1. Long term dynamics of the Serengeti Ecosystem

2. SERENGETI
ECOSYSTEM
KENYA
TANZANIA

14. Wildebeest migration patterns

15. The reason
for dry season
migration
Kris Metzger

18. Migration patterns of Zebra and Gazelle

19. The Serengeti-Mara Ecosystem
24,000 square kilometers
Plains – woodland migration system
28 species of ungulates
10 species large carnivore, hyena most numerous

20. Serengeti Wildebeest Population
1800
1500
1200
Population Size (x 1000)
900
600
300
1950
1960
1970
1980
1990
2000

22. The regulation of the wildebeest population
What caused the increase?
What caused the leveling out?

25. Serengeti Wildebeest Population
1800
Drought
1500
1200
Rinderpest
removed
Population Size (x 1000)
900
600
300
1950
1960
1970
1980
1990
2000

28. Serengeti Wildebeest per capita Dry Season Food
350
300
250
200
150
100 50
1960
1970
1980
1990
2000

29. Serengeti wildebeest regulation
Food limitation allows regulation
of the population so that it levels out
at about 1.3 million animals

30. Serengeti wildebeest competitors
Food limitation leads to competition with some
other grazing ungulates
Thomson’s gazelle
But not Zebra – unknown why

31. Zebra and Thomson’s gazelle

32. Predation
What is the role of predators in the ecosystem?

34. PREDATION AS A LIMITING FACTOR IN NON-MIGRATORY SERENGETI UNGULATES
Tested by predator removal experiment:
In northern Serengeti for most large
predators removed. Then they returned after
1987. Prey populations were compared to an
adjacent non-removal area, Mara Park, Kenya

35. PREDATOR REMOVAL
Thomson’s gazelle 20 kg
Impala 50 kg
Oribi 18kg

36. Conclusions on regulation
Large ungulate species food regulated
Migrant species food regulated
Small resident ungulate species predator regulated

37. Climate change increase in wet season rain will increase
fuel loads and burning
increase in dry season rain will increase
fuel moisture and decrease burning
So how does burning affect the system?

38. Consequences of extensive burning
- The decline of savanna trees

39. Mara triangle 1944

44. Wildebeest grazing reduces grass fuel and area burnt

45. SERENGETI AREA BURNT IN DRY SEASON

46. Increase in wildebeest causes decrease
in burning

47. Complex interactions of wildebeest and the environment
The extent of grass fires is determined by the
degree of grazing imposed by wildebeest

48. 1980
Savanna
1986
1991
2003

49. Complex interactions –changes in tree populations
Savanna trees have gone through a cycle
of increase and decrease followed by increase again lasting about 100 years

51. Trees and elephant predation
1960s – blamed for the decline of mature
Acacia trees throughout savanna Africa.
- Elephant culling

55. Trees and elephant predation
1970s – fire rather than elephant shown to be
the cause of decline (Norton-Griffiths work in 1970s)
Elephant play another role by feeding on seedlings

59. Trees and elephant predation
1960s – the decline of mature Acacia trees throughout
savanna Africa. Elephants are blamed.
Elephant culling in Uganda, Kenya, Zimbabwe and
South Africa. Not in Tanzania.
1970s – evidence that excessive human caused fires reduce tree recruitment and tree populations collapse from senescence and not from elephant predation
1980s – experimental evidence that elephants can prevent regeneration and maintain a grassland state

61. Serengeti elephant population
Hunting
1880s-1920s
Poaching
Ivory ban

63. Serengeti keystones processes
Hyena, Lion
Small carnivores
Wildebeest
Resident
ungulates
Grasses
Dicots
Spatial
heterogeneity

64. Conclusions Serengeti has shown Evidence of natural regulation
Both bottom-up and top-down regulation occurs in the same system
There can be more than one state in species combinations
Keystone species can affect all levels in the system
There is long term natural change
Protected areas can provide baseline data to assess human impacts on other ecosystems

65. The End

66. Trees and elephant predation
1960s – the decline of mature Acacia trees throughout savanna Africa.
Elephants are blamed.
Elephant culling in Uganda, Kenya, Zimbabwe and
South Africa. Not in Tanzania.