Extinction

Extinction occurs when all individuals of a species are gone and have left no descendants. If all the species within a genus are extinct then the genus is extinct If all genera in a family areextinct then the genus is extinct. If all genera in a family are extinct then the family is extinct. Extinction removes a potential branch on the evolutionary tree.

Extinction is Forever

We can conclude a species has gone extinct when the last b f h i h di dmember of that species has died.

Tecopa pupfish - 1977

Dodo - 1581

Elephant Bird (Madagascar) ~ 1500

Moa (New Zealand) –4 species ~ 1400

Quagga - 1883

Passenger Pigeon – 1914Once the most common bird in North America.

Tasmanian Tiger or Thylacine 1936Tasmanian Tiger or Thylacine - 1936

Caribbean Monk Seal - 1952

Golden Toad - 1989

Pyrenean Ibex - 2000Pyrenean Ibex 2000

Baiji River Dolphin - 2006

It is often difficult to prove that no individuals of a species i i h ild I i i f l i lremain in the wild. It is easier to prove for large animals.

Ivorybilled Woodpecker - ?

What makes a species vulnerableWhat makes a species vulnerableto extinction?• Vulnerability to introduced exotics

• OverexploitationOverexploitation

• Rarity

• Habitat loss / Fragmentation• Habitat loss / Fragmentation

S ll l ti i k ti ti lik lSmall population size makes extinction more likely

• A small population is prone to positive-feedback loops p p p p pthat draw it down an extinction vortex

• The key factor driving the extinction vortex is loss of the genetic variation necessary to enable evolutionary responses to environmental change

Smallpopulation

Inbreeding

population

Geneticdriftg drift

Lowerreproductionp

Highermortality

L f

Reduction inindividual

Loss ofgenetic

variability

fitness andpopulation

adaptability

Smallerpopulation

Natural Extinctions• Habitat Disruption

Volcanic Eruptions– Volcanic Eruptions– Asteroid Impact

H bi M difi i• Habitat Modification– Climate Change– Mountain-Building– Sea Level Change

• “Exotic” Species– Natural Dispersalp– Continental Drift

Extinctions are most easily seen in species that have restricted distributions – endemic species.distributions endemic species.

Hotspots of biodiversity are also hotspots of extinction…

Human-Caused Extinction• Overexploitation (Food, fur, collecting, pest

eradication etc )eradication, etc.)• Habitat Degradation/Destruction• Destruction of keystone species• Introduction of Exotic Species

– Competitors– Predators– Diseases

• Pollution Contamination Climate ChangePollution, Contamination, Climate Change

Overexploitation• Human harvesting of wild plants or animals at rates• Human harvesting of wild plants or animals at rates

exceeding ability of populations of those species to rebound

Large organisms with low reproductive rates are• Large organisms with low reproductive rates are especially vulnerable

• Overexploitation by the fishing industry has greatly reduced populations of some game fish such as blue fin tunapopulations of some game fish, such as blue-fin tuna

World’s fish stocks have been reduced by 90%• World s fish stocks have been reduced by 90% since the start of industrial fishing

Human exploitation of other species increases with our population size.

Humans Arrivals are Linked to Large Mammal ExtinctionsExtinctions

• Australia 40,000 years agoA i 15 000• Americas 15,000 years ago

• Madagascar 1000 years ago• New Zealand 1000 years ago

Habitat Degradation• Destruction of Habitat• Destruction of Habitat

– “Save the Rainforests!”Eli i i f li i– Elimination of living space

– Change in habitatR i f l d• Rainforest to pasture lands

– Leads to diminishing resourcesI titi• Increases competition

– Can also be caused by natural processesVolcanoes floods dro ght etc• Volcanoes, floods, drought, etc…

Satellite Images of Amazon DeforestationSatellite Images of Amazon Deforestation between 1975 and 2001

Climate Change alters habitats over the entire Earth.

Habitat Fragmentation Smaller fragments have:Smaller fragments have:

• fewer habitat types

• fewer species

ll l ti• smaller populations

• higher extinction ratesg

Predation• Introduction of predators can impact natives• Introduction of predators can impact natives

– Invasive alien speciesC t th i• Can eat other species

• Compete for food sources• Introduce diseasesIntroduce diseases

Predators reduce the population size of prey species. Predators that are very effective can reduce the size of prey populationsthat are very effective can reduce the size of prey populations to the point of extinction.

The introduction of cats to areas that formerly lackedThe introduction of cats to areas that formerly lacked mammalian predators has caused the extinction of many species of birds, reptiles, and mammals. Introduced rats have caused the extinction of many birds and egg laying reptilescaused the extinction of many birds and egg-laying reptiles.

Lake Victoria had over 150 endemic species of fish belongingendemic species of fish belonging to one family. Each had specialized feeding adaptations.

The introduction of a large predator, the Nile perch, has caused thethe Nile perch, has caused the extinction of about half the species.

CoextinctionCoextinction• Everything is Connected to Everything -

ECE• The loss of one species leads to the loss of p

another – loss of a prey species impacts predatorsp

• Chain of extinction• Can be caused by small impacts in the• Can be caused by small impacts in the

beginning