Demography of an island population of the lizard, Eumeces okadae, on Miyake‐jima, Izu Islands

Abstract

SummaryThe demography of the lizard Eumeces okadae was studied for 4 years on Miyake‐jima, in the Izu Islands, central Japan. Most males matured at 3 years of age with a mean snout‐vent length of 77.5 mm. Females matured at 3–4 years with a mean SVL of 77.8 mm, and reproduced biennially thereafter. Growth continued after maturity with a decreasing rate. In females, annual growth was negligible in reproductive years, but resumed markedly in non‐reproductive years. Clutch size increased with SVL and was used to construct a fecundity schedule. Population density (exclusive of hatchlings) was estimated to be ca. 4000 individuals/ha in August, an exceptionally high density for lizards. Before introduction of the weasel onto Miyake‐jima, low predation pressure had allowed E. okadae to maintain a high population density. Estimated annual survival rates were 36% for hatchlings, 56% for yearlings, 80% for 2‐year‐olds, 63% for adult males and 76% for adult females. The cohort generation time (6.95 years) was so long that the E. okadae population can be characterized by a combination of low natality and slow turnover.