Species Extinction — Definition & Causes

What Is Extinction?

Threatened, Endangered, Extinct: What Do They Mean?

The world is always changing, and species are constantly going extinct. This means no more members of that species are alive on Earth. But, as human activity has started to disturb nature, scientists have had to make some new terms for the state a species is in. Species in danger of becoming extinct are classified as endangered, critically endangered, or extinct in the wild. When organisms become endangered, they usually become the focus of intense scientific research and conservation.

Is it Extinct?

How can scientists tell if a species has died off completely? They don’t just wait until no one sees the species anymore. Instead, they monitor species while they are still alive, keeping track of their numbers and their habitats.

Background Extinction

Species are constantly going extinct all over the world. The rate at which this happens in the biosphere is called the background rate of extinction or the normal extinction rate.

Why is there a normal rate of extinction? It's because a species’ fitness changes as the environment changes. For example, imagine a coral that needs a certain amount of salt in the water to survive. If the coral species does not adapt as the amount of salt in the water changes due to changing climate or other factors, it will die off. Another example is a species being out-competed by an invasive species. If a new species is introduced to a certain niche and does a better job of existing in that niche than the original species, the original species might go extinct.

Mass Extinction Events

Sometimes a large number of species die off at the same time. These are called mass extinctions. There have been five of these events on Earth so far.

How do mass extinctions happen? Think big: Meteors hitting the earth, huge volcanic eruptions, ice ages... The environment rapidly changes, causing a bottleneck where only some species survive.

Some people believe that Earth is facing another mass extinction right now, this time caused by human activity.

Effects of Human Disturbances

Pollution and habitat loss are two human-caused issues which endanger everything from coral reefs to rain forests.

Pollution is any substance introduced into a part of the environment where it shouldn’t exist in excess. For example, the amount of carbon dioxide released from burning fossil fuels and the rate that it is released at alters the climate.

Things like deforestation and development destroy animals’ homes. This habitat loss forces organisms to quickly adapt to new environments or go extinct. Parks, nature and wildlife reserves, marine protected areas, and other protected zones help fight habitat loss.

(Video) A Dodo's Guide to Extinction

by BBC

Extinction is when a species dies out. This can be due to human activities or natural disasters. Some examples include pollution and effects of climate change. When a species population has declined to the point where extinction may happen, it is called an endangered species. In this video, the BBC covers the case of one famous species: the dodo bird.

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$\color{#8925AE}{\text{Extinction}}$ : When a species no longer exists in the wild

$\color{#8925AE}{\text{Endangered Species}}$ : A species that is in danger of becoming extinct

How Do Species Die Out?

Extinction occurs when all members of a species are dead. This moment is typically marked by the death of the last individual of a species. There have been a series of mass extinctions in Earth's history. The majority of the species on Earth have been killed off due to a single event. The rest of the time, there is a baseline level of extinction that occurs throughout the course of time. This means that there are always species becoming extinct.

Why Does This Happen?

Mass Extinction

There are several reasons a species could go extinct. Especially in the case of mass extinction, a large worldwide catastrophe would need to occur. This could include a massive volcanic eruption, a hit from a meteor, or an ice age.

Baseline Levels of Extinction

Far more common than these massive events is the baseline level of species loss, called the background rate of extinction. This can come from multiple sources and typically isn't attributed to a single event. This includes things such as small population sizes and a small gene pool. A small population and gene pool mean that the species is more vulnerable to things like disease, predators, and bad mutations.

Habitat Degradation

Species can also die off because of habitat degradation. A lot of the time this is due to human causes. Many habitats are destroyed for the purpose of agriculture. Therefore, the species that once lived in that habitat are more likely to go extinct. This can eventually lead to ecological succession, which could mean the growth of new biodiversity.