Life history traits contribute to decline of critically endangered lizards at Macraes Flat, Otago

Mark–recapture methods were used to determine population abundance and life history of five grand (Oligosoma grande Scincidae) and two Otago (O. otagense) skink populations over 6 years at Macraes Flat, in southern New Zealand. The population ecology of declining and stable grand skink populations was contrasted and the life histories of grand and Otago skinks were compared. The life histories of both species were similar and characterised by slow maturity and longevity (3–5 and 4–6 years to produce first offspring and longevity up to 18 and 13.5 years in the wild; grand and Otago skinks respectively). With the exception of one grand skink population, all skink populations showed evidence of declines. Annual reproductive output (ARO) was estimated at 1.46 and 1.41 offspring per female per year (grand and Otago skinks respectively). These ARO values were markedly lower than those reported during a previous study at Macraes Flat during the same decade (2.17 and 2.34 respectively). The stable grand skink population excelled (relatively) in all life history traits measured: ARO of 1.66, 30% of newborns persisted 5+ years, adult survivorship averaged 0.84, and 36% of newborns were recruited to the adult population. In contrast, many of the declining populations were seriously deficient in one or more traits. This study raises concerns about the viability of small populations that have dropped below a critical size, beyond which one or multiple life history traits can act to further the decline. It is imperative that conservation managers of k-selected species move outside the ‘improving adult survival’ paradigm and begin to consider other potentially limiting population parameters.