Species — Definition and Examples, Biology Dictionary


Species Definition

A species is a group of organisms that share a genetic heritage, are able to interbreed, and to create offspring that are also fertile. Different species are separated from each other by reproductive barriers. These barriers can be geographical, such as a mountain range separating two populations, or genetic barriers that do not allow for reproduction between the two populations. Scientists have changed their definition of a species several times throughout history.

Species is one of the most specific classification that scientists use to describe animals. Scientists use a system of binomial nomenclature to describe animals without the confusion of common names. This system uses the genus as the first name, which is always capitalized, and the species name is the second name, always lower case. Thus, some animals like the Red fox, Vulpes vulpes, are both in the genus Vulpes and their species name is vulpes. Note the capitalization difference to distinguish between genus and species. Other foxes such as the swift fox, Vulpes velox, are also part of the Vulpes genus, but barriers exist that keep them from interbreeding with the Red foxes. In this way, they remain distinct species.

Taxonomic Rank Graph

Since the days of Carl Linnaeus, the creator of binomial nomenclature, animals have been constantly classified and reclassified into different groups, genre, species and subspecies. Linnaeus, classifying organisms in the 1700s, restricted his classifications to the physical attributes of various organisms. Most organism, surprisingly, he correctly identified as being related. Others, however, he couldn’t have been more wrong about. Modern day genetic techniques have given us a much better window into the historical relationships between animals.

For instance, when Linnaeus first classified the elephant in the early 1700s, he only ever saw one specimen. The specimen was a fetal Asian elephant, the smallest of the known elephants today. Not knowing better, Linnaeus named the species Elephas maximus. Modern day scientists have been forced to reclassify the elephant several times. The first distinction is between the Asian and African elephants, which are much different in size. Scientists then further had to distinguish between elephants that inhabited grasslands and those that lived in forests in Africa. Genetics show the populations do not interbreed and are separated by a reproductive barrier.

In the next century, Charles Darwin and Alfred Wallace separately conceived of the mechanism that creates multiple species from a single species. This process of natural selection applies adversity of different forms that organisms must overcome to reproduce. Organisms that are better adapted to the environment are able to reproduce more, and their offspring can also increase in number. In this way, different lines of the same species can do better or worse, depending on their genetics. Eventually, two successful lines may diverge, creating a reproductive barrier between the two populations. These populations, according to Darwin and Wallace, are now considered separate species.

Since the beginning of time, this process has been occurring and dividing organisms along different successful lineages. This theory has been confirmed by a large body of evidence. Fossil evidence provides clues that animals have been constantly changing over time, in response to a variable environment. Where Linnaeus saw animals as static, unchanging entities, it is now widely accepted that species exist on a spectrum, with some being closer related to certain species than others. Because of this, animals can often hybridize, or mate between species.

Examples of Species

Polar bears and Grizzlies

Oftentimes the only barrier to reproduction is geographic, or based on the physical location of the animals. If this changes, the animals can interbreed, and may merge into one species. This is currently being seen in the wild in polar bears and grizzly bears. As the climate changes, polar bears are forced further south, and must start exploiting different food sources. The change in climate also allows grizzly bears to venture further north, encountering polar bears along the way. The previously separated populations now have a chance to breed, and sometimes they are successful. Hybrids have been seen in the wild, but it is not yet known if they hybrids will be successful.

There are many different situations and examples of reproductive barriers, but if the barrier can be removed, it is likely that two related species will be able to interbreed. Non-related species rarely have a possibility of breeding because they have become too different from each other. For instance, a bat and turtle have a completely different genetic makeup. The genes that control growth in the turtle would not function in a bat, and vis-versa. In fact, they don’t even have the same number of chromosomes, which is a requirement for sexually reproducing organisms to be successful.

Dogs and Wolves

Still other animals, like dogs and wolves, are still technically the same species. While they have the same number of chromosomes and could technically breed, the domestic dog has come a long way from its wild counterpart. Dogs have not only evolved to be more cuddly and soft, but are attuned to human social cues. Wolves operate in a much different social structure. As such, the two are very unlikely to breed in the real world. However, because they can create fertile offspring, scientists consider them the same species.

Dogs and wolves are a good example of species radiation, or the incremental changing in a population that is widely distributed. Think of a Chihuahua. If Linnaeus had classified this animal, he certainly would not have put it in the same category as a wolf. However, a Chihuahua can breed with a slightly bigger dog, which can breed with large dog, which could easily breed with a wolf. In this way, a Chihuahua and a wolf have the same genetic basis, expressed in very different ways.

Related Biology Terms

  • Hybrid – An organism produced by the crossing of two distinct species.
  • Reproductive Barriers – Obstacles that prevent two animals from producing fertile offspring.
  • Binomial Nomenclature – The system of naming individual species with two Latin names, the first related to their genus, the second to their species.
  • Taxonomical Hierarchy – The system into which all organisms are placed for classification.

1. Domestic ferrets and wild black-footed ferrets look almost identical. The black-footed ferret, Mustela nigripes, is native to North America. The domestic ferret, Mustela putorius furo, is native to Europe and only exists in captivity in North America. Could these two populations be one species?
A. No
B. Yes
C. Maybe

2. If scientists tell species apart by how they look, why aren’t males and females that look differently considered different species?
A. They can interbreed
B. Sexual dimorphism is a type of speciation
C. They are considered different species

3. It was recently discovered that what where believed to be two species of trout, one in Russia and one in the US, have almost identical DNA and can reproduce if the eggs and sperm are artificially brought together. The populations are continually separated by saltwater ocean, which they cannot traverse. While some scientists have argued to make them one species, others have argued to keep them separate. What is the argument for keeping them as separate species?
A. They cannot successfully interbreed.
B. They are still separated by a geographical reproductive barrier.
C. There are no good arguments.


The 10 Species of Pigs

Pigs are animals in the genus «Sus», known for their high command of social intelligence.

A domestic pig in a meadow.

A pig is an animal found in the genus Sus and the family Suidae. Pigs range from domestic to wild pigs that are considered to be the ancestor of all pigs. These animals are widely known to be omnivores, and their variety of food is similar to that of human beings. In fact, there are so many considerable similarities between pigs and humans that pigs are often used for human medical research.

10. Javan Warty Pig

The species name of this pig is Sus verrucosus. Javan pig originated from three Islands found in Indonesia called Bawean, Java and Mandura. These regions are mainly forested with an altitude ranging from sea level to 800 meters above sea level. A Javan warty pig has a weight of between 44 to 108 kg and a length of 90 to 190 cm. The distinctive characteristics of this pig are its skinny legs and large body. Their age is determined by the sizes of their warts, as the older the pig, the larger the warts. The warty pig is mostly active during the night. The average lifespan of this pig is eight years though some live to be as old as 14 years. Javan warty pig is an omnivore as it feeds on vegetation and small mammals. It is one of the rear species, and it is among the endangered with a population of about 377 individuals. Efforts have therefore been put in place to conserve them.

9. Domestic Pig

The scientific name of the domestic pig is sus scrofa domesticus. It can also be referred to as swine. The length of this pig ranges from 90 to 180 cm, and an adult pig weight range from 50 to 350 kg. The domestic pig is widely famous because of the consumption of their meat known as pork. Archeological evidence points out that the domestic pig was domesticated from wild boars. This pig has a gestation period of between 112 to 120 days. The Domestic pig lacks sweat glands, meaning it is unable to maintain its body temperatures naturally. This makes pigs resort to behavioral thermoregulation such as covering their body with mud. One common behavior of a domestic pig is nest-making. Due to the increase in needs for human transplants, the domestic pig is the leading non-human organ donator to humans since their organ size is relatively comparable to that of a human.

8. Wild Boar

The other common name of the wild boar is the wild swine. The wild boar originated in southeast Asia before later spreading to the rest of the world. This pig is believed to be the common ancestor of many pig species. Its body structure is massively built and with short and thin legs. Wild boars are omnivores. Its population has decreased over time due to hunting and human encroachment which has made the wild boars disappearance deep into the wild forest. It became extinct in Britain in the early 11th century, and it was only reintroduced in the 1980s through importation.

7. Philippine Warty Pig

Sus philippensis, or Philippine warty pig, has its native origin in the Philippines. Philippine warty pig has a close relation to the Bornean bearded pig. Much of its natural habitat has been lost due to hunting and deforestation.

6. Oliver’s Warty Pig

Sus oliveri is also referred to as Oliver’s Warty Pig or Mindoro Warty Pig.This pig is a small pig in the genus Sus and is only found in Mindoro Islands in the Philippines. Initially, it was thought to be a subspecies of S. philippensis but was later proven to be genetically different. It is known to be a species that is heavily hunted, leading to its classification as being extremely rare.

5. Celebes Warty Pig

Celebes warty pig, or Sus celebensis, is also known as the Sulawesi pig as it is found in Sulawesi in Indonesia. The Sulawesi pig is a medium sized animal that is still largely found in Sulawesi Parts of Indonesia. It can survive in most habitats, and it can even thrive in altitudes of up to 2500 meters above sea level. Frequent hunting has led to the reduction in their population over the years, however conservation efforts have been put in place to prevent extinction.

4. Visayan Warty Pig

The binomial name of the Visayan warty pig species is Sus cebifrons. It is one of the most endangered species of pigs. Its native origin is the Visayan Islands of Philippines. The main causes of endangerment are hunting, habitat loss and food shortage.This pig is mostly an omnivore as it eats roots, fruits tubers and some small animals found in the forest. They can also eat cultivated crops since farmers have cultivated their habitats.

3. Heude’s Pig

Heude’s pig binomial name is Sus bucculentus. Its other name is Vietnam warty pig or the Indochinese warty pig that is found in Vietnam and Laos. This species of a pig was thought to have been extinct until recently when its skull was discovered in the Annamite Range in Laos in the year 1995. Heude’s physical appearance is not known. The skull that was found showed some similarities with the wild boar and some scientist have suggested that it could be identical with the Wild boar species.

2. Bornean Bearded Pig

Bornean bearded pig, or Sus barbatus, is sometimes just referred to as as bearded pig. Its distinctive feature from the rest of the species is its beard. This breed of pig is endemic to the southeastern part of Asia in the Borneo, Sumatra and Malay Peninsula where there is mangrove and rainforest cover. This type of pig often lives in families and begins reproduction at the age of approximately 18 months.



Sloths are literally named for their characteristically slow movement. Adored in pop culture, sloths are the subject of many adorable viral videos, and seen in numerous movies and cartoons. There is much more to these endearing creatures than their famously slow movements. Read on to learn about the sloth.

Description of the Sloth

Sloths are built for life in the trees, where their long, curved claws are used for gripping branches. Depending on the species, the arms will have two or three long claws, which are used to hang upside down underneath branches.

All sloth species have long legs, and rounded heads with small ears. Their fur is long and coarse, and is frequently coated in green algae. This fur grows away from their extremities, unlike most other mammals. This strange growth pattern is attributed to their upside-down style of living.

Interesting Facts About the Sloth

Sloths are truly amazing and interesting creatures. While they might seem slow and boring, their lives, characteristics, and adaptations are anything but!

  • Green Fur – Most sloths have a green tinge to their coats. This color comes from algae growth, and their relationship with the algae is symbiotic. This means that both creatures benefit from the interaction. The algae hitches a ride on a suitable host, and the host receives camouflage from predators, in the form of green coloration.
  • Living Habitat – Sloths are a living, breathing biome! In addition to the algae that grows on their fur, sloths play host to a number of insects and other small creatures. While they carry the usual fleas, ticks, and mites, some also provide a home for many different beetle and moth species.
  • Hold It! – Because these animals spend their lives hanging from trees, using the bathroom can be a challenge. Sloths only climb to the ground once per week to urinate and defecate. During this time they are in extreme danger, and must accomplish their task as quickly as possible. Most sloths live in the same tree for the bulk of their feeding time, and researchers believe that the sloth’s fecal habits actually help fertilize the tree it lives in.
  • Muscular Mayhem – There is good reason for sloths to avoid climbing to the ground more often. Its total body weight is just 25 – 30% muscle. In comparison, most other mammals’ body weight is 40 – 45% muscle. These creatures are built for leisurely hanging, not walking, and they do not do well at it. Because they can’t walk, they must drag themselves using their long front limbs, making them a sitting duck for predators. Better to just stay in the trees as long as possible.

Habitat of the Sloth

Sloths are restricted to a very small ecosystem in which they can succeed. They are extremely specialized creatures, and only do well in tropical rainforests. They are arboreal creatures, which means they live the vast majority of their lives up in the treetops. They will remain on and around a single tree, known as a modal tree.

Distribution of the Sloth

All six species of sloths are found in the rainforests of Central and South America. Each species has different distribution, and some are localized to a very small range. The brown-throated sloth can be found from Honduras to Eastern Peru. The pale-throated sloth is found from Guyana to areas north of the Amazon River in Brazil. The maned sloth is found only in Brazil.

The critically endangered pygmy three-toed sloth is found only on Isla Escudo de Veraguas off the coast of Panama. The Linnaeus’s two-toed sloth is found from Venezuela to areas north of the Amazon River in Brazil. The Hoffman’s two-toed sloth is divided into two populations, one from Honduras to Ecuador, and the other from Peru to Bolivia.

Diet of the Sloth

Sloths are omnivores, eating both plants and small animals. All species feed on the leaves of the cecropia family of trees, but will also browse on a number of other plants. Sloths have also been known to feed on insects, fruits, lizards, and even carrion. They learn what foods to eat by licking their mother’s lips, and this allows baby to determine what foods are safe to eat.

Sloth and Human Interaction

Unfortunately for sloths, human interactions are very commonly detrimental. Indirectly, these plodding animals are struck by cars, and electrocuted trying to climb power lines.

They are also subjected to direct poaching, both for meat and illegally for the pet trade. Thankfully, sloths are protected and aided by a number of rescues and organizations. The Sloth Institute Costa Rica rehabilitates and releases sloths into the wild, and the Aviarios Sloth Sanctuary cares for non-releasable animals.


Sloths have not undergone any domestication.

Does the Sloth Make a Good Pet

Sloths do not make good pets. In many places it is illegal to own one, and you can be subject to hefty fines and seizure of the animal. It is also likely that your sloth was taken from the wild, which could potentially impact the population. These animals are also quite difficult to care for, because they have very specialized diets and lifestyles.

Sloth Care

In zoos, these creatures are provided with balanced nutrition to match their diet in the wild. They are provided with commercial biscuits that are low in starch and high in fiber, to replicate their daily plant intake.

In addition to these biscuits, sloths are also fed a wide variety of different plants to browse on, as well as fresh fruits and vegetables. Their enclosures provide them with lots of climbing opportunities, and various locations to browse on leaves just like they would in the wild.

Behavior of the Sloth

These animals spend the vast majority of their time alone, and only interact with other sloths to breed. They spend most of their time in and around their “home” modal tree, where they browse for food and sleep.

When a female is ready to reproduce, she begins to call at night to any males in the area. The first male to reach her will be the one she breeds with. If multiple males arrive at the same time, they battle in a comically slow fashion, and the female mates with the winner.

Reproduction of the Sloth

Different sloth species have different gestation lengths. The female will give birth upside down, normally to a single baby. The baby will nurse for a month, but begins to taste solid foods after just ten days.

Baby sloths cling to their mothers’ stomachs until they are about three weeks old, then they begin to hang upside down on their own. Depending on the species, the baby will remain with its mother anywhere from six months to two years.


Bony Fish Facts

Scientific Names: Osteichthyes, Actinopterygii, Sacropterygii

  • M.S., Resource Administration and Management, University of New Hampshire
  • B.S., Natural Resources, Cornell University

Most of the world’s fish species are categorized into two types: bony fish and cartilaginous fish. In simple terms, a bony fish (Osteichthyes) is one whose skeleton is made of bone, while a cartilaginous fish (Chondrichthyes) has a skeleton made of soft, flexible cartilage. A third type of fish, including eels and hagfish, is the group known as Agnatha, or jawless fish.

The cartilaginous fish include sharks, skates, and rays. Virtually all other fish fall into the class of bony fish which includes over 50,000 species.

Fast Facts: Bony Fish

  • Scientific Name:Osteichthyes, Actinopterygii, Sacropterygii
  • Common Names: Bony fish, ray-finned and lobe-finned fishes
  • Basic Animal Group: Fish
  • Size: From below a half inch to 26 feet long
  • Weight: Well under an ounce to 5,000 pounds
  • Lifespan: A few months to 100 years or longer
  • Diet: Carnivore, Omnivore, Herbivore
  • Habitat: Polar, temperate, and tropical ocean waters as well as freshwater environments
  • Conservation Status: Some species are Critically Endangered and Extinct.


All bony fishes have sutures in their neurocranium and segmented fin rays derived from their epidermis. Both bony fish and cartilaginous fish breathe through gills, but bony fish also have a hard, bony plate covering their gills. This feature is called an «operculum.» Bony fish may also have distinct rays, or spines, in their fins.

And unlike cartilaginous fish, bony fish have swim or gas bladders to regulate their buoyancy. Cartilaginous fish, on the other hand, must swim constantly to stay afloat.


Bony fish are considered to members of the class Osteichthyes, which is subdivided into two main types of bony fish:

  • Ray-finned fishes, or Actinopterygii
  • Lobe-finned fishes, or Sarcopterygii, which includes the coelacanths and lungfishes.

The subclass Sarcopterygii is made up of about 25,000 species, all characterized by the presence of enamel on their teeth. They have a central axis of bone that acts as a unique skeletal support for fins and limbs, and their upper jaws are fused with their skulls. Two major groups of fishes fit under the Sarcopterygii: the Ceratodontiformes (or lungfishes) and the Coelacanthiformes (or coelacanths), once thought to be extinct.

Actinopterygii includes 33,000 species in 453 families. They are found in all aquatic habitats and range in body size from under a half inch to over 26 feet long. The Ocean sunfish weighs up to over 5,000 pounds. The members of this subclass have enlarged pectoral fins and fused pelvic fins. Species include Chondroste, which are primitive ray-finned bony fishes; Holostei or Neopterygii, the intermediate ray-finned fishes like sturgeons, paddlefish, and bichirs; and Teleostei or Neopterygii, the advanced bony fishes such as herring, salmon, and perch.

Habitat and Distribution

Bony fish can be found in waters all around the world, freshwater and saltwater both, unlike cartilagenous fish who are found only in salt waters. Marine bony fish live in all the oceans, from shallow to deep waters, and in both cold and warm temperatures. Their lifespans range from a few months to over 100 years.

An extreme example of bony fish adaptation is the Antarctic icefish, which lives in waters so cold that antifreeze proteins circulate through its body to keep it from freezing. Bony fish also comprise virtually all freshwater species living in lakes, rivers, and streams. Sunfish, bass, catfish, trout, and pike are examples of bony fish, as are the freshwater tropical fish that you see in aquariums.


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