Extinction Today’s goals - University of Connecticuthydrodictyon.eeb.uconn.edu/.../EEB2208_2014_Lecture05_Extinction.pdf · Extinction “The present geological period has more

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Extinction

“The present geological period has more species than

any other, yet the rate of extinction of species is

greater now than at any time in the past.”

- Primack 2002

Today’s goals

Definitions

Natural extinctions

Extinction rates

Estimating extinction rates

Reading

Primack, Chapter 7

Some definitions

• Extinction = no members of a species remain alive

• Local extinction = gone from a particular area

• Extirpation = local extinction

• Extinct in the wild = individuals remain, but only in captivity/under cultivation

• Ecologically extinct = still persists, but is so rare that it’s ecological role is negligible

• Extant = not extinct

• Endemic = restricted to a certain (usually fairly small) area

Extinction is a natural process

But extremely high rates of extinction are not normal

Mass Extinctions

See Primack, Fig 7.2

Notice overall trend

is still upwards Natural – 5 mass extinctions

1) Ordovician (439 mya) – 85% of spp.

2) Devonian (395 mya) – 85% spp.

3) Permian (253 mya) – 50% all animal families;

77-93% all spp.

4) Triassic (213 mya) – 76% spp.

5) Cretaceous (65 mya) – 85% spp. (dinosaurs)

See Primack, Figs 7.2 and 7.3

Mass Extinctions

mya = millions years ago

2

• only ~10% of all extinctions before modern

times were during mass extinctions

• >99% of all species that ever lived are extinct

• “background rate” ~ 2.5 families/million yrs

• current extinction rate – on par with previous

mass extinctions

Mass Extinctions

See Barnosky et al. 2011. Nature

Early human-caused extinctions

1) 50,000 ya in Australia

2) Pleistocene – 12,000 ya in

North America

� Large mammals and birds

(woolly mammoth, saber-toothed cats,

500 lb armadillos, cheetahs, lions, giant sloths)

3) 8,000 ya to present in South Pacific

a) Polynesians – 750-1800 bird species extinctions

b) Hawaii – by 1778, 50 bird species already extinguished by native Hawaiians

c) Easter Island …

Steadman 2006

Easter Island

18th century European explorers found it

inhabited by 3000 people

• Grassland

• Trees < 3 m

• No large native

animals

Easter Island

• Poor soil

• Few crops

• Limited fresh water

©Rivi

Historical state

• Large trees (21 species)

• Five landbird species

• Large seabird populations (30 species?)

• Human population up to 15,000

• 800 stone statues

Why the change?

• Deforestation

• Tree removal affects hydrology/climate

• Introduced rats

• Overharvest

• No trees to build with

• No food on land

• No vines for fishing nets

3

+

things are bad use more

to compensate

makes things

worse

use more

to compensate

Positive feedback increases the

problem

What is the current extinction rate?

1) 85 (2.1%) mammals, 113 (1.3%) birds since 1600; most in last 150 years

2) 20% of all bird spp. extinct in past 2000 yrs

3) 50% drop in populations of Neotropical migrant birds in eastern U.S. in last 50 yrs

4) 50% of fungus spp. in Europe may have become extinct in past 60 yrs

5) 20% of world’s freshwater fishes extinct or in serious decline

� in N.A. 3% extinct in 100 yrs (27/1033)

� in N.A. 26% soon to be extinct (265/1033)

Extinction rates are changing

Global bird data

Why is the rate declining here?

What is the background rate?

• 1 in a million to 1 in 10 million species

are lost each year

� fossil record for marine animals

• If there are 10 million species on Earth,

then 1-10 extinctions annually

1/106 * 107 = 10 extinctions

1/107 * 107 = 1 extinctions

• Currently, ~1% of birds & mammals go

extinct every 100 years

• This means 1 in 10,000 species go extinct

each year

• ~10,000 bird species on Earth

(1% every 100 years = 0.01% every year = 1 in 10,000)

How does the current rate compare?

• Currently, ~1% of birds & mammals go

extinct every 100 years

• This means 1 in 10,000 species go extinct

each year

• ~10,000 bird species on Earth

• If 5-10 million species: 500-1000 spp/yr

• What assumptions??


4

N = 63 (~90 in class)

+10 did not give a number

Range: 0 – 400 billion

Median: 1000

Mean: 6.6 billion

% of species you estimated on Earth

Range: 0% to 1%

Median: 0.001%

Mean: 0.04%

What did you say?

Assumes 5-10 millions species on Earth

What did you say?

0

2

4

6

8

10

12

14

16

Nu

mb

er

of

stu

de

nts

Number of extinctions

0

2

4

6

8

10

12

14

16

Fre

qu

en

cy

% extinction (log scale)

Assumes your estimate of

the number of species

Phew, … no

extinction debt

What did you say?

.0001 .01 1001.000001

• Background rate: ~1 in 1,000,000

(to 1 in 10,000,000)

• Current rate: ~1 in 10,000

• This is 100-1000x background rate

• Other estimates range from 40-

10,000x background rate


Why so much uncertainty?

There are lots of assumptions

• Past extinction rates are based on (imperfect) fossil record

• Unsure about how many species went extinct that were not found

• Taxonomic definitions may differ

• Do not know how many species on Earth

• Nonetheless, extinction rate today is very high

• Based on background rates, only 1

species of bird or mammal should have

gone extinct between 1850 and 1950

• In fact, about 100 went extinct.

• 7 birds in North America alone:

Some context

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1) Why estimate?

� No data for most groups of organisms

� Future predictions

2) Use Theory of Island-Biogeography

� Big islands have more species than small islands

� Species richness declines with isolation

Herps in West Indies Birds in SE Asia

Note, log scales


1) Why estimate?

� No data for most groups of organisms

� Future predictions

2) Use Theory of Island-Biogeography

� Big islands have more species than small islands

� Species richness declines with isolation

3) Predict species losses as habitat declines

� Species # = c * Areaz

� c and z are constants, but vary depending on the

types of islands and species


S = c * Az

Is the same as:

log S = log c + z(log A)

Understanding this equation is important! Talk about it

with your neighbor to ensure you both get it.

Note, log scales


• only ~10% of all extinctions before modern

times were during mass extinctions

• >99% of all species that ever lived are extinct

• “background rate” ~ 2.5 families/million yrs

• current extinction rate – on par with previous

mass extinctions

Mass Extinctions


log c is this

intersection

z is the slope

of this line

Note, log scales


S = c * Az

log S = log c + z(log A)

(y = bx + c)

Idea behind many estimates

1) If we:

� Treat habitat patches as islands

� Know amount of habitat loss

2) Then we can:

� Predict how many species have gone extinct

� This is how it works …


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Log

Area

Log Species

Data points

for each

“island”

Patch X starts

with A (area) here

Expect this

many

species

Log A

Log S

Habitat loss

reduces the

area to here

Patch X starts

with A here

Now expect

this many

species

Log A

Log S

This

difference

gives the

number of

extinctions

(on a log

scale) Log A

Log S

1) If we:

� Treat habitat patches as islands

� Know amount of habitat loss

2) Then we can:

� Predict how many species have gone extinct

3) Can use this approach for local areas

4) Or, can apply it globally (Wilson 1989)


4) Or, can apply it globally

EO Wilson 1989

� Assume most species found in rain forest

� Assume 5 million species total

� Set z = 0.15 (a conservative value)

� Assume 1% rain forest is lost annually

� = 34 extinctions each day

Similar methods

� Future extinctions: 21-52% of species


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4) Or, can apply it globally (Wilson 1989)

� 34 extinctions each day

� Future extinctions: 21-52% of species

5) Many other estimates have been made

� Lots of assumptions

� Lots of estimated numbers in each calculation

� Lots of uncertainty

� But, all suggest that 10,000s of species will go extinct in next few decades



• Over the next few decades the extinction rate is

more likely to increase than decrease

• Proportion of species threatened with extinction:

� Fish: 3% (752 species)

� Amphibians: 33% (1856 species)

� Revised in 2004; former estimate - 5%!!

� Reptiles: 19% of 1500 species examined

� Revised in 2013; former estimate - 5% (Böhm et al.)

Extinction rate is not slowing

• Over the next few decades the extinction rate is

more likely to increase than decrease

• Proportion of species threatened with extinction:

� Fish: 3% (752 species)

� Amphibians: 33% (1856 species)

� Reptiles: 19% of 1500 species examined

� Birds: 12% (1211 species)

� Mammals: 23% (1130 species)

� Gymnosperms: 32% (242 species)

� Angiosperms: 2% (5390 species)

� Reef-building corals: 33% (231 species)

Extinction rate is not slowing Extinction rate is not slowing

At-risk species

Data deficient(unknown)

Hoffman et al. 2010. Science

% known

extinct

%

endangered

Barnosky et al. 2011. Nature

Mass extinction number 6?mass

extinction

PLEASE TELL ME IF I’M GOING TOO FAST!!!!

IF YOU WANT ME TO GO OVER SOMETHING AGAIN – PLEASE TELL ME

ASK QUESTIONS

(Waiting for student evaluations won’t help)

Documents

Extinction Today’s goals - University of Connecticuthydrodictyon.eeb.uconn.edu/.../EEB2208_2014_Lecture05_Extinction.pdf · Extinction “The present geological period has more