The Extinction
loss of the last member of a species. Extinction is irreversible. Extinction leads to a biologically impoverished world. However, extinction is a naturally occurring process. Extinction is the ultimate fate of all species on Earth. Including humans! Mass Extinctions Throughout the history of life on Earth we have seen mass extinctions before. A mass extinction is a period where many more species are going extinct compared to background levels. Mass Extinctions
65 million years ago, at the end of the Cretaceous Period, the rate of extinction was about as high as we had ever seen on Earth before. The end of the age of dinosaurs. At that time the extinction rate was estimated to be 1 species every 500-1,000 years. Mass Extinctions Recently, for the last 10,000 years, we have been in another period of mass extinction. This period of mass extinction corresponds well with the spread of humans throughout the world.
World wide dispersal Human radiation Where humans went, a wave of extinctions followed, going back at least 10,000 years.
Mass extinctions
The current rate of mass extinctions is getting faster and faster. Just looking at two Classes of vertebrates birds and mammals:
10K 1600 1600 1980 1980 2000
1 species / 800 years 1 species / 3 years We lost 194 bird species and 106 mammal species that we know of, probably even more. 1 species / 6 months Mass extinctions
In addition, there are a great many endangered species. Close to 300 species of birds, and another 300 species of mammals are presently endangered.
We will probably lose most or all of them to extinction in our lifetimes.
Mass extinctions
The current rate of extinctions 1 species every six months (birds and mammals) is a 1000FOLD greater rate than the Earth has EVER seen in the history of life. This should be alarming to you This is very largely the result of human activity. Never, in the history of life, has a single species been responsible for the extinction of so many other species, across so many different taxa. Human-Caused Reductions in Biodiversity
Historically, the cause for many extinctions was a direct assault.... OVERHARVEST More recently the causes have been more indirect. More on the indirect causes a little later... Overharvest For much of the current period of mass extinctions, overharvest is the major cause. Especially for birds and mammals. Oddly, we push into extinction some of our most favored species.
American Passenger Pigeon
Indirect causes Overharvest is still with us in many areas, but as a major cause of extinction it is losing ground to several indirect factors. Inadvertent loses associated with the way humans go about their business around the world. Exotic species An exotic species is one that has been introduced to an area in which it does not naturally occur. Sometimes on purpose, sometimes by accident. Often, an exotic introduction is done ignorant of the effect on other native organisms Once introduced, the species may perish, or flourish Invasive Species Invasive (exotic) organisms may thrive in new territory where they are of free usual predators, diseases, or resource limitations that limited them in original habitat.
Over past 300 years, approximately 50,000 non-native species have become established in the U.S..
Exotic introductions extinctions
At least 4,500 are free-living. 15% cause environmental damage.
Invasive Species Eurasian milfoil
European green crab Cheatgrass Water hyacinth Kudzu vine Asian tiger mosquitoes Purple loosestrife Zebra muscles
Invasive Species Exotic species
Islands, especially remote islands Competitors, diseases, parasites... This goes on all over the world.
Guam: ALL the indigenous birds are, or soon will be, lost. An introduced snake Once established, a successful exotic species is nearly impossible to eliminate. Habitat loss Presently, the main cause of extinctions worldwide. Humans modify the landscape wherever we go.
Just look around,
the effect is everywhere,
Consequence of modification is a loss of species. Habitat loss Today > 60% of endangered birds, and >70% of endangered mammals face extinction due to this threat. Overall, about 2/3 of the worlds endangered species face this threat. Fragmentation Habitat Fragmentation
Habitat fragmentation divides populations into isolated groups vulnerable to catastrophic
events.
Some species are especially sensitive to this type of disruption
Need large unbroken tracts of habitat
Northern Spotted Owl Grizzly bears
Habitat Fragmentation Ecosystem disruption
A complicated problem that is often underestimated. Things look pretty much the same, but they in fact are different. Entire communities can be disrupted in this way. Chemical pollution and bioconcentration Acid rain Global warming Ozone depletion The solution?
PREVENTION is the key, not amelioration. Protection: Laws and fines But the black market is always a problem Impoverishment and empowerment Control exotic species Inadvertent introductions nearly impossible to stop, but we can do better with direct introductions. Caution The solution? Habitat loss and alteration
Set aside properly designed preserves
Time is short Few large tracts of land are left Intensive management is needed
Toxic chemicals and pollution New and better laws
Better enforcement and protection Better waste handling techniques
Who's at risk?
For animals, we can identify a number of features that render a species prone to extinction. Who's at risk? Low level of reproduction Blue whale, condors, polar bears, whooping cranes Highly specialized diet Panda, black footed ferret, everglade kite High trophic level Tiger, eagle, condor, wolf Big
Elephant, bear, tiger, whales Kirtland's warbler, orangutan
Localized endemic
Who's at risk?
Limited or specialized breeding or nesting area required
Island species
Fixed migratory pattern
Blue whale, Kirtland's warbler, whoopers, seabirds
Who's at risk? Preys on livestock or people Wolf, crocodile Oddball behaviors
Red headed woodpecker, colonial nesters, fearless of humans.
Commercial or black market value Tropical fish, rhinos, tigers, ginseng, orchids....