Jonah Patel
Extinction is the death of all members of a species of plants, animals, or other organisms. Over five billion species are estimated to have gone extinct, with notable examples including sabre-toothed cats, dodos, mammoths, and many others. Species become extinct for a variety of reasons, including the introduction of invasive species, climate change, human activity, and natural selection. Extinct species are typically classified as such when the last known specimen dies without leaving a genetic successor, although this can be complicated by the rediscovery of species thought to be extinct, known as Lazarus taxa. In recent times, the high rate of extinctions has alarmed scientists, with human activity being a significant contributing factor. Conservation efforts are crucial to protecting biodiversity and preventing further extinctions.
| Characteristics | Values |
|---|---|
| Number of species that have gone extinct | Over 5 billion species |
| Current number of species | 8.7 million |
| Notable extinct species | Non-avian dinosaurs, sabre-toothed cats, dodos, mammoths, thylacines, trilobites, megalodons, golden toads, passenger pigeons |
| Cause of extinction | Natural occurrences such as climate change, introduction of invasive species, habitat destruction, pollution, overfishing or hunting |
| Human impact | Humans have become a cause of extinction for some species, either as mega-predators or by transporting animals and plants |
| Conservation efforts | Breed animals in captivity for release, create nature reserves, combat animal trafficking |
| Defining extinction | When the last known specimen dies without leaving a genetic successor; when there is no reasonable doubt that the last individual has died |
| Lazarus taxon | Species thought to be extinct but later rediscovered |
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Human activity
One of the most well-known examples of human-caused extinction is the dodo bird, which was hunted to extinction by humans and the invasive species we introduced, such as pigs and cats. Early humans also overhunted megafauna like mammoths and mastodons, driving them to extinction. This phenomenon, known as the "overkill hypothesis", occurred when humans were suddenly introduced to environments where animals had never experienced human predation techniques before, leading to swift extinctions.
Today, agriculture and industrialization are major contributors to species extinction. Agriculture is one of the biggest threats to Earth's ecosystems, with activities like logging, farming, and aquaculture causing habitat loss for many species. Industrialization has also driven up extinction rates, with water pollution, dams, and other industrial activities endangering species like Chinese river dolphins, foothill yellow-legged frogs, and sockeye salmon. Climate change, exacerbated by human activities, is another significant threat, with some species like the golden toad already extinct due to changing environmental conditions.
Invasive species introductions by humans continue to be a problem, with intentional and accidental introductions sometimes leading to catastrophic consequences. For example, the chytrid fungus Batrachochytrium dendrobatidis (Bd), which has spread worldwide through human activity, has devastated amphibian populations, contributing to the extinction of species like the mountain mist frog and possibly the corquin robber frog.
Conservation efforts are crucial to preventing further extinctions and regenerating endangered populations. The current rate of human-driven biodiversity loss is unsustainable and poses a grave threat to the planet's health and all life that depends on it.
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Climate change
The rise in global temperatures is a key factor in species extinction. All plants and animals have an optimal temperature range, and as temperatures rise, many species are forced to either adapt or migrate, putting them under significant pressure to survive. This is particularly true for species with restricted thermal ranges, such as those occupying climatic extremes in polar regions. These species are more likely to become extinct due to their limited ability to adapt to changing temperatures.
The impact of climate change on species is also evident in the decline of flying insects. European scientists have found a 75% reduction in the mass of flying insects in natural parks since 1990, with climate change and pesticides being the main causes. This is a significant concern, as bees are responsible for pollinating 71% of the crop species that provide 90% of humanity's food.
In addition to temperature rise, climate change causes extreme weather events such as droughts, hurricanes, and rising sea levels, which further contribute to species extinction. For example, the Bramble Cay melomys (Melomys rubicola) became extinct due to the destruction of its habitat by rising sea levels. Similarly, the Mediterranean monk seal population has dropped by 60% in the last 60 years.
Invasive alien species (IAS) are another consequence of climate change, negatively impacting native biodiversity and contributing to species extinction. The proliferation of invasive species is often facilitated by changing climate conditions, further exacerbating the problem.
To mitigate the impact of climate change on species, it is essential to prioritize nature conservation and implement strategies for climate change adaptation. Reducing CO2 emissions and embracing tools such as the IUCN Red List and the Integrated Biodiversity Assessment Tool can enhance species survival in a changing climate.
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Geological events
One notable example is the End Permian extinction event, approximately 252 million years ago. This event, likely caused by global warming and volcanic eruptions, led to the decimation of numerous marine and terrestrial species. The subsequent recovery and repopulation of the Earth with new species demonstrate the impact of geological events on the formation of novel life forms.
Mass extinctions, while rare, provide opportunities for new species to emerge. Following mass extinction events, small, isolated communities may form, leading to rapid genetic changes. These changes can result from factors such as population bottlenecks, founder effects, genetic drift, and inbreeding. If these isolated populations survive and expand into new niches, they may evolve into distinct species, constituting abrupt events in geological terms.
In addition to mass extinctions, other geological events can also contribute to the emergence of new species. For instance, volcanic eruptions, tectonic shifts, and climate changes can create physical barriers, separating populations and driving speciation. The separation of populations can lead to reproductive isolation, where groups become genetically differentiated from their parent population over time.
Furthermore, geological events can introduce novel environmental conditions that favour certain traits and drive evolutionary adaptations. Species that acquire advantageous traits can exploit new niches, leading to rapid changes in other traits as they adapt to their changed surroundings. These adaptations can result in the formation of new species.
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Invasive species
Several species in U.S. territories have gone extinct due to invasive species. For example, the Guam flycatcher (Myiagra freycineti) was a common bird species on the island of Guam until the accidental introduction of the brown tree snake (Boiga irregularis) in the 1940s. The last sighting of the flycatcher was in 1983. In Florida, invasive Burmese pythons are threatening several species, such as the Key Largo woodrat and the Key Largo cotton mouse. A review of critically endangered species on the IUCN Red List revealed that invasive species threaten 14% of critically endangered terrestrial vertebrate species globally, with birds being the most affected.
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Natural selection
Invasive alien species, introduced intentionally or accidentally into new habitats, can directly impact native species by preying on them, competing for resources, or introducing harmful pathogens. Human activities, such as habitat destruction, pollution, overfishing, and hunting, have significantly contributed to modern extinctions. For example, the dodo bird, the passenger pigeon, and the West African Black Rhino have all been hunted to extinction by humans.
Climate change, including global warming and sea-level changes, has also played a significant role in extinction events. The end of the last ice age, 10,000 years ago, led to the extinction of many North American animals, including mammoths and mastodons, due to a combination of climate change and overhunting by early humans. Similarly, the Sabre-toothed Cat's extinction has been linked to the decline of large herbivores they hunted, as well as climate change and competition with humans.
Extinction is a natural part of the evolutionary process, and most species that become extinct are never scientifically documented. However, scientists are alarmed by the current high rate of extinctions, with human activities being a significant contributing factor. The introduction of exotic and invasive species, often driven by human actions, can alter the biodiversity of ecosystems and lead to the extinction of native species.
Conservation efforts are crucial to protecting biodiversity and preventing further extinctions. Initiatives such as breeding animals in captivity for subsequent release, creating nature reserves, and combating animal trafficking can help preserve species and maintain ecological balance. Additionally, the use of environmental DNA (eDNA) can help determine when species are under threat of extinction, guiding conservation actions.
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Frequently asked questions
Extinction is the death of all members of a species of plants, animals, or other organisms.
The identification of a new species is done by studying fossils and remains. In recent times, environmental DNA (eDNA) is also used to determine when species are under threat of extinction.
A species is considered extinct when the last known specimen dies without leaving a genetic successor.
Notable extinct animal species include non-avian dinosaurs, dodos, sabre-toothed cats, mammoths, thylacines, and passenger pigeons.
Species become extinct due to natural occurrences such as climate change, inability to deal with evolving diseases, and competition. In recent times, human activities have also caused extinctions, such as habitat destruction, pollution, and overfishing or hunting.
