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Context for extinctionContext for extinction

How many species are there? How many species are there?

How do we find out?How do we find out?

Context for extinctionContext for extinction

1.1. Extrapolate numbers based on observation that for every temperate species, Extrapolate numbers based on observation that for every temperate species, there are two tropical counterparts = there are two tropical counterparts = 3-5 million.3-5 million.

2.2. Use information on rate of discovery of new species to project forward, Use information on rate of discovery of new species to project forward, group by group = group by group = 6-7 million6-7 million..

3.3. Species size:species richness relationship – in terrestrial animals (~ 1 cm to Species size:species richness relationship – in terrestrial animals (~ 1 cm to a few meters), approximate empirical rule for each 10-fold reduction in a few meters), approximate empirical rule for each 10-fold reduction in length there are 100 x the number of species = length there are 100 x the number of species = 10 million10 million..

4.4. Do intensive counts in small areas of each taxa, extrapolate to rest of Do intensive counts in small areas of each taxa, extrapolate to rest of available habitatavailable habitat

Estimates of beetle species richness (more than 1000 species recorded in one Estimates of beetle species richness (more than 1000 species recorded in one tree) in the canopies of tropical trees (about 50,000 species), and tree) in the canopies of tropical trees (about 50,000 species), and assumptions about the proportion of non-beetle arthropods that will also be assumptions about the proportion of non-beetle arthropods that will also be present in the canopy, plus others that do not occupy the canopy – present in the canopy, plus others that do not occupy the canopy – 30 million 30 million arthropods. arthropods.

http://www.youtube.com/watch?v=gZRgibEVXJU

Total # DescribedPhylum Order E & T speciesChordates Mammals 361 5,702

Birds 316 9,956 Reptiles 124 9,347 Amphibians 35 15,000 Fishes 165 40,000

Arthropods Insects 71 1,065,000 Crustaceans 22 40,000

Plants Flowering plants 783 272,655 Conifers and cycads 5 980 Ferns and allies 30 13,025

Molluscs 126 70,000 Cnidaria Corals 2 2,175

Total # DescribedPhylum Order E & T speciesChordates Mammals 361 5,702

Birds 316 9,956 Reptiles 124 9,347 Amphibians 35 15,000 Fishes 165 40,000

Arthropods Insects 71 1,065,000 Crustaceans 22 40,000

Plants Flowering plants 783 272,655 Conifers and cycads 5 980 Ferns and allies 30 13,025

Molluscs 126 70,000 Cnidaria Corals 2 2,175 Viruses 0 5,000 Bacteria 0 4,750 Protists 0 80,000 Fungi 0 80,000 Platyhelminthes 0 25,000 Rotifera 0 1,800 Bryozoa 0 5,000 Nematoda 0 25,000

Total # Described %Phylum Order E & T species DescribedChordates Mammals 361 5,702 99

Birds 316 9,956 99Reptiles 124 9,347 99Amphibians 35 15,000 99Fishes 165 40,000 75?

Arthropods Insects 71 1,065,000 12Crustaceans 22 40,000 ?

Plants Flowering plants 783 272,655 55Conifers and cycads 5 980 1 Ferns and allies 30 13,025 87

Molluscs 126 70,000 35Cnidaria Corals 2 2,175 ?Viruses 0 5,000 1 Bacteria 0 4,750 0.5 Protists 0 80,000 5 Fungi 0 80,000 5 Platyhelminthes 0 25,000 ? Rotifera 0 1,800 ? Bryozoa 0 5,000 ? Nematoda 0 25,000 ?

http://ocean.si.edu/oceancensus

How many species are there??

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 SpeciesUS Foreign Total

Mammals 85 276 361Birds 93 223 316Reptiles 36 88 124Amphibians 26 9 35Fishes 153 12 165Molluscs 123 3 126Insects 67 4 71Arachnids 12 0 12Crustaceans 22 0 22Corals 2 0 2Animal totals 619 615 1,234

Flowering plants 782 1 783Conifers and cycads 3 2 5Ferns and allies 30 0 30Lichens 2 0 2Plant totals 817 3 820

Grand totals 1,436 618 2,054

Context for extinctionContext for extinction

How many species are there? How many species are there?

How do we find out?How do we find out?

How many have recently gone extinct? How many have recently gone extinct?

Are current rates of extinction higher than historic (pre-human) rates?Are current rates of extinction higher than historic (pre-human) rates?

Trends in recorded animal species extinctions since 1600, for which Trends in recorded animal species extinctions since 1600, for which a date is knowna date is known

• All extant species will become extinct All extant species will become extinct eventually – more than 99% of species that eventually – more than 99% of species that ever existed are now extinct.ever existed are now extinct.

• Individual species last on average 1- 10 million Individual species last on average 1- 10 million years. If we assume 10 million species, we years. If we assume 10 million species, we would then predict 100 to 1000 extinctions would then predict 100 to 1000 extinctions each century.each century.

• Current rate: birds and mammals = 1% per Current rate: birds and mammals = 1% per century (100-1000 x background rate).century (100-1000 x background rate).

Nene - Nene - Branta sandvicensisBranta sandvicensis

Extinction: happens to all species eventually

Extinction

stochasticresults from normal, random changes; more important for smaller populationsconservation solution: maintain large population sizes

deterministicconsequence 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, survivalAllee 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)

Heath hen extinction, Martha's Vineyard

0

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1900 1903 1906 1909 1912 1915 1918 1921 1924 1927 1930

N

refugeestablished

fire reduces habitat, followed by heavygoshawk predation

disease

extinction

N ~ 50

1927, N =13,mostly males

1932

and severe winter

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

F vortex

A vortex

Extinction vorticesR 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

Time

N

normal demographic fluctuations

decline in N – small catastrophe

increased pop’nvariance

Extinctions are forever - ?

ivory-billed woodpeckersmoky madtomblue pikespoonhead sculpindeepwater sculpin

Extinctions are forever - ?

ivory-billed woodpeckersmoky madtomblue pikespoonhead sculpindeepwater sculpin

1942 – last seen in US waters of L. Ontario1972 – last seen in Canadian waters1999 – 3 caught in targeted trawls2004 – 12005 – 17 in standard assessment trawls2009 > 75 (depth > 90 m)

Lazarus effect…

When is population size too small (hopeless)?Przewalski’s horse 13 Guam rail 10 black-footed ferret 6 European bison 6 Speke’s gazelle 4 dusky seaside sparrow 2…1..…0

note: these are all captive (regulated) populations….