Literaturdatenbank
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Baard, E. H. W. (1997). The dynamics of two sympatric tortoise communities in a stressful environment. Proceedings: Conservation, Restoration, and Management of Tortoises and turtles - An International Conference.
Added by: Admin (17 Aug 2008 18:17:12 UTC) |
| Resource type: Journal Article BibTeX citation key: Baard1997 View all bibliographic details  |
Categories: General Keywords: Habitat = habitat, Homopus, Homopus areolatus, Psammobates, Psammobates geometricus, Schildkröten = turtles + tortoises, Südafrika = Southern Africa, Testudinidae Creators: Baard Collection: Proceedings: Conservation, Restoration, and Management of Tortoises and turtles - An International Conference |
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| Abstract |
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Testudinidae Geometric tortoises (Psammobates geometricus) and common parrot-beaked tortoises (Homopus areolatus) occur sympatrically in the isolated Harmony Flats nature reserve (10 ha) between the towns of Strand and Gordon's Bay, Western Cape Province, South Africa. The reserve is completely surrounded by urban development and isolated from any surrounding natural environments. Since its establishment in 1986, the reserve and tortoise populations have been under severe environmental stress in the form of frequent unnatural fires, alien vegetation encroachment, and lack of recruitment from surrounding areas. Despite efforts to inform local residents about the value of the reserve in terms of its floristic component and the endangered tortoises occurring there, lack of public concern for this reserve has resulted in at least three deliberately lit wildfires, each destroying a portion of the two tortoise communities. Close monitoring of population numbers indicated that H. areolatus has been able to successfully cope with these fires in terms of population numbers, whereas P. geometricus experienced an 88% drop in numbers over a period of seven years, with little recruitment from resident breeding pairs. Possible reasons for the decline of P. geometricus appear to be (1) its specialised habitat requirements, (2) low recruitment rates, (3) slow recovery after catastrophes (its inability to cope with frequently recurring fires), (4) competition with the more successful H. areolatus, and (5) the possibly negative impact of disease following relocation to this site. A preliminary population viability analysis of the geometric tortoise population indicated that, should prevailing threats continue to operate, this most southern population of the species faced extinction before the end of this century. Steps to enhance its continued survival were initiated and by December 1993 the population appeared on its way to recovery. Population numbers were up, young were added to the population, and the habitat had recovered adequately. However, on New Year's Eve 1993 a deliberately lit wildfire wiped out approximately 80% of the recovered habitat and 78% of the remaining resident geometric tortoise population. The H. areolatus population was also reduced by approximately 51%. Steps to rescue remaining geometric tortoises from surrounding areas have been put into operation, but there is no guarantee that the same catastrophe will not recurr. It is clear that the right areas (such as the Harmony Flats nature reserve) situated in the wrong places are often extremely vulnerable to non-stochastic, human-induced catastrophes and that the success of these areas as viable sites depends exclusively upon the ability of management authorities to eliminate or at least mitigate potential sources of threat.
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