| dc.description.abstract | Maasai Amboseli Game Reserve, which covers
some 3000 km2 of southern Kenya, was ecologically
undescribed at the commencement of study.
This fact, coupled with its economic importance
as a natural resource and widespread concern
over its apparent degradation by livestock and
elephants, prompted the present study. The objectives
were to provide an ecological description
of the environment and large mammal communityof
the Amboseli basin, the area within the
Reserve of interest to conservationists. The
ecological study was intended as a baseline for
evaluating the management options and needs of
the area. This thesis deals wi th the ecological
aspects of study only.
The study is divided into three sections
which describe the structure, seasonal dynamics
and long-term changes of the Amboseli ecosystem.
The study area covers the wet and dry season
ranges of the large mammal communi ty, wi th the
main emphasis placed on the dry season concentration
area in which the overall biomass is limited
by the availability of forage.
The methods of study depended primarily on
sampling techniques from both ground and. aerial
counts taken at regular monthly intervals. such
samples formed the basis of a monitoring scheme
in which a large number of parameters of the
large mammal community and their environment were
recorded simultaneously. This enabled an analysis
to be made of the density and spatial distributions
of various species in relation to pasture conditions,
water availability, habitat type and other
species and to determine how these relationships
varied on a seasonal basis.
The Amboseli basin environment was strongly
influenced by late Pleistocene volcanics and an
important consequence was the establishment of
Lake Amboseli, a closed basin. Over the millenia
tilelake became infilled and eventually dessicated.
The soils remain saline and alkaline since the basin
still acts as the sump of the closed Amboseli
drainage system. The water table is elevated and
highly mineralized, though this is appreciably
less so in the soutner-nbasin where fresh water
inflows from Kilimanjaro create a number of permanent
swamps. Rainfall is low and erratic, generally
less than 400 mm. since the area falls in
the rainshadow of Kilimanjaro. The habitats are
markedly influenced by the salinity and alkalinity
of the basin as well as by the high water table.
Most of the basin is covered in open short grass
plains, and in the south by woodlands and swamps.
Surrounding the basin , bushed grassland characteristic
of the physiognomic type for the general
region prevails. However, virtually no permanent
sources of water are found here.
The large mammal community is comprised of a
broad .spectrum of herbivores and carnivores. Maasai
and their livestock are an integral part of the
community and contribute about 50% of the biomass.
Most of the species using the basin do so in the
dry season only. DtITing the rains the populations
largely disperse into the surrounding area of Ilkisongo
Maasailand. The principal areas of dispersion
for wild herbivores are the Emotoroki and El
Mau plains to the north and north east. Elephant
disperse over a wider range towards Selengei and
Namanga River. Livestock mainly use the northern
slopes of Kilimanjaro,and in the north, the Lengisim
area. A return to the basin follows the end
of the rains. The biomass wi thin the dry season
area can be correlated Witll climatic parameters.
During the dry season most species of wildlife
and livestock are limited to the immediate
basin vicinity by their dependence on the permanent
water in the swamps. \tJtihin this area most
species show a changing distribution in relation
to habitat throughout the dry season, although
there is a large variation in habitat specificity
ben/een the different species. The utilization
patterns of many species are probably linked
by a grazing succession. At least in the swamps
the succession is probably facilitative, the early
grazing by large herbivores improving the pasture
for later grazing by srraller herbivores.
Livestock show a similar utilization pattern to
wild herbivores and it is speculated that similar
feedback mechanisms operate in both cases to produce
such a convergence. Both are limi ted by the
availabili t-y of food wi thin the dry season range
when it is exhausted during prolonged dry seasons.
The mortality of livestock in a drought was found
to be appreciably higher than in wildlife.
The role of man in the ecosystem is paramount
and factors influencing the balance of Iivestock
and wildlife numbers are considered in some detail.
Haasai are found to be a highly efficient exploiter
of the ecosystem and the food chain efficiency 10f
the pastoral system compares favourably with that
of the wildlife component. In recent years water
development, veterinary and medical facilities and
famine relief in drought periods have made the
Haasai less dependent on the ecosystem and progressively
less able to manage witllin a subsistence
economy. Furthermore the wildlife attractions of
the area have encouraged a large tourist trade that
has progressively competed with the Maasai for
land rights in the basin.
In the near future it can be expected that
the dry season range will be gazetted as a National
Park while the Maasai will be given legal
tenure to land in the wet season range, areas
currently poorly used in the dry season by virtue
of their distance from water. In other words
tllerewill be an increasing separation of human
and wildlife ecology. The dual use of the wet
season areas is likely to continue, but in view
of the futvxe establishment of ranciling, wildlife
populations may well be limited by the food
available (or its accessability) in this part of
their range rather than in the dry season concentration
area.
Large scale habitat changes have occured in
Amboseli over the last two decades. The most conspicuous
feature is the decline of the Acacia xanthophloea
woodland, over 90% of the trees having
died during this interval. The primary cause of
habitat changes has been the salinization of the
basin area. Increases in the long term rainfall
have raised the water table some 3 to 4 m, resulting
in progressive increases in the level of soluble
salts in the rooting horizon of the Acacia ~-
L~o.phloea and other plants. This has caused a
marked shift from a hydrophytic to halophytic plant
community. Such Changes also appear to have affected
the compositions and possibly total biomass levels
of the large mammal cor.~unity. Elephants have
probably played a catalytic role .in woodland decline.
There is no evidence that their populations
are suffering compression from human encroachment
since the migration trails used as long ago as last
century are still used.
There is evidence to suggest that the recent
habitat changes are producing a habitat type
which existed last century when the climate was
slightly more moist than during the intervening
period. It appears that tileearly successional
stages of the basin community are subject to
acceleration and reversal by changes in rainfall
regime and water table fluctuations. | en |
