Recherches ecologiques sur une savane sahélienne du Ferlo septentrional, Sénégal : quelques effets de la sécheresse sur le peuplement mammalien

The results of the 1972-73 drought on the mammal populations of the IBP study area, at Fété Olé, Sénégal, are summarized. Some desert species, like Desmodilliscus braueri and Gazella dama were observed more often than usual. The numbers of Taterillus pygargus, the commonest granivorous rodent, decreased sharply but the species succeeded to breed despite the almost complete lack of grass cover : these rodents probably fed upon the surplus of seeds of the preceeding year remaining on the ground. Most Carnivore populations declined in numbers during this unusually dry period

Les mammifères

size is 4 young. A female may have a litter every 6 weeks changing its burrow each time. However births only take place after the rains, from November to March. The population turnover is high, mortality rate among adults averaging 25 % per month. Data are given on population fluctuations over two consecutive years. Net production in a given year is strongly influenced by the importance of the previous rains. On quadrat QR, production (fresh weight) was 392.8 g/ha in 1969-70 after « normal » rains, and only 42.4 g/ha in 1970-71 after sub-normal rains. On quadrat QF, the respective figures were 599.0 g/ha in 1969-70 and 63.6 g/ha in 1970-71. A first estimation of the trophic impact of Taterillus pygargus on the production of seeds is made : out of the 40- 60 Kg/ha produced, 2.1 to 6.6 Kg/ha arc consumed by this species alone. Size is 4 young. A female may have a litter every 6 weeks changing its burrow each time. However births only take place after the rains, from November to March. The population turnover is high, mortality rate among adults averaging 25 % per month. Data are given on population fluctuations over two consecutive years. Net production in a given year is strongly influenced by the importance of the previous rains. On quadrat QR, production (fresh weight) was 392.8 g/ha in 1969-70 after « normal » rains, and only 42.4 g/ha in 1970-71 after sub-normal rains. On quadrat QF, the respective figures were 599.0 g/ha in 1969-70 and 63.6 g/ha in 1970-71. A first estimation of the trophic impact of Taterillus pygargus on the production of seeds is made : out of the 40- 60 Kg/ha produced, 2.1 to 6.6 Kg/ha arc consumed by this species alone

Les conséquences d'un supplément alimentaire sur la dynamique des populations de rongeurs au Sénégal. II - Le cas de Taterillus pygargus en zone sahélienne

A food supplement was provided every second day during the nine months of the dry season to a population of the gerbil Taterillus pygargus on the former IBP study site of Fété-Olé, Northern Senegal. The effects of this supplementary food were assessed by comparison with the population of a control quadrat set up in the same dry bush savanna. During the first three months of food provisioning, a spectacular increase of Taterillus pygargus numbers was noticed on the provisioned quadrat (QA), as compared to the control area (QT). This was entirely due to a concentration of mature individuals, mostly adult males. Food provisioning also had a beneficiai effect upon the growth curve of young individuals, and on the adult body weight, in both sexes. The breeding season of the females was also lengthened on the provisioned quadrat, but the production of young was not significantly different on the two quadrats. However, food provisioning du ring the lean part of the year was unable to prevent or slow down the sharp population decline of this species which took place from January to June 1977, at Fété-Olé as well as all over Northern Senegal. Such a population crash cannot therefore be ascribed to a mere shortage of foo

Mars Express High Resolution Stereo Camera spectrophotometric data: Characteristics and science analysis

The High Resolution Stereo Camera (HRSC) on the Mars Express (MEx) spacecraft in orbit about Mars is delivering images of the Mars surface and atmosphere from its high-inclination, elliptical orbit that are intended to cover most of the Mars surface by the end of the mission. These are acquired in four specific spectral passbands that sample the scene at different parts of the extended visual spectrum from near 0.4 μm to about 1μm and in five additional channels, four used for stereo and one nadir, that use the same fifth spectral passband. These channels view from different angles and can be used for photometric and spectral analysis. The data allow a variety of studies of the surface and atmosphere of Mars, but these require detailed understanding of the data characteristics, as there are several effects, including of the observation geometry and the atmosphere, that need to be treated. This article is a report to the science community on the current understanding of the HRSC color data after an initial analysis and also a demonstration of their capabilities for study of Mars, which, from this study, appear to be considerable. We first discuss the characteristics and calibration of the HRSC spectral data. The atmospheric influence on the photometric appearance of the surface materials is explored, and methods of compensating are considered. Reflectances are calculated for surface units by assuming the dark material is basalt and scaling the entire HRSC scene using a laboratory basalt spectrum for the selected dark material area; the results and the correction factors for different orbits are compared. We present several examples of what could become a large volume of future science results utilizing the HRSC spectrophotometric data in conjunction with photo-interpretation. For example, we find relatively few but very important distinct spectral components at the HRSC resolution, including what we interpret as iron oxide-rich material, unoxidized basalt, and polar ice, consistent with past works. The major spectral components are distributed in ways that suggest compositional mixing and the need to revise the current geologic understanding of major regions