摘要:

SummaryDistribution ofDendrohyraxv.validusTrue which inhabits the forest belt of Mt Kilimanjaro, Tanzania, is discussed along with factors influencing this distribution. During December 1972 data were collected from the northern, eastern, southern and western slopes at 2000, 2310 and 2620 m a.s.l. to discover the effect of aspect and altitude on vegetation in relation to the densities of the tree hyrax. Using point‐centred quarter method (PCQ) the area around each tree was inspected for recent and abandoned defaecation sites; the tree species and its circumference at breast height were also recorded.Apparent densities of hyrax, as reflected by the density of defaecation sites, were higher on the southern and western slopes (av. twenty‐three and thirteen hyrax/ha) although a density of seventy hyrax/ha was obtained for the northern slope at the 2620 m elevation. The eastern slope was poorest with only one defaecation site recorded. Higher densities were obtained for the 2310 m elevation indicating less disturbance of this belt through logging and also showing the influence ofOcotea usambarensisEngl, on the southern andNuxia congestaFres. on the western slopes which are abundant at this elevation. The tree hyrax showed definite preference for certain tree species and for the larger individuals.Since food is not limiting, it is suggested that the availability of shelter, strong preference for solitary living, and the inability to withstand rigorous environment limit the density of hyrax within the forest, as well as providing a possible explanation for the inability of this hyrax to venture far outside the for

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1976.tb00241.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryPublished hypotheses to account for habitat changes wrought by elephants begin from the assumption that elephant‐forest systems possess a stable equilibrium point. The ‘elephant problem’ is conceived as a displacement of this equilibrium by man. Controversy centres around which human activities caused the dislocation of equilibrium and by which mechanisms these activities resulted in local high densities of the elephantLoxodonta africana.A study on elephant‐forest relationships in the Luangwa Valley of Zambia casts doubt upon the basic assumption of these hypotheses and an alternative hypothesis is therefore offered. It begins from the opposite assumption–that there is no attainable natural equilibrium between elephants and forests in eastern and southern Africa. The relationship is viewed instead as a stable limit cycle in which elephants increase while thinning the forest and decline until reaching a low density that allows resurgence of the forest. This in turn triggers an increase of elephants and the cycle repeats. The period of the cycle, if the hypothesis is correct, is in the order of 200 years in the Luangwa Valley.The activities of man can impose an artificial equilibrium on the system such that trees and elephants are trapped at the low density phase of the cycle. When interference is relaxed, as with the conversion of an area to a national park, the cyclic relationship reasserts.The parameters of a system possessing a stable limit cycle need not differ in kind or interrelationship from those of a system with a stable equilibrium. Whether one or other outcome manifests may depend only on the numerical values of the parameters. If the elephant‐forest system is characterized by a stable limit cycle the period and amplitude should change along a climatic gradient and may contract to a stable equilibrium in some climatic zones. A set of predictions is offered to facilitate rejection of the

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1976.tb00242.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryNine different diurnal activities of elephant—grazing, browsing, debarking, drinking, wallowing, resting in the shade, resting in the open or sun, certain social activities and walking—were monitored during the day. Possible reasons for seasonal differences in time spent per hour engaged in each of these activities are gi

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1976.tb00243.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Summary(1) Communities were identified in the field from presence/absence records of species using a form of progressive approximation. These communities were then mapped from aerial photographs of the Reserve area and boundaries were later checked on the ground. The quantitative characteristics of the communities were described in terms of cover and frequency.(2) The data were subjected to standard computer analyses and these results are used in an assessment of the validity of the original subjective techniques.(3) A hypothetical scheme is suggested which explains the principal lines of vegetation variation in terms of water availability and soil salinity. A number of related vegetation catenae may be recognized in addition to an east–west trend of increasing tree cover which is attributed to decreasing salinity along the riverine strip.(4) It is concluded that the effects of grazing and burning regimes are superimposed upon those of the physical environment and that further rapid changes in vegetation composition will take place within the next few decade

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1976.tb00244.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1976.tb00245.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1976.tb00246.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1976.tb00247.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

ISSN:0141-6707    

DOI:10.1111/j.1365-2028.1976.tb00248.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY