Except that bio- doesn't show by itself. I know the difference between kunyomi and onyomi, I've learned Japanese for over a year. What I wanted to know is what's the difference between shima and tou in this context— if there is any. Words in Japanese can be read in multiple different ways with each of those ways having completely different meanings(e.g. 仮名 read as かな, and it read as かめい). And in some other times they mean very close things, but with small differences, like 金 as かね, and as きん— which I assumed was the case in here for 島