Background Information on Extinction and Endangered Species
Background Information on Extinction and Endangered Species
Some Key Facts about Extinction
* all words shown in bold can be used as vocabulary words for this lesson; click here for some assessment questions on this material
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Extinction is an event in which an entire species that used to live on earth no longer exists. Dinosaurs are a well known example of a group of sepias that have gone extinct. We know they existed because we see evidence of their presence in the fossil record but there are no dinosaurs alive today. Fossils can tell us about which animals have gone extinct, but what do we know about extinction as a process? Is is still going on today?
Extinction a natural process which has been occurring since life evolved. Extinction can occur for many reasons. Some examples include climate change, evolution of another local species, and outside forces (like a meteor hitting the earth or humans destroying environments). When species go extinct, their absence may leave an "environmental niche" some other species may fill.
Generally, extinction occurs at a low 'background rate' matched by the rate at which new species appear. Thus the biodiversity is constantly changing.
There have been periods in the Earth's history when biodiversity crashes known as mass extinctions have occurred. These are times when more than 50% of the Earth's species vanish in the geological instant of a few million years. Two important mass extinctions in the history of life on Earth are the Permian Extinction and the Cambrian Extinction.
Scientists have debated the exact cause of both mass extinction and individual species extinction. For example, some scientists argue the major cause for the Cambrian Extinction (dinosaurs) was a meteor impact on the earth, whereas others argue other climate changes played an equally important role.
http://www.enchantedlearning.com/subjects/dinosaurs/extinction/
Right now humanity's impact on the earth has increased extinction rates to levels rivaling the five mass extinctions of past geologic history.
CNN transcript on current mass extinction -- Millennium
2000: Environment
http://www.cnn.com/TRANSCRIPTS/0001/02/se.35.html
Human Impact Triggers Massive Extinction– Environmental
News Service
http://ens.lycos.com/ens/aug99/1999L-08-02-06.html
Because we can only estimate the number of species living on our plant, the exact rate of species loss is unknown. However, we do know that globally the current rate of species loss may be as much as 50 times higher then any time in the past 100,000 years.
Some of the major ways humans are impacting the earth are by habitat destruction, overexploitation, and introduction of nonnative species.
Habitat destruction throughout the world has been caused by agriculture, urban development, forestry, mining, and environmental pollution. The IUCN (International Union for Conservation of Nature and Natural Resources) estimates that the destruction of physical habitat is responsible for 73% of species designated as endangered, extinct, vulnerable or rare.
Overexploitation causes species to become extinct by drastically reducing their population as a result of excessive commercial harvest or sport hunting.
Non-native species introduced by mistake (as people travel from place to place) or intentionally for agricultural or other purposes may disrupt local environments and cause extinction. One way this introduction can impact native species is by changing the dynamics in the predator-prey food chain. IUCN estimates displacement by introduced species is responsible for 68% of species designated as endangered, extinct, vulnerable or rare.
Species that are identified as in danger of going extinct are listed as "endangered species" and protected by the Endangered Species Act and the US Fish and Wild Life Service.
