EEB215H1 Chapter Notes - Chapter 5: Species Richness, Natural Disaster, Genetic Diversity
15 Dec 2016
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Chapter 5 – Extinction is Forever
- 5 episodes of mass extinction in the fossil record
o natural mass extinctions
- extinction is a natural process
- if speciation rate equals or exceeds rate if extinction, biodiversity will remain constant or
increase
- current extinction rates much greater than speciation rates
- linked to human activity
- sixth extinction episode
o caused by human activities rather than natural disaster
The Meaning of “Extinct”
- extinct – no members of species found alive anywhere in the world
- extinct in the wild – only in captivity or other human controlled situations
- locally extinct or extirpated – no longer found in a specific area it once inhabited, but still
found elsewhere in the wild
- globally extinct – species that no longer lives anywhere in the world
- functionally/ecologically extinct – persists at such reduced numbers that its effects on the
other species in the community are negligible
o great risk of becoming globally extinct
- The current, human-caused mass extinction
o Species richness has decreased as humans asserted their dominance
o Elimination of large mammals from Australia and America
▪ Hunting and burning forests
o Extant – still living
o Majority of human-caused extinctions have occurred in the last 150 years
o Island species have higher extinction rates than mainland species
o Extinction rates have declined since 1950 due to efforts to protect rare species
o Count of extant species masks true scale of current extinction crisis
o Extinction debt – the presumed eventual loss of species following habitat
destruction and fragmentation
- Local extinctions
o Average of 200 populations per species, but some have more than others
o Loss of populations is roughly equal to proportion of habitat loss
o Action needed to prevent further local extinctions as well as global extinctions
o Loss of local populations diminishes value of area
- Extinction rates in aquatic environments
o Only 14 species known to have gone extinct in world’s history
▪ Probably an underestimate
▪ Marine species not as well known as terrestrial species
▪ May also show greater resiliency to disturbance
▪ These losses may be major though
o Many species of whales and large fishes have declined dramatically because of
human activities and are in danger of extinction
o Freshwater species have higher rate of extinction than marine
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