Unifying indices of heat tolerance in ectotherms

1. Researchers commonly rely on indices of heat tolerance to infer the limits of performance in nature. Unfortunately, many methods are used to estimate heat tolerance, creating difficulties when synthesizing or comparing results among studies. Here, we relate several measures of heat tolerance based on the concept of a performance curve. 2. To evaluate our ideas about the link between two measures of heat tolerance, we measured knockdown times and knockdown temperatures of terrestrial isopods (Porcellio scaber). We fit a linear model relating knockdown time to environmental temperature; this model was used to predict the knockdown temperature (i.e., the temperature at which the knockdown time equaled zero). 3. Our model predicted a knockdown temperature within 0.1 1C of the observed value. This result reinforces the possibility of conceptually unifying several measures of thermal physiology. & 2008 Elsevier Ltd. All rights reserved.