GEOGRAPHICAL VARIATION IN STRUCTURE OF RODENT COMMUNITIES IN DESERT ZONE OF MONGOLIA

We analyzed the spatial organization of Mongolian desert rodent fauna by the use of stepwise discriminant function analysis and cluster anal ysis. Geographical variation in niche breadth and niche position among rodent communities from Southern, Western and Eastern Gobi was consid eres in coordinated for the whole fauna. To reduce the environmental c onstraints in regional communities, niche breadth was estimated along comparable parts of discriminant scores and was measured by use of Sha nnon-Weaver index. Absolute niche overlap values were calculated for e ach community type as a probability of displacement along the discrimi nant axis. Guild structure of the fauna, demonstrated by our analysis, reflects the adaptation of species to the range of main landscape typ es of the desert zone. Species mainly shift their preferences along th e axes of ecological space independently. This is also true regarding changes in niche breadth and niche overlap. These results challenge th e viewpoint that the spatial guilds are stable coadapted assemblages. An extreme value of the coefficient of variation in niche overlap amon g nearest neighbors in Southern Gobi indicates the absence of dense ni che packing. The most even distribution of niche overlap values reveal ed by the nearest neighbor analysis is a characteristic of the Western Gobi community. We did not find any features of regularity in body si ze distribution among Mongolian desert rodents. Species pairs from one genus with low niche overlap have the same body weight ratio as speci es pairs with high overlap.