Owing to habitat loss and fragmentation, large mammal populations all over the world are becoming increasingly small and isolated. It is therefore a conservation priority to understand mechanisms influencing the demography of such populations, which can easily be driven to extinction. The Przewalski's horse Equus ferus przewalskii remains one of the world's most endangered species and reintroduced animals are still vulnerable. Over 9 years, we analysed factors affecting mortality and female fecundity at the individual level in a predator-free, closed population of Przewalski's horses, which grew from 11 to 55 individuals. Similar to other wild equids, the annual growth rate of the population was r= 0.169. Typically, adult mortality was much lower than juvenile mortality, the latter being correlated with neither inbreeding coefficient of foals nor population density. We found no link between female fecundity and operational sex ratio of the herd, or inbreeding coefficient, lactation status and body condition of the mares. Although food therefore seemed not to be limiting in this population, density (number of horses ha À1 ) clearly reduced fecundity, especially in subadult mares. Thus, our results show that space can slow the growth rate of a population before resources become limited, a potential source of concern for increasingly shrinking habitats of endangered large mammals. Possible mechanisms causing this may be found in incest avoidance or other social parameters. Finally, in large herbivores, population density is said to exert influence in a sequential order: juvenile survival first, followed by fecundity of young females, then adult females, and adult survival last. Although we observed no link between density and juvenile survival in the studied population, our results otherwise support this hypothesis.
Livestock grazing is a key factor in many grassland ecosystems and can substantially influence the conservation of grassland species. The Crau steppe in southern France is a protected area that is traditionally grazed by sheep. The Critically Endangered Crau plain grasshopper Prionotropis rhodanica is endemic to the area and a flagship for the conservation of this unique ecosystem. Its population has declined significantly during the last 2 decades, but the reasons remain poorly understood. One potential factor is an altered habitat structure caused by changes in the grazing regime. We examined the microhabitat preferences of the species and compared the habitat structure of populated sites with those where the species is now extinct (former habitat). We found that populated sites had denser and higher vegetation, whereas former habitat had higher cover of stones and bare ground. Vegetation structure in the habitat of the smallest subpopulation was similar to areas of former habitat, suggesting a marginal habitat quality. Our results show that P. rhodanica requires 50–70% vegetation cover and suggest that grazing has contributed considerably to the population decline, but it remains unclear whether this is a direct effect of habitat degradation or an indirect effect by attracting predators associated with grazing activities. We recommend careful management of grazing to improve habitat quality, which would also benefit other invertebrates and insectivores. Continued monitoring is required to conserve habitat specialists in protected areas.
The onager Equus hemionus onager, a wild ass for domestic use, and land conversion have been identified as the main threats to the two remaining onager endemic to Iran, is categorized as Critically Endangered on the IUCN Red List. Its biology and conservation populations. In addition, geographical isolation could cause the loss of genetic variability in these two relatively requirements are poorly documented. We report our observations, made in 1997 and 2000, on the behaviour small populations, and also makes them more susceptible to the potential eCects of stochastic events such as drought and ecology of the two remaining populations, located in the Touran Protected Area and the Bahram-e-Goor or disease. Public awareness, appropriate protection, and scientific studies must be urgently supported by both Reserve. Recent population counts by the Department of Environment of Iran (471 in the Protected Area and 96 national and international organizations in order to prevent the extinction of these two apparently dwindling in the Reserve) are markedly lower than the estimate of 600-770 made in the 1970s in the Touran Protected Area. populations of onager. We observed social interactions between stallions and mares outside the breeding season that contrasts with Keywords Ass, behaviour, conservation status, Equus hemionus, Iran, onager. the known social structure of this subspecies. Poaching, competition with domestic animals, removal of shrubs The Asiatic wild ass Equus hemionus is one of seven ass Equus h. khur as Endangered, and the Mongolian wild ass E. h. hemionus and the Gobi khulan E. h. luteus as equid species, the others being E. kiang and E. africanus, the zebras E. zebra, E. grevyi and E. burchelli, and the wild Vulnerable on the IUCN Red List (IUCN, 2002; Moehlman, 2002). Wild populations of onagers (goor in Farsi) occur horse E. ferus przewalskii (Moehlman, 2002). In historical times isolated populations of Asiatic wild ass ranged from only in Iran, and there is an introduced population in Saudi-Arabia and a hybrid population of onager * kulan Turkey to northern China, and from Kazakhstan to Saudi-Arabia and India (Duncan, 1992). Equus hemionus now in Israel (Duncan, 1992; Ziae, 1996). The setting of conservation priorities for E. hemionus occurs in China, Mongolia, Turkmenistan, Kazakhstan, Iran and India (Moehlman, 2002). Of the six subspecies faces a number of problems: the taxonomy of the subspecies is still in debate, with the apparent occurrence of E. hemionus the Syrian wild ass E. h. hemippus is categorized as Extinct, the kulan E. h. kulan and onager of several morphologically indistinguishable subspecies, populations are widely dispersed, and little is known E. h. onager as Critically Endangered, the Indian wild about any trends in population sizes. The Equid Specialist Group of the IUCN has highlighted the lack of data
Information on population sizes and trends of threatened species is essential for their conservation, but obtaining reliable estimates can be challenging. We devised a method to improve the precision of estimates of population size obtained from capture-recapture studies for species with low capture and recapture probabilities and short seasonal activity, illustrated with population data of an elusive grasshopper (Prionotropis rhodanica). We used data from 5 capture-recapture studies to identify methodological and environmental factors affecting capture and recapture probabilities and estimates of population size. In a simulation, we used the population size and capture and recapture probability estimates obtained from the field studies to identify the minimum number of sampling occasions needed to obtain unbiased and robust estimates of population size. Based on these results we optimized the capture-recapture design, implemented it in 2 additional studies, and compared their precision with those of the nonoptimized studies. Additionally, we simulated scenarios based on thresholds of population size in criteria C and D of the International Union for Conservation of Nature (IUCN) Red List to investigate whether estimates of population size for elusive species can reliably inform red-list assessments. Identifying parameters that affect capture and recapture probabilities (for the grasshopper time since emergence of first adults) and optimizing field protocols based on this information reduced study effort (−6% to −27% sampling occasions) and provided more precise estimates of population size (reduced coefficient of variation) compared with nonoptimized studies. Estimates of population size from the scenarios based on the IUCN thresholds were mostly unbiased and robust (only the combination of very small populations and little study effort produced unreliable estimates), suggesting capture-recapture can be considered reliable for informing red-list assessments. Although capture-recapture remains difficult and costly for elusive species, our optimization procedure can help determine efficient protocols to increase data quality and minimize monitoring effort.
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