British Columbia is home to more species of mammal than any other Canadian province.
BC's high mammal percentage is owed to so many reasons, especially the vastness of the landscape playing host to the wildlife. Extending nearly 1000 miles north to south and 400 miles east to west, BC has enough room and zones for such variety.
That being said, insular regions such as the islands contain many fewer types of mammals than the mainland. Water boundaries seem to play a more important role in excluding diverse populations than do the mountains of the mainland. These separations have also led to scientific discussion regarding subspecies, and research is ongoing in regards to how island populations might differ genetically from mainland populations.