Abstract

MARQUEZ, Cruz et al. Population status of giant land tortoises (Geochelone spp., Chelonya: Testudinae) from the Galapagos islands. Ecol. apl. [online]. 2004, vol.3, n.1-2, pp.98-111. ISSN 1726-2216.

The present status of populations of giant land tortoises (Geochelone spp) in the Galápagos Islands was studied. Geographical distribution, mark and recapture methods, population structure, population density, sex ratios, predation and other threats were considered in this context. Old records show that the present distribution and population demography of giant tortoises is much more restricted than that seen during the 16th to 18th centuries and, although there were further population changes between 1974 and 1992 - 2002, the population distribution is still similar to that estimated by McFarland (1974). Present population demographics differ from those of 1974, the values of Student’s t range from 29 to 175 (P < 0.001). Population densities vary from 57 to 799 tortoises / km2. The present population structures of G. vandenburghi and nigrita for males, females and juveniles differ from those of 1974. However, these three population classes in G. ephippium and G. microphyes have remained unchanged since 1974. Comparing the present population structures of the six remaining populations with those of 1974, Chi-squared tests show that population structure differs in some populations but not others. Present sex ratios (females: males) of tortoises are in general higher than those of 1974. There are now fewer populations of tortoises affected by predators and competitors. Potential threats to surviving tortoise populations have been generally eliminated. Wild pigs and dogs in both Santiago and Isabela islands have been eradicated although domestic ones remain as a permanent, potential threat. The islands of Pinta, Espanola and Santa Fe no longer have goats, although they are still present in Isabela, Santiago and San Cristobal.

Keywords : Populations status; giant tortoises; Galapagos Islands.

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