Dying Out of Africa

Impala on Crescent Island

Crescent Island, Lake Naivasha, Kenya

Just in Kenya, we visited Crescent Island Wildlife Sanctuary. Samples of wildlife from all over Kenya were introduced for Sydney Pollack’s adaptation of the Isak Dinesen (Karen Blixen) novel Out of Africa featuring Glenn Close and Robert Redford. Impala, Grant’s gazelle, wildebeest, waterbuck, etc.

And now these animals are dying.

Cadaver after uneaten cadaver–we encountered about 20–lay in various forms of decay. As we walked around the island, my students began to ask why so many remains dotted the savannah, shrubland and acacia forest.

It’s island biogeography. Sexy stuff. At first we wondered if it were nothing more than the animals’ old age and no where else for them to go and die. But the sheer number of dead animals started to make this seem unlikely. The lifespan for most of these ungulates is around 12 years, wildebeest 20.

We considered overpopulation with the commensurate overgrazing and resultant malnutrition and disease. Most of the grass was eaten down to beige stubble. This seemed to make the most sense to us.

Then I listened to Christopher Joyce’ article When Big Carnivores Go Down, Even Vegetarians Take The Hit. He reports on how the loss of predators like wolves in the US and Canada results in an ecology where overgrazing by herbivorous prey of these carnivores leaves less for other animals to eat. The population explodes, then gets sick from overexploitation of available resources and dies.

Seems a possible explanation for the mystery of Crescent Island Wildlife Sanctuary. To my knowledge, predators were never introduced here. The backdrop of the movie was the peace undulating movements of unhurried giraffes, not a hurried panic away from lions. And ecologically, where there are no tertiary consumers or the effective replacement of that dynamic by hunting, the herbivores eat themselves to death.

What do you think? Are there other possible explanations?

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