Serengeti Biodiversity
Biodiversity:
Differentiation in the genotypology and
phenotypology of organisms as a function of
evolution by natural selection
Natural Selection:
Differential survivorship as a result of
adaptive characteristics of an organism
with its environment, resulting in greater
reproductive success.
Driven by… mutation
Ecosystem:
An bounded or unbounded interconnected
biosphere of mutually affected organisms
within an environment.
The Serengeti-Mara Ecosystem (SME) one of the oldest
ecosystems on Earth
The Serengeti is the East African
Acacia savanna –
a Plains–Savanna biome.
The majority is in Tanzania, but the
northern part is in Kenya as the Masai
Mara National Reserve.
World Heritage Site of UNESCO
because of its large migratory
ungulate populations, high diversity of
large mammals and birds, prehistory
sites (Olduvai).
25,000 km2
Shortgrass
Soils are high in nutrients
Acacia woodlands in the west to Lake Victoria
Flood plains developed from ancient lakebeds near Victoria
In the far northwest, broadleaved woodlands and the highest
rainfall forms a refuge for the migrating ungulates at the end of the
dry season
1M wildebeest
200,000 zebra
Lion
Cheetah
Elephants
Leopards
Hyenas
Giraffe
Topi
Bushbuck
Warthog
Hippo
Rock hyrax
Grants gazelle
Impala
500 species of birds
Shaped by Two Powerful Forces
1. The Great Migration: Herds of ungulates 25 miles long follow fresh
grasses across the plains.
2. Fire: Anthrogenic and natural causes
Marked by shifts from grassland to woodland
Grasslands have naturally converted to woodland twice in the last one
hundred years, once in 1900 and again in 1970.
…many more impala in the park now because they are more adapted for
the woodland environment.
Researchers believe that the emergence of the woodland environment
was caused by a decline in the elephant population. Why?
Elephants
1960s: thought to cause decline of because often seen pushing over trees… calls for
culling of elephants.
Burning declined to a minimum in 1980 and has remained low because of heavy grazing
by wildebeest – why does this matter?
Areas burned since 1980 have been between 5% and 25%, indicating that significant
recruitment of trees should have occurred. But it didn’t’… why?
Elephants ate young tree recruits so extensively that no recruitment took place.
Demonstrates that there are multiple ecosystem states, in this case a woodland state
and a grassland state both with elephants.
Implications for conservation vs protectionism and need for long-term research.
Food supply limits population of wildebeests and large ungulates, but…
Smaller smaller species are limited by mainly by predation. Why?
Higher exposure to carnivores (predators have harder time killing very large
ungulates.
Threshold of prey size where the main mode of limitation switches rapidly from food
to predators as prey become smaller (about 150 kg, is approximately that of
wildebeest).
Migration allows populations to escape predator limitation to some extent.
Recent studies show that lions' hunting success is determined by the availability of
dense cover for ambush rather than by the density of prey.
These studies predict that the increase in dense cover due to the increase in young
tree populations has benefited lions by enabling them to catch more prey; and
greater hunting success should yield a decline in prey numbers. It has for small and
medium sized prey.
The downward trend has been most pronounced since 1980, which covers the
period when there was a substantial increase of young trees. Thus, plant structure
indirectly affects predator functional responses and thereby herbivore numbers.
Role of Predators
Wildebeest affect the populations of species far beyond their immediate food or
predator species. They maintain diverse assemblage of small flowering plants on the
plains.
Removal of grazing for a decade changes the shortgrass plains into tallgrass.
With this change of grass structure there are changes in grasshopper diversity—
some 49 species occur in tallgrass, whereas fewer than 13 species occur in
shortgrass.
As the wildebeest population has increased, plant species diversity has declined.
Grassland structure also determines the types of bird species.
Wildebeest affect most components of an ecosystem. Loss of the wildebeest
migration would radically alter the ecosystem.
Wildebeest: Lynchpin
Species
Serengeti Research Institute:
http://www.ntz.info/gen/n00555.html
Serengeti Biodiversity Program:
http://www.zgf.de/?projectId=74&id=65&l
anguage=en
http://www.savetheserengeti.org/news/highwaynews/report-serengeti-biodiversitycentre/#axzz1usRLfxf5