Large mammal migrations
The annual large mammal migration between the
MMNR, the Serengeti National Park, the Ngorongoro Conservation Area
and neighbouring community areas, consisting of around two million
wildebeest, zebra and Thompson’s gazelle, is the defining
characteristic of the Greater Mara-Serengeti Ecosystem. The
migration is not only a major attraction drawing high number of
visitors to the area, but also plays a keystone role in the
Ecosystem, and impacts on the abundance and diversity of the large
mammal community by affecting competition and predation, as well as
having a host of other complex indirect ecological effects. In
addition, a smaller, separate “northern”
migration consisting of the same species remains within the Kenyan
part of the ecosystem, mixing with the larger migration in the MMNR
between July and September.
Ecosystem
MMNR forms a small part of a much larger protected
area complex (including the Serengeti National Park, Ngorongoro
Conservation Area, and a number of game reserves), which together
cover over 25,000 sq km. This ecosystem is large enough to maintain
many of its natural ecological processes and functions that have
been lost in smaller or more fragmented areas, as illustrated not
only by the continued existence of the large mammal migrations
discussed above, but also a host of other seasonal animal movements
and ecological processes, such as fire regimes and key hydrological
cycles. The conservation of these large-scale ecological processes
helps ensure that the Mara-Serengeti Ecosystem retains sufficient
ecological resilience to adapt and respond to ecological and
environmental fluctuations, and remains one of the world’s
most important areas for conservation and ecological
research.
Fauna
Although best known for the annual large mammal
migrations, the MMNR also supports a huge diversity and abundance
of resident ungulates and other herbivores, which combined with the
annual migrations, provide sufficient food to support one of the
highest densities of carnivores in Africa (including lions, hyenas,
leopards, and cheetahs). The MMNR is particularly important in this
regard, as it is one of the few areas in Kenya that is large enough
(when considered with the greater ecosystem) to support
ecologically viable populations of lions. In addition, the area
contains a number of other species of conservation concern,
including elephants, which have been shown to play a keystone role
in the area’s ecology, and one of only two remaining
indigenous Black rhino populations in Kenya. The MMNR is also
classified as an Important Bird Area by BirdLife International and,
as a result of the abundance of game in the area, six out of the
seven species of vulture found in Kenya (Egyptian, Hooded, Griffon,
Nubian, White-backed and White-headed) can be seen in the Reserve,
and in total over 500 bird species are known to occur, including 53
birds of prey.
The Mara River
The Mara River is the only perennial river in the
Mara-Serengeti Ecosystem, and rises in the Mau Escarpment from
where it flows through the MMNR and the Serengeti National Park to
Lake Victoria. It is the primary, and occasionally the only,
dry-season source of water for wildlife in the MMNR and Serengeti
National Park, and the survival of the large mammal migrations in
their current form depends on seasonal access to this river,
especially during periodic droughts. Its main tributaries are the
Amala and the Nyangore Rivers, which drain from the western Mau
escarpment, and the Sand and Talek Rivers, which rise in the Siana
and Loita Hills.
Woodland-grassland habitat mosaic and
cycles
The Mara-Serengeti Ecosystem has undergone a
series of well-documented woodland-grassland cycles over the last
100 or so years, and recent research suggests that the ecosystem
can exist in multiple states of woodland or grassland, and that
long-term change between different states is a natural phenomenon.
Figure 3 overpage illustrates the grassland-woodland dynamic and
the main factors that cause the transitions between stable states.
As illustrated, fire incidences, themselves modulated by rainfall
patterns, are the main factor influencing vegetation states;
however, keystone species (such as wildebeest and elephants) also
play an important role in maintaining and influencing these states
through their grazing/browsing patterns.
