Physiological Impacts

Weather extremes can cause the conditions of a microclimate to quickly exceed normal limits; these extremes can have catastrophic effects on organisms, particularly ectotherms. A heat wave is an example of a weather extreme that can cause harmful increases in microclimate temperature. In order to quantify the catastrophic effects of extremes on organisms, a physiological index, lethal temperature 50 (LT50), which describes the conditions when 50% of a population dies, has been used. However, the LT50 only provides a way of quantifying lethality at the population level, and there are more subtle effects that may precede these threshold events. Therefore, recent studies have emphasized the importance of quantifying the sublethal effects of weather extremes on organisms.

One of the new ways for quantifying damage from heat stress is to make measurements at the subcellular level. Extreme high temperatures can cause proteins to denature (unfold), but this damage can be prevented by the activity of heat shock proteins (HSPs), which prevent inappropriate interactions between the ends of damaged proteins that have begun to unfold. By measuring levels of HSPs, scientists can determine the

Figure 2 Comparison between air temperature and body temperatures. Note that body temperatures do not track air temperature and vary for different organisms located in the same microhabitat. Data collected at Strawberry Hill, OR, USA, on 15 July 2006 by L. Yamane and L. VanThiel.

Time (min)

Figure 2 Comparison between air temperature and body temperatures. Note that body temperatures do not track air temperature and vary for different organisms located in the same microhabitat. Data collected at Strawberry Hill, OR, USA, on 15 July 2006 by L. Yamane and L. VanThiel.

relative heat stress an organism experiences. If organisms are responding to acute heat stress at the subcellular level, it is likely that there are other sublethal effects on the physiology of an organism. Making links between extreme temperatures, sublethal effects, and the ability of an organism to grow, survive, and reproduce is an area of active research.

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