Species are the building blocks of biodiversity. The number and combination of species in an area reflect the variation in non-biological environmental factors, and indicate that the ecosystems in the area are healthy and intact. Knowledge of species is necessary for the understanding of biodiversity as a whole.
In Norway, around 40 000 species are found , but the actual numbers present are probably approximately 60 000. These numbers do not include bacteria and viruses. The largest group of terrestrial animals in Norway (same as elsewhere) is the insects, of which roughly 16 000 species exist. For most of these, however, information about their distribution is lacking. In addition, thousands of insect species are probably yet to be found.
Most species present in Norway today are immigrants from the time right after the last ice age (10 000 years ago). The history of immigration, together with non-biological environmental factors, have played an important role in determining the Norwegian biodiversity as we know it today. In addition, human activity through thousands of years also made an impact. Traditional, man-made cultural landscapes are among the ecosystems with highest number of species present.
For some groups of species we have relatively detailed knowledge; birds, mammals, vascular plants and freshwater fishes. For other groups, knowledge is lacking. This is particularly true for the single-celled protists. It is generally assumed that protists, together with invertebrates and other large groups of which knowledge is sparse, contribute to Norwegian biodiversity with approximately half of the existing species.
A few species are found exclusively in Norway. Others have a wider distribution, but may display characteristics unique for Norway. Such local variation is part of the genetic diversity within species.
Species diversity is, at the same time, genetic diversity. Genetic variation results in a variety of appearances and properties between individuals of the same species. Sometimes, when a population display particular genetic characteristics that differ significantly from populations in other areas, the population may qualify as a sub-species. Another example of genetic variation are the hybrids, which are the result of a natural crossing between species. Hybridisation is a phenomenon that sometimes may be a source to new species or sub-species.