In 1847, Carl Gustav Bergmann, who worked at the University of Göttingen, formulated a rule that, in a simplified form, reads like this: “In a warmer climate, warm-blooded animals of the same or related species are smaller, and in a colder climate they are larger.”
At first, the conclusions of the German biologist, anatomist and physiologist were perceived by the scientific community with doubt, but over time it became obvious that Bergman could not have more accurately described one of the principles of evolution.
Indeed, such a pattern not only exists, but is also clearly visible. For example, an animal with one of the widest habitats is the wolf. The Arabian wolf, which lives in Oman, Israel and other countries of the Middle East, is a skinny, short creature weighing about 15 kilograms. Despite its size, it is a ferocious predator, a biblical symbol of malice and rage.
Northern Woodland Wolf and Egyptian Wolf (below)
In Alaska and northern Canada, there are wolves twice as large and five times as heavy. The wolves from the north of India, who raised Mowgli, hardly reached a weight of a quarter of a centner, but the beast on which Ivan Tsarevich rode would have pulled, if it existed in reality, no less than 60 kilograms, like a seasoned wolf in the forest zone of Russia.
The situation is similar with the puma. The range in weight among individuals living on the equator and in the south of Canada or Argentina is from 60 to 110 and even, in exceptional cases, 120 kilograms.
Changes are noticeable as you climb the mountains. The higher and, accordingly, colder, the larger the animals. If we consider animals of similar species, then Bergman’s rule is even more obvious: the Malayan bear, whose average weight is 45 kilograms, is ten times inferior in weight to the average polar bear.
The polar bear is one of the largest terrestrial representatives of mammals of the order of carnivores. Its length reaches 3 m, weight up to 1 ton. It lives in the polar regions in the northern hemisphere of the Earth.
The Malayan bear is the smallest representative of the bear family: it does not exceed 1.5 m in length. It lives in India.
Want big differences? Please! Mentally place next to the smallest southern deer, the kanchila from Sumatra, and the largest northern one, the elk from Kamchatka or Alaska. The difference is simply fantastic: 25 centimeters at the withers and 1200 grams of weight for the first and almost 2.5 meters and 650 kilograms for the second. This comparison may not be very correct, but it is clear.
SAVE WARMTH
What is the secret why animals grow as the climate gets colder? It's all about thermoregulation. The colder it is, the more important it is to preserve body heat and minimize heat transfer to the environment. After all, maintaining a constant body temperature requires energy, that is, ultimately, food. It needs to be obtained, which means wasting energy. Why waste it again?
At first glance, the larger the surface of the body, the more heat a living creature loses. But it is pointless to consider heat losses in themselves - what is important is their relationship to heat production. Animals not only lose heat, but also produce it, and the larger the volume of the body, the more joules it emits into the atmosphere.
Tiny kanchile deer and moose from Alaska
As body size increases, the increase in volume outpaces the increase in surface area: an animal that becomes twice as wide, taller, and longer will have a fourfold increase in body area and an eightfold increase in volume.
Thus, the ratio of heat loss to its production will be twice as beneficial for a “grown” animal. In reality, of course, everything is not so mathematically precise, but that is the trend.
Of course, like any rule related to living nature - that is, to the most complex dynamic systems of many components - there are exceptions to Bergman's rule. Their reasons can be very diverse.
From the scarcity of food supply, which simply does not allow animals to “gain weight” and forces them to become smaller, to the dispersal of animals beyond their usual range. In such situations, the picture may not be “ideal” because not enough time has passed.
Animals that moved to the north or south have not yet had time to evolve, because, like most similar processes, in warm-blooded animals the change in size due to climate occurs quite quickly by paleontological standards, but slower than can be seen with the naked eye.
However, the largest animals - elephants, hippos, giraffes - live where it is very hot. And this does not contradict Bergman's rule. Such giants have access to extremely abundant food resources. And it would be strange not to use them - since you can eat up to a large size, which in itself is pleasant, and at the same time “remove” yourself from the threat of predators who cannot cope with the giants.
But these animals are constantly at risk of overheating, since their heat production is enormous - therefore, when solving problems of heat transfer, they have to resort to all sorts of tricks. For example, sitting most of the time in the water, like hippos, or growing huge ears, like elephants.
POLE CLOSER - EARS SMALLER
Bergmann's rule is rarely considered in isolation from another ecogeographical rule, authored by the American zoologist Joel Allen. In 1877, Allen published a paper in which he drew the attention of specialists to the relationship between climate and the body structure of warm-blooded animals of related species: the colder the climate, the smaller their protruding body parts relative to their overall size.
Conversely, the warmer the climate, the longer the ears, tails and legs. Again, you don’t have to look far for examples: fennec fox and arctic fox. The desert fox is famous for its huge sail-like ears, while the arctic fox has small ears that barely stick out from its thick fur in winter.
Arctic fox and fennec fox (below)
Indian and African elephants live in warm climates, while their relative the Siberian mammoth lived in a land of frost. The African elephant has huge ears, the Indian elephant has noticeably smaller ones, and the mammoth’s were completely undignified by elephant standards.
Patterns in the size of protruding body parts are also related to heat transfer. Active heat transfer occurs through the tails, ears and legs, so in the north or in the highlands it is advantageous to minimize their size. Moreover, we are talking here not only about wasted heat loss, but also about keeping the organ intact. Long tails and large ears can simply freeze so that tissue necrosis develops - this sometimes happens to dogs that city dwellers bring to the tundra from places with a temperate climate. In such cases, the ears and tails of the unfortunate four-legged animals have to be amputated.
Indian elephant
And where it’s warm, the long-tailed and long-eared ones are the most suitable place. Since active heat loss occurs through these organs, they are not a burden here, but, on the contrary, a means of cooling the body, acting like a radiator on a computer cooler. Let's take the elephant as an example. His large ears, rich in blood vessels, receive blood.
Here it cools, giving off heat to the environment, and returns to the body. The same can be said about the processes in the trunk. We don’t know, but only guess, how energy-consuming it was for mammoths to own a trunk. What saved the ancient animals was that the trunk had a fairly solid layer of fat and, like the rest of the mammoth’s body, was covered with thick hair.
Are there any other rules describing the dependence of the appearance of animals on climate? In 1833, that is, before Bergman postulated his rule, the German ornithologist Konstantin Wilhelm Gloger, working in Breslau (present-day Wroclaw), noticed: in related species of birds (and, as further observations showed, in mammals and some insects too) pigmentation is more diverse and brighter in warm and humid climates than in cold and dry ones.
Those who were lucky enough to get into the storage room of the Zoological Museum of Moscow State University could see dozens of wolf skins hanging there one after another. Reddish-brown no more than a meter long, fawn a little longer, gray even longer and, finally, huge, human-sized, almost white with a slight admixture of gray and black hairs. Red southern and white northern wolves are an example of Gloger's rule.
Another example is the pink starling, an inhabitant of warm countries, and the common starling, dark with light specks. At first it was assumed that this distribution was due to the need for camouflage: among the bright greenery with multi-colored flower petals, it is easy to miss the bird of paradise with its riot of colors in its plumage, but the white partridge will be in full view.
Pink starling and common (below)
And the rainbow hummingbird will be just as uncomfortable in the tundra - and there is a high probability that even before it freezes, the bird will end up in someone’s teeth or claws. The camouflage version is not denied even now, but it turned out that another factor is at work here: in a warm and humid environment, the synthesis of pigments is more active.
There is an interesting exception to Gloger's rule. This is the so-called industrial melanism, first discovered in England and then in North America. An example of this is butterflies that live in places with developed industry. Factories emitted smoke and soot, birch trunks and lichens darkened. White butterflies became noticeable against their background, and birds ate them.
Those insects that, due to a random mutation, turned out to be melanistic (black) survived. Gradually, the number of black individuals in populations began to reach 90%, but once upon a time 99% were white.
Veniamin Shekhtman
DISCOVERY Magazine August 2014
Ecology
Hands for a person are one of the most important parts of the body. We do almost everything with our hands, even communicate. However, man is not the only creature on the planet with dexterous hands and fingers. The limbs of animals, which are commonly called paws, can surprise a lot. We invite you to learn about the most unusual paws in the animal world.
Amazing animals
Threatening Aye-Aye
Aye-aye- an amazing creature that lives in Madagascar, which can “show the middle finger” like no one else in the world. Aye-aye or little arm- a small primate that can be called the strangest of all primates. It has ugly, bony paws with long fingers and claws, reminiscent of heroes from fairy tales about vampires and werewolves.
Moreover, the middle finger of the hand is slightly larger than the others and protrudes noticeably. With his help the beast knocks on trees looking for voids in the bark, where tasty insects on which it feeds can hide. If an aye-aye finds a treat, it bites through the wood and uses its sinister long finger to snag the prey.
Little hands, despite their threatening appearance, completely harmless for everyone except insects, however, the inhabitants of Madagascar are very unfriendly to these animals, considering meeting them a bad sign. If an aye-aye is seen near a village, he will be killed immediately, as it is believed that otherwise misfortune will befall the village.
Helen the Flying Frog
In 2009, while traveling through the forest near the Vietnamese city of Ho Chi Minh City, biologists came across an amazing frog. This frog is long about 9 centimeters, as it turned out, belonged to a new species of flying frogs unknown to science, which are known for their ability to jump from one tree to another and float in the air using special webbed paws.
Biologist Judy Rowley, who discovered this frog in Vietnam, gave it its name flying frog helen in honor of his mother Helen Rowley.
The most amazing animals
Many-toed mole
Moles- very cute animals, with the possible exception of Mole Starsnout, which lives in the USA and Canada. Moles have amazing limbs, which they simply need in order to travel underground.
The large, flat front paws work like shovels, and the long claws on the toes allow dig underground holes and tunnels, in which moles find shelter and food.
In 2011, researchers University of Zurich suggested why mole paws dig the ground so well: moles have one extra finger– sickle-shaped spare thumb.
This thumb has no motor joint, mole leans on him while digging, which gives its shovel claws extra strength. Studies have shown that the bone of this finger develops from the bones of the wrist at the embryonic stage somewhat later than the bones of the other fingers. Moles really have not 5, but 6 fingers on your paws!
Sticky gecko
Geckos boast amazing paws that allow them to cling almost for any surface. The lines on the soles of their paws are covered with hairs called bristles, which are also covered with bristles.
The latter structures are so small that they allow geckos to stick to the surface on which they move. They allow you to strengthen van der Waals force, a weak electrical force that holds many things together, including most organic matter.
Pinnipeds- very, special and interesting animals that can live both on land and in water. Their paws turned into flippers, which is why these sea animals are called pinnipeds. They eat fish, squid and crustaceans.
How are fur seals different from seals?
Fur seals and seals are close relatives and very similar. But seals have ears, but seals don't. In addition, fur seals jump very deftly on their flippers, while seals crawl on their bellies.
Seals
Seals (Odobenidae)- wonderful hunters. They have well-developed vision because most of the time they are underwater, where the lighting is very poor. These animals are able to find food even in the dark. The body of pinnipeds, with the exception of the head, is covered with a layer of fat 10 cm thick, and in some - even more. Pinnipeds have the fattest milk among all mammals. Seals do not chew the fish at all, but swallow it whole. If the fish is very large, then the pinnipeds tear it into pieces. Seals can withstand temperatures down to -80C°.
Why do seals need flippers?
If there are fleas on the skin, a fur seal scratches with its back flippers, and a seal scratches with its front flippers. In the water, the seal paddles primarily with its front flippers, while the harbor seal paddles with its back flippers.
sea hare
photo: Már Höskuldsson’s
The most baleen among pinnipeds is the sea hare (Erignathus barbatus). His mustache is thick and curly. But in water they become straight and very long and help the seal find food on the seabed.
Elephant seals
photo by Jim Frazee
Elephant seals (Mirounga)- giants from the seal family. Their length is about 6 m, and their weight is more than 3 tons. These animals were named so not only because of their size, but also because of their nose, similar to a trunk, which hangs at the end of the muzzle of elephant seals. Elephant seals use their long trunk, up to 80 cm long, as a means of intimidation. In times of danger, the male raises his trunk upward and his menacing roar echoes over the sea. The sea giant is very clumsy on land, but it swims well and dives deeply. It is capable of diving to a depth of 1,400 meters for food.
harp seal
photo by Steve Arena
The claws of the harp seal (Pagophilus groenlandicus) are reliable protection against enemies. They are very sharp. The wounds inflicted by this animal do not heal for a long time.
Walrus
photo by Allan Hopkins
Walruses (Odobenus rosmarus) found in Arctic regions of the world. Today there are three subspecies. Pacific walruses(Odobenus roasmarus divergens) live mainly in the Bering Sea. During the warm summer months they can travel as far as the Beaufort Sea and the East Siberian Sea. Atlantic walruses(Odobenus rosmarus rosmarus) are found in the eastern and western Atlantic Ocean. Laptev walruses(Odobenus rosmarus laptevi) are found in the Laptev Sea. Walruses inhabit areas of the Arctic that are mostly composed of ice. Walruses prefer areas with shallow water so they can easily access food. This slow-moving marine mammal spends most of its time in or around the water.
The walrus is one of the largest pinnipeds. This animal is known for its massive tusks, which are actually just enlarged teeth. These fangs can break through 20 cm of ice. They can grow up to 90 cm, but the average size is approximately 50 cm. Males are larger than females, weighing up to 1200-1500 kg, and females - from 600 to 850 kg.
Leopard seal
photo V Maxi Rocchi
Leopard seal (Hydrurga leptonyx)- the most bloodthirsty predator among pinnipeds has a reputation as the most fierce and formidable seal, as it feeds not only on large fish and penguins, but also attacks other seals.
Crested seal
In a male crested fish (Cystophora cristata) there is a huge skin bag on the head. He knows how to inflate his tufted sac so much that sometimes even the animal’s head is not visible behind it.
Seals
Found in the World Ocean eight different species of fur seals (Arctocephalinae). Only one of these fur seal species is found in the northern hemisphere, while the other seven are found in the southern hemisphere. They spend most of their time swimming in the open ocean and hunting for food. Fur seals feed on fish and plankton, but also tend to hunt squid and eels. Often these pinnipeds become prey for large aquatic animals such as sharks, killer whales, sea lions, and sometimes adult leopard seals.
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Keeping warm is very important for those animals that live in cold climatic zones, so many of them are noted for their physique adapted to such conditions.
Basic data:
Changing body shape. Many inhabitants of cold areas have a different body shape, size and proportions from the shape, size and body proportions of animals of the same species inhabiting warm areas. This body structure is a sign of better adaptability to the regulation of heat exchange. This fact is explained by the example of two rules.
Bergman's rule. It is obvious that animals that live in cold climates have round bodies. According to Bergaman's rule, a round body shape helps retain heat better. An excellent example illustrating this rule is the cylindrical bodies of mammals living in cold water, in particular seals.
Bergaman's rule says that among animals of the same species living over a large range, the largest individuals are found in cold regions. The closer to the south, the smaller their sizes. For example, the most active tiger is the Amur tiger. Smaller - Bengali. And a very small one - a Javan tiger. So, according to the rules, large wolves must live in the Arctic.
Allen's rule. According to Allen's rule, animals inhabiting cold areas of their range have smaller protruding body parts (limbs, tail, ears) than representatives of the same family living in warm areas. The body size is reduced in order to reduce heat transfer and prevent unnecessary heat loss. Thus, the ordinary Arctic fox has a short body, limbs and tail, a convex forehead, and short ears and mouth. The red fox has a more elongated body, a long tail and muzzle, as well as ears that protrude strongly. And the steppe fox has long limbs and huge ears. Animals need large ears to improve heat transfer and to prevent their bodies from overheating.
OR DID YOU KNOW THAT...
Chinchillas have very thick fur because up to 40 hairs grow from one hair follicle.
During the winter thaw, it rains in Arctic latitudes, after which the wet wool of musk oxen often freezes, forming an ice shell that prevents the animal from moving.
1 cm2 of northern fur seal skin is covered with up to 50,000 hairs.
Reindeer often make long journeys in search of shelter from cold winds; they try to warm themselves by pressing their bodies against each other.
Mammals that live in cold areas maintain a constant body temperature, thanks, first of all, to the air layer present in their fur. Many animal species have a thick layer of fat under their skin. Some species escape the cold with the help of a special body structure.
North of the Arctic Circle
The coldest part of the mammals' range is the Arctic. With the exception of the polar bear, which lives even at the North Pole, most species live in the southern regions. Many Arctic residents have thick, long, and usually white fur. Their fur coats are designed on the principle of double window frames, between which there is air - a thermal protective layer. In the summer, the fur of most species thins out. The polar bear wears a white outfit with shades of yellow throughout the year. The sun's rays penetrate through the white hairs to the bear's skin and heat it. Bear fur consists of a thick undercoat, so the bear's skin remains dry even while swimming in icy water. In addition, a thick layer of subcutaneous fat protects it from the cold.
The wolverine also has very thick fur. Since ice crystals never form on the wolverine's fur, the Eskimos sew its skins into a backing for clothing. Other “frost-resistant” animals, musk oxen, have hair 50-70 cm long growing from their thick undercoat. Both layers have excellent heat retention properties and protect the animal even in the most severe frosts. The musk ox sheds during the short arctic summer.
Thermoregulation IN THE MOUNTAINS
In mountainous areas, night temperatures are usually much lower than daytime temperatures. Mammals living high in the mountains must adapt not only to seasonal temperature fluctuations, but also to daily ones. Wind, rain and snow in winter are not very pleasant phenomena, which is why most highland inhabitants, like those living in the Arctic, have thick fur. Chinchillas, Vicunas, guanacos, llamas and alpacas living in the Andes have very warm fur. People shear guanacos, llamas, Vicunas and alpacas for warm wool. In forested mountains, the difference between day and night temperatures is not so great. This is used by many species of mountain goats and sheep, which descend to these places from a higher altitude for the winter.
Thermoregulation IN WATER
Some marine mammals live near the Arctic and Southern Arctic Circles, while walruses are found only in the Arctic. Certain species of pinnipeds live off the coast of Antarctica, constantly being in icy water. Narwhal and beluga whales spend their entire lives here, and gray, humpback and blue whales appear in these regions during the summer. In cold water, heat transfer is much more intense than in cold air. A person who finds himself in such conditions can only live for a few minutes. The cylindrical shape of whales and seals prevents them from generating excessive heat, and their thick layer of blubber helps them maintain a constant body temperature when they are in icy water. The thickness of the fat layer, depending on the type of animal, ranges from several centimeters to half a meter. In addition, pinnipeds have a special circulatory system - it acts as a heat exchanger. The principle of its operation is based on the fact that the vessel through which blood enters the limb is intertwined with a network of small vessels that carry blood from the limb. With established heat exchange between oppositely directed blood flows, minimal cooling of the blood that circulates inside the animal’s body is achieved.
COLD PROTECTION
With the onset of severe frosts, a layer of snow for many animals becomes an excellent shelter that retains heat. Small mammals such as lemmings dig complex underground corridors, topped with a thick layer of snow. The ermine also hides underground in winter. The giant brown bear living in Alaska sleeps in a den in winter, and male polar bears hide under the snow only during snow storms, while pregnant females hibernate in a snowy den. A female polar bear climbs into a den and curls up into a ball. The den is covered with snow. In this case, the snow forms a kind of insulating layer. Wolves, reindeer and moose are not afraid of frost. Moose do not go into hibernation, but take energy from fat reserves that they fattened up in the summer and fall. They move very little and only in the very frost do they seek shelter in thickets of plants and other sheltered places. Chipmunks and many other small mammals hibernate during the winter.
The most ancient method of movement is walking or leisurely running, in which the animal rests on the entire surface of the feet and hands (or most of them). Therefore, this method of movement is called plantigrade walking. It is not particularly fast, but guarantees stability and maneuverability. During plantigrade walking, at each moment of movement, only one limb is raised, while the other three serve as support and provide balance.
Consistently rearranging the limbs of the left and right half of the body, the animal moves forward. Plantigrade behavior has been preserved in many insectivores: (hedgehogs, shrews), rodents (mice, voles, marmots) and in some carnivores (bear). The paws of animals that climb trees, such as squirrels, are constructed almost in the same way as plantigrade walkers. Only their fingers are longer, and many have well-developed claws.
Digital gait and phalangeal gait
What about animals that live in open spaces? After all, they need to run fast to escape from predators or, conversely, to catch up with prey. Of modern mammals, the most adapted to running are the ungulate species, which have a special structure of the hand and foot. But before such a limb was formed, as, for example, in antelopes or horses, their ancestors switched from relying on the entire foot to relying on the phalanges of the fingers, i.e., to digital walking.
On the one hand, finger walking allows you to generate greater speed and also move by jumping. But on the other hand, the area of support on the surface of the earth decreases and the physical load on the phalanges of the fingers increases (this is easy to see by walking on tiptoe), which means there is a risk of dislocating your fingers. Therefore, we have to sacrifice the mobility of the joints for the sake of their greater strength: the phalanges of the fingers have become shorter, lost mobility, and the bones of the metacarpus and metatarsus, on the contrary, have become much longer.
Among modern mammals, digitigrades are representatives of the carnivorous group, such as cats and dogs. The effectiveness of this method of movement is evidenced by the fact that the fastest mammal on Earth, the cheetah, which reaches speeds of up to 110 km/h, is classified as digitigrade.
Why does a cheetah run fast, but not for long?
Unlike digital runners, ungulate mammals are able to run not only fast, but also for a long time. This is possible due to the more durable structure of the limb and the presence of horny hooves. Ungulates rest on the very ends of their toes, which are covered with hooves that protect them from injury on hard soil or stones. Therefore, the running of digitigrade carnivores is a combination of speed and maneuverability, and the running of their potential victims - herbivorous ungulates - is a combination of speed and endurance.
In terrestrial mammals, the hind limbs, as a rule, are always better developed compared to the forelimbs. For example, in hares this difference is very significant. They usually move in short hops, pushing off with both front and hind legs. When running fast, hares make long jumps. During movement, they carry their hind legs far forward relative to the front ones, which at this moment serve as support for the body. The main load when running falls on the hind limbs.
Ricocheting run
Very rarely, the forelimbs cease to be used as support at all during running. A striking example of a “bipedal” method of moving by jumping is kangaroos. This method of movement is called ricocheting running.
By simultaneously pushing off with their strong hind legs and using their tail as a rudder and counterweight, kangaroos are able to make huge leaps one after another, bouncing off the ground (“ricocheting”) like a tennis ball. Large species of kangaroo move in leaps 6-12 meters long, developing speeds of up to 40 km/h. True, they cannot run for long at such a speed and get tired quickly.
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