Lecture 13 Flashcards
What are the limitations on estimating background rate of extinction in terms of the fossil record?
- Fossil formation is not possible (or likely) in all environments (habitats).
- shallow seas = best for fossil formation.
- other habitats = less represented in the fossil record. - Soft-bodied organisms do not preserve well.
- Fossils of land animals are scarcer than those of plants.
- Not always possible to accurately classify species in the fossil record (fragments of a species found).
- Chrono species.
- Pseudoextinction.
- Extinction rates generally measured at the taxonomic level of family (not species or genus).
What conditions are required for a fossil to form?
Fossil can form through freezing, drying, or encasement (in tar or resin), but these types of fossils are very rare.
Most fossils form when a plant or animal dies in a watery environment and is buried in mud ans slit.
After an organism’s soft tissues decay in sediment, the hard parts (e.g. bones) are left behind. Over time sediments builds over the top and hardens into rock.
What is a chronospecies and why does it matter for background rate of extinction?
A single species, changing morphologically, genetically, or ecologically over a long time scale.
Changes occur in a way that the original species and its descendants are identified as separate species.
What is a pseudoextinction and why does it matter for background rate of extinction?
When a species is presumed to have gone extinct, but has instead become a different species (or sub-species).
Incomplete fossil record can lead us to believe a species has gone extinct, when it simply evolved into a different species.
What are the biotic mechanisms of extinction?
- a species can be competitively excluded by a closely related species.
- the organisms that the species exploits (e.g. what it feeds on) may come up with an unbeatable défense.
- a new predator may expand its territory.
- a species can be wiped out by a disease.
What are the abiotic mechanisms of extinction?
The niche or habitat te species occupied can no longer support the species.
Most likely abiotic factors:
- temperature or climate fluctuations.
- extreme sea level changes.
- impact events (meteorites).
- volcanism.
What is a mass extinction?
Extinction of a large number of unrelated species (biodiversity loss) over a short period of geological time.
Extinction are globally distributed.
What are the 5 mass extinctions in history?
- Late Ordovician.
- Late Devonian.
- Late Permian.
- Late Triassic.
- Late Cretaceous.
How do mass extinctions affect the evolution of life?
There is a very rapid period of speciation among the few species that do survive - there is more room for the surviving species to spread out and so many niches in the environments that need to be filled.
As populations separate and move away, they adapt over time to the new environmental conditions and eventually can be considered a brand new species and biodiversity expands quickly..
Describe the Late-Ordovician period.
Most complex multicellular organisms lived in the sea.
Almost all major taxonomic groups were affected during this extinction - marine organisms suffered the most.
What the the causes of the late-Ordovician extinction?
The global temperatures cooled and the sea levels fell.
Plant and animal diversity was adapted to shallow, warm waters - could not survive in colder, deeper oceans.
Land moved to the South Pole due to plate tectonics = formation of glaciers = removal of water from oceans leading to rapid fall in sea levels.
- shallow seas were drained.
Describe the late-Devonian period and its extinction.
Land was colonized by plants and insects, oceans had massive reefs built by corals.
-famous for thousand of fish species that developed in this period (fossils).
Super GHG climate conditions - very warm and there was a lot of CO2 in the atmosphere.
Extinction lasted 20 million years due to a series of “extinction pulses”
- no single cause, likely multiple causes.
What are the theories behind the Devonian extinction?
Rapid reduction in atmospheric CO2 that led to the earth cooling and the extinction of many organisms.
As plants expanded onto land to form the first forests, they depleted CO2 in the atmosphere.
describe the late-Permian period of extinction.
Largest of all known extinctions.
Termed “The Great Dying.”
All life today is descended from the few survivors of this period.
What are the causes of the Permian extinction?
Series of great volcanic eruptions.
Eruptions would have released CO2 into the atmosphere = GHG effect - heating up the atmosphere and acidifying the oceans
- when CO2 dissolves in sea water it forms carbonic acid = pH decrease = more acidic.
Eruptions lead to released aerosols and dust clouds = blocked sunlight and disruption of photosynthesis on land and the ocean = food chain collapse.
Eruptions caused acid rain when the aerosols washed out of the atmosphere.
