topic 12 extinction Flashcards
define speciation
○ Birth of a species
○ Evolution of reproductive isolation within an ancestral species, resulting in two or more descendant species
define extinction - when is it certain?
○ Death of a species
○ When the last existing member of a given species dies
○ In other words…there aren’t any more left!
○ – It is a scientific certainty when there are no surviving individuals
left to reproduce
• Background Extinction- define
– A long-lasting rate at which taxa become extinct
– Constant within clades but vary greatly between clades
define functional extinction
– Only a handful of individuals are left
– Odds of reproduction are extremely slim
define mass extinction
– A highly elevated rate of extinction of taxa; extends over a
relatively short geological interval
– Must eliminate >60% of species in a relatively short period of
geological time with wide-spread geographic and taxonomic
impacts
– May occur periodically
causes of extinction
• Genetics and demographics • Small npop = increased risk • Mutations ○ Cause flux in natural selection ○ Beneficial traits are overruled • Loss of genetic diversity ○ Shallow gene pools promote massive in breeding
describe habitat degradation - toxicity
• Toxicity
Kills off specimens directly through food/water
– Indirectly via sterilization
– Can occur in short spans (single generation)
– Can also occur over several generations
describe habitat destruction
• Habitat destruction Can be caused by natural processes Ø Volcanoes, floods, droughts, etc. – Elimination of living space – Change in habitat Ø Rainforest à to range lands for cattle – Other anthropogenic causes
directr and indirect effects of invasive species
• Direct effects – Competition – Predation – Pathogens & parasites • Indirect effects – Habitat alteration
invasive sp exs.
– Rosy Wolfsnail in Hawaii à eight native snail species
– Red Fox in Australia à several species including lesser bilby
– Brown Tree Snake in the Island of Guam after WWII à more than
half of Guam’s bird & lizard species
– Feral cats in New Zealand à flightless Stephen Island Wren as
early as 1900
describe planned extinction
Human controlled v Thought to help humans v Deadly viruses – Smallpox Ø Extinct in the wild – Polio Ø Near extinct (only in small parts of the world – Afghanistan & Pakistan)
how long was phanerozoic
• An Eon of over 540 million years Ø Jack Sepkoski (1984) studied the marine record based on 30,000 marine genera in more than 4,000 families with hard skeletons
diversity in cabrian + ordovician vs rest of paleozoic? after paleozoic?
Ø Rapid increase of diversity in Cambrian & Ordovician Ø Plateau during rest of Paleozoic Ø Post-Paleozoic increase Ø Some major extinction events throughout the eon are also evident
mass extinction?
• A sharp decrease in number of species on
Earth in a short period of time
• Coincides with a sharp drop in speciation
• Statistically distinct from background
extinction levels
5 mass extinctions?
5 Mass extinctions at the end of: – Ordovician (~443 mya) – Devonian (~359 mya) – Permian (~251 mya) – Triassic (~200 mya) – Cretaceous (~65 mya)