Latitudinal gradients in species richness in northern areas: some exceptional patterns

Most taxonomic groups show a distinct and well-known pattern that species richness decreases from lower to higher latitudes, i.e. from tropics to polar regions. The reasons for this pattern are thought to be related to the amount of energy available, but the exact mechanisms involved in how availability of energy is translated to higher species diver sity are not usually known. Some specific groups of animals and plants, however, show a clear exception to the general patterns so that the number of species actually increases towards the north. These groups might provide us with an alternative explanation for the general ecological pattern and these groups are also important when analysing the priority groups for biodiversity conservation in boreal and arctic areas. I will present and discuss the patterns and possible reasons for two exceptional groups: birds breeding on northern peatlands and sawflies in boreal and arctic areas. It turns out that in some groups amount of available habitat and/or its heterogeneity may override the impor tance of any large-scale impacts on species diversity. Taxonomic groups showing a peak in species richness at northern latitudes should deserve special attention when analysing possible effects of global changes like climatic warming on these ecosystems.