Comparative abundance and population structure of sympatric Afrotropical tortoises in six rainforest areas: the differential effects of 'traditional veneration' and of 'subsistence hunting' by local people

摘要

Hinge-back tortoises are actively hunted by human populations in sub-Saharan Africa, and are currently threatened in wide areas of their ranges. The wide wetlands and moist rainforests of the Niger Delta (southeastern Nigeria, west Africa) house three sympatric species of hinge-back tortoises: Kinixys erosa, K. homeana, and K. belliana nogueyi. These tortoises are subjected to strong hunting pressure for several reasons (mainly domestic consumption), but in a few places in Bayelsa and Rivers States (eastern axis of the Niger Delta), they are traditionally venerated as "holy animals" bringing happiness. These few places may represent ideal laboratories for monitoring the effects of hundreds of years of "traditional conservation" on the wild populations of a tropical reptile. Here, I compare the apparent abundance, sex ratio, body sizes, microhabitats, and seasonal occurrence of free-ranging Kinixys populations inhabiting three of these "traditional sanctuaries" with the same ecological aspects of conspecifics from three neighbouring areas where the tortoises are actively hunted. K. homeana was the most common species at all sites, followed by K. erosa, whereas K. belliana was extremely rare. Adult sex ratio did not depart significantly from equality both in K. erosa and in K. homeana, and was not influenced by locality or by type of "management" (veneration or harvesting). The frequency of juveniles of K. homeana was significantly higher in areas with traditional veneration than in areas of harvesting, but the same pattern was not observed in K. erosa. There was a significant decrease in terms of the number of observed specimens between areas of traditional protection and areas of usual harvesting in all species, and this trend was more obvious in K. homeana than in K. erosa. The ratio "number of observed erosaumber of observed homeana" was not dependent on the presence of traditional veneration. Mean body sizes were not different in harvest areas and in veneration areas in K. homeana, but the same comparisons were not done for K. erosa because sample sizes were too small. Tortoises in veneration areas inhabited a wider range of microhabitats than in harvest areas, where they were found almost only in dense bushes. Specimens of both K. erosa and K. homeana were observed mainly during the wet season, and this excess of observed specimens was significantly affected both by locality and by type of management, i.e., the frequency of observed specimens of both species during the dry season was significantly higher in areas with traditional veneration than in areas with local harvesting. The conservation implications of the ecological patterns observed are discussed. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved. [References: 32]