L25: Extinction, ancient and recent Flashcards
What is speciation?
The process in which two or more contemporaneous species evolve from a single ancestral population.
What are the causes that underline modern extinction?
1) Habitat loss and fragmentation
2) Invasive species
3) Overharvesting/ overhunting
4) Climate change
Number of species according to the United Nations Environmental Programme (UNEP)
Eight million seven hundred thousand (give or take 1.3 million).
How many species are threatened with extinction?
More than 26,500 species are threatened with extinction in December 2018.
That is more than 27% of all assessed species.
What is extinction?
1) Extinctions occur when the last individual of a species dies out.
2) Functional extinctions occur when individuals remain but the odds of sustainable reproduction are low i.e the species is effectively extinct even though individuals remain.
(Lomolino et al., 2011)
What is mass extinction?
Episode of relatively abrupt (few millions of years) replacement of virtually entire biota.
Exact causes still debated! But…drastic environmental changes.
(Lomolino et al., 2011)
1) Recent extinctions and overhunting causes
isolation and “naive” biota
Humans:
- Habitat loss, population decline
- Introduction of exotic species
- Overhunting
Examples of extinction:
Thylacine- Tasmanian Tiger
Example of extinction of a whole family
Extinct since 1933 (Union for conservation of Nature)
Carnivorous marsupial of modern times.
Native to contiental Australia, Tasmiania and New Guinea.
Last extant member of its family.
Why are invasive species problematic?
Alteration of habitat
Change in the diversity, abundance, and distribution of members of the preexisting communities
Competition with native species
Broad and cascading effects throughout communities and ecosystems
Extinction
Lake Victoria and Cichlids
Lake Victoria: introduction of Nile perch (Lates niloticus) in the 1950s appears to have been primary cause of the extinction of 200 endemic cichlids!
(Goldschmidt et al., 1993).
What is Melomys Rubicola?
A small rodent that lived on a single island off Australia and is thought to be the worlds first mammal to be a casualty of climate change (sea level rise).
What are the two different ways of looking at extinctions?
Number of extinctions
Number of families
Examples of mass extinctions
Cretacous: 50% of animal families, including the last of the dinosaurs and many marine species
Permian: 60% of animal families, including many marine species, insects, amphibians, and all remaining trilobites
Ordovican: 50% of animal families, including many trilobites.
Causes of mass extinction of end crataceous/ tertiary
Asteroid: Chicxulub crater
Acid rain, fires, climate cooling due to dust and smoke, earthquakes, and volcanic eruptions.
Mass extinction causes: summary
Ordovician-Silurian
Climate change cooling and warming
Marine regression
