adaptive radiation & extinction

Question 1

views of life since Cambrian explosion

Answer 1

1. ‘cone of increasing diversity’
2. ‘decimation and diversification’

both show adaptive radiation (increasing diversity)
both show extinction (loss of diversity)
diversity is determined by the rate of each process

Question 2

adaptive radiation

Answer 2

a small number of ancestoral species increaes to giver a large number

radiations are very clear when observed in a small taxonomic group

e.g galapagos finches

Question 3

caused of adaptive radiation

Answer 3

colonization of a new area free of competators : adaptations to exploit new resources

adaptive breakthrough : adaptations to exploit new resources

extinction of competitors : adaptations to explot previously used resources

replacement of competators : superior adaptation or environmental change

Question 4

evidence of extinction

Answer 4

direct observation
- recent extinctions with anthropogenic causes

fossil record

• presence of forms no longer living
• difficult to infer why it happened

Question 5

small scale extinction

Answer 5

local and occur over a short period of time

loss of species with limited distribution; can accumulate to cause complete extinction

Question 6

mass extinction

Answer 6

global or continental occur over long streches of time

loss of species and taxa

Question 7

causes of small scale extinctions

Answer 7

biotic
- parasite, pathogens, competitors - losing an evolutionary arms race

physical
- change in climate

developmental constarints prevent adaptations to change

(extinction happens because environmental changes happen faster than the rate of adaptation)

Question 8

factors affecting chance of extinction

Answer 8

population size
- small or isolated population more likely to become extinct that large connected ones

longevity
- short lifespan more susceptible than long lived species

rate of increase
- few young and reproduce irregularly more susceptible than species with high reproductive outputs

stability of environment

Question 9

the ‘big five’ mass extinctions

Answer 9

late ordovivian - 400 mya 
late devonian - 350 mya 
end permian - 250 mya 
late truassic - 210 mya 
end cretaceous - 80 mya 

the average ate of extinction appears to have declined

Question 10

the K-T mass extinction

Answer 10

60-75% of species lost
seperates the Cretaceous - Tertiary boundary
affected every group of animals and plants
best evidence given by microfossils - Foraminfera
- dinosaurs and ammonites went extinct (allowed adaptive radiation of mammals)
- crocs survived

Question 11

asteroid-impact theory : the K-T mass extinction

Answer 11

• 7.5 - 9 miles in diametre
• 108 megatos blast
• concurrent impact s as an even larger asteroid broke up
• global dust blocks sunlight for several years:
  • global warming
  • acid rain
  • vulcanisation
  • global fires

Question 12

evidence to support the asteroid-impact theory

Answer 12

• iridium anomaly (iridium in rock strata)
• chicxulub creter (impact crater, mexico)
• rock structures
• simultaneous extinction:
  • amonites
  • bivalves
  • brachiopods
  • vertebrates (dinos)

Question 13

passive replacement

Answer 13

the replacing fauna took advantage of the lack of the replaced one and did not compete directly with it.

Question 14

early mammals

Answer 14

• early mammals small, low abundance
• arboreal
• mammals lay low for 40 myr until extinxtion of dinos : allow for adaptive radiation
• modern orders adapted into vacated niches