Herbivore

Herbivores are animals whose diets consist entirely of plants. They have two ecological functions. First, they eat plants and keep them from overgrowing. Second, they are food for carnivores, which subsist almost entirely upon their flesh, and omnivores, which eat both plants and animals. Herbivores live on land or in oceans, lakes, and rivers. They can be insects, other arthropods, fish, birds, or mammals.

Wild Herbivores
Insects are the largest animal class, with approximately one million species. Fossils show their emergence 400 million years ago. Insects occur worldwide, frompole to pole, on land and in fresh or salt water. They are the best developed invertebrates, except for some mollusks. They mature by metamorphosis, passing through at least two dissimilar stages before adulthood. Metamorphosis can take up to twenty years or may be complete a week after an egg is laid. Many insects are herbivores. Some feed on many different plants; others depend on one plant variety or a specific plant portion, such as leaves or stems. Relationships between insects and the plants they eat are frequently necessary for plant growth and reproduction. Among the insect herbivores are grasshoppers and social insects such as bees. Artiodactyls are hoofed mammals, including cattle, pigs, goats, giraffes, deer, antelope, and hippopotamuses. Most are native to Africa, but many also live in the Americas, Europe, and Asia. Artiodactyls walk on two toes. Their ancestors had five, but evolution removed the first toe and the second and fifth toes are vestigial. Each support toe—the third and fourth—ends in a hoof. The hippopotamus, unique among artiodactyls, stands on four toes of equal size and width. Artiodactyls are herbivores, lacking upper incisor and canine teeth, but pads in upper jaws help the lower teeth grind food. Many are ruminants, such as antelope, cattle, deer, goats, and giraffes. They chew and swallow vegetation, which enters the stomach for partial digestion, is regurgitated, chewed again, and reenters the stomach for more digestion. This maximizes nutrient intake from food. Deer are hoofed ruminants whose males have solid, bony, branching antlers that are shed and regrown yearly. The deer family, approximately 40 species, occurs in Asia, Europe, the Americas, and North Africa. Deer live in woods, prairies, swamps, mountains, and tundra. Their size ranges from the seven-foot-tall moose to the one foot-tall pudu. Deer first appear in the fossil record ten million years ago. Deer eat the twigs, leaves, bark, and buds of bushes and saplings, and grasses. Females have one or two offspring after ten-month pregnancies. Common species are the white-tailed and mule deer in the United States; wapiti in the United States, Canada, Europe, and Asia; moose in North America and Europe; and reindeer in Russia, Finland, and Alaska. Antelope, a group of approximately 150 ruminant species, have permanent, hollow horns in both sexes. Most are African, although some are European or Asian. They eat grass, twigs, buds, leaves, and bark. There are no true antelope in the United States, where their closest relatives are pronghorns and Rocky Mountain goats (goatantelope with both goat and antelope anatomic features). The smallest antelope, the dik-dik, is rabbit-sized. Elands, the largest antelope, are oxsized. Unlike deer horns, antelope horns are unbranched. Most antelope run rather than fighting, and are all swift. Antelope live on plains, marshes, deserts, and forests. Females birth one or two offspring per pregnancy. Impala and gazelles, such as the springbok, are found in Africa. In Asia, Siberian saigas and goat antelope (takin) inhabit mountain ranges. Chamois goat antelope live in Europe’s Alps. Giraffes and hippos are unusual artiodactyls. Giraffes inhabit dry, tree-scattered land south of the Sahara. Their unusual features are their very long legs and necks. Males are over sixteen feet tall, including the neck. Both sexes have short, skin-covered horns. Long necks, flexible tongues, and upper lips pull leaves—their main food— from trees. Giraffes have brown blotches on buff coats and blend with tree shadows. They live for up to twenty years. They have keen senses of smell, hearing, and sight, and can run thirty-five miles per hour. Due to their two-ton weights, they live on hard ground. Giraffes rarely graze, and go for months without drinking, getting most of their water from the leaves they eat, because it is difficult for them to reach the ground or the surface of a river with their mouths. Females have one offspring after a fifteen-month gestation. The unusual feature of hippos is that they walk on all four toes of each foot. Perhaps this is because they weigh three to four tons. Hippos are short-legged, with large heads, small eyes, small ears, and nostrils that close underwater. Huge hippo mouths hold long, sharp incisors and canines in both jaws. Hippos once lived throughout Africa. Now they are rarer, due to poaching for ivory.Ahippo can be fifteen feet long and five feet high at the shoulder. Semiaquatic, hippos spend most daylight hours nearly submerged, eating aquatic plants. At night they eat land plants. Females bear one offspring at a time.

Aquatic Herbivores
Fish are aquatic vertebrates, having gills, scales and fins. They include rays, lampreys, sharks, lungfish, and bony fishes. The earliest vertebrates, 500 million years ago, were fishes. They comprise over 50 percent of all vertebrates and have several propulsive fins: dorsal fins along the central back; caudal fins at tail ends; and paired pectoral and pelvic fins on sides and belly. Fish inhabit lakes, oceans, and rivers, even in Arctic and Antarctic areas. Most marine fish are tropical. The greatest diversity of freshwater species is found in African and rain-forest streams. Fish vary in length from half an inch to fifty feet, and some weigh seventy-five tons. Many, including giant whale sharks, are herbivores. Fish respiration uses gills, through which blood circulates. When water is taken in and expelled, oxygen enters the blood via the gills and carbon dioxide leaves. Fishes reproduce by laying eggs that are fertilized outside the body, or by internal fertilization and development with the birth of welldeveloped young.

Domesticated Artiodactyls
Bovids are domesticated artiodactyls. Most have horns and hooves. Bovid horns are spiraled, straight, tall, or L-shaped from the sides of the head. All have hooves to help them grip the ground. Most are ruminants. Their breeding habits are similar. Males fight over females and the strongest wins. Gestation, four to eleven months, yields two to three young. The young nurse for several months and then join the herd. Young males leave female herds to live with other bachelors. Cattle are domesticated bovids, raised for meat, milk, and leather. Modern cattle come from European, African, and Asian imports. Breeding modern cattle began in Europe in the mid-1800’s. Today, three hundred breeds exist. Dairy cattle, such as Holsteins, make copious milk. Beef cattle, such as Angus, were bred to yield meat. As of 1990, about 1.3 billion cattle were found worldwide. Sheep are also artiodactyls. Wild sheep occur in some places, such as the North American bighorn and Mediterranean mouflon. Sheep were domesticated eleven thousand years ago from mouflon.Today, domesticated sheep have a world population of approximately 1.3 billion and inhabit most countries, being more widely distributed than any other domesticated animal. These ruminants have paired, hollow, permanent horns. Male horns are massive spirals; those of females are smaller. Adult body length is five feet and weights are 250 to 450 pounds. Females birth two or three young after five-month gestations. Sheep can live for up to twenty years. Sheep provide wool, meat, and milk. About eight hundred domesticated breeds exist, in environments from deserts to the tropics. Those bred for wool, half the world’s sheep, live in semiarid areas, are medium sized, and produce fine wool. Most are in Australia, New Zealand, and South America. Mutton-type sheep, 15 percent of the world sheep population, produce meat. Fat-tailed sheep, 25 percent of the sheep population, produce milk. In 1990, the five leading sheep countries were Australia, China, New Zealand, India, and Turkey. The United States raised less than 1 percent of the world total. Goats are ruminants, closely related to sheep, but have shorter tails, different horn shape, and bearded males. They eat grass, branches, and leaves and breed from October to December. A five-month gestation yields two offspring. Numerous goat breeds are domesticated worldwide for meat and milk, and as pets and burden carriers. Domesticated Angora goats yield silky mohair. Goat milk is as nutritious as cow milk and used in cheese-making. It is clear that wild herbivores are ecologically important to food chains. This is because they eat plants, preventing their overgrowth, and they are eaten by carnivores and omnivores. Domesticated herbivores—cattle, sheep and goats, used for human sustenance—account for three to four billion living creatures. Future production of better strains of domesticated herbivores via recombinant deoxyribonucleic acid (DNA) research may cut the numbers of such animals killed to meet human needs. Appropriate species conservation should maintain the present balance of nature and sustain the number of wild herbivore species living on earth.