What causes species to disappear? After they're gone, what happens next? And are humans to blame for this mass extinction? This article will explore everything about extinction: what it means, why it happens, how human activities affect it, and some real-life examples. So, let's get started!

What is the definition of extinction?

Extinction occurs when all members of a species have died. Before a species becomes extinct, it can become locally extinct, extinct in the wild, or functionally extinct.A species is considered locally extinct when it has died out in a particular geographical area.The brown bear (Ursus arctos) is locally extinct in California. It no longer has an existing population in the state but exists in other parts of North America. The California population is believed to have consisted of a now-extinct subspecies, known as the California brown bear (U. a. californicus).A species is considered extinct in the wild when they are no longer found in the areas they used to inhabit and are only found in captivity.The northern white rhinoceros (Ceratotherium simum cottoni) (Fig. 1) is a subspecies of rhinoceros that is extinct in the wild, and the only surviving individuals are two females kept in the Ol Pejeta Conservancy in Kenya.A species is considered functionally extinct if there are not enough members to fulfill its ecological niche and sustain a population.Wild oysters are considered functionally extinct in certain parts of the world because overfishing has already destroyed over 85% of all the oyster reefs. Oysters sold in markets are most likely farmed, which means that they no longer fulfill their role in the ecosystem.

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Some events can cause the extinction of more than one species. Co-extinction is the disappearance of a species as a result of another disappearance. For example, the extinction of prey could also cause the extinction of the predatory species. On the other hand, mass extinction is the disappearance of over half the extant species worldwide. Paleontologists believe that there have been five mass extinctions, based on the sudden and dramatic disappearance of more than half of extant species in five strata in the fossil record.Speciation and extinction have been taking place throughout the history of the world. These processes have shaped the evolutionary changes documented in the fossil record.  While it takes thousands to millions of years to recover from mass extinction events, these create gaps in the Earth's ecosystems, where new groups of organisms can emerge.Mass extinctions are often followed by adaptive radiation, the process in which a single species rapidly evolves into a large number of species adapted to different ecological niches. This happens because these organisms can colonize new regions with little competition. For example, the extinction of the non-avian dinosaurs allowed mammals to emerge and flourish.

What are the causes of extinction?

In this section, we will discuss a few possible environmental and genetic factors that can cause extinction.

Environmental factors

Natural disasters have caused many extinction events throughout history. For instance, the end-Cretaceous extinction event, which occurred about 66 million years ago, is believed to have been caused by a massive meteor impact near the Yucatan Peninsula. This impact likely led to the extinction of non-avian dinosaurs. However, some scientists suggest that the Deccan Traps, a series of volcanic eruptions in western India, could also be responsible for their extinction. Another example is the end-Permian mass extinction event, where volcanic activity caused the oceans to lack oxygen, leading to the death of around 96% of marine species. Interestingly, some dinosaurs survived the end-Cretaceous extinction event and evolved into modern-day birds.

Genetic factors

When a population becomes small, it can enter an extinction vortex, where the population shrinks until there are no individuals left. This is because when the population is small, genetic variation is lost due to inbreeding and genetic drift. Inbreeding happens when closely-related individuals reproduce, leading to offspring with little genetic variation. Genetic drift, on the other hand, is when chance events cause changes in allele frequencies.

If the environment stays the same, the population may survive. But if there are changes, like the emergence of diseases, the population may not be able to adapt. This is because with less genetic variation, it is less likely that there are individuals with the traits needed to survive under the new conditions.

An example of this is the greater prairie chicken, which used to inhabit the western prairies of North America. Due to habitat loss, their population declined rapidly. In Illinois, their population went from millions in the 19th century to only 50 individuals in 1993. Scientists found that reduced genetic variation and fertility caused this decline. To address this, they introduced prairie chickens from other states, which increased genetic variation and led to an increase in the population.

Are humans causing extinction?

The Anthropocene period, the sixth mass extinction, is believed to have already begun due to human activities. Activities such as habitat loss, overexploitation by hunting and harvesting, and the introduction of invasive species are contributing factors to extinction. In fact, the extinction rate caused by humans is about 1,000 times higher than the background extinction rate.

The explosive growth of the human population, from approximately 1 billion in 1850 to over 7.8 billion in 2020, has contributed to this problem. The world's population is projected to reach 10 billion by 2050, leading to massive habitat loss. Habitat loss reduces the survival rate of organisms and leads to the extinction of many species. Without their habitat, resources like food and territory are lost. While nature can cause habitat loss, human activities account for most habitat loss today, with deforestation being a prime example. Deforestation is often the result of human land use for agriculture, resource extraction, and land conversion.

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In addition to habitat loss, rising greenhouse gases have led to changes in the world's climate. By the middle of the 21st century, rising surface temperatures are expected to force many species to seek habitats with similar climate conditions up mountain slopes and closer to the poles.

Background extinction is the type of extinction that occurs continually, as opposed to mass extinction, where the decline in diversity is sudden and dramatic. Scientists estimate the background extinction rate to be around 1 per million species per year.

What are some examples of extinction caused by humans?

The flightless bird used to inhabit the forests of the island of Mauritius and was hunted down and consumed by sailors. The sailors found the bird to be easy prey because it approached them without fear. Additionally, pigs, rats, and dogs that the sailors brought with them also hunted down the young offspring of the dodo. As a result of these factors, the dodo became extinct in 1662. Today, the only evidence that remains of the dodo are a few skeletal remains and illustrations.

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The passenger pigeon is another classic example of human-induced extinction. They used to inhabit the hardwood forests of the northern United States and migrate in flocks so huge that they would darken the sky. However, the species rapidly declined in the 19th Century due to overhunting and habitat loss.

When the forests that they inhabited were cleared for farming, they were forced to search for food in the farmlands, where they caused severe damage. In turn, the farmers hunted them down relentlessly. They were also hunted down and sold in the market for private consumption. By the 1890s, they were nearly wiped out in the wild. Although some conservation efforts were made, such as a bill introduced in Michigan to illegalize hunting down passenger pigeons for ten years, it was too late. In 1914, the last passenger pigeon died in captivity, marking the end of a once-thriving species.

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Where can I find the list of extinct species?

The IUCN Red List is a critical tool for assessing the conservation status of various plant, animal, and fungi species. It provides insight into the possible conservation measures that can be taken to prevent their extinction. The Sunda Pangolin is currently listed as critically endangered due to various threats such as residential and commercial development, biological resource use, transportation and service corridors, and natural systems modification. The IUCN Red List also assesses conservation actions in place, including international management or trade controls. However, it also highlights the need for area-based regional management plans to tackle land/water protection. It is alarming to note that the IUCN Red List describes over 380 vertebrate species that went extinct after 1500 AD, with 86 of them wiped out by overhunting or overfishing. This underscores the importance of conservation efforts to protect species from human-induced extinction.

Extinction - Key takeaways Extinction is the disappearance of a species throughout the world. It occurs when a species can no longer use its ecological niche for survival. Speciation and extinction have been taking place throughout the history of the world. These processes have shaped the evolutionary changes documented in the fossil record. Environmental and genetic factors can cause extinction. These include natural disasters and loss of genetic variation. Human activities have also caused extinction through habitat loss, overexploitation, and the introduction of invasive species. The IUCN maintains a list of extinct species and species threatened with extinction. It also indicates the conservation status of the species.

References

Advanced Placement for AP Courses Textbook by Texas Education Agency The IUCN Red list Campbell Biology Eleventh Edition by Person Higher Education Smithsonian on the passenger pigeon Columbia Climate School on wild oysters Britannica on extinction Princeton University on the Deccan Traps

Extinction

What is extinction of species? 

Extinction occurs when all members of a species have died.

What causes extinction? 

Environmental and genetic factors can cause extinction. These include natural disasters and loss of genetic variation.Human activities have also caused extinction through habitat loss, overexploitation, and the introduction of invasive species.

What animals are extinct?

Animals that are extinct include the dodo bird and the passenger pigeon.

How are humans causing extinction?

Habitat loss, overexploitation by hunting and harvesting, and the introduction of invasive species are just some ways that humans are causing extinction.

Can we prevent extinction explain?

Extinction has been occurring throughout evolutionary history, even before humans have existed. However, human activities have contributed to a dramatic increase in rates of extinction. We can prevent extinction by addressing activities that put tremendous pressure on species through conservation measures.

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