Demography of an island population of the lizard,Eumeces okadae, on Miyake-jima, Izu Islands |
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Authors: | Masami Hasegawa |
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Institution: | (1) Natural History Museum and Institute, Chiba Aoba-cho 955-2, 280 Chiba, Japan |
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Abstract: | Summary The demography of the lizardEumeces 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 allowedE. 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 theE. okadae population can be characterized by a combination of low natality and slow turnover. |
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