15/ extinction Flashcards
how many species are threatened w extinction today
1 million/25%
what is local extinction
loss of a population from a particular area, eg wolves from britain
what % of species that have ever lived have gone extinct
99
types of extinction in the fossil record
- background extinction: sum of all normal species terminations during a defined time interval
- extinction events: times when many species go extinct for a shared reason, typically regional
- mass extinction events: rapid global disappearance of life, wide range of species died out worldwide
what is extinction rate measured in in the fossil record
number of FAMILIES going extinct per mil yrs - believe we’ve identified all families
what trend does extinction rate in the fossil record show
- apparent decline in total extinction rate
- but no general trend when accounting for statistical artefacts
- provides estimate of background extinction
where are there anomalies in the extinction rate in the fossil record. more detail on notes, don’t think i need it
- late ordovician 444 mya. Marine invertebrates- nautiloids, trilobites, brachiopods, crinoids, bryozoans, corals. glaciation
- late devonian 372 mya. reef building organisms. large igneous province lip, ocean anoxia
- late permian 252 mya. trilobites, pelycosaurs, placoderms. lip, ocean anoxia
- late triassic 201 mya. conodonts and large amphibians. lip, ocean anoxia
- late cretaceous 66 mya. non avian dinosaurs, pterosaurs, ammonites, plants. meteorite impact, lip
what species survive mass extinction
- often share generalist characteristics
- become widespread
- ‘disaster taxa’
significance of recovery after mass extinction for conservation concerns
- if mass extinction removes certain species from ecosystem, niche may be filled by other species
- but if most components of an ecosystem are removed recovery may involve creation of new ecosystems
what is species senescence theory, orthogenesis
- species undergo a lifecycle like individuals: birth, development, reproduction, death
- orthogenesis: change in organisms was due not to natural selection but to unchecked directional trends within a lineage
- every lineage will eventually go extinct
- not true - at odds w natural selection
red queen and court jester theory for why some species go extinct
- red queen: biotic factors. must keep up with evolution to avoid going extinct
- court jester: abiotic factors. theory this is major changes cause
false example for senescence
- irish elk/giant deer
- evolved irreversible trajectory towards larger and larger antlers
- sexual selection favoured larger antlers and body size
- nat selec favoured smaller size in response to increasing temps at end of last ice age
species selection
- some lineages have characteristics that make them more likely to speciate OR less likely to go extinct
planktonic foraminifera
- when they die shells drop down to sea floor - time series as fossils build up
- close as possible to perfect fossil record
- morphology closely related to ecological niche - spines associated w transition to carnivorous diets, keels facilitate dispersal to new habitats
biggest cause of speciation and extinction in planktonic fora
- speciation: diversity - competition
- extinction: climate
- speciation more biotic/red queen, extinction more abiotic/jester
requirements of species selection
- variation - must differ in focal trait
- heritability
- differential success - trait must confer dif probs of speciation or extinction
broad vs strict sense species selection
- broad: aggregate traits eg body size
- strict: emergent traits eg range size
