ABSTRACT
Any human or natural system’s environment varies from day to day, month to month, year to year, decade to decade, and so on. It follows that systematic changes in the mean conditions that define those environments can actually be experienced most noticeably through changes in the nature and/or frequency of variable conditions that materialize across short time scales and that adaptation necessarily involves reaction to this sort of variability. This is the fundamental point in Hewitt and Burton (1971), Kane et al. (1992), Yohe et al. (1999), Downing (1996) and Yohe and Schlesinger (1998). Some researchers, like Smithers and Smit (1997), Smit et al. (2000), and Downing et al. (1997), use the concept of “hazard” to capture these sorts of stimuli, and claim that adaptation is warranted whenever either changes in mean conditions or changes in variability have significant consequences. For most systems, though, changes in mean conditions over short periods of time fall within a “coping range” - a range of circumstances within which, by virtue of the underlying resilience of the system, significant consequences are not observed for short-term variability (see Downing et al. (1997) or Pittock and Jones (2000)). There are limits to resilience for even the most robust of systems, of course. It is therefore as important to characterize the boundaries of a system’s coping range as it is to characterize how the short-term variability that it confronts might change over the longer term.
