Theory 025/Life & Evolution /Conservation biology
Extinction Risk Scales With Generation Time
Risk is ranked by body size. The clock that matters may be how fast a lineage turns over.
Extinction risk scales inversely with generation time rather than with body size, so a small short-lived species can be at higher risk than a large long-lived one in the same habitat.
01The evidence
Extinction risk correlates with body size across many groups, but the correlation weakens when generation time is included, and some small-bodied groups show high risk.
02The tension
Body size is used as a proxy because it is easy to measure. It bundles generation time, range size and abundance, and the proxy fails where those factors diverge.
03The mechanism
A population recovers from a bottleneck at a rate set by generation time. Species with long generations recover slowly and accumulate risk across disturbances, while short-lived species can rebound between events.
That makes generation time the mechanism, and it predicts risk should track it better than size once abundance is controlled.
04What this is not
Size proxies predict risk from mass. This predicts it from turnover, which separates small slow species from large fast ones.
05Predictions
- P1Risk should correlate with generation time better than with mass.
- P2Small long-lived species should be high risk.
- P3Recovery rate should scale with generation time.
06Refutation
Risk tracking mass at controlled generation time would restore the proxy.
07What it changes
It would change how risk is ranked in conservation assessments.