Since we expect the rate a at which new species enter the system to be small, we will look at the behavior of the species-area curve as alpha approaches 0. Let L=1/sqrt(alpha), let N(r) be the number of different types (or species) in (-L^r/2,L^r/2]^2 in the stationary distribution, and write u^+ for the positive part of u.

Theorem 1. As alpha approaches 0,

The function h(r) = log N(r) / 2log L corresponds to plotting species number versus area on log-log paper. Theorem 1 says that if we do this for alpha close to 0, then the result will be close to a curve that is identically 0 out to r = 1 and then has slope 1 after that.

Theorem 2. If r > =1, then as alpha approaches 0,

It is, at first sight, disappointing that our limiting curve given in Theorem 1 consists of two line segments with slopes 0 and 1, rather than a single line with an "interesting" slope. However, if we assume that the species area curve is approximately linear on [0,1] we can compute the slope from the change in value between r = 1 and r = 0

Taking alpha=10^{-k}, [L=1/sqrt(alpha)] and letting k = 4, 8, 12 gives slopes of .331, .241, .190, a range of values comparable to that observed in the data. We are unfortunately not able to prove that the species area curve is linear over the indicated range. However, the following three simulated species-area curves for the process on a 1000 x 1000 grid with alpha = 10^{-6} supports this conclusion.

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