The job of this chapter is to present some spatial diversity patterns. It is not to judge them or explain them. That part of my agenda comes much later in the book, i.e. Chapters 7, 8, 9 and 12. So read this chapter (and the next two also) as if it were merely an attempt to define what it is that needs explaining.

Species–area curves

You will find more species if you sample a larger area. That rule has more evidence to support it than any other about species diversity. Ecologists noticed it before any other diversity pattern. Williams (1964) credits H. C. Watson with its discovery in 1859 (Figure 2.1). Dony (1963) credits him with the discovery in 1835. I have also seen de Candolle cited as its originator a few years before 1859.

But, as Williams (1943) pointed out, it is not one pattern. Williams detected three. There are actually four:

1. Species–area curves among tiny pieces of single biotas.

2. Species–area curves among larger pieces of single biotas.

3. Species–area curves among islands of one archipelago.

4. Species–area curves among areas that have had separate evolutionary histories.

Williams did not distinguish between the second and third patterns. Preston (1962a, b) did.