Lecture 6: Extinction

how long does a typical species exist?

1-10 million years (before they go extinct or evolve into another species)

how much of the species that have ever existed on earth are extinct?

99%

what are the 3 ways that organisms respond to a changing environment?

• migrate

• adapt

• go extinct

what does it mean for a species to be globally extinct?

the species can be found nowhere in the world

what are the 4 different levels of extinction?

• mass extinction

• extinct

• extinct in the wild

• locally extinct or extirpated

when is a species considered extinct?

when after a thorough search, no member of that species is found alive anywhere in the world

what does it mean for a species to be extinct in the wild?

when individuals of that species/group are only alive in captivity

• eg. golden frog, native to Panama

what does it mean for a species to be locally extinct or extirpated?

when a species is no longer found in a specific area where it was once found?

• wolves extirpated from most of US

• bobcats were once extirpated from Ohio

• American burying beetle extirpated from most of 35 states it used to live in

why is it difficult to determine if a species has gone extinct?

• hard to know if a species is fully extinct or not

• it can take a long time for a species to be reported as extinct

what is a mass extinction?

when 75% or more of species is lost in a short period of geological time, meaning less than 3 million years

how many mass extinctions have there been?

5

what was the mass extinction that killed the dinosaurs called? how many years ago did it occur?

cretqceous (76% od species lost). occurred 65 mya. resulted from asteroid impact

which mass extinction had the highest extinction rate? how many mya did it occur? what caused this mass extinction?

permian (95% of species lost). occurred 250 mya. result from volcanic activity, toxic gases that acidified the ocean, and an increase in methane and CO2

what is the background extinction rate?

the average rate of extinction observed over the history of all life. it is estimated using the fossil record.

based on the historical background extinction rate, how much higher is the current background extinction rate? and what does this mean?

current extinction rates are 100-1000X greater than what we would expect, meaning that 1-10 species go extinct each year

why is the current loss of species a concern?

• rate: seems to be 100-1000x faster than any other time in geologic history. estimated that about 900 species have gone extinct in the last 500 years

• cause: the last 5 mass extinctions have been caused by natural disasters, whereas today, most species go extinct due to humans

• place: extinctions are not localized to one part of the planet - extinctions are occurring globally

what is the current (6th) mass extinction called?

the anthropocene

why is the anthropocene mass extinction different? what is it caused by?

will be the first mass extinction caused by one species (humans) and not a natural event

caused by:

• overexploitation

• pollution

• hunting/wildlife trade

• climate change

• invasive species

how many species are currently estimated to be at risk of extinction?

1 million

what factors make a species at higher risk of extinction? (3)

• restricted geographic range

• small population size

• specialized habitat needs or narrow tolerances

what does endemic mean?

living only in one area

what is a species with a restricted geographic range?

a specie that lives in only one region, eg. Pemba flying fox, which is endemic to the island of Pemba

why is a species with a small population size more at risk of extcinction?

• decreases genetic diversity = harder to adapt to environmental changes

• can cause an inbreeding depression, which can decrease reproductive and immune functioning

• eg. 80% of Tazmanian devil population killed by fatal facial cancer

why is a species with specialized habitat needs at higher risk of extinction?

they have narrower tolerances, which lowers the chance of survival

name a species that exhibits all 3 characteristic that put a species at risk of extinction

the Kirtland’s warbler

• small population

• restricted geographic range

• needs young jack pines with spacing for breeding

what group of vertebrates are most endangered?

amphibians: frogs, toads, salamanders

how much of all amphibian species are at least threatened at some level?

1/3

what is the current background extinction rate for amphibians?

almost 2.5%

why are amphibians good ecological indicators?

they can give good information about how environmental changes are affecting species

• permeable, moist skin used in respiration (chemicals and UV light affect their skin)

• they have life cycles that involve both freshwater and land, so they are affected by many changes

• their eggs lack protective membranes

why are frogs declining and at risk of extinction?

• habitat loss and destruction: very small home ranges, and as we fragment their habitats, they are unable to move

• climate change: very sensitive to changes in their environment. finding that frogs are breeding earlier due to warmer temperatures, but there is not enough food for tadpoles

• chytrid fungus (invasive species): causing sickness in many species. the golden frog was affected by this

how many amphibian species have declined because of the chytrid fungus?

501 amphibian species, or about 1 in 16 known species

• poison dart frog succumbs to chytrid fungus

• harlequin frog is at risk

• golden frog is at risk - all of them currently live in captivity