Tuesday, May 24, 2016

Evolutionary Ferrari faces uncertain future

Cheetahs are increasingly having to look over their shoulders in case a lion or leopard might steal their hard-earned catch.
Cheetahs are increasingly having to look over their shoulders in case a lion or leopard might steal their hard-earned catch.

The cheetah is a truly spellbinding animal to watch.

There is something about that laser-like gaze as it focuses on its prey, followed by a few slow carefully placed steps, then unwinding those huge hind-leg muscles it accelerates its lean body to deliver the highest top speed of any animal.

A cheetah is all business – built for speed - the Ferrari of the animal world. But if you think cheetahs have a charmed life think again, because the cheetah, especially females, have the hardest life of any of the big cats on the African plains. It is such a hard life, many zoologists think they are heading for extinction.

Places such as Tanzania's Serengeti are an evolutionary cauldron, a place where myriad species compete for prey determined to evade capture. Each species is trying to carve out an evolutionary niche to exploit the environment better than the competition.

On one hand, evolution has been good to cheetahs - they can outpace all other big cats, literally leaving leopards and lions in the dust. They can catch the speediest antelopes inaccessible to the rival species.

Cheetahs have superb eyesight complete with a darkly coloured slither of fur along the tear line, thought to reduce the tropical sun's glare allowing them to have a dazzle-free view of the landscape and potential prey.

On the other hand, being exquisitely evolved for speed has its problems. In the TV documentary Cheetah – Price of Speed, Earth Touch Productions highlights these problems with dramatic film of cheetahs on the African plains.

Cheetahs are light-boned creatures - once their prey is brought down and killed it can easily be stolen from them by the bigger and more powerfully built leopards and lions. All that effort and up to 70 per cent of their catches are taken. There is a fine balance between this evolutionary weight-control regime and starvation.

A cheetah can reach speeds of 100km/h but that takes a toll – it has to stop and draw breath, its heart pounding at 250 beats per minute. Cheetahs kill by lunging for the throat and strangling their prey. This minimises noise from the victim which would immediately attract bigger cats.

Rather than a flat-out sprint, the cheetah's skill lies in a series of rapid direction changes as they pursue their fleeing quarry. Their claws are only semi-retractable so a portion of the claw is permanently exposed enabling them to grip the ground in the constantly direction-changing chase.

However, claws and feet built for speed are not good for climbing trees. That's a severe disadvantage because it means cheetahs can't stash their kills out of reach of other predators. When cheetahs make a kill it has to be eaten fast – gorged. They don't win prizes for table manners.

This is in contrast to leopards which have rather refined dining habits. Leopards have retractable claws, preserved nice and sharp for grabbing prey and for tree climbing. They can drag their kills into trees, store them and eat at leisure, secure in the knowledge that their larder is beyond the reach of thieves. Leopards prepare their meal by carefully removing unwanted parts from their prey. Up-market dining in the big cat world.

Only if hard pressed would lions and leopards hunt in the midday heat. Cheetahs, to avoid the competition, are often forced to work these anti-social hours out there on the plains under the scorching sun. If they're unlucky they can expend a huge amount of effort for little or no reward.

Female cheetahs mainly live alone and are solo parents. Their offspring have to be nearby their mother at all times, even when mum is hunting. This is because they can't be tucked nicely away in trees and they don't have the social protection that lion cubs have in prides. Cheetah mums have to carry out the stressful and dangerous business of hunting as well as keeping a close eye on the cubs.

If all this wasn't enough, evolution has dealt cheetahs another blow, possibly a death blow. Tests show that cheetahs have low genetic variability.

The cause is thought to be a drastic population reduction during migrations 100,000 years ago and Ice Age climate changes. The result was extensive in-breeding. Today cheetahs lack the genetic variation and adaptability to secure a future in which they can adequately compete with leopards and lions.
It would be incredibly sad to see this stunning speedster driven to extinction.

Dr Roger Hanson is a New Plymouth-based chemical engineer with a PhD from the University of Cambridge.


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