Autore: Elīna Brice

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Animal adaptation

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Animal Physical Adaptations. The need to eat exposes animals to the danger of being attacked and eaten themselves. To avoid this fate, all animals have physical adaptations that enable them to escape being attacked or to survive an attack once it is underway.

The simplest form of defense is a rapid escape, which calls for keen senses and well-developed systems for movement. Many plant-eating mammals depend on this strategy for survival and must maintain a constant lookout for danger. A less-demanding survival strategy, found in many small animals such as insects, involves deception. These animals use camouflage to blend in with their backgrounds, or they mimic inedible objects such as twigs or bird droppings. If a predator does come too close, they still have the option of making a dash for safety.

A more sophisticated form of mimicry occurs in animals that resemble species that are poisonous. This is common in insects, and it also occurs in some snakes. Poisonous insects, such as bees and wasps, are often brightly colored to warn other animals that they are best left alone. By adopting these colors and developing similar body shapes, non-poisonous insects benefit from the same protection. The physical adaptations involved can be elaborate. The hornet clearwing moth, for example, is yellow and brown like a stinging hornet. On its first flight, it loses most of its wing scales, resulting in transparent wings that make the resemblance even more convincing.

An alternative defense, seen in a wide range of animals, uses armor or spines to fend off an attack. Animal armor includes hard shells, overlapping scales, and in the case of armadillos, bands of hardened plates connected by areas of softer skin. If they are threatened, many of these animals can shut their bodies away inside their armor, making them difficult to attack. The disadvantage of this defense is that the animal cannot escape. If its armor is broken open, death is almost certain. [3]

Animal Behavioral Adaptations. In simple animals, behavior is governed almost entirely by instinct, meaning that it is pre-programmed by an animal’s genes. In more complex animals, instinctive behavior is often modified by learning, producing more-flexible responses to the outside world.

Many forms of behavior help animals to survive severe environmental conditions. Two examples are hibernation, which enables animals to survive cold and food shortages in winter; and estivation, which allows animals to survive drought and heat in summer. True hibernators, such as bats and some rodents, become completely inactive during winter, and their body temperature falls close to freezing. While in this state, they survive entirely on food reserves stored in their bodies. Estivating animals, which include land snails and some amphibians, seal themselves up when conditions become dry and only become active again when it rains. Between these two extremes, many other animals show less drastic patterns of behavior that are triggered by cold or heat. Winter wrens, for example, often crowd together for sleep when temperatures fall below freezing. On warmer nights, they sleep on their own.

Special forms of behavior also help animals to find food, to avoid being eaten, and to protect their young. One of the most advanced forms of this behavior is the use of tools. Several kinds of animals, particularly primates and birds, pick up implements such as twigs and stones and use them to get at food. More rarely, some tool-using animals seek out a particular object and then shape it so that it can be used. Woodpecker finches probe for insect grubs by making tools from cactus spines, and chimpanzees sometimes dig for termites using specially prepared twigs.

Defensive behavior is exhibited by individual animals and also by animal groups. Group defense is common in herding mammals, particularly in species such as the musk-ox, which form a protective ring around their calves when threatened by wolves. It can also be seen in swallows, starlings, and other songbirds, which instinctively mob hawks and other birds of prey. By grouping together to harass their enemies, they reduce the chances that they or their young will be singled out and attacked.

Individual defensive behavior is often based on threatening gestures that make an animal look larger or more dangerous than it actually is. Sometimes it involves some highly specialized forms of deception. One of the most remarkable is playing dead. Seen in animals such as the Virginia opossum and some snakes, this last-ditch defense is effective against predators that habitually hunt moving prey but leave dead animals alone. After the predator has inspected the “dead” animal and moved on, the prey comes back to life and makes its escape. [3]

Burmese Python - heat sensors along the upper lip as well as its keen sense of smell help it to find prey. As with other snakes, the python's loosely hinged jaws can be stretched far apart, enabling it to swallow animals with bodies much larger in diameter than the python's head. They are good climbers and have prehensile tails. [4]

South African Burrowing Bullfrog - when disturbed, they inflate their bodies. A conspicuous spade-like tubercle on each foot pushes soil to either side as the frog shuffles backward into the ground. They spend much of the year underground, but come to the surface after a heavy rain to breed. [5]

California King Snake - king snakes are wholly or partially immune to the venom of rattlesnakes and will kill and eat them. This behavior gives them a good reputation with humans in rural areas. [6]

White -Throated Monitor - monitors swallow small prey or pieces of large prey whole rather than chew it as do iguanas and other lizards. Like snakes, they have a strong bony roof to the mouth which protects the brain from being damaged by the passage of large mouthfuls. They can also greatly increase the size of their mouth cavity by spreading the hyoid apparatus and dropping the lower jaw. Their long, deeply-slit tongue is also snakelike and is often protruded to follow olfactory “tracks". Other similarities with snakes are the shape of the vertebrae, the chamber structure of the heart, and the absence of a urinary bladder. Powerful legs allow them to run swiftly. Long, sharp claws make them good climbers; claws also are used as tools to dig out dens or enlarge rodent dens for their own use. When lizards walk and run, they amble from side to side, flexing their bodies laterally. The muscles that are responsible for this flexing work in a different direction to expand the chest for breathing. Thus at higher speeds flexing predominates and breathing suffers. Monitors, however. have shown no constraint on oxygen consumption because they have a throat pump. As the monitor breathes, air is drawn both into the lungs and into an expanding cavity in the throat area. The cavity contracts, pumping the air into the lungs. [7]

Reticulated Giraffe - giraffe drink water if it is available but can go weeks without it; they rely on the morning dew and the water content of of their food. Their very long necks are an adaptation to feeding at high levels in the treetops. The neck veins contain valves and a network of tiny veins (rete mirabile) to prevent blackouts when the animal lowers its head to drink. In addition to keeping track of predators, their extreme long-range visual acuity enables visual communication with other giraffe over several miles. Giraffe can run at speeds up to 35 mph. [8]

Lappet-faced Vulture - agile enough to catch live animals and does so regularly in summer months when carrion is scarce. The rasp-like tongue helps pull flesh into the mouth and their long necks allow them to probe into a large carcass. Lack of feathers on head and neck means they do not have the problem of preening blood-stained feathers. Huge beak enables them to "gnaw" flesh off large bones even when corpse has dried out. Takes precedence over all other vulture species at carrion site. Other vultures have been seen waiting for Lappet-faced Vultures to arrive; they are the only ones strong enough to tear through the hide of a large dead animal. [9]

Wallaroo - very agile. Furry pads on feet are good for rock climbing. Will actively dig for water, sometimes up to one meter deep; however, they conserve body water by hiding in hollows under granite boulders during hottest part of day. Wallaroos are the kangaroo best adapted to heat and dryness. [10]

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Pēdējo reizi labots: 21.01.2007
Autore: Elīna Brice