Download Extinctions

THE REAL WORLD...
Context for extinction
How many species are there?
How do we find out?
Context for extinction
1. Extrapolate numbers based on observation that for every temperate species,
there are two tropical counterparts = 3-5 million.
2. Use information on rate of discovery of new species to project forward,
group by group = 6-7 million.
3. Species size:species richness relationship – in terrestrial animals (~ 1 cm to
a few meters), approximate empirical rule for each 10-fold reduction in
length there are 100 x the number of species = 10 million.
4. Do intensive counts in small areas of each taxa, extrapolate to rest of
available habitat
Estimates of beetle species richness (more than 1000 species recorded in one
tree) in the canopies of tropical trees (about 50,000 species), and assumptions
about the proportion of non-beetle arthropods that will also be present in the
canopy, plus others that do not occupy the canopy – 30 million arthropods.
http://www.youtube.com/watch?v=gZRgibEVXJU
Total
Phylum
Order
E&T
Chordates Mammals
361
Birds
316
Reptiles
124
Amphibians
35
Fishes
165
Arthropods Insects
71
Crustaceans
22
Plants
Flowering plants
783
Conifers and cycads
5
Ferns and allies
30
Molluscs
126
Cnidaria
Corals
2
# Described
species
5,702
9,956
9,347
15,000
40,000
1,065,000
40,000
272,655
980
13,025
70,000
2,175
Total
Phylum
Order
E&T
Chordates Mammals
361
Birds
316
Reptiles
124
Amphibians
35
Fishes
165
Arthropods Insects
71
Crustaceans
22
Plants
Flowering plants
783
Conifers and cycads
5
Ferns and allies
30
Molluscs
126
Cnidaria
Corals
2
Viruses
0
Bacteria
0
Protists
0
Fungi
0
Platyhelminthes
0
Rotifera
0
Bryozoa
0
Nematoda
0
# Described
species
5,702
9,956
9,347
15,000
40,000
1,065,000
40,000
272,655
980
13,025
70,000
2,175
5,000
4,750
80,000
80,000
25,000
1,800
5,000
25,000
Total
Phylum
Order
E&T
Chordates Mammals
361
Birds
316
Reptiles
124
Amphibians
35
Fishes
165
Arthropods Insects
71
Crustaceans
22
Plants
Flowering plants
783
Conifers and cycads
5
Ferns and allies
30
Molluscs
126
Cnidaria
Corals
2
Viruses
0
Bacteria
0
Protists
0
Fungi
0
Platyhelminthes
0
Rotifera
0
Bryozoa
0
Nematoda
0
# Described
%
species Described
5,702
99
9,956
99
9,347
99
15,000
99
40,000
75?
1,065,000
12
40,000
?
272,655
55
980
1
13,025
87
70,000
35
2,175
?
5,000
1
4,750
0.5
80,000
5
80,000
5
25,000
?
1,800
?
5,000
?
25,000
?
How many species are there??
http://ocean.si.edu/oceancensus
So far, the Census of Marine Life comprised 15,304 species of fish and
194,696 to 214,696 species of animals and plants, estimated to be roughly
10 percent of the world's total.
The census is adding about 150 to 200 species of fish and 1,700 species of
animals and plants each year.
Total Endangered & Threatened Species
US Foreign Total
Mammals
Birds
Reptiles
Amphibians
Fishes
Molluscs
Insects
Arachnids
Crustaceans
Corals
Animal totals
85
93
36
26
153
123
67
12
22
2
619
276
223
88
9
12
3
4
0
0
0
615
361
316
124
35
165
126
71
12
22
2
1,234
Flowering plants
782
Conifers and cycads 3
Ferns and allies
30
Lichens
2
Plant totals
817
1
2
0
0
3
783
5
30
2
820
Grand totals
1,436
618
2,054
Context for extinction
How many species are there?
How do we find out?
How many have recently gone extinct?
Are current rates of extinction higher than historic (pre-human) rates?
Trends in recorded animal species extinctions since 1600, for which
a date is known
• All extant species will become extinct
eventually – more than 99% of species that ever
existed are now extinct.
• Individual species last on average 1- 10 million
years. If we assume 10 million species, we
would then predict 100 to 1000 extinctions
each century.
• Current rate: birds and mammals = 1% per
century (100-1000 x background rate).
Nene - Branta sandvicensis
Extinction: happens to all species eventually
Extinction
stochastic
results from normal, random changes; more important for smaller
populations
conservation solution: maintain large population sizes
deterministic
consequence of some progressive change in environment - addition of
predator, loss of food source, degradation/loss of habitat
conservation solution: identify and manage causes
Extinction
Probability of extinction increases as population size
decreases
Probability increases with length of time
Extinction
higher probability per unit time for species with:
•
•
•
•
•
smaller range
fewer subpopulations
low migration among subpopulations
highly stochastic environment
low genetic diversity?
Extinction
primary species of concern tend to be large animals
•
•
•
•
no clonal propagation
long generation time
small number of progeny
low dispersal rates – inability to recolonize or escape catastrophic
events
• species in stable environments
Causes of extinction
Population extinctions occur due to:
• intrinsic factors
– demographic stochasticity – changes in sex ratio, reproduction,
survival
Causes of extinction
Population extinctions occur due to:
• intrinsic factors
– demographic stochasticity – changes in sex ratio, reproduction,
survival
Allee effect - threshold density or N below which population goes
to extinction
• due to social interactions, physical alterations of environment,
probability of finding a mate, etc.
stanfordalumni.org
Causes of extinction
Population extinctions occur due to:
• intrinsic factors
– demographic stochasticity
– genetic stochasticity - founder effect, genetic drift, inbreeding –
genetic load
Causes of extinction
Population extinctions occur due to:
• intrinsic factors
– demographic stochasticity
– genetic stochasticity
• extrinsic factors
– environmental stochasticity
• variation in predators, pathogens, food supply (biotic)
– catastrophe
• fires, floods, droughts (abiotic)
900
Heath hen extinction, Martha's Vineyard
800
700
N
600
500
400
N ~ 50
refuge
established
fire reduces habitat,
followed by heavy
goshawk predation
and severe winter
1927, N =13,
mostly males
300
200
disease
100
1932
extinction
0
1900 1903 1906 1909 1912 1915 1918 1921 1924 1927 1930
extrinsic factors
intrinsic factors
Most extinctions are due to multiple factors interacting
simultaneously
For example: causes of fish extinctions in N. America:
physical habitat alteration (73%)
introduced species (68%)
chemical pollution (38%)
hybridization (38%)
overharvest (15%)
Extinction vortices
Extinction vortices
A vortex
F vortex
Extinction vortices
R vortex (demographic, based on intrinsic rate of increase, r)
• chance decrease in N increases variance of the population growth rate
Var(r)
• population becomes more vulnerable to environmental stochasticity
normal demographic
fluctuations
decline in N – small catastrophe
N
increased pop’n
variance
Time
Extinctions are forever - ?
ivory-billed woodpecker
smoky madtom
blue pike
spoonhead sculpin
deepwater sculpin
Extinctions are forever - ?
ivory-billed woodpecker
smoky madtom
blue pike
spoonhead sculpin
deepwater sculpin
1942 – last seen in US waters of L. Ontario
1972 – last seen in Canadian waters
1999 – 3 caught in targeted trawls
2004 – 1
2005 – 17 in standard assessment trawls
2009 > 75 (depth > 90 m)
Lazarus effect…
When is population size too small (hopeless)?
Przewalski’s horse
Guam rail
black-footed ferret
European bison
Speke’s gazelle
dusky seaside sparrow
13

10

6

6

4

2…1..…0
note: these are all captive (regulated) populations….