Literaturdatenbank
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van Heezik, Y. M., Cooper, J. E., & Seddon, P. J. (1994). Population characteristics and morphometrics of angulate tortoises on dassen island, south africa. Journal of Herpetology, 28(4), 447–453.
Added by: Admin (27 Jun 2009 12:36:31 UTC) |
| Resource type: Journal Article BibTeX citation key: VanHeezik1994 View all bibliographic details  |
Categories: General Keywords: Chersina, Chersina angulata, Habitat = habitat, Schildkröten = turtles + tortoises, Südafrika = Southern Africa, Testudinidae Creators: Cooper, van Heezik, Seddon Collection: Journal of Herpetology |
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| Abstract |
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Testudinidae Angulate tortoises (Chersina angulata) were probably introduced onto Dassen Island, South Africa, at the beginning of this century. Historical records indicate distance from the mainland appears to prevent emigration from, or immigration to, this island population. We estimated population size and density using a mark-recapture method, and determined sex ratio and population structure in 1978 and again in 1989. These figures were compared with published values for a mainland population. Population sizes and sex ratios did not differ significantly between 1978 and 1989: density was 31.2/ha and 34.2/ha, and sex ratios were 1:1.18 and 1:1.17 in favor of males, respectively. In both years the population showed a preponderance of adults. However, mean and maximum adult body size was greater in 1989. The island population was similar to the mainland population in terms of sex ratio and density, but differed in that there were proportionately more large males and females on the island. Factors that might cause an increase in size of island tortoises include predation on different sized tortoises by mainland compared with island predators. Reduced competition on the island and the potential effects of isolation may also affect body size. We suggest that the limits to the size of the island tortoise population will be primarily determined by numbers of breeding penguins and rabbits, whose activities remove vegetation used by tortoises for food and cover.
Added by: Admin |