Phenotypic diversity and population dynamics: another look (with particular reference to the common shrew Sorex araneus)

We studied temporal changes in the level of phenotypic diversity, measured by the total phenotypic variance for several characters of skull morphology, in two populations of the common shrew Sore:e araneus Linnaeus, 1758. We compared a population from central Siberia having a high-amplitude four-year cycle with a population from southern Finland having noncyclic dynamics. The level of total phenotypic diversity varied significantly among years in both populations, but was correlated neither with density nor with breeding success in either of them. We did, however, find differences between the two populations. When we compared changes in the level of phenotypic diversity with changes in the level of developmental stability, as measured by chance developmental variance (fluctuating asymmetry), the cyclic Siberian population exhibited increased developmental variability in the peak year, which was associated with relatively small proportion of other sources of variation (and genetic variation in particular). In other years, the role of chance variation was less and the proportion of other sources of variance was higher. On the other hand, in the noncyclic Finnish population, oscillations in the level of phenotypic diversity were mainly caused by changes in developmental stability. These results illustrate that not only dynamics of genotype variety, but also the alterations in the level of developmental stability can be of great importance for changes in phenotypic diversity.