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.
• Successive rock layers contain different groups or assemblages of fossil species.
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 Epoch Cause Species Lost
Precambrian Glaciation Stromatolites
Cambrian O2 Depletion Olnellids
Ordovician Glaciation of Gondwana
Brachiopods
Devonian Meteor, Glaciation Early corals
Permian Pangea Trilobites
End Cretaceous Meteor, Volcanoes Dinosaurs
Holocene Humans All forms
Permian mass Extinction
- Permian Period (286-248 million years ago) Formation Of Pangea
- Terrestrial faunal diversification occurred in the Permian
- 90-95% 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 (144-65 million years ago) 1st 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 (2nd 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 auk Dodo 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
Characteristic Examples
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
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%
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
Habitatloss
Habitatdegradation
Introducingnonnativespecies
Commercialhunting
andpoaching
Sale ofexotic pets
anddecorative
plants
Predatorand
pest control
Pollution
Climatechange
Basic Causes
• Population growth• Rising resource use• No environmental
accounting• Poverty
Case Studies - Elephants
Endangered 1. Ecological pressures – shrinking habitat2. 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, 1914 1. Ecological pressures – clearing virgin forests for
agriculture lost food & nests, 1 egg laid per year2. Socio-political pressures – Supply meat for
growing east coast cities3. 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 4 19871. Ecological pressures – shrinking habitat2. Socio-political pressures – alligator nuisance,
sustainable use, tourism3. 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
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 10-100 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