The species-area relationship is one of the most robust empirical patterns in ecology: the number of species S a habitat supports scales with its area A as a power law, with exponent z almost always between about 0.15 (contiguous mainland samples) and 0.40 (isolated islands or fragments cut off from immigration):
S(A) = c · A^z
a = A_total / N (equal-area split into N patches)
S(N) = c · a^z = c · (A_total/N)^z
Extinction debt = S(1) − S(N)
% lost = [S(1) − S(N)] / S(1) × 100
Because 0<z<1, the curve is concave: doubling the area does not double the species count, it adds progressively fewer. This lab assumes isolated fragments draw species from the same regional pool with limited inter-patch dispersal — a conservative, well-documented worst case used in the "single large or several small" (SLOSS) reserve-design debate — so the species an N-fragment system can sustain is bounded by what a single typical fragment of size A_total/N supports. Splitting a reserve of fixed total area into more, smaller pieces therefore predicts fewer species overall, even though not one hectare of habitat was removed: the gap between S(1) and S(N) is the extinction debt — species doomed to local loss purely from isolation, sometimes decades before they actually disappear.
- Total habitat area (A) — the reserve's total footprint; held fixed while you fragment it.
- Species-area exponent (z) — how strongly isolation punishes small patches; islands and heavily isolated fragments have higher z, so they lose more to fragmentation than well-connected mainland patches at the same N.
- Richness coefficient (c) — a taxon- and region-specific baseline (e.g. birds vs. beetles vs. trees have very different c), scaling the whole curve up or down without changing its shape.
- Number of patches (N) — move this slider and watch S(N) slide down the curve on the right while the habitat map fragments into more, smaller pieces of equal total area.