SPECIES RICHNESS IN MAMMALIAN HERBIVORES - PATTERNS IN THE BOREAL ZONE

Latitudinal gradients in species diversity are well established for a number of plant and animal taxa. Both historical and present-day envir onmental factors have been suggested to be responsible for observed pa tterns. We tested the hypothesis that current environmental features o f the environment (primary productivity and regional landscape structu re) may explain the longitudinal variation in species richness of mamm alian herbivores in the Holarctic boreal zone, Mammalian herbivore spe cies diversity was strongly correlated with a number of environmental variables measured. We reduced the data set by a principal components analysis (PCA), and found that in the Palearctic, species richness is positively related to warm climate (high temperature sum), the number of hardwood species, and the area of boreal forest. In the Nearctic, s pecies richness increases as the length of the growing season and the number of coniferous tree species increase. Thus indirect measures of primary productivity as well as tree species number may accurately pre dict species richness in mammalian herbivores. In addition, there seem s to be a strong species-area effect at the regional level. The larger and more homogeneous in terms of forest coverage a boreal section is, the more species coexist there.