Have just been delving into Lecture 2, about concepts of biodiversity, by Dr Ian Henderson. Clever man demonstrated all these concepts by relating them to our closest local beach, Himatangi, which is a long, sandy surf beach. As he described, there isn't much variety of habitat there to support different kinds of shellfish.
Anyhow, there are four components to think about when you think about biodiversity: richness, equitability, disparity and endemism. And the upshot of having such a long uniform beach, is that there is low richness, i.e. only a few species are present. There is also low equitability on this beach, as 95% of the shells you find are the one species, Spisula, so the next shell you see tends to be the same as the last. Disparity is all about having more species, and the species being more different. You need to find a beach with more rocky pools etc to find that. But.... the last concept, endemism, Himatangi has more of (I think, if I read it right!) Turns out that some of the bivalves we find very commonly on our beaches are actually endemic, and found only in New Zealand.
I still love Himatangi though! Biodiversity may be low, but I am a "West Coast beach" girl, born and bred by the coast in Taranaki. And there is nothing I like better than long walks along this sandy beach, listening to the sounds of the surf and the gulls, and feeling the wet sand between my toes.