ESPM2_Biodiversity+Loss2010-1

ESPM2_Biodiversity+Loss2010-1 - 10/26/2010 Todays lecture...

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10/26/2010 1 Threats to biodiversity Are we in a sixth mass extinction crisis? ESPM 2 Oct 26 2010 Today’s lecture 1. Extinction rates: past, present and future 2. What are the main causes of species endangerment? 3. What are the consequences of species loss for human well-being? Past Extinction Patterns • RECAP: Mass extinctions • 99% of the species that ever lived have Marine animal families gone extinct – Mass extinctions – Finite lifetime • “Background extinction rate”
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10/26/2010 2 Importance of mass extinctions Impact Relatively small proportion of total Earth extinctions (4-8%) But, wiping out whole lineages (higher order taxa). E.g. 50% of families of marine animals in Permian; all dinosaurs end Cretaceous Creating a “clean slate” Timing Extinction event relatively rapid in geologic time (but exact time length unknown) Recovery is long – from records on coral reefs – 5 – 10 million years! Finite lifetimes and “background species extinction rates” • Ultimately all species go extinct • >90% of species extinctions over Earth’s history occurred outside of mass extinctions – Turnover Are today’s rates elevated over background? Lifetimes and Background Rates Background rate = Extinctions per million species per yr 0.09 2.5-5 0.2-0.4 reciprocal Same as E/MSY, extinctions per million species per year Past extinctions: “low certainty” due to incomplete fossil record
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10/26/2010 3 Recorded extinctions since 1600 From Lawton 1995 Mammal extinctions: are they different from background? DATA: 59 mammals extinct in 400 years Best known group EXPECTATION: Mammal life-span = 2.5-5 x 10 6 years; Extinction rate = 0.2-0.4 x 10 - 6 /year # Mammals = 4500 species Expected extinctions = 4500 species * (0.2 x 10 -6 extinctions/year)* 400 years = 0.36 extinctions CONCLUSION : 59/0.36 = 150 x higher than expected Range 82x – 150x Probably an underestimate: Some mammal extinctions unacknowledged; 11% mammals threatened How well documented are current extinctions? • Higher extinction rates from well- known taxa • Few recorded insect extinctions ? From Lawton 1995 – Half are Lepidoptera • Insect species have 10x longer “lifetimes” than mammals but this would only account for a factor of 10 difference in rates • What conclusions might you draw from these observations? Current extinction rates: Moderate to high certainty (best known groups) Future extinction rates (to 2050): High uncertainty – modeled based on most important threats 12-52% of species in well-known groups known to be threatened…
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10/26/2010 4 One method for estimating future extinction rates: tropical deforestation From Cox 1973 • Higher diversity in the tropics (marine and terrestrial) • Many tropical species are “narrowly endemic” – susceptible to deforestation
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ESPM2_Biodiversity+Loss2010-1 - 10/26/2010 Todays lecture...

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