The large number of species, wide habitat tolerance, diverse diets and well developed brains of carnivores have combined to lead to the evolution of a wide range of behaviors and social systems. Only the higher primates have more complex behavior patterns and social systems than the social carnivores. This flexibility in behavior within the order can be seen between species and, perhaps most interestingly, within a species as it adapts to different environmental demands.
Many carnivores are solitary in that when they move about looking for food they do so on their own, or at most as a mother with her dependent offspring. However, detailed studies of theses so-called solitary species have revealed that although they may appear to be solitary, they share a terri-
probably because the females and their cubs are more detectable by strange males that may kill the cubs. In wooded savannas the males can leave the pride and look for other females to mate with when the cubs are quite small. It is easier to hide them from infanticidal males in the thicker bush. The cheetah (Acinonyx jubatus) is the only other cat whose adult individuals form long-lasting relationships, in that cheetah males also form coalitions of 2-3 individuals that cooperatively defend a territory.
The basic social system of dogs is different from the cats and is based on monogamy. However, canids show far more flexibility in their social systems both within and between species than the cats. African wild dogs (Lycaon pictus) and dholes (Cuon alpinus) live in very tight and close knit packs that always hunt together, but where the alpha pair are the breeders. Gray wolves (Canis lupus) may do the same, or go off in pairs. Red foxes (Vulpes vulpes) often forage alone, but may not always maintain a monogamous mating system and sometimes a territory may comprise one adult male and several vixens.
The mustelids, with over 50 species, are the largest carnivore family. They appear to be predominantly solitary, although sea otters may occur in "rafts" of several hundreds. The European badger (Meles meles) is one of the best studied carnivores and illustrates the fact that so many carnivores are tory with others of their kind and cooperate and communicate with their fellow group members.
The civets and genets (Viverridae) are a good example of the solitary template for carnivores from which the array of social systems seen in the order probably evolved. Solitary males live in comparatively large territories that encompass the smaller territories of several females. However, with palm civets, subordinate, usually younger males, occupy small areas within the dominant male's territory, avoiding contact with the dominant male as he moves through the area.
Bears are also mainly solitary, however, flexibility in behavior allows concentrations of brown and polar bears to collect at food sources. For example, brown bears (Ursus arctus) gather during the salmon migration on the northwestern seaboard of North America and polar bears may gather at a whale carcass in the Arctic Circle. Somewhat surprisingly, polar bears also concentrate during times of food shortage. During summer and fall when the ice has broken up, a number of males may fast together in peace at certain preferred sites along the coast. Testosterone levels are low and there is no food to compete for.
Many of the 37 species of cat are truly solitary and only one, the lion (Panthera leo), is highly social. Lions live in prides of 2-12 related females and their young. The members of a pride do not stay together all the time but they defend a common territory and are friendly towards each other when they meet. Males form coalitions, usually of 2-4, but up to 7. Males join prides, but their tenure is variable and they may be displaced by a stronger coalition, or themselves move on to another pride. Pride and territory size is variable with respect to resources, as is the association between the females and the males. In open areas males spend much time with the pride,
"blatantly solitary, but secretly social rafts" and has evolved a tendency to live in groups. Several badgers, mainly close relatives, may share a territory and live together in a large set, but forage on their own. The honey badger (Mellivora capen-sis) is another species that has been found to have a rather different social system than was thought before a detailed study was conducted. This time what was considered to be social, is in fact a solitary trait. Although sometimes seen traveling in pairs, a larger male and smaller female, these are not mated pairs, but mother and son. The single cub is dependant on its mother until it is larger than her. Males do however sometimes come together in groups of up to six and have very large overlapping home ranges when the solitary living females come on heat.
Mongooses show a very wide diversity of social systems. Most tend to be solitary, but three species, banded mongoose (Mungos mungo), dwarf mongoose (Helogale parvula), and meerkat (Suricata suricatta) have evolved complex and different social systems. In dwarf mongooses the dominant pair are most likely to breed, whereas in the banded and meerkat groups several females do so. One of the larger mongooses, the nocturnal white-tailed (Ichneumia albicauda) is another seemingly solitary species that exhibits a degree of sociality as several females have been found to have overlapping ranges.
The hyenas, with only four species, are the smallest carnivore family. Three species, the brown hyena (Parahyaena brunnea), spotted hyena (Crocuta crocuta), and aardwolf (Proteles cristatus) have been well studied and have shown a remarkable degree of diversity and flexibility in social systems. The spotted hyena is highly social living in female dominated clans of 5-80 individuals, living in fiercely defended clan territories that may be as large as 400 mi2 (1,000 km2), or as small as 16 mi2 (40 km2), depending on resources. In the Serengeti, with its migratory prey system, the clan system is flexible so that the hyenas can commute from their territories through other hyena territories to get to the feeding grounds. The brown hyena always forages on its own yet may share a territory with as many as 14 other hyenas. All clan members carry food to the den to feed cubs, not just the par-
A wild dog (Lycaon pictus ) pack attacks a hyena in Masai Mara, East Africa. (Photo by K & K Ammann. Bruce Coleman, Inc. Reproduced by permission.)
ents. The aardwolf is monogamous, yet during the mating season some males may be cuckolded by their mates, who may copulate with neighbors.
The procyonids have not been well studied, and although some species like the ringtail appears to be solitary, most appear to move in large groups. It is thought likely that all species maintain complex social relationships within and among the sexes. This is an important family for understanding sociality in carnivores and more studies are needed.
Why these differences in social system, and particularly why do some species form groups? An obvious answer is that carnivores form groups in order to cooperate in hunting. While this may be partly true, it does not explain why, for example, invertebrate-eating meerkats are so social. Even in the case of large prey hunters like lions and spotted hyenas it has been found that hunting group size is not necessarily related to hunting success, nor that this strategy leads to the acquisition of more food than solitary hunting. For the smaller species it has been suggested that being in a group helps prevent predation by increased vigilance and cooperative defense. While this is also sometimes true—meerkat individuals take turns in guarding while the rest of the group is foraging—it does not explain why other species like European badgers, red foxes, and brown hyenas forage solitarily yet sometimes live in groups.
The evidence suggests that these and many other group-living carnivores are influenced by the dispersion pattern of their food. For many carnivores, food is often irregularly dispersed in patches and some patches moreover are richer than others. Territory size is influenced by the distance between the patches, and the number of animals living in the territory by the richness of the patches. This is known as the Resource
Dispersion Hypothesis (RDH) and has been found to explain group size and territory size in a number of carnivores. It also explains why group size and territory size are not related. A group of brown hyenas living in an area with a large number of rich food patches close together will have a small territory and contain more members than one living where food patches are poor and widely dispersed. Similarly, in conditions where food patches are poor but close together both group size and territory size will be small. Once there is enough food in a territory to support several individuals it makes sense to share these with close relatives rather than a bunch of strangers. Any coincidental benefits that accrue then will be shared by relatives and also they can assist each other, for example by helping to feed each others young. For lions, the major advantage accruing to females living in the pride is the cooperative defense of their cubs against infanticidal males.
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