FA-65695 / Ecological population dynamics / Member archive

Stochastic growth rate and quasi-extinction: stable equality · case 05

A population whose long-run growth is exactly one is called growing.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Geometric mean growth exp(mean ln lambda) determines trend (declining <1, stable ==1, growing >1); arithmetic mean reported alongside; trajectory multiplies N by each lambda; quasi-extinction time is the first 1-based year with N < threshold or None; return [geo, arith, trajectory, hit, trend]; None for empty, non-positive lambdas or N0<=0.

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: exact halving to threshold	`[1.0, 1.166667, [50.0, 50.0, 100.0], null, "growing"]`	`[1.0, 1.166667, [50.0, 50.0, 100.0], null, "stable"]`	Failed

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