explored. Indeed, in at least one species, Hydro-medion sparsutum (Coleoptera, Perimylopidae) it appears that bimodality in SCP distributions represents either a transition from a summer strategy of moderate freezing tolerance to a winter one of moderate chill tolerance, or a bet-hedging strategy, resulting in freeze intolerant and freezing tolerant individuals, in response to continual freeze-thaw cycles (Bale et al. 2001).

Supercooling point frequency distributions Irrespective of the cause of the bimodality of insect SCP distributions, it is often considered a stumbling block for conventional statistical analyses (Worland and Convey 2001). Block (1982) suggested that the bimodal distributions can be arbitrarily divided into high and low groups, and that the ratio of the numbers of individuals in each of these groups provides a useful measure of bimodality. Similarly, Rothery and Block (1992) provided a method for quantifying the variation in SCPs once a bimodal distribution has been divided into two groups. Unfortunately, neither method allows the significance of the bimodality to be determined. In contrast, and for a somewhat different purpose, Tokeshi (1992) developed a method for identifying the significance of bimodality in frequency distributions, and a means for determining the modal values for each of the groups in the distribution. In a similar vein, the transformations that are used

Was this article helpful?

0 0

Post a comment