Developmental instability and inbreeding in natural bird populations exposed to different levels of habitat disturbance

As habitat disturbance and inbreeding increasingly stress natural populatio ns, ecologists are in urgent need of simple estimators to measure their imp act. It has been argued that developmental instability (DI) could be such a measure. Observed associations between DI and environmental or genetic str ess, however, are largely inconsistent. We here test whether an interaction between habitat disturbance and inbreeding could, at least partly, explain these discordant patterns. We therefore studied individual estimates of fl uctuating asymmetry (FA) and of inbreeding in three populations of the crit ically endangered Taita thrush that are differentially exposed to habitat d isturbance following severe forest fragmentation. As predicted, the relatio nship between DI and inbreeding was pronounced under high levels of disturb ance, but weak or nonexistent under less disturbed conditions. Examining th is relationship with mean d(2), an allelic distance estimator assumed to re flect ancestral inbreeding, did not reveal any significant trend, hence sug gesting that inbreeding effects in the Taita thrush are fairly recent.