EXTINCTION

Evidence from the past The fossil record remains first and foremost among the databases that document changes in past life on Earth. The fossil record clearly shows changes in life through almost any sequence of sedimentary rock layers. sedimentary rock Successive rock layers contain different groups or assemblages of fossil species.assemblage

3 Types of Extinction 1.Local extinction (extirpation)  species no longer found in an area where it was once found Still found elsewhere (= population extinction) 2.Ecological extinction  so few members of a species are left that it can no longer play its ecological role in the ecosystem 3.Biological extinction  species is no longer found anywhere on the earth

Mass Extinctions EpochCauseSpecies Lost PrecambrianGlaciationStromatolites CambrianO 2 DepletionOlnellids Ordovician Glaciation of Gondwana Brachiopods Devonian Meteor, Glaciation Early corals PermianPangeaTrilobites End Cretaceous Meteor, Volcanoes Dinosaurs HoloceneHumansAll forms

Permian mass Extinction -Permian Period ( million years ago)  Formation Of Pangea - Terrestrial faunal diversification occurred in the Permian % of marine species became extinct in the Permian (largest extinction in history) - Causes? = Formation of Pangea reduced continental shelf area, glaciation, Volcanic eruptions

The End-Cretaceous (K-T) Extinction - Numerous evolutionary radiations occurred during the Cretaceous ( million years ago)  1 st appearance of dinosaurs, mammals, birds, angiosperms - A major extinction occurred at the end of the period - 85% of all species died in the End-Cretaceous (K-T) extinction (2 nd largest in history) - Causes? = Meteor impact in the Yucatan, Volcanic eruption  both supported geolocially, cause climate change, atmospheric changes

Extinction Rates Biologists estimate that 99.9% of all species ever in existence are now extinct –Background extinction – local environmental changes cause species to disappear at low rate –mass extinction – catastrophic, widespread (25 – 75% of existing species –mass depletion – higher than background but not mass Cause temporary biodiversity reductions  but create vacant niches for new species to evolve 5 million years of adaptive radiation to rebuild diversity after extinction

Premature extinction from human causes Passenger pigeon Great aukDodo Dusky seaside sparrow Aepyornis (Madagascar) Main factors  Overhunting, Habitat Destruction & Introduction of Exotic Species

Differences in Cause of Extinction Historically most mass extinctions were caused by Catastrophic Agents- such as meteorite impacts and comet showers, Earth Agents- such as volcanism, glaciation, variations in sea level, global climatic changes, and changes in ocean levels of oxygen or salinity Currently a mass extinction is being caused by the actions of 1 species  Us

Which species are most vulnerable? Vulnerability of species affected by … –Numbers – low numbers = automatic risk –Degree of specialization = generalists adapt better than specialists –Distribution = widely distributed organisms, may migrate out of harms way & different effects by area –Reproductive potential – if low = vulnerable –Reproductive behaviors – how complex, picky, … –Trophic level – higher are more vulnerable to biomagnification & trophic cascades

CharacteristicExamples Low reproductive rate (K-strategist) Specialized niche Narrow distribution Feeds at high trophic level Fixed migratory patterns Rare Commercially valuable Large territories Blue whale, giant panda, rhinoceros Blue whale, giant panda, Everglades kite Many island species, elephant seal, desert pupfish Bengal tiger, bald eagle, grizzly bear Blue whale, whooping crane, sea turtles Many island species, African violet, some orchids Snow leopard, tiger, elephant, rhinoceros, rare plants and birds California condor, grizzly bear, Florida panther

Indian Tiger Range 100 years ago Range today (about 2,300 left)

Black Rhino Range in 1700 Range today (about 2,400 left)

African Elephant Probable range 1600 Range today (300,000 left)

Asian or Indian Elephant Former range Range today (34,000–54,000 left)

Vulnerability of ecosystems 1.Diversity  at species, genetic, ecological or functional levels ** Remember, Diversity = Stability ** 2.Resilience  Ability of a living system to restore itself to original condition after being exposed to a minor outside disturbance 3.Inertia  ability of a living system to resist being disturbed or altered

Biome% of Area Disturbed Temperate broadleaf forests Temperate evergreen forests Temperate grasslands Mixed mountain systems Tropical dry forests Subtropical and temperate rain forests Cold deserts and semideserts Mixed island systems Warm deserts and semideserts Tropical humid forests Tropical grasslands Temperate boreal forests Tundra 94% 72% 71% 70% 67% 55% 53% 44% 37% 26% 18% 0.7%

Leading causes of wildlife depletion & extinction 1.Habitat loss, fragmentation or degradation Agriculture, urban development, pollution Prevent dispersal, mating, gene flow 2.Deliberate or accidental introduction of non-native species Rapid reproduction, no competitors, no predators, upset energy flow

Overfishing Habitat loss Habitat degradation Introducing nonnative species Commercial hunting and poaching Sale of exotic pets and decorative plants Predator and pest control Pollution Climate change Basic Causes Population growth Rising resource use No environmental accounting Poverty

Case Studies - Elephants Endangered 1.Ecological pressures – shrinking habitat 2.Socio-political pressures – recovery of elephants in smaller habitats = widespread habitat destruction, other species now poached for ivory 3.Economic pressures – poaching for ivory Ecological Role – keystone species, maintains grassland community by removing trees Consequences – loss of ecosystem type

Case Studies – Passenger Pigeon Extinct September 1, Ecological pressures – clearing virgin forests for agriculture lost food & nests, 1 egg laid per year 2.Socio-political pressures – Supply meat for growing east coast cities 3.Economic pressures – easy capture in large dense flocks, roosts  markets in the east Ecological Role – once most numerous bird on the planet Consequences – linked to spread of lyme disease

Case Studies – American Alligator Recovered June Ecological pressures – shrinking habitat 2.Socio-political pressures – alligator nuisance, sustainable use, tourism 3.Economic pressures – confused with American Crocadile hunted for skins Ecological Role – keystone predator, gator holes in everglades, top carnivore Consequences – loss of fish & bird populations & change whole everglades ecosystem structure / now healthy systems

Alligator mississippiensis

Remember That current changes in species numbers will be exacerbated by global warming

When is endangered really “in danger” Is there a number where the population is too small to survive? MVP = minimum viable population  the smallest number of individuals necessary to ensure the survival of a population in a region for a specified timer period Time range typically years Most indications are that a few thousand individuals is the MVP if time span is > 10 years

Genetic Bottlenecks If populations recover from times with small numbers other problems can persist Genetic bottlenecks Think of a traffic bottleneck  many cars approach and stop, only a few get through. Same with genes – genetic diversity is dramatically reduced When populations are reduced to small numbers interbreeding occurs and genetic diversity plummets

Cheetahs A few thousand years ago cheetahs experienced a population crash They have since recovered but they are almost all genetically identical Why is this a problem? 1.Inbreeding increased the chances of deformity from recessively inherited diseases 2.Identical genes gives identical vulnerability to disease 3.Weakened physiology – exaggerated recovery time from activity makes them vulnerable

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