Lecture 34- Are we living in a time of mass extinction?

Question 1

Are we living in a time of mass extinction?

Answer 1

-yes (probably)

Question 2

What do our big brains struggle with?

Answer 2

• uncertainty and risk, leading to alarmism or a false sense of security
• some people say the rate of extinction is really bad and some say it is fine
• often people are too confident about their ideas

Question 3

What does the fossil record say?

Answer 3

• extremely unreliable as a source of information due to the fact that some things conserve well and others don’t
• shells conserve well, large bones not so well, animals in swamps well in dry areas not so well

Question 4

What were the previous extinctions in history?

Answer 4

• pleistocene (0.01 mya): large mammals and birds
• Cretaceous (65 mya): ruling reptiles (dinosaurs), many marine species including many foraminiferans and mollusks
• Triasic: (180 mya) 35 % of animal families, including many reptiles and marine mollusks
• Permian: (250 mya) 50% of animal families, including over 95% of marine species, many trees, amphibians, most bryozoans and brachiopods, all trilobites
• Devonian (345 mya): 30% of animal families, including agnathan and placoderm fishes and many trilobites
• Ordovician (500 mya): 30% of animal families, including many trilobites

Question 5

How many species that existed in history are extinct?

Answer 5

-95-99%

Question 6

When do most extinctions occur?

Answer 6

• between mass events
• and have uncertain causes: a) dinosaurs (meteorite?)
  b) pleistocene megafauna: -N. America, N. Zealand, Aus= humans and climate?

Question 7

What do we need to recognize in trying to compare the extinction rate in the geological past with that of today?

Answer 7

The metric needs to recognise that:
• the number of species getting about in the geological past was different to today
• observations made from the fossil record occur over long time periods (relative to observations of current extinction)

Question 8

How do you calculate the rate of extinctions per million years?

Answer 8

number of extinctions/ number of speceis x 1000 000/number of observation years

Question 9

What are some of the uncertainties that we have to account for?

Answer 9

• the number of recorded extinct species
• if use the constant you skew the story, as the rate of extinction is not constant
• also recorded= only few people before 1900 would record this

Question 10

Which animal group is hit the hardest?

Answer 10

• seems like mammals but we don’t have much info on the other groups particularly invertebrates
• have little information about number of invertebrates so very unreliable estimate

Question 11

What is the problem with definition of extinction? (creates uncertainty)

Answer 11

• the definition of extinction, if set the bar too low= then an overestimate
• if set too high= underestimate
• the definition at this time might underestimate the number of species going extinct
• the bar is high
• The death of the last individual of a species is difficult to observe. So should species be considered extant until it is certain that they are extinct, or vice versa.

Question 12

What is the definition of extinction?

Answer 12

Australian EPBC Act (1999)
-there is no reasonable doubt that the last member of
the species has died

Question 13

What is the lazarus effect?

Answer 13

• animals thought extinct and rediscovered
• e.g. leadbeater’s possum, mountain pygmy possum, parma wallaby, dibbler, new holland mouse, sandhill dunnart, gilbert’s potaroo

Question 14

How many species are there today?

Answer 14

-About 1.6 million species have been catalogued in museums and herbaria….but this a mere fraction of the number of species thought to exist

Question 15

What are the techniques that try to estimate the number of species?

Answer 15

• Species-effortcurves
• Samples from rain forest canopies
• Guess-work

Question 16

What is taxonomic bias?

Answer 16

• the picture indicates how many species each group has (relative to size) (beatle= big, mammal= small)
• most research is done on mammals and birds

Question 17

What is the scientific bias with reporting in extinct species?

Answer 17

• popularity context

- the attractive species researched more thus more extinct species reported there

Question 18

What is the species effort curve?

Answer 18

• sampling effort:
• data in biology is mess
• realtionship betwenn sampling effor and no of specues
• form of sampling effort, = species effort curve
• specieas area curve
• no of species vs area
• the more area you sample the more species but then reach a plateau

Question 19

What are the species effort curves for birds and crabs?

Answer 19

• took 87 years to find 50% bird species and then much harder to find new species, 150 years to find the rest
• with crabs, in 10 years managed to find the rest as more funding

Question 20

What is the method of determining number of species in the rainforest? (invertebrates)

Answer 20

-One method of sampling species:

-net over tree, fog and drop then count

Question 21

What is the other way of estimating number of species?

Answer 21

-guesswork

Question 22

How many species are there today?

Answer 22

Species-area curves, rainforest canopies (1980s)
– 30-100 million
• Rates of discovery, additional samples, re-analysis of data (1990s)
– 3-7 million
• Currently (additional discoveries) – 5-30 million

Question 23

What is the point estimate of the current extinction rate?

Answer 23

• Mammals are perhaps the best known taxon for both the fossil record, and current extinctions
• number of extinctions/number of speceis x 100000/number of observation years
• 69/4300x100000/400= 40.1 species/ million years
• The background fossil record suggests the background rate of extinction for mammals is about 0.4 species/ million years
• As a point estimate the current extinction episode is 40.1/ 0.4= 100 x background rate!

Question 24

What do point estimates require?

Answer 24

-Point estimates require reliable data for past and current extinctions….
-The data are actually highly uncertain due to…..
• Taxonomic bias
• Taxonomic uncertainty
• Definition: what

Question 25

What is the best estimate for extinction rates at the moment?

Answer 25

-The current extinction rate for mammals lies between 17 and 377 times the background rate measured over the past 65 million years…..The best estimate of the current rate is 36 to 78 times the background rate.