Complex sentence: Due to the harsh climatic conditions, there are not especially many species among Enontekiö's fauna; however, there are Arctic species that are unknown to southern Finland, e.g. Norway lemming, Arctic fox, snowy owl, Eurasian dotterel, ptarmigan, and ring ouzel.
Split into simpler sentences: Due to the harsh climatic conditions, there are not especially many species among Enontekiö's fauna. But there are Arctic species that are unknown to southern Finland, e.g. Norway lemming, Arctic fox, snowy owl, Eurasian dotterel, ptarmigan, and ring ouzel.