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Threats to Global BiodiversityThreats to Global Biodiversity

We wish to know:• What is biodiversity? Why is it important?• What are the threats to biodiversity?• How can we estimate rates of species loss?

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What is Biodiversity?What is Biodiversity?

• the variety and variability among living organisms and the ecological complexes in which they occur

• number and variety of species, ecological systems, and the genetic variability they contain.

• In its narrowest sense biodiversity refers to the number of species on the planet

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How Many Species Exist?How Many Species Exist?

• Some 1.4 to 1.8 million species are "known to science" -- meaning that they have been classified by a specialist

• Most experts estimate the world's species diversity at 10 to 30 million, but that is very approximate

• Except for land vertebrates and flowering plants, the number of undescribed species greatly exceeds the number described

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New DiscoveriesNew Discoveries

Psudoryx nghetinhensis, recently discovered in north-central Viet Nam.

is really two, such as this Australian mountain brushtail possum, or the recent splitting of the African elephant into a savannah and forest species.

Ichthyologists describe about 300 new fish species each year

Less uncommon is the discovery that one species

Discovery of a new large mammal is noteworthy.

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Number of Known, Living, SpeciesNumber of Known, Living, SpeciesAmong species known to science, the diversity of insects is overwhelming in number. For this reason, most animal species live on land, but more phyla, the highest level of classification, live in the sea.

~ 1.8 million species

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Number of Animal Species Number of Animal Species Currently KnownCurrently Known

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Number of Known Species of Number of Known Species of Higher PlantsHigher Plants

Plant diversity of the world consists primarily of the flowering plants (angiosperms), which are divided into the grasses and other monocots, and a great variety of dicots. Most flowering plants live on land; algae prevail in the sea.

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What is the real number of living What is the real number of living species? species?

10 million +

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How do we know that?How do we know that?

More than 70% of the species living in a tropical forest reside in the canopy, the uppermost layer of the forest, and one of the least understood environments on Earth

The Smithsonian Tropical Research Institute (STRI) From Didham and Fagan

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ExtinctionExtinction

• Five great extinctions• 440 mya, 370 mya, 245 mya

(Permian), 210 mya, 65 mya (K-T)

• Followed by adaptive radiations

• The sixth extinction• Phase 1: began 100,000 years

ago with spread of humans• Phase 2: began 10,000 years

ago with dawn of agriculture• Phase 3: began 250 years ago

with industrial and scientific revolutions

http://www.actionbioscience.org/newfrontiers/eldredge2.html

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ExtinctionExtinction

• Definition: The end of a phyletic line without phyletic replacement

• Five levels of extinction• Extinction of a species from almost all of its range• Extinction of a whole species• Extinction of groups of lower taxonomic rank• Extinction of groups of higher taxonomic rank• Mass extinction (Many groups in an epoch)

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Examples of ExtinctionExamples of Extinction

• Level 1• American Bison-Estimated 50 million animals

prior to European settlement - 541 left by 1889• White rhino - Common species in southern Africa

nearly extinct by 1894. Now stable in South Africa, but extinct in Uganda, CAR, Zaire, Sudan

• Black rhino - Four subspecies virtually extinct and predicted to go extinct in next few years, other three are listed as vulnerable

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Examples of ExtinctionExamples of Extinction

• Level 2 - Whole species• Irish elk - Went extinct 11,000 years ago, probable

cause was change in habitat, although cause is debated

• Steller’s sea cow - Member of order Sirenia that went extinct from overhunting by the 1800s.

• Level 3 - Genera and families• Saber-toothed cats - Extinct in Pleistocene. Likely

from loss of prey, but possibly overspecialization.

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Examples of ExtinctionsExamples of Extinctions

• Level 4-Phyletic groups• 11,000 years ago 2/3 of America’s mammals

over 100 lbs. were lost rivaling the dinosaur extinctions. Over 100 genera, 36 of 45 families and 9 of 12 orders went extinct

• South America, Australia, and North America lost 70% of megafauna, while Africa lost 20%

• Level 5 – Mass extinctions• See previous lecture

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The Pleistocene ExtinctionThe Pleistocene ExtinctionClimate change

Over-kill

The combination

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Modern Threats to biodiversityModern Threats to biodiversity

Human actions now threaten species and ecosystems to an extent rarely seen in earth history.

The Sextet of threats:• Over-harvest• Exotic species• Habitat loss• Climate change• Pollution • Domino effects

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Over-ExploitationOver-Exploitation

Hunting, especially commercial hunting and poaching, has driven many species to extinction.

Passenger pigeon for meat, snowy egret for fashion, rhinos for their horns.

Bushmeat harvest is a crisis of tropical forests today

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Over-ExploitationOver-Exploitation

Imagine a tropical parrot inhabiting Michigan?

The Carolina parrot, once abundant in eastern N. America, now extinct

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Bushmeat tradeBushmeat trade

• For the tropical forests of central and west Africa (the Congo Basin rainforests), greatest threat to vertebrate species is over-hunting for subsistence and commerce

• For people living in these areas, up to 90% of total animal protein may be derived from wild animals

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Invading speciesInvading speciesNon-indigenous species (invaders) often are more effective predators or competitors, thereby eliminating native species. Island (and lake) species may be especially vulnerable.

Some of Victoria’ cichlids

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Michigan invadersMichigan invaders

The gypsy moth arrived in the U.S. in the early 1900s, and in Michigan in the 1950s. With few natural enemies, it devours the leaves of forest trees. Although some defoliation is tolerable, if in two successive years and coupled with a drought, trees can be killed.

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Michigan invadersMichigan invadersThere is little doubt that the sea lamprey was primarily responsible for decline of lake trout in upper Great Lakes (Coble et al. 1990). This is evidenced by the timing of the collapse, coincidence of wounds and scars, simultaneous collapse in unfished bays, and continued decline after fishing had fallen to low levels. Detailed analysis of catch and effort data provided no support for over-fishing as the cause of declines, except in Lake Superior.

                           

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Winning the War against Winning the War against InvadersInvaders

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Global deforestationGlobal deforestation

Original tropical forest extent was ~ 15 m km2; today it is about 8 m km2. At present rates of loss, ~ 10% of the original tropical forests will remain by end of 21st century.

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Habitat Habitat FragmentationFragmentation

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Habitat Habitat Fragmentation Fragmentation and Extinction and Extinction

RiskRisk

Forest fragments in Warwickshire, England, from 400-1960

Habitat loss often is accompanied by habitat degradation and habitat fragmentation. Remnant populations persist at very low densities

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Under a 2 x CO2 scenario, the bobolink’s habitat would shift northwards

Global WarmingGlobal Warming

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Domino EffectsDomino Effects

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Studies of plant and animal biogeography have established a log-linear relationship between number of species in an area, and areal extent. An example for the reptiles and amphibians for the Caribbean is shown with the area axis reversed, to illustrate that reduction in area leads to a reduction in species.

Species-Area Species-Area RelationshipsRelationships

z = slope

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Estimating Rates of Species LossEstimating Rates of Species Loss

• The relationship between number of species and area of habitat is S = c A z

• the rate of loss of tropical forest from satellite imagery is 1-2% annually

• the resulting loss rate of species results in an overall loss of 25 - 50% of the world’s species by 2100

• Assuming tropical forests harbor 10 million species, this loss is 27,000/yr (and 3/hr)

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Historical vs present-day extinctionsHistorical vs present-day extinctions

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How much biodiversity will remain in 2100?

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hotspot designation: A terrestrial biodiversity hotspot is an area that has at least 0.5%, or 1,500 of the worlds ca. 300,000 species of green plants, and that has lost at least 70% of its primary vegetation. (Current total = 34)

http://www.biodiversityhotspots.org/xp/Hotspots

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SummarySummary

• Biodiversity refers to the number and variety of species, of ecosystems, and of their genetic variation

• About 1.4-1.8 million species are known to science. Because many species are undescribed, some 10-30 million species likely exist at present

• Biodiversity is threatened by the “sinister sextet”• Habitat loss represents the single biggest threat,

along with invasive species. Over-harvest and climate change also are significant.