IUCN / SSC Cat Specialist Group - Digital Cat Library |
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| Fabiano, E.C. | |
| Demografia hist¢rica e contemporƒnea de guepardos na Nam¡bia, µfrica austral | |
| 2013 Full Book | |
The origin of the contemporary genetic diversity of cheetahs is thought to be the result of a severe decline around the Last Glacium Maximum (8,000 - 20,000 years ago, ya), followed by an expansion around the mid-Holocene ( 5,000 years) and a subsequent bottleneck within the past century due to a combination of anthropogenic factors and weather variability. Alternative hypotheses exist. However, all remain largely untested despite advances in molecular analytical tools over the past decades. Likewise, the effects of anthropogenic factors on population viability merit quantification as well as trends in abundance and density using robust surveying techniques. This study aims to contribute novel information on these aspects. First, we explored the historical demography of the largest free-ranging cheetah population over the past 60,000 years. Second, we assessed the population's genetic viability and its sensitivity to perturbations on vital rates and uncertainties on current population size and carrying capacity estimates. Lastly, we assessed trends in density, abundance, and behavioural ecology aspects of cheetahs. First, demographic scenarios indicated that the population has a complex demographic history, characterised by periods of decline intercalated with periods of stability with no signal of expansion contrived during the past 60,000 ya. The population seems to have been stable over the past 300 years. Additionally, scenarios modeled on abrupt reductions had low levels of support in relation to models assuming gradual reductions. Second, we found the present population to be viable, although susceptible to perturbations such as the proportion of breeding females, adult female survival rates, and uncertainties in current abundance estimates and on carrying capacity. These parameters also influenced the total population size. However, the direction of the impact was related to perturbation levels. Lastly, and mostly applicable for males, we observed density estimates of 5 to 20 km-2 that were largely similar across most of the six multi-year surveys. Furthermore, male cheetahs showed high site fidelity. Overall individuals displayed a nocturnal activity pattern. First, the study shows that the population's contemporary genetic diversity (and possibly that of other populations to which our population is genetically connected) is the result of a gradual decline, likely caused by fluctuations and reductions of suitable habitat due to Pleistocene and Holocene climatic oscillations, as well as recent increases in aridification in Namibia. Second, that the population viability is largely dependent on aspects related to females, and that threshold values seem to exist beyond which certain conservation actions may have a negative influence on viability. Lastly, male density seems to be regulated by home range dynamics, as density remained similar across surveys except during periods of social instability caused by vacant home ranges. The instability caused by removals may lead to higher reproductive variance. Overall, the study shows that a realistic estimate of the risk of extinction faced by this population requires an integration of results obtained with several analytical approached, and that long-term conservation plans should incorporate such a body of information. |
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