extinction Flashcards
(28 cards)
what are the different types of extinction
-Contemporary:
=Local extinction
=Species extinction
-Geological
=Background extinction
=Extinction events
=Mass extinction events
whats the global extinction crisis
-1 million species threatened with extinction
-Across a wide and growing range of taxonomic groups, an average about 25% of species are threatened with extinction when assessed using the IUCN Red Listcriteria.
whats local extinction
-Loss of a population from a particular area
-E.g. wolves from Britain
whats species extinction
-complete loss of a species
-can be human enforced with hunting
whats extinction like in the fossil record
-Extinction is a feature of life on Earth
-Because of current concerns we tend to focus on species/local extinctions and forget extinction has been happening since life on earth began
-99% of all species that ever existed have gone extinct- vast majority of species that exists probably went extinct
what are the Types of extinction in the fossil record
-backround
-extinction events
-mass extinction events
whats background extinction
-the sum of all normal species terminations during a defined time interval
whats extinction events
-times when many species go extinct for a shared reason, typically regional rather than global in scale but pertaining to selective extinction of clades
whats mass extinction events
-times of geologically rapid global disappearance of much of life, when many species of wide ecological range died out worldwide
what are the extinction rates in fossil record
-Marine fossil record spanning 600 million years
-Extinction measured as number of families going extinct per million years- in taxonomic families
-Apparent decline over time is a statistical anomaly.
-No general trend after accounting for statistical artefacts.
-Provides estimate of background extinction rates as a point of comparison.
-”Typical” extinction rates represented as data between the dashed lines (99% confidence intervals)
-Reveals anomalies - mass extinctions identified as data points outside the 99% confidence interval of the line of best fit
-Outliers are extinction rate peaks
-Characterised by breadth and brevity
what happened in the End-Ordovician, 444 mya
-Declines: nautiloids, trilobites, brachiopods, crinoids, bryozoans, corals
-Cause: glaciation
what happened in the Late Devonian, 372 mya
-Declines: Trilobites, brachiopods, bivalves, corals, nautiloids, sponges, crinoids, fishes
-Complete loss: ostracoderms, placoderms
-Causes: Large Igneous Province (LIP), ocean anoxia
what happened in the End-Permian, 252 mya
-Declines: Brachiopods, crinoids, syanapsids
-Complete loss: blastoids, trilobites, rugose & tabulate corals, pareiasaurs
-Causes: LIP, ocean anoxia
what happened in the End-Triassic, 201 mya
-Declines: Bivalves, ammonoids, gastropods
-Complete loss: conodonts, basal archosaurs
-Causes: LIP, ocean anoxia
what happened in the End-Cretaceous, 66 mya
-Declines: bivalves, gastropods, foraminifera
-Complete loss: Dinosaurs, pterosaurs, plesiosaurs, mosasaurs, ammonites, belemnites
-Causes: Meteorite impact, LIP
whats the recovery like after mass extinction
-Survivors of mass extinctions are not random
-Often share “generalist” characteristics
-Become cosmopolitan (e.g. Lystrosaurus after the end-Permian mass extinction)
-Sometimes referred to as “disaster taxa”
-Significance for modern conservation concerns:
=if a mass extinction removes certain species from ecosystems, the scaffold of the ecosystem may be available after the crisis for new species to occupy;
=but, if most components of an ecosystem are removed by a larger extinction event, recovery may involve the construction of new ecosystems.
-Characteristics of mass extinction survivors may indicate trajectories of recovery if the current extinction crisis proceeds unchecked.
What causes only some species to go extinct
-Species senescence:
-Suggestion that 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, example is Irish elk
-biotic and abiotic factors
Irish elk
-Evolved on an irreversible trajectory towards larger and larger antlers
-Irish elk went extinct when the antlers became too large
-could no longer hold up their heads,
-got entangled in the trees.
species senescence
-No mechanism for ‘Orthogenesis’
-Completely at odds with natural selection
-Species don’t have ‘allotted’ lifespans (e.g. Nautilus)
-On closer examination the ‘evidence’ falls away
-example is Irish elk:
=Sexual selection favoured large antlers and large body size
=Natural selection favoured smaller size in response to rapid changing towards warmer, more temperate climates at the end of the last ice age
how does biotic factors lead to extinction
-Competition and the Red Queen
how does abiotic factors lead to extinction
-random perturbations to the physical environment such as climate change, tectonic events, or even bolide impacts that change the ground rules for the biota… Court Jester hypotheses, share the basic tenet that changes in the physical environment rather than biotic interactions themselves are the initiators of major changes in organisms and ecosystems
whats Planktonic foraminifera
-when they die, shells drop to ocean floor and gives a time series
-this can study their morphology
-amazing fossil record
-pressure is a lot so frequently have lots of minerals
-Figures show the relative frequencies of foram species according to ocean depth habitats (top) and species morphologies (bottom)
-Morphology is closely related to ecological niche e.g.
-Spines associated with transition to carnivorous diets
-Keels facilitate dispersal to new depth habitats
what are the Factors explaining the probability of speciation and extinction
A: species age
D: species diversity
C: Climate
E: Ecology
-Longer bars indicate predictors that explain more of the variation in foram diversity in speciation probability (top) and extinction probability (bottom)
whats the Red Queen and the Court Jester
-Probability of speciation is more strongly driven by biotic factors (the “Red Queen”)
-Probability of extinction is more strongly driven by environmental factors (the “Court Jester”)
