Species-Area Curve & Extinction Debt

Species — sustained Species — extinction debt Forest inside plot Cleared outside plot

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Species-area curve (log-log)

Solid line: S = c·A^z (z≈0.3) — the real curve. Dashed line: what a naive 1:1 proportional loss would predict. The green dot tracks today's equilibrium; the orange ring shows species still physically present but already committed to debt.

How the mechanic works

S = c · A^z
z ≈ 0.25 – 0.35 (empirical)

Doubling the sampled area does not double the species count — it multiplies it by 2^z, roughly 1.2×. The curve rises steeply at first, then flattens: diminishing returns. Run the relation backwards for habitat loss and the same shape means a shrinking fragment loses a smaller fraction of its species per unit of area lost while it's still large, but the loss rate accelerates sharply once the fragment gets small — and a population briefly stranded above the new capacity slowly bleeds down to it (extinction debt) rather than dropping instantly.