Long term dynamics of the Serengeti Ecosystem

SERENGETI ECOSYSTEM KENYA TANZANIA

Wildebeest migration patterns

The reason for dry season migration Kris Metzger

Migration patterns of Zebra and Gazelle

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

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

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

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

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

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

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

Zebra and Thomson’s gazelle

Predation What is the role of predators in the ecosystem?

PREDATION AS A LIMITING FACTOR IN NON-MIGRATORY SERENGETI UNGULATES Tested by predator removal experiment: In northern Serengeti for 1980-87 most large predators removed. Then they returned after 1987. Prey populations were compared to an adjacent non-removal area, Mara Park, Kenya

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

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

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?

Consequences of extensive burning - The decline of savanna trees

Mara triangle 1944

Wildebeest grazing reduces grass fuel and area burnt

SERENGETI AREA BURNT IN DRY SEASON

Increase in wildebeest causes decrease in burning

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

1980 Savanna 1986 1991 2003

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

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

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

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

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

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

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

The End

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.