The Bear

 

Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Northern Hemisphere and partially in the Southern Hemisphere. Bears are found on the continents of North America, South America, Europe, and Asia. Common characteristics of modern bears include large bodies with stocky legs, long snouts, small rounded ears, shaggy hair, plantigrade paws with five nonretractile claws, and short tails.

While the polar bear is mostly carnivorous, and the giant panda feeds almost entirely on bamboo, the remaining six species are omnivorous with varied diets. With the exception of courting individuals and mothers with their young, bears are typically solitary animals. They may be diurnal or nocturnal and have an excellent sense of smell. Despite their heavy build and awkward gait, they are adept runners, climbers, and swimmers.

Bears use shelters, such as caves and logs, as their dens; most species occupy their dens during the winter for a long period of hibernation, up to 100 days. Bears have been hunted since prehistoric times for their meat and fur; they have been used for bear-baiting and other forms of entertainment, such as being made to dance. With their powerful physical presence, they play a prominent role in the arts, mythology, and other cultural aspects of various human societies.

In modern times, bears have come under pressure through encroachment on their habitats and illegal trade in bear parts, including the Asian bile bear market. The IUCN lists six bear species as vulnerable or endangered, and even least concern species, such as the brown bear, are at risk of extirpation in certain countries. The poaching and international trade of these most threatened populations are prohibited, but still ongoing.

The bat

 

Bats are mammals of the order Chiroptera. With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more manoeuvrable than birds, flying with their very long spread-out digits covered with a thin membrane or patagium. The smallest bat, and arguably the smallest extant mammal, is Kitti's hog-nosed bat, which is 29-34 millimetres (1 1/8-1 3/8 inches) in length, 150 mm (6 in) across the wings and 2-2.6 g (1/16-3/32 oz) in mazz. 

The largest bats are the flying foxes and the giant golden-crowned flying fox, Acerodon jubatus, which can weigh 1.6 kg (3 1/2 lb) and have a wingspan of 1.7 m (5 ft 7 in). The second largest order of mammals after rodents, bats comprise about 20% of all classified mammal species worldwide, with over 1400 species. These were traditionally divided into two suborders: the largely fruit-eating megabats, and the echolocating microbats. But more recen evidence has supported dividing the order into Yinpterochiroptera and yangochiroptera, with megabats as memebers of the former along with several species of microbats. 

Many bats are insectivores, and most of the rest are frugivores (fruit-eaters) or nectarivores (nectar-eaters). A few species feed on animals other than insects; for example, the vampire bats feed on blood. Most bats are nocturnal, and many roost in caves or other refuges; it is uncertain whether bats have these behaviours to escape predators. Bats are present throughout the worls, with the exception of extremely cold regions. They are important in their ecosystems for pollinating flowers and dispersing seeds; many tropical plants depend entirely on bats for these services. 

Bats provide humans with some direct benefits, at the cost of some disadvantages. On the befefits side, bat dung has been and in may places still is mined as guano from caves and used as fertiliser. Bats consume insect pests, reducing the need for pesticides and other insect management measures. They are sometimes numerous enough and close enough to human settlements to serve as tourist attractions, and they are used as food across Asia and the Pacific Rim. 

On the disadvantages side, fruit bats are frequently considered pests by fruit growers. Due to their physiology, bats are one type of animal that acts as a natural reservoir of many pathogens, such as rabies; and since they are highly mobile, social, and long-lived, they can readily spread disease among themselves. If humans interact with bats, these traits become potentially dangerous to humans. Depending on the culture, bats may be symbolically associated with positive traits, such as protection from certain diseases or risks, rebirth, or long life, but in the West, bats are popularly associated with darkness, malevolence, withcraft, vampires, and death...

Invasive species

An invasive species is a species that is not native to a specific location (an introduced species), and that has a tendency to spread to a degree believed to cause damage to the environment, human economy or human health. The term as most often used applies to introduced species that adversely affect the habitats and bioregions they invade economically, environmentally, or ecologically. 

Such species may be either plants or animals and may disrupt by dominating a region, wilderness areas, particular habitats, or wildland-urban interface land from loss or natural controls (such as predators or herbivores).  This includes plan species labeled as exotic pest plants and invasive exotics growing in native plant communities. The European Union defines "Invasive Alien Species" as those that are, firstly, outside their natural distribution area, and secondly, threaten biological diversity.

The term is also used by land managers, botanists, researchers, horticulturalists, conservationists, and the public for noxious weeds. The term "invasive" is often poorly defined or very subjective and some broaden the term to include indigenous or "native" species, that have colonized natural areas, for example, deer considered by some to be overpopulating their native zones and adjacent suburban gardens in the Northeastern and Pacific Coast regions of the United States.

The definition of "native" is also sometimes controversial. For example, the ancestors of Equus ferus (modern horses) evolved in North America and radiated to Eurasia before becoming locally extinct. Upon returning to North America in 1493 during their hominid-assited migration, it is debatable as to whether they were native or exotic to the continent of their evolutionary ancestors.

Notable examples of invasive plant species include the kudzu vine, Andean pampas grass, and yellow star-thistle. Animal examples include the New Zealand mud snail, feral pigs, European rabbits, grey squirrels, domestic cats, carp and ferrets. Invasion of long-established ecosystems by organisms from distant bio-regions is a natural phenomenon, but has been accelerated massively by humans, from their earliest migrations though to the age of discovery, and now international trade.

While all species compete to survive, invasive species appear to have specific traits or specific combinations of traits that allow them to outcompete native species. In some cases, the competition is about rates of growth and reproduction. In other cases, species interact with each other more directly. Researchers disagree about the usefulness of traits as invasiveness markers. One study found that of a list of invasive and noinvasive species, 86% of the invasive species could be identified from the traits alone.

Another study found invasive species tended to have only a small subset of the presumed traits and that many similar traits were found in noinvasive species, requiring other explanations. Common invasive species traits include the following: 

- Fast growth
- Rapid reproduction 
- High dispersal ability
- Phenotype plasticity
- Tolerance of a wide range of environmental conditions
- Ability to live off of a wide range of food types
- Association with humans
- Prior successful invasions

Typically, an introduced species must survive at low population densities before it becomes invasive in a new location. At low population densities, it can be difficult for the introduced species to reproduce and maintain itself in a new location, so a species might reach a location multiple times before it becomes established. Repeated patterns of human movement, such as ships sailing to and from ports or cars driving up a down highways offer repeated opportunities for establishment (also known as a high propagule pressure).

An introduced species might become invasive of it can outcompete native species for resources such as nutrients, light, physical space, water, or food. If these species evolved under great competition or predation, then the new environment may host fewer able competitors, allowing the invader to proliferate quickly. Ecosystems which are being used to their fullest capacity by native species can be modeled as zero-sum systems in which any gain for the invader is a loss for the native. However, such unilateral competitive superiority (and extinction of native species with increased populations of the invader) is not the rule. 

Invasive species often coexist with native species for an extended time, and gradually, the superior competitive ability of an invasive species becomes apparent as its population grows larger and denser and it adapts to its new location. An invasive species might be able to use resources that were previously unavailable to native species, such as deep water sources accessed by a long taproot, or an ability to live on previously uninhabited soil types. For example, barbed goatgrass was introduced to California on serpentine soils, which have low water-retention, low nutrient levels, a high magnesium/calcium ratio, and possible heavy metal toxicity. Plant populations on these soils tend to show low density, but goatgrass can form dense stands on these soils and crowd out native species that have adapted poorly to serpentine soils.

Eagle

Eagle is a common name for many large birds of prey of the family Accipitridae; it belongs to several groups of genera that are not necessarily closely related to each other. Most of the sixty species of eagles are from Eurasia and Africa. Outside this area, just fourteen species can be found - two in North America, nine in Central and South America, and three in Australia.

Eagles are large, powerfully built birds of prey, with a heavy head and beak. Even the smallest eagles, like the booted eagle (Aquila pennata) (which is comparable in size to a common buzzard (Buteo buteo) or re-tailed hawk (B. jamaicensis)), have relatively longer and more evenly broad wings, and more direct, faster flight - despite the reduced size of aerodynamic feathers. Most eagles are larger than any other raptors apart from some vultures.

The smallest species of eagle is the South Nicobar serpent eagle (Spilornis klossi), at 450 g (1 lb) and 40 cm (16 in). The largest species are discussed below. Like all birds of prey, eagles have very large hooked beaks for tearing flesh from their prey, strong muscular legs, and powerful talons. The beak is typically heavier than that of most other birds of prey. Eagles' eyes are extremely powerful, having up to 3,6 times human acuity for the martial eagle, which eanbles them to spot potential prey from a very long distance.

This keen eyesight is primarily attributed to their extremely large pupils which ensure minimal diffraction (scattering) of the incoming light. The female of all known species of eagle is larger than the male. Eagles normally build their nests, called eyries, in tall trees or on high cliffs. Many species lay two eggs, but the older, larger chick frequently kils its younger sibling once it has hatched. 

The dominant chick tends to be the female, as they are bigger than the male. The parentes take no action to stop the killing.

Sharks

Sharks are a group of fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus. Under this broader definition, the earliest known sharks date back to more than 420 million years ago.

Since then, sharks have diversified into over 505 species. They range in size from the small dwarf lanternshark, a deep sea species of only 17 centimetres 6,7 inch) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (39 foot) in length. 

Until the 16th century, sharks were known to mariners as "sea dogs". The etymology of the word "shark" is uncertain. One theory is that it derives from the Yucatec Maya word "xok", pronounced "shok". Evidence for this etymology comes from the Oxford English Dictionary, which notes shark first came into use after Sir John Hawkins' sailors exhibited one in London in 1569 and posted "sharke" to refer to the large sharks of the Caribbean Sea. 

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Balaenidae

Balaenidae is a family of whales of the suborder mysticete that contains two living genera. Historically, it is known as the right whale family, as it was thought to contain only species of right whales.

Through most of the 20th Century, however, that became a much-debated (and unresolved) topic amongst the scientific community. Finally, in the early 2000s, science reached a definitive conclusion: the bowhead whale, once commonly known as the Greenland right whale, was not in fact a right whale.

The family of Balaenids, therefore, comprises the right whales (genus Eubalaena), and in a genus all to its own, the very closely related bowhead whale (genus Balaena). Their principle distinguishing feature is their narrow, arched, upper jaw, which gives the animals a deeply curved jawline. This shape allows for especially long baleen plates.

Snakes

Snakes are elongated, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with their highly mobile jaws.

To accommodate their narrow bodies, snakes´paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one fuctional lung. Some species retain a pelvic girdle with a pair of estigial claws on either side of the cloaca.

Living snakes are found on every continent except Antarctica, and on most smaller land masses - exceptions include some large islands, such as Ireland and New Zealand, and many small islands of the Atlantic and central Pacific. Additionally, sea snakes are widespread throughout the Indian and Pacific Oceans.