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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SERENGETI

ECOSYSTEM

KENYA

TANZANIA



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The reason

for dry season

migration

Kris Metzger



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The Serengeti-Mara Ecosystem

  • 24,000 square kilometers

  • Plains – woodland migration system

  • 28 species of ungulates

  • 10 species large carnivore, hyena most numerous


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Serengeti Wildebeest Population

1800

1500

1200

Population Size (x 1000)

900

600

300

0

1950

1960

1970

1980

1990

2000


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The regulation of the wildebeest population

  • What caused the increase?

  • What caused the leveling out?


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Serengeti Wildebeest Population

1800

Drought

1500

Rinderpest

removed

1200

Population Size (x 1000)

900

600

300

0

1950

1960

1970

1980

1990

2000


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Serengeti Wildebeest per capita Dry Season Food

350

300

250

200

150

100

50

0

1960

1970

1980

1990

2000


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Serengeti wildebeest regulation

Food limitation allows regulation

of the population so that it levels out

at about 1.3 million animals


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Serengeti wildebeest competitors

  • Food limitation leads to competition with some

  • other grazing ungulates

  • Thomson’s gazelle

  • But not Zebra – unknown why



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Predation

What is the role of predators in the ecosystem?


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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


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PREDATOR REMOVAL

Thomson’s gazelle 20 kg

Impala 50 kg

Oribi 18kg


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Conclusions on regulation

  • Large ungulate species food regulated

  • Migrant species food regulated

  • Small resident ungulate species predator regulated


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  • 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?


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Consequences of extensive burning

- The decline of savanna trees






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Complex interactions of wildebeest and the environment

The extent of grass fires is determined by the

degree of grazing imposed by wildebeest


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Savanna

1986

1980

1991

2003


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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


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Trees and elephant predation

1960s – blamed for the decline of mature

Acacia trees throughout savanna Africa.

- Elephant culling


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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


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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


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Serengeti elephant population

Hunting

1880s-1920s

Poaching

Ivory ban


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Serengeti keystones processes

Hyena, Lion

Small carnivores

Wildebeest

Resident

ungulates

Grasses

Dicots

Spatial

heterogeneity


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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



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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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