What is extinction?
Extinction is the process in which organisms die out. If birth rate is less than the death rate, over time, extinction of that species will occur.

What is mass extinction?
Definition: Mass extinctions are periodic rises in the extinction rate above the background level. They are events which are not caused by changes in habitat or competition but catastrophes
.
There have been five mass extinctions in the past.
1. The Late Ordovician- 438 million years ago, caused by a drop in sea level as glacier formed,
then rise in sea level as glaciers melted-Lots of marine species went extinct
2. Late Devonian- 360 million years ago, Cause unknown
3. Permian- 245 million years ago, cause unknown, possible meteor, climate change or volcanic
eruptions, the worst mass extinction of all time
4. Late Triassic- caused by massive floods of lava
5. The Cretaceous Tertiary (K-T) 65 Million years ago, which ended the reign of the dinosaurs
This era was the end of the Crustaceous era and beginning of the Tertiary era. A six-mile wide
asteroid landed on earth and had devastating effects. 3/4 of the species on earth died out, including the dinosaurs.
The graph below demonstrates these facts:
Extinctions.gif
http://www.whither-progress.org/images/evolution/Extinctions.gif

Breakdown of the causes of the previous mass extinctions:
extinction970404.jpg
http://www.dinosaur.org/extinction970404.jpg



Extinction Facts:


Extinction rates:

The typical rate of extinction differs for different groups of organisms. Mammals, for instance, have an average species "lifespan" from origination to extinction of about 1 million years, although some species persist for as long as 10 million years. There are about 5,000 known mammalian species alive at present. Given the average species lifespan for mammals, the background extinction rate for this group would be approximately one species lost every 200 years. Of course, this is an average rate -- the actual pattern of mammalian extinctions is likely to be somewhat uneven. Some centuries might see more than one mammalian extinction, and conversely, sometimes several centuries might pass without the loss of any mammal species. Yet the past 400 years have seen 89 mammalian extinctions, almost 45 times the predicted rate, and another 169 mammal species are listed as critically endangered. http://www.pbs.org/wgbh/evolution/library/03/2/l_032_04.html

Table of rates from known extinctions since 1600:




Extinct
Threatened
Extant
Time to 50% extinction

Animals
Molluscs
191
354

60,000


Crustaceans
4
126

--


Insects
61
873

--


Vertebrates
229
2,212

600


Fishes
29
452

900


Amphibians
2
59

3,000


Reptiles
23
167

2,000


Birds
116
1,029

350


Mammals
59
505

250


Total
485
3,565

15,000

Plants
Gymnosperms
2
242
758
--


Dicotyledons
120
17,474

1,000


Monocotyledons
462
4,421

1,700


Palms
4
925
2820
70


Total
584
22,137

1,100









http://darwin.eeb.uconn.edu/eeb310/lecture-notes/extinctions/node2.html

Causes of extinction:
There are three main causes of extinction
  • Over exploitation,
  • Development (urbanization, agriculture, mining, etc..)
  • Invasive exotics
Others ways: Killing animals for profit, hunting and trapping, over harvesting, introduced species, destruction of habitat, and pollution


How to overcome extinction:
-The best way to overcome extinction is to become well adapted to physical and biological stresses that occur repeatedly in ones
environment. This can be explained as being pre-adapted to unexpected stress. A good example is tree species surviving forest fires

Effects of extinction on the enviroment:
  • More intense extinction of tropical forms.
  • Extinction strikes in both the land and the sea, though higher rates are generally cited among marine forms.
  • On the land, while animals suffer repeatedly, plants seem to be more resistant to mass extinctions.
  • There has been a suspicion that fish might also be more than usually resistent to mass extinction events, but this idea has been rejected as an artefact of preservation
  • Causes major restructuring of the biosphere
  • Diversity is removed
  • Unlikely survivors expand
  • Predator's prey would overpopulate, depleting their own resources, and the prey itself could eventually could become extinct.


Are we in a mass extinction?

cnn[1].gif

How is the current extinction different from past extinctions?
The extinction we are in right now, known as the 6th extinction, is human caused. There are two phases
-Phase 1: First humans disperse to different parts of the world. Shortly after humans started spreading, many species began to die out.
Humans overhunted animals such as Mammoth and Buffalo and spread diseases to species, causing death.
-Phase 2: Started around 10,000 years ago when humans started using agriculture. Agriculture represents the biggest change in the
history of life.
http://www.actionbioscience.org/newfrontiers/eldredge2.html


Scientists agree the world faces mass extinction, "biodiversity," is in serious trouble. "Biodiversity includes all living things that we depend on for our economies and our lives," says Brooks Yeager, vice president of global programs at the World Wildlife Fund in Washington, D.C.Most scientists agree that human activity is causing rapid deterioration in biodiversity. Rapidly growing human settlements, logging, mining, agriculture and pollution are destroying ecosystems, upsetting nature's balance and leading many species to extinction.Among scientists, it is almost unanimous that we have entered a period of mass extinction not seen since the age of the dinosaurs, an emerging global crisis that could have disastrous effects on our future food supplies, our search for new medicines, and on the water we drink and the air we breathe. Estimates vary, but extinction is figured by experts to be taking place between 100-1,000 times higher than natural "background" extinction.http://archives.cnn.com/2002/TECH/science/08/23/green.century.mass.extinction/

This graph shows the past and predicted future of extinction rates:
gene-fig-1-8-extinction11[1].jpg


How do humans affect extinction?

Humanity's main impact on the extinction rate is landscape modification, an impact greatly increased by the burgeoning human population. Now standing at 5.7 billion and growing at a rate of 1.6 percent per year, the population of the world will double in 43 years if growth continues at this pace. By draining wetlands, plowing prairies, logging forests, paving, and building, we are altering the landscape on an unprecedented scale. Some organisms do well under the conditions we've created: They tend to cope well with change, tolerate a broad range of habitats, disperse widely, and reproduce rapidly, and they can quickly crowd out more specialized local species. City pigeons, zebra mussels, rats, and kudzu and tamarisk trees -- these are examples of what biologists call "weedy" species, both animals and plants. Many weedy species will probably survive, and even thrive, in the face of the current mass extinction. But thousands of others, many never known to science, are likely to perish.
http://www.pbs.org/wgbh/evolution/library/03/2/l_032_04.html

How are humans speeding up extinction?

Some animals are used for their fur, feathers, or other parts of their bodies. Other animals are killed because of their conflict with how humans want to use land. But, large numbers of species disappear solely because their homes have disappeared as land is being changed from its natural state to urban and agricultural areas. Unless humans balance their needs with the needs of other species, the rate of extinction will continue to rise. Are humans effected by extinction?

What is the fate of our own species likely to be, if we really are in the midst of a sixth mass extinction? One possibility is that as diversity and abundance wither, the species causing it all -- Homo sapiens, the most dominant species in history -- could also be on the road to oblivion. But another possibility is that Homo sapiens, which has proved to be a very effective weedy species itself, will persist. That's the view of paleobiologist David Jablonski, who sees us as one of the survivors, "sort of picking through the rubble" of a world that has lost much of its biodiversity -- and much of its comfort. For along with that species richness, the ecosystem is likely to loose much of its ability to provide many of the valuable services that we take for granted, from cleaning and recirculating air and water, to pollinating crops and providing a source for new pharmaceuticals. And while the fossil record tells us that biodiversity has always recovered, it also tells us that the recovery will be unbearably slow in human terms -- 5 to 10 million years after the mass extinctions of the past. That's more than 200,000 generations of humankind before levels of biodiversity comparable to those we inherited might be restored.
http://www.pbs.org/wgbh/evolution/library/03/2/l_032_04.html


How are human activities affecting the amount of nitrogen in the environment?
The effects from nitrogen emissions from humans is more than that of any other species or industry. The effects of reactive nitrogen on species contributes to their extinction.

Global trends in the creation of reactive nitrogen on Earth by human activity
figure-2-15.jpg
http://www.greenfacts.org/en/global-biodiversity-outlook/l-3/6-threat-biodiversity.htm#1p0



How are ecosystems affected by mass extinctions?
'Although the number of animals bounced back quite quickly, the ecosystems they formed were dramatically restructured, and the complexity of these systems didn't recover for 30 million years.' Sarda Sahney said this about doing a study at the University of Bristol. Previous research into about mass extincinos focused on the number of species, and presumed that life recovered quickly, but new research, like that of Sarda Sahney, looked at ecosystems and found that they actually took much longer to recover.
"Millions of years required for recovery from mass extinction.(Brief article)." Geographical 80.4 (April 2008) 10(1). Global Reference on the Environment, Energy, and Natural Resources. Gale. Pace Academy. 28 Oct. 2009
<http://find.galegroup.com/grnr/start.do?prodId=GRNR>.