The former stayed near the floor, where they fed on bottom-dwellers; the latter swam up near the sun, eating insects at the surface. Their habitats and behaviors were so different that they rarely met, and never interbred. And all was well. The answer had to do with invasive crayfish, which were likely introduced into the lake ecosystem by humans. Actually, it can be. Regular speciation happens when members of one species are divided by changes in their habitat or behavior.
Reverse speciation is when those distinct species come together again, until they become one species yet again. Quite the contrary: Extinction was a fundamental part of the theory that Charles Darwin, the grandfather of evolution, put forth in in his seminal Origin of Species.
Today some researchers say that reverse speciation may be becoming more common—especially in environments altered by humans. Examples of this kind of hybridization abound: The endemic grey ducks of New Zealand are threatened with extinction not only from habitat loss, but also because of interbreeding with invasive mallard duck species. The sudden disappearance of plants and animals that occupy a specific habitat creates new opportunities for surviving species. Over many generations of natural selection , these lineages and their descendent lineages may evolve specializations suited to the newly freed up resources and may take over ecological roles previously held by other species, or may evolve brand new ecological strategies.
In this way, mass extinction can level the evolutionary playing field for a brief time, allowing lineages that were formerly minor players to diversify and become more prevalent. By removing so many species from their ecosystems in a short period of time, mass extinctions reduce competition for resources and leave behind many vacant niches , which surviving lineages can evolve into. It was only when the non-avian dinosaurs went extinct 65 million years ago in the end-Cretaceous mass extinction, that mammals really diversified.
In less than 20 million years, they evolved into the great variety of mammals we know today — forms that play many of the same roles in terrestrial ecosystems that their dinosaur predecessors had. Learn more about adaptive radiations , in which a lineage rapidly diversifies and the newly formed lineages evolve different adaptations.
Tyson Brown, National Geographic Society. National Geographic Society. For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource. If a media asset is downloadable, a download button appears in the corner of the media viewer.
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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Extinction is the complete disappearance of a species from Earth.
Species go extinct every year, but historically the average rate of extinction has been very slow with a few exceptions. The fossil record reveals five uniquely large mass extinction events during which significant events such as asteroid strikes and volcanic eruptions caused widespread extinctions over relatively short periods of time. Some scientists think we might have entered our sixth mass extinction event driven largely by human activity.
Our planet is dependent on an interconnected system. If we lose one species, how does that impact the whole system? What if we lose hundreds?
Help your students understand the gravity of extinction with these classroom resources. In the mids, Charles Darwin famously described variation in the anatomy of finches from the Galapagos Islands. Alfred Russel Wallace noted the similarities and differences between nearby species and those separated by natural boundaries in the Amazon and Indonesia. Independently they came to the same conclusion: over generations, natural selection of inherited traits could give rise to new species.
Use the resources below to teach the theory of evolution in your classroom. Dinosaurs gambol and charge through our imagination as scaly reptilian creatures with menacing teeth, claws, spikes, and hammering, bony bulbs. They roamed Earth roughly million years ago, and most were wiped out by an extinction event roughly 65 million years ago.
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