Macroevolution Test 2

List and describe the two kinds of extinction

Background extinction

• affecting lineages all the time

• occurs at stable rates across geologic time

Mass extinction

• extinction in one group very subtly

• interval during which extinction exceeds background rate

• a small number of really exceptional extinctions

Describe the general patterns in evolution though time

• Marked by increases and decreases through time

• Seem to have higher rates a long time ago, and seems to decrease over time

• extinction is also going down

• called turnover

  • origination of lots of things, then extinction of lots of things

• Maybe the decrease in extinction is because some phenotypes have become better?

  • increase in adaptation, and therefore less extinction?

Describe the origination of the Alvarez hypothesis

• noticed feraminefera

• great indicator fossil, very characteristic of deposit

• Rock made up 3 layers

  • oldest layer was super diverse with fossils

  • middle

  • most recent was more uniform

• Didnt know how to date

• looked for irriduim

• super rare, can use rate to quantify time (more irridium = more time has passed)

• found a stupid large amount of irridium (like, impossibly large amount)

• Something in the atmosphere (bc irridium comes from atmosphere) must have affected the earth around time of dinosaurs!

Describe the predictions of the impact hypothesis

• meteorite dust in rocks of end cretaceous (K) (eg. global iridium layer)

• impact crater contemporaneous with global iridium anomaly

• Debris from impact, dating to end-K

• Glass particles from heat of impact

• Impact models should predict large scale environmental  disturbance

Why is it that the signature of a mass extinction can be subtle?

the signature of discrete events can be blurred (eg. by all the problems w fossilization, that sort of stuff); Signor-Lipps effect

Describe the Signor-Lipps effect

• neither first nor last individual of a taxon will fossilize

• Therefore, youngest fossil of a species will likely predate actual time of extinction'

  • Imperfect fossilization > fossilization creates a jagged pattern, so not necessarily at true evolution

• Hollow distribution curve consistent with Signor Lipps effect

• Most species are rare, and therefore disappear way before actual extinction rate

  • Highest occurrence of rare species may be at extinction level or much earlier

  • Highest occurrence of common species likely will be at or near extinction level

Describe the end ordovician extinction

• after cambrian period

• ~44 million years ago

• ~85% species level extinction (marine)

• Major groups affected were:

  • graptolites

  • branchiopods

  • trilobytes

  • conodonts

Describe Late devonian extinction

• not quite as severe as ordov. extinction

• ~75% species level extinction (marine)

  • Little effect on terrestrial life

• ~375 mya

• Major groups effected:

  • trilobytes

  • branchiopods

  • reef builders (stromatoporoids. rughouse and tabulate corals)

  • graptolites (completely wiped out)

  • cystoid echinoderms (completely wiped out)

Describe the end permian mass extinction

• biggest mass extinction ever

• ~251 million years ago

• 96% species level extinction

• Major groups affected:

  • Tabulate corals (completely wiped out)

  • trilobites (completely wiped out)

  • eurypterids (completely wiped out)

  • branchiopods

  • bryzoans

  • blastoid enchioderms (completely wiped out)

  • crinoids

  • ammniotes

  • gastropods

  • forams

Describe the End Triassic extinction

• ~200 mya

• 80% species level extinction

• Major groups effected:

  • Conodonts (completely wiped out)

  • large amphibians

  • therapsids

  • archosaurs

Describe the end cretaceous extinction

• ~66 mya

• 76% species level extinction

• major groups affected:

  • Ammonoids (completely wiped out)

  • non avian dinosaurs (completely wiped out)

  • plesiosaurs (completely wiped out)

  • mosasaurs (completely wiped out)

  • sharks

  • plankton

List and briefly describe the three causes of extinction

• gamblers run

  • the only absorbing boundary is complete loss (ie. extinction)

  • Thus, the only “end possiblility” is complete loss

• Adaptation

  • May affect the probability of extinction, either via too much adaptation or not enough

• Catastrophe

  • Dramatic (and relatively rapid) environmental change

What is Van Valen’s law of extinction?

extinction probability is constant over time

• found in group after group after group

Describe Gambler’s Ruin as a cause of extinction

• Probabilistic expectation of resource “extinction”

• A gambler who continues to play a completely fair game will eventually lose all of their money, because the only absorbing boundary is complete loss

• Same thing goes for species

• Smaller population is mDescribe the ore susceptible to extinction (closer to extinction)

• positive relationship between pop size and survival time

Describe the overspecialization hypothesis

predicts that extinction probability will increase with time (as organisims become too specialized)

• adapt/specialize so much that they become super dependent

Describe the incumbancy hypothesis

predicts that extinction probability will decrease with time (as organisims become better adapted to their niche)

• basically, the longer a species is around, the better it is at being on earth

Describe the Red Queen Hypothesis

• predicts that extinction probability will be constant over time because selection  selection is always changing (eg. due to coevolution) and a species must constantly adapt or face extinction

• background extinctions are a failure to adapt

• ever changing selection can explain why clades don’t become “extinction resistant”

• extinction is due to a lineage wide failure to adapt to ever changing conditions

Describe catastrophe as a cause of extinction

Dramatic (and relatively rapid) environmental change

• Rapid but not instantaneous

  • may take years for things to get wiped out

• Multiple causes often implicated

• some extinctions due directly to catastrophic event; many more likely due indirectly to transformations of earths systems

List candidate causes for mass extinctions

• flood basalts

• extraterrestrial impact

• sea level fall

• climate change

• methane clathrates

• Oceanic O2 decline

• Oceanic hydrogen sulfide3 emission

Describe flood basalts as a candidate cause for mass extinction

• massive sustained igneous extrusions

• emit particulates that can inhibit photosynthesis, disrupt food chains

• emit Sulphur oxides, causing acid rain

• emit carbon dioxide, causing later global warming

• before meteor was known about, people thought this was what killed the dinosaurs

Describe extraterrestrial impact as a candidate cause for mass extinction

• violent impact by large asteroid or comet

• emit particulates that inhibit photosynthesis, disrupt food chains

• can cause megatsunamis, global forest fires

describe sea level fall as a candidate cause for mass extinction

• reduce (highly productive) continental shelf area

• Restructure ocean currents, disrupting terrestrial climates

Describe climate change as a candidate cause for mass extinction

• global cooling reduces habitable area for tropical species, causes shifts towards equator > leads to global terrestrial drying (as freshwater sequestered in ice/snow)

• Global warming reduces area for temperate/polar species, causes shifts towards poles > leads to wetter periods (as freshwater released in ice/snow)

Describe methate clathrates as a candidate cause for mass extinction

• clathrates are when a lattice of one substance encases another substance

• H2O entraps methane in methand clathrates in ice

• rapid changes in temperature or pressure can trigger release of methane from stored continental shelf clathrates

• has been suggested for end permean extinction

Describe oceanic O2 decline as a candidate cause for mass extinction

• anoxia occurs when middle or upper layers of ocean become deficient in oxygen

• typically associated with periods of global warming (usually triggered by volcanism)

• can trigger oceanic mass extinctions, and restructure global food webs

Describe oceanic hydrogen sulfide emission as a candidate cause for mass extinction

• proposed that the end permian warming disturbed balance between photosynthesizing plankton and sulfate reducing bacteria, triggering massive hydrogen sulfide emissions

• hydrogen sulfide poisons both marine and terrestrial life, and depletes the ozone layer

How do background and mass extinctions differ in selectivity?

Background extinction is proposed to be darwinian (the unfit species are the ones that die) while mass extinction i proposed to be wanton and random, with survivors no better adapted to the environment

What traits predict survival of a species through a mass extinction?

• abundance

  • basically numerical insurance- the more individuals, the harder it is to wipe them all out

• larval dispersal mode

  • the farther the species can colonize, the less likely it is that there will be a disaster that will affect all individuals in a species

• habitat (infaunal vs. epifaunal)

  • animals in soil may be protected in a way

• species range size

  • vast spatial expanse > more likely you can hide/avoid extinction

how do we recognize adaptations

• evidence from design

  • architecture of the phenotype

  • adaptation for a particular function

• complexity

• Performance (or, ideally, fitness experiments

Describe the 0. 0. 0.

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