it lessens to metabolic strain of maintaining that tolerance window so the organism can focus that energy on other processes such as reproduction.

Organisms seek to maintain an optimal temperature within their range. At this temperature metabolic activity is at its highest rate. In the graphs above on can see the bell shaped curves depicting the difference in thermal ranges of temperate vs tropical terrestrial ectotherms as well as current and predicted mean temperature. When organisms are exposed to temperatures at the edge of their thermal limits the stress can induce decreased functionality and eventually spasms and death. (11)

Kiefer et al (8) examined the body temperatures and thermoregulatory behavior of coastal T. torquatus in Brazil in two different studies. They showed that the mean activity body temperature for T. torquatus is correlated with air temperature. The results are displayed below. Kiefer et al found that, "the maintenance of T. torquatus mean body temperatures in the range of 34-36 ^oC is a tendency for the species". To maintain this temperature T. torquatus must engage in behavioral thermoregulation. For ectotherms finding suitable microhabitats is essential. Microhabitats are the spaces under rocks, the shade under leaves etc that over some form of benefit. T. torquatus and ectotherms need microhabitats that have cooler temperatures then air temperature or a way to escape the heat of solar radiation. Another way of actively thermoregulating for T. torquatus is to position itself perpendicular to the sun's rays (because of the scale type this reduces heat) and reducing contact with hot surfaces (9). Kiefer et al found a correlation between increasing active thermoregulation and increasing local temperatures.

(9) Mean activity body temperature vs mean air temperature for  T. torquatus

The increasing temperatures associated with Climate change reduce the overall effect of active thermoregulation. Part 3 examines climate change velocity and range shifts.