Island species diversity

I'm on a roll lately looking at journals, so here's another item of interest. It's no surprise that habitat diversity tends to increase species diversity, but can yo uqnatify that, and what does a graph of the relationship look like? The fice authors of this article take a shot at working that out. With island species, diversity usually increases and never decreases with habitat diversity, but the relationship isn't linear. It's more of a hump-shaped line on the graph.