摘要:

SummaryFrom February to April of 1989 transects were run in four forested areas of northern Congo (Brazzaville) to census elephant populations using dung counts. A total of 401.0 km of line transects was completed during the survey. An overall extrapolated density of 0.7 elephants/km2was obtained with a variation from 0.3 to 0.9 elephants/km2. This study shows for the first time that elephants occur in high densities in a number of sites in northern Congo. When elephant dung density is plotted against distance from the nearest village for each transect a significant positive linear correlation results. Based on this correlation we hypothesize that the population of elephants in much of northern Congo is high. Local reports and our own observations indicate that elephant poaching is heavy in northern Congo and that the CITES ban on trade in African elephant ivory has had a limited effect on the level of poaching.

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1991.tb01000.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SummaryAerial sample survey, foot survey, vehicle survey, dry‐season droppings count and wet‐season droppings count were used for estimating elephant (Loxodonta africana africana) densities on the Nazinga Game Ranch, Burkina Faso and evaluated against the results of an aerial total count. Results of all survey techniques except the dry‐season dropping count method had low accuracies relative to the aerial total count. It is concluded that the droppings count method was the best and most cost‐effective survey technique available for estimation of elephant de

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1991.tb01001.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SummarySatellite tracking of elephants was found to be a valuable tool despite numerous technical problems. A local reference beacon is vital for obtaining an adequate number of accurate locations. Two out of ten satellite transmitters failed within two months of deployment, but an average of one location per collar transmitter was obtained every 3.4 days for the period October 1987‐May 1988. The study was made in the wet season in northwestern Namibia. Seasonal home ranges of elephants as determined by satellite tracking were larger than recorded elsewhere in Africa (c. 5800‐8700km2). Elephants from Etosha National Park moved to within 20 km of the Angolan border, and elephants in the Kaokoveld moved across previous bioclimatic demarcations of populations. The validity of previous classifications of elephants into discrete populations in northwestern Namibia is questio

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1991.tb01002.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SummarySix samples of taggedColophospermum mopanewere monitored for five years in locations with varying soil characteristics but with similar elephant densities. Physiognomic variation among the samples was related to soil differences, which also correlated with different browsing habits by elephants. The impact of elephant browsing further influenced both the physiognomy and demography ofC. mopane.Results from this study suggest that the influence of soils and elephants onC. mopanealter successional transitions from grassland to woodland. Soils that promote coppicing ofC. mopaneyield less stable woodlands when associated with elephants than soils promoting woodlands with large bolus, non‐coppicing trees. The dynamics of the latter are determined more by tree recruitment as influenced by such agents as other browsers or frequency and seasonality of bush fires. Implications for forest/elephant management are discusse

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1991.tb01003.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SummaryFour road counts and four series of daily road counts of 28.4% sampling intensity were carried out at Wildlife Ranching and Research Ltd (WRR), Athi River, Kenya, between December 1966 and July 1987 to test the applicability of the method to the WRR environment. The results, however, exhibited high variation. Difficulties were encountered when applying the Anderson&Pospahala (1970) method to detect the existence of visibility bias in the distribution of Thomson's gazelle. An alternative approach, based on the regression of group size on the right angle sighting distance was applied to detect the existence of visibility bias.

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1991.tb01004.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SummaryA study was made of the vegetation of three plots used in the Nigerian Man and Biosphere Research Programme for Savanna Studies. The aim is to provide detailed information on the vegetation of the plots which may possibly contribute to an understanding of factors influencing savanna structure and relative abundances of forbs, grasses and woody species. Results show that there are differences in the species composition of the plots. There are more forb species than grass species in each plot. The woody basal areas and crown areas of the plots do not depend entirely on the density but also on the size of the woody species. There are differences in herbage yield in the plots that could be attributed to differences in soil properties, species composition and level of human and animal activities between the plots.

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1991.tb01005.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SummaryIn some populations of the African butterfly,Acraea encedon, there are two kinds of females, one producing offspring in a normal 1:1 sex ratio, the other producing females only; in other populations the sex ratio is apparently normal. All‐female broods had hitherto been mainly associated with populations in which field sampling revealed an excess of females. The all‐female brood trait is described from a population at Dar es Salaam which field sampling suggested was normal, and this indicates that the trait may be much more widespread and common than had previously been supposed. This discovery also extends the known distribution of the trait across Africa from Sierra Leone to eastern Tanzania. The butterfly is also a polymorphic Müllerian mimic ofDanaus chrysippus, which is a highly unusual phenomenon as Müllerian mimicry is almost invariably monomorphic. The relative frequencies of two corresponding colour forms of the two species of butterflies at Dar es Salaam adds support to the hypothesis that they are indeed Mullerian mimics. The results of breeding experiments suggest that the polymorphic forms inAcraea encedonare allelic with domi

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1991.tb01006.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SummaryThe morphogenesis of the foetal membranes and placenta of the root‐ratTachyoryctes splendenswas studied by light microscopy. Implantation of the blastocyst is antimesometrial. The mode of implantation is secondary interstitial and the decidual reaction is similar to that in other rodents. Amniogenesis is by cavitation with a temporary open epamniotic cavity. Inversion of the yolk sac is complete but the disappearance of the parietal segment occurs relatively late. With the breakdown of both the decidua capsularis and parietalis, the yolk sac wall near the margins of the placenta becomes bathed in a pool of maternal blood and tissue debris resembling the haemophagous organ. The yolk sac villi are well vascularized. The allantoic cavity is persistent up to the limb bud stage. The definitive placenta is haemochorial and shows conspicuous endodermal sinuses or placental pit

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1991.tb01007.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1991.tb01008.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1991.tb01009.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY