FA-65829 / Ecological population dynamics / Member archive

Count-based population viability (diffusion approximation): distance to threshold · case 04

Risk is computed from the first census rather than the current population.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Log growth increments ln(N[t+1]/N[t]); mu = mean, sigma^2 = sample variance (q-1); d = ln(N_last/threshold); d<=0 gives probability 1.0; zero variance gives 1.0 if mu*T <= -d else 0.0; otherwise P = Phi((-d-muT)/(s sqrtT)) + exp(-2 mu d/s^2) Phi((-d+muT)/(s sqrtT)) capped at 1; return [mu, var, P] rounded 6; None with fewer than three counts, non-positive counts or threshold.

Why this case matters

Population projections set harvest quotas, conservation status and pest-control timing; a wrong update order, boundary or rate conversion silently changes management advice.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: fluctuating stable	`[0.009758, 0.046826, 0.203751]`	`[0.009758, 0.046826, 0.191687]`	Failed

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