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Threats to Biodiversity: Extinction Brook Milligan Department of Biology New Mexico State University Las Cruces, New Mexico 88003 brook@nmsu.edu Fall 2009 Brook Milligan Threats to Biodiversity: Extinction Fossil Record and Extinctions

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Threats to Biodiversity: Extinction

Brook Milligan

Department of Biology New Mexico State University Las Cruces, New Mexico 88003 brook@nmsu.edu

Fall 2009

Brook Milligan Threats to Biodiversity: Extinction

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Fossil Record and Extinctions

Brook Milligan Threats to Biodiversity: Extinction

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Fossil Record and Extinctions

Brook Milligan Threats to Biodiversity: Extinction

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Background Extinction Rates: Fossil Estimates

Species lifetime: 106 – 107 years Extinctions per year based on lifetime: 10−6 – 10−7 107 species extant 1–10 species extinct per year Rate: fraction of species extinct per year: 1 × 10−6 – 1 × 10−7

Brook Milligan Threats to Biodiversity: Extinction

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Large Percentage of Threatened Species

Brook Milligan Threats to Biodiversity: Extinction

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Impact of Human Occupancy on Extinction

Brook Milligan Threats to Biodiversity: Extinction

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Time Course of Observed Extinctions

Brook Milligan Threats to Biodiversity: Extinction

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Estimates of Current Extinction Rates: Pacific Avifauna

Hawai’i

60 endemic land birds extinct since human colonization 1,500–2,000 B.P. 20–25 species extinct in last 200 years

New Zealand

at least 44 endemic species extinct in last 1,000 years

Easter Island

at least 25 seabird species originally 8–10 species no longer breed on Easter Island 13–16 species no longer breed even on offshore islets 6 species of land birds originally; all now extinct

Polynesia

ranges of most living species much smaller than originally most species became extinct within the last 3,000 years most islands had 1–4 endemic species of flightless rails; almost all are now extinct 2–3 congeners per island typically; now only one

Brook Milligan Threats to Biodiversity: Extinction

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Estimates of Current Extinction Rates: Galapagos Islands

Unlike rest of Pacific, uninhabited before European discovery in 1535 A.D. Little human impact until 19th century 0–3 vertebrate extinctions in 4,000–8,000 years prior to human contact 21–24 populations lost since human contact Over 100× increase in extinction rate

Brook Milligan Threats to Biodiversity: Extinction

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Extinction of Mammoths

Climate implicated: end of Pleistocene climate change

Brook Milligan Threats to Biodiversity: Extinction

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Extinction of Mammoths

Climate implicated: end of Pleistocene climate change Actually, not likely due to climate Mammoth species on Aleutian Islands until relatively recently

much after end of Pleiostocene much after major climate change

Brook Milligan Threats to Biodiversity: Extinction

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Estimates of Current Extinction Rates

Rate is increasing through time for birds: Figure 7.4 (page 140) Declining with age of occupation: Figure 7.6 (page 143) Large percentage of major taxa threatened with extinction: Table 7.2 (page 142) 1% per hundred years for birds and mammals Fraction: 10−4 per year At least 100× background extinction rate

Brook Milligan Threats to Biodiversity: Extinction

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Island Biogeography

Brook Milligan Threats to Biodiversity: Extinction

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Island Biogeography

Species-area relationship S = CAZ (1) S = number of species per island A = island area C, Z = parameters describing shape of relationship (often 0.15 ≤ Z ≤ 0.35)

Brook Milligan Threats to Biodiversity: Extinction

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Species-Area Relationship

2000 4000 6000 8000 5 10 15 20 25 Area Species 0.15 0.25 0.35

Brook Milligan Threats to Biodiversity: Extinction

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Species-Area Relationship: log-log

10 50 500 5000 5 10 20 Area Species 0.15 0.25 0.35

Brook Milligan Threats to Biodiversity: Extinction

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Species-Area Relationship: Carribean

5e+01 5e+02 5e+03 5e+04 1 2 5 10 20 50 Area Species

St. Nevis

Puerto Rico Cuba S(A)=0.19 A^0.46

Brook Milligan Threats to Biodiversity: Extinction

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Predicting Extinction Rates

Brook Milligan Threats to Biodiversity: Extinction

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Species-area Predictions of Extinction: Singapore

Last 180 years: 95% original forest removed Expectation: 30% forest species lost Actual: 32% lost between 1923 and 1998

Brook Milligan Threats to Biodiversity: Extinction

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Species-area Predictions of Extinction: Neotropics

15% plant species doomed to extinction resulting from clearing during 1986–2000. 12% Amazon bird species predicted to go extinct

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Species-area Predictions of Extinction: Global

0.2–0.3% of all species (i.e., 10,000–15,000 spp.) lost per year (= 34 species per day) 2–11% of all species extinct per decade

Brook Milligan Threats to Biodiversity: Extinction

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Limitations of Species-Area Relationship

Based on “typical” values which may not characterize specific groups Assumes complete extinction of endemics, not colonization of secondary forest Assumes random elimination of habitat, even though preserves

ften focused on species-rich areas

Ignores habitat fragmentation effects

Brook Milligan Threats to Biodiversity: Extinction