Adaptive radiation Flashcards
adaptive radiation has its roots where
galapagos
What did Darwin collect
dozen different species of Galapagos birds- diverse bird fauna
What do differences in size and shape of beak reflect
different diets, habitats
fill different niches
eg some crack open seeds with large beaks, some drink blood
Despite the variation between birds, what did darwin discover
all represent a single lineage, come from a common ancestor, more closely related to each other than to any birds found elsewhere
Galapagos birds are related to other Galapagos birds, not european forms in the same habitat
How did the birds end up on the galapagos
flock from S america got lost or was blown offshore by a storm, landed there then began to evolve
Specialised on different habitats because there were so many different habitats- drove them apart
jack of all trades is master of none
generalists compete well if resources unpredictable year to year- rapidly shift to exploit whatever is available
but struggle if resources are stable year to year and season to season as have to compete with specialists
Rapid radiation
after colonisation, finches rapidly occupied new niches
adaptive radiation 3 main features
undergone by finches
- high diversity
- wide range of niches occupied ( wide range of diets, feeding adaptions, behaviours)
- Occurs over geologically short period
Hawaii
twice land mass vs galapagos
higher rainfall, lusher
higher productivity and more area (species-area effect) to support diversity, and longer to adapt - hawaii seen more radiation
silversword alliance
adaptive radiation of 50 species of plant in hawaiian islands- best known is the mount haleakala silversword
Grow everywhere from arid volcano craters to rainforest bogs
Include trees, shrubs, vines, rosettes, mats
Had extremely rapid evol
Tarweeds
western north america
Origins of silversword alliance
small, weedy asters- members of the group that include daisies, sunflowers etc
not v diverse
Showed evol potential when hit HAwaii
Drosophila
also colonised Hawaiian islands
Speciated to create 1000 species
Why are islands a good model system
small area, short time frame
behave like continents but on a smaller scale- easier to study
Show same evol processes but smaller
Radiations play out same way
Madagascar’s lemurs
result of dispersal from africa to madagascar
NO monkeys to compete with so diversified eg omnivores, herbivores, nocturnal and diurnal
following colonization of a vacant habitat,
species are able to occupy empty niche
facebook effect
can’t invent something like facebook, because already exists
Difficult to displace an established competitor
When do adaptive radiations take off
when little/no comp
Cretaceous-Tertiary (K-T) boundary
Disappearance of dinos, marine reptiles, pterosaurs
K-T boundary is a thin band of clay separating Cretaceous and Tertiary- when dinos etc went exctinct
Cretaceous: T rex an triceratops
Tertiary: no more dinos
Iridium spike
elevated levels of iridium in the K-T boundary clay
Rare in the cretaceous and tertiary
Proposed an asteroid accounted for it
additional evidence for the asteroid
- spherules (beads of silicate solidified from molten rock ejected by impact)
- shocked quartz ( quartz metamorphosed by intense pressure: found in meteor craters)
- Chicxulub
Chicxulub
giant impact crater buried under the yucatan
What happens when you wipe out an ecosystem
Plants and animals dispersing to the barren lava undergo adaptive radiation because they have no comp
Mass extinction: opportunities for survivors to colonise disturbed environments and radiate
Eliminate competitors and make areas of the earth barren
mammal radiation
fossil evidence and molecular clocks show modern mammals eg marsupials, primate, bats all originate around the time of the impact
Rapid incr in body size
Without comp by dinos
New kinds of mammals: whales,, horses- new feeding strategies, habitats, locomotion
bird extinction
fossils show birds were diverse in the cretaceous, but these were distantly related to modern forms
Disappear at the K-T boundary and don’t show up again
Bird radiation
fossils and molecular clocks show birds had massive radiation after asteroid impact
New kinds: owls, penguins
Lizard radiation
modern lizards- iguanas, pythons etc diversify to take adv of niches left vacant by extinction of cretaceous lizards
Worm lizards radiate- underwent major radiation after the extinction, spread to Europe and Africa
Creative destruction
creation of new systems is a destructive process
5 big mass extinctions
cretaceous-tertiary, triassic-jurassic, permian-triassic, late devonian and cambrian-ordovician
Suggests history of life may be repeated radiation and extinction
cambrian explosion
modern arthropods, chordates appear in early cambrian
incr diversity
new kinds of organisms eg swimmers, grazers, burrowers
Biggest adaptive radiation in history
Happens quickly
First appearance of complex animals- brains, jaws, guts more complex
First predators
Beginning of modern life on earth
Ediacaran extinction as a driver of cambrian explosion?
appearance of modern phyla preceded by destruction of the old order
Vegetable-like animals of edicaran period disappeared and modern phyla radiate in the aftermath
Creative destruction: origins of new complex, multicellular life lay in extinction of the old
another way radiations can occur
organisms hit on novel ways of making a living
innovation
Terrestriality
migration of plants, arthropods and vertebrates onto land creates a whole new ecosystem- doesnt compete with old, marine ecosystem
By moving onto land, plants able to radiate into prev unoccupied habitats
Creates new niches for plant eating arthropods, so can move onto land and radiate
New niches for predatory vertebrates created, so can move onto land and radiate
Flight evol
opens up new niches
airborne predators, fish eaters etc
Animals exploit low density resources or seasonal ones
punctuated equilibrium
idea that evol occurs in fits and starts
adaptive radiation = punctuated evol
bursts of evol occur when there’s opportunity- eg new habitat colonised, extinction
Once all available niches occupied, settles down again
