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 Brook Milligan Threats to Biodiversity: Extinction
Fossil Record and Extinctions Brook Milligan Threats to Biodiversity: Extinction
Background Extinction Rates: Fossil Estimates Species lifetime: 10 6 – 10 7 years Extinctions per year based on lifetime: 10 − 6 – 10 − 7 10 7 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
Large Percentage of Threatened Species Brook Milligan Threats to Biodiversity: Extinction
Impact of Human Occupancy on Extinction Brook Milligan Threats to Biodiversity: Extinction
Time Course of Observed Extinctions Brook Milligan Threats to Biodiversity: Extinction
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
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
Extinction of Mammoths Climate implicated: end of Pleistocene climate change Brook Milligan Threats to Biodiversity: Extinction
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
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
Island Biogeography Brook Milligan Threats to Biodiversity: Extinction
Island Biogeography Species-area relationship S = CA Z (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
Species-Area Relationship 25 0.35 20 15 Species 0.25 10 0.15 5 0 0 2000 4000 6000 8000 Area Brook Milligan Threats to Biodiversity: Extinction
Species-Area Relationship: log-log 0.35 20 0.25 10 Species 0.15 5 10 50 500 5000 Area Brook Milligan Threats to Biodiversity: Extinction
Species-Area Relationship: Carribean Cuba 50 S(A)=0.19 A^0.46 20 Puerto Rico Species 10 5 St. Nevis 2 1 5e+01 5e+02 5e+03 5e+04 Area Brook Milligan Threats to Biodiversity: Extinction
Predicting Extinction Rates Brook Milligan Threats to Biodiversity: Extinction
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
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 Brook Milligan Threats to Biodiversity: Extinction
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
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 often focused on species-rich areas Ignores habitat fragmentation effects Brook Milligan Threats to Biodiversity: Extinction
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