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3 Acta Theriologica. Supplement

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Species richness relative abundances and habitat use in local assemblages of Sorex shrews in Eurasian boreal forests

100%

Sheftel B. I. , Hanski I.

tom 47

nr 1

Using a large body of observational data on the occurrence of Sorex shrews in boreal forests, we test two models that predict the structure of small mammal communities along a gradient of increasing habitat productivity. Tilman's (1982) model predicts a humped curve of species richness along productivity gradients. In contrast, we found a linear increase in species richness with increasing logarithm of the pooled density of shrews, which we use as a measure of habitat productivity for shrews. The model of Hanski and Kaikusalo (1989) assumes a trade-off between exploitative and interference competitive abilities, and it predicts that the size structure of small mammal communities should shift from the dominance of small species (superior in exploitative competition) in unproductive habitats to the dominance of large species (superior in interference competition) in productive habitats. Shrew assemblages show such a shift. Though it is not possible to draw definite conclusions about the role of interspecific competition from our observational data, the changing size structure of local shrew assemblages with increasing habitat productivity is a predictable feature of their community structure.

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

80%

Zakharov V. M. , Pankakoski E. , Sheftel B. I.

nr 04

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.

Cytogenetic homeostasis and population density in red-backed voles Clethrionomys glareolus and C.rutilus in central Siberia

80%

Dmitriev S. G. , Zakharov V. M. , Sheftel B. I.

nr 04

We examined frequency of chromosome aberration in somatic cells in sympatric growing populations of bank vole Clethrionomys glareolus Schreber, 1780 and ruddy vole C. rutilus Pallas, 1779 in central Siberia (Yenisei river island, 62°N, 89°E) from 1992 to 1994. The island was reinhabited from the mainland populations in 1992 after abnormally high flooding which eliminated the previous island populations of the species. The frequency of chromosome aberration increased parallel to the population density of island populations of both species in 1992-1994. In the mainland population of C. rutilus in 1994, the year of low density for this highly cyclic population, significantly lower frequency of chromosome aberration was found as compared with an island population characterized by high density in this year. These results are interpreted as a disturbance of cytogenetic homeostasis indicating an alteration in an organism's condition in the overcrowded populations of both species under study.