Cooling rate (°Cmin

Figure 7.7 The frequency distribution of cooling rates recorded at an alpine site (a) Museum Rock and (b) Summit Rock in New Zealand.

Note: (i) at 0°C, (ii) at -3.1°C and (iii) at -4.5°C.

Source: Sinclair (2001). Oikos 93, 286-293, Blackwell Publishing.

number of warm days declines with latitude. It is this variation that is likely to be at the root of clinal variation of the 56H8 hsp70 allele of Drosophila melanogaster (Bettencourt et al. 2002). In alpine New Zealand, measurements of the temperature in microhabitats of the cockroach Celatoblatta quin-quemaculata and laboratory examination of critical temperatures indicated that there is substantial inter-annual variation in the risks of mortality (Sinclair 2001a). This variation is due mostly to the absence of well-developed snow cover in El Niño years. Moreover, cooling rates in field habitats differ substantially from those used in the laboratory, highlighting the need for more accurate information on microclimates to provide appropriate experimental conditions (Fig. 7.7). This work also highlights the substantial effect that increasing environmental variability, as a consequence of global climate change, might have on insects.

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