Biology 5C ~ Lecture 23 ~ Causes and Consequences of Extinction

What is extinction?

-The complete disappearance of a genetic lineage worldwide (and forever)

-It is unpreventable but rates vary

-Occur for many reasons and many different types

-Global

First way a species can go extinct phylogenetically:

-The species terminates
-All living members die

Second way a species can go extinct phylogenetically:

-The species evolves from a previous form enough to be called a "new" species

--Sometimes called "pseudoextinction"

--Parts of original gene pool persist

Background extinction:

-The sum of all normal terminations during a defined time interval

-Termination of specific lineage is not predictable

-Mean rate across larger groups of species is predictable

-Ongoing extinction of the individual species

What causes background extinction?

-climate change

-loss of habitat

-and competitive disadvantages related to other species

Extinction events:

-Species go extinct for a shared reason which may be regional scale or may apply to only certain clades or certain ecological guilds

-Often dramatic environmental changes

Mass extinctions:

-Global disappearance of "much of life" when many species of a broad ecological range died out worldwide and somewhat "rapidly"

-Continuum of extinction events of all magnitudes

First mass extinction:

-End Ordovician

-444 mya

-Hypothesized reason for occurring: glaciation

Second mass extinction:

-Late Devonian

-372 mya

-Hypothesized reason for occurring: LIP, ocean anoxia

Third mass extinction:

-End Permian

-252 mya

-Hypothesized reason for occurring: LIP, ocean anoxia

Fourth mass extinction:

-End Triassic

-201 mya

-Hypothesized reason for occurring: LIP, ocean anoxia

Fifth mass extinction:

-End Cretaceous

-66 mya

-Hypothesized reason for occurring: Meteorite impact, ocean anoxia

Sixth mass extinction:

-Current loss of biodiversity scales with these events

LIP (Large Igneous Province):

-large accumulation of igneous rocks arising when magma travels through crust to surface

Causes of mass extinction:

-Meteors, volcanic eruption, major changes in earth's atmosphere

-Severe and extreme environmental stresses

Victims from mass extinction:

-Random and suffer from "bad genes" (cannot adapt to new conditions) or "bad luck" (chance events)

-Broad diet smaller size, wide geographical range

Recovery time for mass extinctions:

-Rapidity of recovery appears proportional to scale of extinction

-Creation of entirely new ecosystems takes longer

"Disaster taxa":

-Short-lived lineages that do not contribute to environmental major clades or long-term ecosystem structure

"Resetting evolution":

-Many lineages survive even the most severe extinction and reestablish, occupying the same positions within ecosystems

-Mass extinctions allow for the radiation of clades that may otherwise not have been able to radiate (Age of the reptiles, mammals)

Macroevolution:

Evolution of larger scale structures and traits usually examining patterns/processes above species level

Biotic Drivers of macroevolution:

-The red queen

-Evolution is a balance between biotic factors and in particular competition

-Species diversity in a red queen world depends primarily on intrinsic factors (factors that originate inside the organism or cell)

Red Queen Hypothesis:

each species has to run (evolve) as fast as possible just to stay in place -- because predators, competitors, and parasites also continue to evolve

Abiotic Drivers of Macroevolution:

-The court jester

-Species diversity depends on extrinsic factors

-Macroevolutionary patterns driven by changing environments

The court jester hypothesis:

-Evolution, speciation, and extinction rarely happen except in response to unpredictable changes in physical environment

Review: All species will someday go:

-Extinct which is a normal part of life on earth

Review: Extinction is typically defined as:

-The global loss of genetic lineage

Review: Background extinctions occur:

All the time, while extinction events and mass extinctions are larger in scale

Review Extinction events impact:

-Ecology and evolutionary trajectory in important and complex ways