Unlike humans, plants and animals can't do anything about these problems. They do not use technology, and they do not trade. On the other hand, some plants and animals getting to the islands find that conditions here are very good for them. Deer, raccoons, rats, and squirrrels have become dangerous competitors or predators to the species that were already here. These islands' size and distance from the mainland are important factors.
Distance helps control which species get here.
Size determines the variety and amount of resources, and so helps control which species can flourish here. For plants and animals another fact about islands is also very important. The shape of an island determines how much land area is affected by ocean conditions. Haida Gwaii with its many inlets has more coastal and less interior areas than rounder islands with smoother coastlines. This factor helps control which kinds of species can flourish here.