Lecture 15: Extinction Flashcards
3 types of evolution:
1) local extinction
2) species extinction
3) mass extinction
Local extinction :
loss of a species from a particular area. e.g. wolves & bears lost from Britain
Species extinction :
loss of a species e.g. dodo & great auk
mass extinction:
Period of geological time when extinction rate peaks. Characterised by brevity and breadth e.g. dinosaurs
brevity =
geological e.g. 100,000 years
breadth =
taxonomic breadth
why do species go extinct?
- Racial Senescence
- competition from better adapted species
- environmental change
racial senescene;
‘species undergo a life cycle like an individual organism’
- about Orthogenesis
Orthogenesis;
evolution, once started, continues under its own momentum
%? of all species have gone extinct
99%
examples of racial senescence;
- irish elk; thought that antlers grew & grew, became negative to species so they died
- Gryphea; ‘devils toenails’ bump grows and traps animal in-side
why is racial senescence NOT likely?
1) no mechanism known to produce orthogenesis
2) species don have an allotted life span e.g. lingula
3) On close inspection evidence crumbles
examples of racial senescence REAL REASONS:
- irish elk; badly adapted to post ice age forests
- Gryphea; no evidence it evolved from Ostrea. No evidence that coiling increased. Mud caused locking of shells.
Competition from better adapted species:
“species went extinct because of competition (or predate or disease) from better adapted species”
e.g. reptiles and mammals stance
evolution is never
static
Coevolution:
-parasites and hosts (/predators & prey) influence each others evolution
–>predators run faster –> selective pressure on prey to run faster –> prey runs faster –> selective pressure on predator to run faster –>
(RED QUEEN HYPOTHESIS)
Environmental change - established idea..
panama land bridge formed, North american mammals moved down & outcompeted south american mammals
Environmental change - possible that..
This was exacerbated by Andean rain shadow making south American mammals less well adapted that temperate north american mammals
Mass extinctions:
- ORDOVICIAN 440mya marine inverts
- DEVONIAN 370mya marine inverts, fish
- PERMIAN 245mya marine inverts, trilobites,reptiles
- TRIASSIC 210mya marine inverts, reptiles,freshwater fish, insects
- CRETACEOUS 65mya marine inverts, ammonites, marsupials, belemnites, plesiosaurs, mosasaurs, pterosaurs, dinosaurs.
Permian extinction:
- 50% of families, 95% of species
- MARINE SPECIES; late permian land masses join together.
- lost 50% of land coast, loss of shallow waters
- TERESTRIAL SPECIES;
- coastal areas have less extreme climate because temperature fluctuations are mediated by the sea.
Cretaceous extinction:
- 25% of all families
- we know ASTEROID IMPACT
- an asteroid hit earth
- kicked dust out in to the atmosphere
- dust obscured the sun
- in sea-phyloplankton died
- on land -plants dies (though seeds survived)
- no food for dinosaurs
- mammals survived as nocturnal and were adapted
Evidence for cretaceous extinction:
band of IRIDIUM around earth surface in rock records. found in space rocks, not to common on earth.
Mass extinctions and evolution:
- mass extinction has a profound effect on evolution.
- even well adapted species may go extinct
- only one primate (Purgatorius) made it through cretaceous - IF IT HADNT WE WOULDNT BE HERE TODAY
