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Tuesday 1st February 2011
What makes lions different from other large cats? Well, yes, the males have manes and lions have tufts on their tail tips, but the main difference is that they have a system of sociality not found among any other cat species. It is also a system of sociality not found among the more truly social animals like African Wild Dogs and wolves, banded mongooses and meerkats, and baboons and vervet monkeys. It is a social system cobbled together cat-wise from doubtless solitary ancestors.
This has led many to delve into both the origins and value of sociality to lions. With so many other non-social large and small cat species around to compare with, it would not seem difficult to unearth a reasonable explanation – but this has still remained elusive. Especially a convincing argument why lions became social, or as social as they are, has continued to be hazy. This is not for want of a diversity of studies on the subject, mainly originating from Craig Packer and his associates at the Serengeti Lion Research Project, who have perhaps shown a diversity of benefits to lions once they became social, but not why they became social.
George Schaller initiated the Serengeti project in the 1960’s and it has continued practically uninterrupted since then. Much of what is written about lions has come from that long-term project. Unfortunately, this means that much of what is known comes from a rather strange habitat (open grass plains) not typical of where most of the rest of Africa’s lions reside. Lions are extremely adaptable and flexible in their behaviour, and lions in different habitats behave differently.
Nevertheless, Schaller was among the first to document that lions did have a system of sociality, and he described it as fission-fusion. Rarely were all pride members present in one place, and females could remain separated from each other for considerable periods of time. Such females would split off in groups (especially when they had similar-age cubs) or in pairs or as singletons. Males would do the same. In other studies observations were similar – on very rare occasions (like when the lions had killed a large animal like a giraffe or buffalo) was the entire pride together, and sometimes single or paired females would split off for weeks. This fission-fusion tendency is therefore common, and rather goes against the concept of a social lion.
The crèche concept
But let’s look at some of the reasons proposed for this semi-social arrangement. One is that females gain reproductive advantages by joining together and raising their joint offspring in crèches – the cubs are communally suckled. We can throw that out immediately, as there is no evidence that lion females do better raising cubs than their solitary relatives like leopards, tigers, pumas, and cheetahs. Female lions are alone when they give birth to their cubs, and keep them in a den for the first 4-6 weeks of life. During that time, the female is behaving as a solitary cat while she might receive “visits” from other females and occasionally males. She can leave the cubs for over 24 hours at a stretch while hunting alone or with the other females during a time when the cubs are most vulnerable. Even when the cubs are joined in their crèches, no female remains behind to ensure their safety while others are off hunting. Cub mortality is high during the first year, and probably higher than we realize as it is only possible to accurately count cubs that emerge from dens. It is therefore not surprising that one third of 30 females followed in a Botswana study either produced no surviving cubs before they died, or had not produced any surviving cubs when data collection ended after 10 years.
The defence of offspring concept
Second, it was proposed that females in a group are more effective in defending existing cubs from infanticidal males than single females. This can be placed in the “perhaps” category, as the data on infanticide are not very clear. Females joined together in defensive alliances can be a powerful force in terms of showing a potentially threatening male the door, but to propose this as a selective force for joining together is a weak argument. For example, the Serengeti data show that approximately 25% of cub mortality results from infanticide. But that means that 75% occurs from other causes, listed as starvation, abandonment, and “unknown” by the researchers. In addition, tiger, leopard and puma females also have to deal with infanticidal males, but remain solitary. And although it is often stated that lions are the only felid species with social females, this ignores some very interesting studies among feral domestic cats that often form matrilineal groups. Any cat owner with more than one female living an outdoor life will have seen this trend. Male domestic cats are not infanticidal, but the domestic cat observations give an important clue to another possible reason why female lions group together.
Lions and urban gangs
So third, it might be beneficial to join into groups to defend territory. Craig Packer strongly espouses this, saying in a recent scientific publication that the bigger the female group, the better the territory. He likens it to urban gangs – the more members, the more territory can be defended, and then choice real estate is available. Apparently in the Serengeti, territorial battles are fierce and deadly, and Packer even relates incidences where pride males kill females in neighbouring territories to reduce the competition. My own research studies revealed a different scenario. First of all, lion territories are anything but rigid. In Botswana, and as I am sure in the Serengeti, occupation of a particular piece of territory is greatly variable. Botswana lions have wet season territories and dry season territories. All pride territories overlap, and all prides trespass. And yes, there are incidents in Botswana where neighbouring pride females are “discovered” while trespassing, but the resulting conflict is peaceable – lots of posturing and glaring, but no killing. And as for males killing females? Forget that. Botswana male lions go out of their way to find females in neighbouring prides, and the best way to describe the interaction is amorous. Second of all, solitary leopards and tigers and pumas also have territories that they defend. Maybe, like feral domestic cats, more joined females are better in terms of defending a particular territory, but it still falls short of an explanation for sociality. Perhaps in the Okavango Delta in Botswana there is more prey available across the wet and dry seasons than in the Serengeti, so lions can evaluate the risk of injury by defending territory in Botswana better than the Serengeti scenario of possible starvation if they do not.
Food is most likely the answer
And fourth, a proposal was put forward that food might have something to do with it. A solitary female lion during times of food scarcity in the Serengeti fared as well as groups of four or more in terms of food intake. But the whole food issue was confused by the theory that females needed to maintain large groups to defend territories and defend dependent cubs. So overall, the food question became too complicated by other themes deemed important by the Serengeti researchers to take on any level of importance.
However, I believe food is crucial to explain the levels of lion sociality that exist. The African savannas abound with a diversity of prey. And herbivores come in all sizes and shapes, from small antelopes weighing a few kilos to buffalos and giraffes and hippos and elephants weighing thousands of kilos. African savannas also abound with a great diversity of predators, and most of them compete heavily for small prey. Jackals and servals and caracals prey on rabbits and duikers and young impalas. Leopards and Wild Dogs and cheetahs take impalas and the young of wildebeest and other medium-sized herbivores. Hyenas can go for adults of the larger herbivores, but only when they operate as a clan. Lions are the largest predators in Africa, but when they are alone, they eat what many other predators do – medium sized prey.
Throughout history, there have been herbivores that grow very large. Giant ground sloths, mammoths, mastodons, woolly rhinoceroses, giant elks, lots of dinosaurs, etc. The theory is they do this to escape predation, and they also live in herds to form an even more formidable challenge to a predator. So what is the response of the predator – also grow bigger to take advantage of all those big prey animals? Dinosaurs did this – Tyrannosaurus rex was a formidable predator, but this strategy has not been mirrored among mammals. There were of course bigger predators in the past than there are now, look at sabertooth cats for example. But being a big predator comes with biomechanical consequences – you sacrifice speed for size for example. And it is difficult to be stealthy. And you cannot catch small prey when big animals are not around.
So let’s come back to the African plains. Lots of competition for the small and medium-sized prey among many predator species. But very little competition for adults of large prey animals – and these constitute tons of food happily living on the savannas – a resource not utilized. So along come lions. They are too small by themselves to tackle an adult giraffe or buffalo, but they can do it when they group together. So in my mind, the driving selective force to make lions social was entirely about food. Once they were social, the other benefits followed.
How did this sociality begin? Not difficult to envisage. All cat females form groups with their dependent offspring. Instead of dispersing when grown, stick together and tackle big prey in season. Make a good living off animals no other predator is capable of bringing down. And then retain the flexibility of hunting small prey as a solitary cat while you are at it, so you have the best of both worlds.
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Posted by Pieter Kat at 11:31
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