Evolution and Extinction

Extinction

When all members pf a species have died out

Is the ultimate fate of all species, but also plays an critical role in diversification of a lineage

• New species arise when others go extinct

It does not necessarily need to be at the species level

Extinction is a natural process

It has been recognized as a part of the evolutionary process

Extirpaiton

extinction can be localized

Example: the species goes extinct in Kansas, but not Missouri

Fossils

an obvious source of informatin on extinction

Finding skeletal reamins of creatures that are no longer found

We can date the rocks surrounding a fossil to determine the age of the fossil, since fossil records are an incomplete record of life on Earth

This can help inform our phylogeny

• when we have a phylogeny we can predict what age we should find specific fossils

Background Extinction

rates are estimated to be 0.1 to 1 extinction per million species per year

• These are natural rates of extinction, also termed as background extinction rates

There are around 2 million species on Earth, estimated to be at least 4 million total, this gives and estimate of 0.4 to 4 extinction per year

Bakcgrond extinction is biased toward species with smalll geographic ranges and species that are uncommon/rare

Difficult/ impossible to “prove” that a species has gone extinct

What Causes Extinction

Change is the cause of extinction

• a species is adapted to a set of conditions, when those conditions change the species can be in trouble

• only true if the change is happening faster than the species can evolve

Mass Extinction

Occurs occasionally and are associated with geological periods

These are widespread events that significantly decreases the diversity of life on the planet

Usually wipe out more than 70% of the species

There are 6 widely accepted mass extinction events, they are caused by different facros

• The Great Dying

  • at the end of the Permian (252 million years ago)

  • 70-90% of species went extinct

  • The cause was believe to be climate change associated with volcanic activity

• The K-T (Pg)

  • wiped out the cool dinosaurs

  • The cause was due to climate change associated with asteriod impact in the Ycatan

  • about 75% of species went extinct

• Late Pleistocene

  • 50,000 years ago

  • Not recognized as one of the “big 5” but resulted in extinction of much of the megadauna worldwide

  • Though to be related to climate change and human activity (in North America)

Bias in Mass Extinction

Mass extinctions wipe out large numbers of species

Tends to be bias towards large species

• T. rex went extinct but birds did not

Several reasons:

• Large species require more land on which to live one

• Large species require more food

• Large species habe longer generation time

The Effect of Extinction

Opens niches in the ecosystem and allows space for living species to evolve

• Niche: all the resources a species needs to live

When niches overlap it leads to competition between species

When the ecosystem is intact there is little to no room for a species to evolve (all “spots” are taken)

• Moving to another resource puts you in competition

When species go extinct then niches open up and the surviving species can change to exploit the new competition free areas

• Synapsids (mammal ancestors) went extinct at the end of the Permain, allowed dinosaurs to take over

• Dinos lost the lottery with the K-T allowing mammals and birds to take over

Adaptive Radiation

The species that survive the filter of extinction now live in a less diverse system

Every niche is open

Any mutations is a win

Adaptive radiation: a rapid diversification in a lineage due to low diversity and open niches

In mass extinctions this has resulted in a change in the dominant groups

The same phenomena can be observed when groups colonize a new area

• a few species of birds colonize Hawaii and rapidly diversify

• from a few colonizing species to at least 66 endemic species