Abstract
BackgroundInformation on the age structure within populations of an endangered species can facilitate effective management. The Blue Mountains Water Skink (Eulamprus leuraensis) is a viviparous scincid lizard that is restricted to < 40 isolated montane swamps in south-eastern Australia. We used skeletochronology of phalanges (corroborated by mark-recapture data) to estimate ages of 222 individuals from 13 populations.ResultsThese lizards grow rapidly, from neonatal size (30 mm snout-vent length) to adult size (about 70 mm SVL) within two to three years. Fecundity is low (mean 2.9 offspring per litter) and is affected by maternal body length and age. Offspring quality may decline with maternal age, based upon captive-born neonates (older females gave birth to slower offspring). In contrast to its broadly sympatric (and abundant) congener E. tympanum, E. leuraensis is short-lived (maximum 6 years, vs 15 years for E. tympanum). Litter size and offspring size are similar in the two species, but female E. leuraensis reproduce annually whereas many E. tympanum produce litters biennially. Thus, a low survival rate (rather than delayed maturation or low annual fecundity) is the key reason why E. leuraensis is endangered. Our 13 populations exhibited similar growth rates and population age structures despite substantial variation in elevation, geographic location and swamp size. However, larger populations (based on a genetic estimate of effective population size) contained older lizards, and thus a wider variance in ages.ConclusionOur study suggests that low adult survival rates, as well as specialisation on a rare and fragmented habitat type (montane swamps) contribute to the endangered status of the Blue Mountains Water Skink.
Highlights
Information on the age structure within populations of an endangered species can facilitate effective management
Our skeletochronological estimates of age (= n lines of arrested growth (LAG) – 1) agree well with those predicted by the Von Bertalanffy function fitted to our mark-recapture data (Figure 1)
Intuition suggests that larger swamps should contain more lizards, but our analyses show no such pattern
Summary
Information on the age structure within populations of an endangered species can facilitate effective management. Estimation of the age structure of endangered populations can facilitate their efficient management An alternative way to estimate an individual’s age is skeletochronology, based on histological analyses of growth marks in the skeleton [4,5]. This technique relies upon seasonal variation in rates of skeletal growth, and is especially effective for ectothermic vertebrates that live in highly seasonal environments [6,7]. The Blue Mountains Water Skink (Eulamprus leuraensis, Wells & Wellington, 1983) is a medium-sized
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