How can national parks or wildlife refuges be compared to islands?

The study of island biogeography has been used to help wildlife managers in national parks and wildlife refuges assess and predict the biodiversity of the areas they see. How are national parks or wildlife refuges compared to islands?How can national parks or wildlife refuges be compared to islands?
Since islands are isolated from continents they do not experience immigration (depending on their distance to a mainland or other island) as a national park or wildlife refuge on the mainland would.How can national parks or wildlife refuges be compared to islands?
there fragments of a once virtually endless ecosystem





if there was a forest from miles to miles and one day we saved a small chunk and chopped the rest that would be like an island





problem is that MANY of them are too small to really support a rich biodiverse ecosystem and they simply do not have enough land to sustian themselves and the edge effects, fragmentation really limits the productivity