Controlling the herbivorehunter balance

Modern-day forest large carnivores notably now consist of a variety of big cats at low densities (from the Siberian tiger Panthera tigris altaica of Eurasian conifer forests weighing up to 300 kg to the diminutive 2-3 kg kodkod Oncifelis guigna of the temperate mixed forests of Chile and Argentina) and the wolf. The wolf Canis lupus was formerly the most common predator in the woodlands and grasslands of the world. Large populations are now largely restricted to a few relatively remote territories, such as Alaska, northern Canada and eastern Europe, although the natural range of the grey wolf is probably greater than that of any other living mammal, apart from humans. Wolves are highly intelligent social animals that travel very great distances in search of their prey, often migrating with them. Their packs have a well-defined hierarchy with the alpha-male, to which all the other individuals defer, at its apex. These large animals co-operate to bring down and kill animals that are often much larger than themselves. Once a potential victim, typically a young, old, sick or wounded animal, has been identified the pack will continue to harry it even if it manages to rejoin its companions. Wolves can eat enormous amounts of meat in very short periods, and at frequent intervals, but are capable of going without food for several days.

Radio-tagging has recently thrown remarkable light on the early life ofwolves, which often roam alone for at least 2 years after weaning. An 11-month-old grey wolf cub was found injured beside a ring road west of Parma, Italy, in February 2004. Park rangers were called and it recovered under the care of a veterinary scientist. It was released on a snowy day in March weighing a healthy 28 kg and its subsequent progress traced by means of a global positioning satellite unit on its collar. Whereas previous radio-tagged wolves had rarely travelled more than 50 km, this one followed a wandering path, crossing the Italian Maritime Alps to a nature reserve in Cuneo Province and staying there for a time with resident wolves. It eventually crossed into France and continued west and by September 2004 had travelled a total distance of over 1000 km and reached a point 350 km in a straight line from its point of release.

There are a number of varieties of wolf, of which the grey Mexican wolf C. lupus baileyi, now found in the wild again, was at one time reduced to just five animals, all of them in captivity. The task of gradually returning them to the wild was a long and complicated one, involving the mating of two healthy animals which became the alpha-male and alpha-female ofthe new pack, getting them used to a much wider territory and finally releasing them in an area where they taught themselves the art of tracking and killing appropriate prey.

In the absence of large carnivores, elk populations in Yellowstone National Park became excessive. The re-introduction of wolves was very successful in regulating the deer here. The carnivores, which were sedated, flown in from a distance and then released, soon adapted to their new habitat and prey. After initially feeding only on deer, they also learnt how to pull down and kill bison Bison bison, formidable animals able to kill badly placed wolves by kicking or goring them with their horns. In former times, relationships between wolves and the European bison B. bonasus (Fig. 5.16), a more long-legged animal than its American cousin, were much the same, with the wolves concentrating their attention on the young and sickly members of the herd.

The existence of antipathy between particular pairs of carnivore species, such as foxes and pine martens, is well established. In most cases, as with foxes and wolves, there is no direct competition for food or other benefit, but the result may well be conclusive as far as the less powerful predator is concerned. Foxes feed on rodents, fruit and invertebrates, and sometimes scavenge the remains of wolf kills; whereas wolves consume large herbivores, particularly moose. Nevertheless, foxes are killed by both wolves and lynx in the Bialowieza Forest, Poland, and wolves are recorded as killing them elsewhere (Yalden, 2003).

Of the larger omnivores, bears are formidable animals and can be dangerous if disturbed, but are certainly much less ferocious than the considerably smaller wolverine Gulo gulo, which is capable of driving even a bear or cougar Felis concolor from its kill. The latter is believed to be the most widely distributed carnivore in the New World. Bears arose in the Miocene (5-24 Ma) as an offshoot of a central stock which gave rise to dogs, wolves and foxes. Though they have many colour variations, the present world population consists of

Ecology Balance

Figure 5.16 European bison Bison bonasus, which was once a common forest herbivore. Though now comparatively rare, populations exist in the southern mountains and Biaiowieza forest of Poland, in Russia, Lithuania, Belarus, Ukraine, eastern Slovakia and the Romanian Carpathians. Substantial remnants of American bison B. bison herds still survive. Both animals greatly influenced forest ecosystems in earlier times. (Drawn by Peter R. Hobson.)

Figure 5.16 European bison Bison bonasus, which was once a common forest herbivore. Though now comparatively rare, populations exist in the southern mountains and Biaiowieza forest of Poland, in Russia, Lithuania, Belarus, Ukraine, eastern Slovakia and the Romanian Carpathians. Substantial remnants of American bison B. bison herds still survive. Both animals greatly influenced forest ecosystems in earlier times. (Drawn by Peter R. Hobson.)

only eight true species. Bears tend to be wide-ranging, spending only part of their time in forests, exemplified by the North American grizzly bear Ursus arctos horribilis which also spends time in the tundra and alpine zones. This often has an overall length of more than two metres; if disturbed it often rears up on its hind legs to view the situation, and can run as fast as a horse for short distances. Although capable of killing caribou and moose it generally feeds on smaller animals, carrion and plant material. The black bear Ursus americanus has a much wider distribution, being found in forests, swamps and mountains from Alaska to the subtropical forests of southern USA. Males are much larger than the females, but both are considerably smaller than the grizzly. Even so a sow will weigh 140 kg, so the weight of the average baby (about 240 g) is unusually small though it grows rapidly on the rich diet of milk it receives in the winter den. It is closely related to the Asian black bear Ursus thibetanus. Extinct in Britain long before the Norman Conquest, bears were hunted by the King of Spain in the first half of the fourteenth century and still survive in other parts of Europe. Sloth bears Melursus ursinus are found in forested areas south of the Himalayas.

The role of the primates in forest ecosystems, and in the Holocene especially, as agents of change, is of very great importance. They are remarkable for their range of size, from the tiniest monkeys adapted to exploit the very ends of slender branches to the huge gorillas, and for their very high intelligence and adaptability. It is indeed their remarkably large brains and ability to devise new strategies that makes the whole group so formidable, and the importance of their social attitudes so great, which can vary from the geniality of the huge orang-utans of Borneo to the sometimes vicious behaviour of the chimpanzees of Uganda. Social behaviour in the great apes with well-defined dominance ruled by the alpha-male, and bonds reinforced by grooming, is complex. Orang-utans normally live alone because food is scarce, but come together when it is not. As many as 20 may feed simultaneously on the fruit of a single masting tree. They have extraordinarily good memories, know just where particular tree species grow and also when they are likely to fruit. In captivity they have learnt to use tools such as the hammer and saw. The ruthlessness and efficiency with which chimpanzees, which eat meat as well as leaves and fruit, hunt other primates including Colobus monkeys through the tree tops is awe inspiring.

In recent times the rise of the hominids and modern humans has had an overwhelmingly important influence on forest structure, and all too often forest elimination. Amongst other features it was the development ofrelatively shorter and lighter forelimbs and the bipedal habit, which enabled them to run faster and to see further in tall grassland, that marked out the hominids. It is interesting to observe, however, that the great apes walk on their hind legs if wading in lakes and rivers when their body weight is largely supported by water. Humans are the only animals in which the thumb is fully opposable, so enabling them to use tools very efficiently. Together with the use of fire, this was to enable them largely to master many wooded environments.

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