Long term dynamics of the serengeti ecosystem
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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

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Long term dynamics of the Serengeti Ecosystem

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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

0

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

Rinderpest

removed

1200

Population Size (x 1000)

900

600

300

0

1950

1960

1970

1980

1990

2000


Serengeti Wildebeest per capita Dry Season Food

350

300

250

200

150

100

50

0

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


Savanna

1986

1980

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.


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