LemmingsLemmings are small rodents, usually found in or near the Arctic. Together with the voles and muskrats, they make up the subfamily Arvicolinae (also known as Microtinae), which forms part of the largest mammal radiation by far, the superfamily Muroidea, which also includes the rats, mice, hamsters, and gerbils.
Lemmings mostly weigh between 30 g and 112 g (1 to 4 oz) and are about 7 cm - 15 cm (2.75 to 6 in) long. They usually have long, soft fur and very short tails. They are herbivorous, feeding mostly on leaves and shoots, grasses, and sedges in particular, but also roots and bulbs in some cases. Like many rodents, their incisors grow continuously, allowing them to exist on much tougher forage than would otherwise be possible.
Lemmings do not hibernate through the harsh northern winter, but remain active, finding food by burrowing through the snow, and utilising grasses clipped and stored in anticipation. They are solitary animals by nature, meeting only to mate and then going their separate ways, but like all rodents they have a high reproductive rate and can breed rapidly in good seasons.
There is little to distinguish a lemming from a vole. Most lemmings are members of the tribe Lemmini (one of the three tribes that make up the subfamily)
Population fluctuations
Lemming populations go through rapid growths and subsequent crashes that have achieved an almost legendary status, largely because of the well-known Disney Studios film, White Wilderness, which was produced in 1958 and reappeared on television at regular intervals for many years afterwards. White Wilderness popularized, using staged footage, the myth that during population booms Norway Lemmings become suicidal and leap en masse off cliffs into the sea. For this reason, the term "lemming" is often used in slang to denote those who mindlessly follow the crowd, even if destruction is the result.
In fact, the behaviour of lemmings is much the same as that of many other rodents which have periodic population booms and then disperse in all directions, seeking the food and shelter that their natural habitat cannot provide. (The Australian Long-haired Rat is one example.)
Myths about lemmings go back many centuries, and in the 16th and 17th centuries there was much speculation in learned circles that lemmings were in fact spontaneously generated by conditions of the air. This was argued against, successfully, by the natural historian Ole Worm, who provided one of the first published dissections of a lemming. In his investigation, Worm showed that a lemming contained anatomy similar to most other rodents, including testes.
The populations of predatory creatures like foxes and owls follow the population changes of lemmings and voles.
The order Rodentia is the most numerous of all the branches on the mammal family tree. Currently there are, depending on the authority consulted, between 2000 and 3000 species of rodent—roughly half of all mammal species. Rodents are found in vast numbers on all continents except Antarctica (they are the only placental order other than bats (Chiroptera) to reach Australia without human introduction), most islands, and in all habitats bar the oceans.
Groups commonly confused with rodents, or erroneously thought to be rodents, include the aforementioned Chiroptera (bats), Scandentia ( treeshrews), Insectivora ( moles, shrews and hedgehogs), and Lagomorpha (hares, rabbits and pikas) and carnivore mink.
Most rodents are small. The tiny African Pygmy Mouse is only 6 cm in length and 7 grams in weight. On the other hand, the Capybara can weigh up to 45 kg (100 pounds) and the extinct Phoberomys pattersoni is believed to have weighed 700 kg.
Rodents have two incisors in the upper as well as in the lower jaw which grow continuously and must be kept worn down by gnawing; this is the origin of the name, from the Latin rodere, to gnaw, and dent, tooth. These teeth are used for cutting wood, biting through the skin of fruit, or for defense. These teeth have enamel on the outside and exposed dentine on the inside, so they self-sharpen during gnawing. Rodents lack canines, and have a space between their incisors and premolars. Nearly all rodents feed on plants, seeds in particular, but there are a few exceptions which eat insects or even fish.
Capybara, the largest living rodentRodents are important in many ecosystems because they reproduce rapidly, and can function as food sources for predators, mechanisms for seed dispersal, and as disease vectors. Humans use rodents as a source of fur, as a model organism in animal testing, for food, and even in detecting landmines [1].
Natural History
The fossil record of rodents began after the extinction of the dinosaurs some 65 million years ago. The earliest rodents resembled squirrels and from these stem rodents, they diversified. By the end of the Eocene epoch, beavers and squirrels appeared in the fossil record. Their origins were from Laurasia, the joined continents of North America, Europe, and Asia. Some species colonized Africa, giving rise to the earliest hystricognaths. From there they rafted to South America, an isolated continent during the Oligocene and Miocene epochs. By the Miocene, Africa collided with Asia, allowing rodents such as porcupines to spread into Eurasia. During the Pliocene, rodent fossils appeared in Australia. Even though marsupials are prominent residents in Australia, it is the rodents that dominate the mammalian fauna: making up almost 25% of the mammals on the continent. Meanwhile, the Americas collided. Rodents expanded into unknown territory: mice headed south and porcupines headed north.
Lemmings mostly weigh between 30 g and 112 g (1 to 4 oz) and are about 7 cm - 15 cm (2.75 to 6 in) long. They usually have long, soft fur and very short tails. They are herbivorous, feeding mostly on leaves and shoots, grasses, and sedges in particular, but also roots and bulbs in some cases. Like many rodents, their incisors grow continuously, allowing them to exist on much tougher forage than would otherwise be possible.
Lemmings do not hibernate through the harsh northern winter, but remain active, finding food by burrowing through the snow, and utilising grasses clipped and stored in anticipation. They are solitary animals by nature, meeting only to mate and then going their separate ways, but like all rodents they have a high reproductive rate and can breed rapidly in good seasons.
There is little to distinguish a lemming from a vole. Most lemmings are members of the tribe Lemmini (one of the three tribes that make up the subfamily)
Population fluctuations
Lemming populations go through rapid growths and subsequent crashes that have achieved an almost legendary status, largely because of the well-known Disney Studios film, White Wilderness, which was produced in 1958 and reappeared on television at regular intervals for many years afterwards. White Wilderness popularized, using staged footage, the myth that during population booms Norway Lemmings become suicidal and leap en masse off cliffs into the sea. For this reason, the term "lemming" is often used in slang to denote those who mindlessly follow the crowd, even if destruction is the result.
In fact, the behaviour of lemmings is much the same as that of many other rodents which have periodic population booms and then disperse in all directions, seeking the food and shelter that their natural habitat cannot provide. (The Australian Long-haired Rat is one example.)
Myths about lemmings go back many centuries, and in the 16th and 17th centuries there was much speculation in learned circles that lemmings were in fact spontaneously generated by conditions of the air. This was argued against, successfully, by the natural historian Ole Worm, who provided one of the first published dissections of a lemming. In his investigation, Worm showed that a lemming contained anatomy similar to most other rodents, including testes.
The populations of predatory creatures like foxes and owls follow the population changes of lemmings and voles.
The order Rodentia is the most numerous of all the branches on the mammal family tree. Currently there are, depending on the authority consulted, between 2000 and 3000 species of rodent—roughly half of all mammal species. Rodents are found in vast numbers on all continents except Antarctica (they are the only placental order other than bats (Chiroptera) to reach Australia without human introduction), most islands, and in all habitats bar the oceans.
Groups commonly confused with rodents, or erroneously thought to be rodents, include the aforementioned Chiroptera (bats), Scandentia ( treeshrews), Insectivora ( moles, shrews and hedgehogs), and Lagomorpha (hares, rabbits and pikas) and carnivore mink.
Most rodents are small. The tiny African Pygmy Mouse is only 6 cm in length and 7 grams in weight. On the other hand, the Capybara can weigh up to 45 kg (100 pounds) and the extinct Phoberomys pattersoni is believed to have weighed 700 kg.
Rodents have two incisors in the upper as well as in the lower jaw which grow continuously and must be kept worn down by gnawing; this is the origin of the name, from the Latin rodere, to gnaw, and dent, tooth. These teeth are used for cutting wood, biting through the skin of fruit, or for defense. These teeth have enamel on the outside and exposed dentine on the inside, so they self-sharpen during gnawing. Rodents lack canines, and have a space between their incisors and premolars. Nearly all rodents feed on plants, seeds in particular, but there are a few exceptions which eat insects or even fish.
Capybara, the largest living rodentRodents are important in many ecosystems because they reproduce rapidly, and can function as food sources for predators, mechanisms for seed dispersal, and as disease vectors. Humans use rodents as a source of fur, as a model organism in animal testing, for food, and even in detecting landmines [1].
Natural History
The fossil record of rodents began after the extinction of the dinosaurs some 65 million years ago. The earliest rodents resembled squirrels and from these stem rodents, they diversified. By the end of the Eocene epoch, beavers and squirrels appeared in the fossil record. Their origins were from Laurasia, the joined continents of North America, Europe, and Asia. Some species colonized Africa, giving rise to the earliest hystricognaths. From there they rafted to South America, an isolated continent during the Oligocene and Miocene epochs. By the Miocene, Africa collided with Asia, allowing rodents such as porcupines to spread into Eurasia. During the Pliocene, rodent fossils appeared in Australia. Even though marsupials are prominent residents in Australia, it is the rodents that dominate the mammalian fauna: making up almost 25% of the mammals on the continent. Meanwhile, the Americas collided. Rodents expanded into unknown territory: mice headed south and porcupines headed north.
No comments:
Post a Comment