Sunday 7 May 2023

Cheetahs and Wild Sheep

The cheetah (Acinonyx jubatus) is surely one of the most familiar of African animals, due in large part to their prominence in wildlife documentaries such as Cheetah Family & Me. They are charismatic, distinctive, and not especially rare or difficult to find. Unlike, say, tigers, they are not internationally listed as an endangered species, although their population has declined rapidly enough over the last few decades that they do qualify for the lesser rating of "threatened" or "vulnerable" species. 

This does, however, disguise some significant regional variation.

How we should divide the cheetah into subspecies is not absolutely clear. From at least the 1970s, five subspecies were recognised, Two of those were merged in 2017, on the grounds that the East African form could not be reliably separated from its southern relative genetically. Even then, cheetahs have so little genetic variation across their range - due to an apparent population bottleneck when they almost died out at the end of the Last Ice Age - that support for the existence of two of the other subspecies remains a little shaky. Still, four subspecies is, for the time being, the general consensus.

By far the most common, representing around two thirds of the estimated worldwide population of 6.500 cheetahs is the southern subspecies (A. j. jubatus) which lives across southern and eastern Africa from Namibia and South Africa in the southwest right the way round to Kenya in the northeast. As the repetition of the "jubatus" part of the name indicates, this includes the first cheetah to be scientifically described - although Johann Schreber was doing so on the basis of a skin he had seen, rather than a live animal. These are the ones you're most likely to see on wildlife documentaries, although it has to be said that all of the subspecies look essentially identical and we can only tell them apart with genetics.

This southern subspecies once lived across essentially the whole of Africa south of the equator and outside of the tropical rainforests. The northern half of the continent is inhabited by two subspecies, one in the northwest and one in the northeast. They too, once used to live across the whole of the region, but are now found in only about 10% of the places that they were a couple of centuries ago. The northeastern subspecies (A. j. soemmeringii), for instance, is now found for certain only in Ethiopia, Chad, and small regions of the CAR and Uganda; it may also still survive in some neighbouring countries but only in very small numbers if it does. This subspecies may represent something like 90% of the cheetahs outside of southern Africa.

Northwestern Africa has fared even less well than the northeast. The main surviving population is in southern Algeria, but some also live in Niger, Burkina Faso, and Benin and, conceivably, a few neighbouring countries. Their total population may be no more than 250, and, if cheetahs as a whole are not endangered, it's hard to argue that this subspecies (A. j. hecki) isn't.

The fourth subspecies is both more interesting and more imperilled.

This was first named by British zoologist Edward Griffith in 1821, although he'd only ever seen a drawing. At the time, he described it as an entirely new species, and it was this species that was used as the basis for the genus Acinonyx when Joshua Brookes named that seven years later. Part of the reason that Griffith didn't realise he was re-describing a known species was probably that his animal didn't live in Africa - it lived in India.

In fact, we now know that the Asiatic cheetah (A. j. venaticus) once lived across most of southwestern Asia. They were found from Israel and the Arabian peninsula to the edges of Bengal in the east, and as far north as the Caucasus and the Central Asian steppes in the north. Indeed, they were common just a few centuries ago. Akbar the Great, Mughal Emperor from 1556 to 1605, is said to have owned over a thousand cheetahs that he kept as hunting animals and, while that may have been the most dramatic example, he was hardly alone.

Asiatic cheetahs are the one undoubted subspecies, apparently having diverged from their African kin at least 30,000 years ago and possibly twice that far back. In fact, it's this animal, not the African one, that gives the species its English name; "cheetah" is originally Hindi, whereas most other European languages use some variant of the French "gu├ępard" which in turn comes from an archaic Italian word meaning "leopard-cat".

It's worth noting that 30,000 years ago would be well before the supposed population bottleneck in the ancestry of all cheetahs, which may mean that that the story about cheetah genetic variation is more complex than generally thought. Nonetheless, judging from the fossil record, cheetahs do seem to have originated in Africa, and only later emigrated to Asia. There was a fossil species, the "giant cheetah" (Acinonyx pardinenis) that once lived in Asia, and died out during the Ice Ages but the dates don't work for it to be an ancestor of the living species. Instead, it probably derived from a common ancestor that lived in Africa around 3 or 4 million years ago - we do have some fossil cheetahs from Tanzania at around this age, but they are too fragmentary to be given a species name.

If we hear far less about Asiatic cheetahs than the African sort, it's hardly surprising, since they're almost extinct - and don't have the benefit of being a full species or visibly distinct in the way that, say, snow leopards are. The decline in their population began in the late 19th century, but accelerated after World War II, with them having vanished almost entirely from the continent by the mid-'80s. Since then, only three tiny populations are known to have survived in central and north Iran, containing between them, at best, 40 adults.

But how best to go about preserving such endangered animals in the wild? Are there particular places that would be suited to doing so? Where an animal prefers to live and what it prefers to eat is something we can reasonably work out for a common species, but with one consisting of just 40 adult animals, it's less easy than it might otherwise be. We may know where are they are now, but it isn't necessarily where they'd do best, even assuming we could take human interference out of the picture.

We know where cheetahs live in Africa and what they eat. They live in open country, such as savannah, grassland, and even desert, and they prefer wide plains on which they can run down fast-fleeing prey. There is, after all, a reason that the only parts of Africa that never historically had cheetahs are the dense jungles of the Congo. They prefer to eat moderately-sized hoofed animals, often those that are too fast for other predators to chase, which mostly means gazelles, springbok, and impalas.

So we'd expect that Asiatic cheetahs would eat the local equivalent. There are no impalas or springbok in Asia, but, historically, three different species of Asian gazelle-like animal lived in the area formerly inhabited by cheetahs. One of these, the blackbuck, lives only in India, so while it was doubtless a major prey species in the past, it isn't of much use to those cheetahs now living in Iran. The other two do live in the right area but (while they are common elsewhere) they, too have limited populations there. Which is probably part of the reason for the cheetah's own decline.

This implies that to preserve the cheetahs, we also need to preserve Iranian gazelles. But it has also been pointed out that cheetahs can, and will, eat other animals too, and it has been argued that they survive perfectly well doing so and that some of these might live in areas that are easier to protect from human threats. The result has been a few decades of debate about the best way to preserve the Asiatic cheetah population given the limited resources available to do so.

A recent analysis of historical records going back centuries shows that, while gazelles seem to have always been the most common prey of Asiatic cheetahs, even when the cheetahs were widespread and common, they regularly fed on other animals too. The most common of these was the urial, the wild ancestor of domestic sheep, followed by hares, wild asses, wild goats, and wild boar in that order.

Analysis of Asiatic cheetah dung has shown that this is far from the case today. Gazelles are only a minor part of the diet of modern Asiatic cheetahs, presumably because they are so difficult to find. Instead, urials and wild goats are now the most common prey items, with hares coming in third, and the two local species of gazelle below that. Since wild sheep and goats aren't hugely common either, the main reason for their dominance in the diet is likely that the cheetahs have been forced into hillier, more precipitous terrain away from human settlements. Since many of the habits of these animals (such as the time of day they are active) are similar to those of gazelles, and they're about the right size, they may make particularly attractive targets.

What's significant, though, is that urials were already the second-most common prey of Asiatic cheetahs even when they could still roam freely and pick off whatever they wanted. Certainly, there has been a change, but if it was common enough to be mentioned in even quite old historical records, cheetahs must always have been more adaptable than we had thought. They probably catch the urials when they descend to the bottom of the hills that they live in, rather than chasing them through rocky and uneven terrain at higher altitude, but this wasn't something forced on them by desperation. 

With only a few dozen Asiatic cheetahs left alive, we can hardly say that their future looks rosy. But at least this gives a hint that we might have more choice than we thought when it comes to providing them with safe reserves in which to live. If nothing else, things aren't looking quite so bleak for conservation efforts.

[Photo by Ehsan Kamali, available under CC-BY-4.0.]

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