I

2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 Logj0 rainfall

Figure 1.3 Variation in survival time (mean ± SE) under dry conditions in nine keratin beetle species across a rainfall gradient in southern Africa.

Source: Data from Le Lagadec et al. (1998).

possible if physiological characteristics were species specific. Moreover, these findings are not unusual, at least as far as can be ascertained from studies of the levels at which life history traits are partitioned in vertebrates (Read and Harvey 1989), and from other investigations at lower levels for insects (Chown et al. 1999).

2. Even though there is a continuum of variation in many traits, clear physiological strategies can be identified. For example, despite considerable variation in the responses of insects to cold, insects can be clearly categorized as those that are freezing tolerant, those that are freeze intolerant, and one (but probably more) which survive subzero temperatures using cryoprotective dehydration (Sinclair et al. 2003b). Similar categorizations have been developed for responses to hypoxia, osmoregulation, and thermoregulation.

3. Insects do not occupy all of the available physiological 'space'. In other words, evolution has restricted occupation of all permutations of complexity to a limited diversity of workable solutions given the physical laws and biotic history

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