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Lose the cheetah, and then what?

by Rebecca Nesbit

For the first time since the dinosaurs disappeared, humans are causing species to go extinct faster than new species can evolve. The causes of extinction are varied but include habitat loss, illegal poaching, overharvesting and the introduction of invasive species.

But extinction itself can be a cause. Hunting one species to extinction will affect anything that depends on it. This is often something that eats it, and even predators can be food – including for scavengers such as vultures, and for the parasites which live on them.

A paper just published in the Journal of Animal Ecology used a food web of plants and animals in the Serengeti to estimate what is likely to happen when species go extinct. It is often large-bodied species that go extinct first - for example top predators, such as cheetahs, and herbivores such as antelopes. This paper used the International Union for Conservation of Nature (IUCN) red list  for estimates of the order in which endangered species will go extinct.

The scientists used a computer model to calculate the effect of losing the 14 species likely to go extinct first. Their findings suggest that the loss of these species won’t immediately cause any other extinctions. But in their model the loss of these 14 species did lead to changes in the structure of the food web. This change in structure may well affect the ability of the system to cope with future disturbances.

There could also be a tipping point just down the line – one species may now have become the one which holds things together so lose that and you get many more extinctions.

It is of course extremely difficult to predict what effect extinctions will have. But one important thing is the order in which the extinctions occur – will the cheetah become extinct before the antelope, or will the antelope die out first and force the cheetah to try eating other things?

So what’s the moral of the story? Let some species go extinct and you may be fine. But you’re taking a risk – there are lots of factors affecting how wide reaching the effect of this extinction is – and the ecosystem may be less robust even if it still keeps the rest of its species for now.

de Visser, S., Freymann, B. & Olff, H. (2011) The Serengeti food web: empirical quantification and analysis of topological changes under increasing human impact. Journal of Animal Ecology 80, 465–475

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