The Causes of Species Extinction

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  • 0:03 Past Extinctions
  • 1:26 Catastrophic Events
  • 2:30 Disease & Predators
  • 3:58 Competition & Climate Change
  • 5:45 Lesson Summary
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Lesson Transcript
Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

What do dinosaurs, passenger pigeons, and a species of Australian rat all have in common? They have all gone extinct. This lesson will examine the causes of species extinction from mass extinctions in the past to human-caused extinctions today.

Past Extinctions

Scientists believe that over 99% of all species that have ever existed on Earth have gone extinct, meaning all members of a species have died and the species ceases to exist. Yep, from dinosaurs to saber tooth cats, Earth has seen many species come and go.

So far on Earth, there have been five mass extinctions, meaning a large percentage of the species on earth go extinct. The most recent occurred 65 million years ago, where 85% of species died off. You may know this as the dinosaur extinction, but other species went extinct too. However, that wasn't the most severe extinction - that belongs to the Permian extinction, which occurred 250 million years ago and some estimates suggest 96% of organisms died. Pictured here are fossils of trilobites. All species of trilobites went extinct during the Permian extinction.


Some of these mass extinctions are believed to be caused by a catastrophic event, like an asteroid or increased volcanic activity. But extinctions are occurring all of the time, even if they are not part of a mass extinction. And catastrophic events are not the only culprits. Disease, competition, new predators and climate change can also cause species to go extinct. Let's examine each of these causes of species extinction.

Catastrophe Events

When you hear 'extinction,' a major catastrophic event probably pops into your mind, so let's start there. An asteroid likely caused the extinction that wiped out the dinosaurs 65 million years ago. Of course there's debate among the scientific community, but many believe the asteroid impact caused dust to block out the sun, which reduced Earth's temperature.

But is it just asteroids that cause mass extinctions? Again, there's debate within the scientific community, but the mass extinction that occurred at the end of the Triassic period has been attributed to lowering sea levels, which were caused by the volcanic rift that formed in the present day Atlantic Ocean. The lowering sea level killed off many marine species.

The largest mass extinction that occurred at the end of the Permian period is believed to be caused by increased global temperatures coupled with volcanic eruptions, which caused the temperature to increase even more. It's important to remember that, even in catastrophic events, extinctions don't happen over night, but over a period of a few hundred years to thousands of years.

Disease & Predators

Okay, enough about catastrophic events, let's look at some examples of species that have gone extinct from disease and predators.

Of course diseases can kill off some members within a species, but can disease really kill off an entire species? Yes, believe it or not, it can! Yikes! Case in point: the rat species Rattus nativitatis inhabited Australia but went extinct in 1908. Scientists believe the black rat, which was an invasive species, or a species that is nonnative to a region, was to blame. The black rat reached Australia via a ship and transmitted disease through fleas to Rattus nativitatis, which may have caused them to go extinct. Island populations, like Rattus nativictatis, are especially susceptible because they are not exposed to the same diseases as mainland critters.

Another cause of extinction is the introduction of predators. The dodo was a flightless bird that once thrived on the island of Mauritius, which is located in the Indian Ocean. Prior to human inhabitation of the island in 1505, the dodo had no predators. But once humans inhabited the region, they became the dodo's first predator, killing the flightless bird for food. Later, invasive species that were introduced by humans came to the island. Between humans and the introduced rats, pigs, and monkeys, the once predator-free dodo bird became a popular food source for several species, and by 1681, the dodo was extinct.

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