AEC 360  Ecology

Lecture 19:  Extinction and Conservation

I.  Causes of extinction

    A.  Natural causes

    B.  Habitat fragmentation
        1.  Lemurs and Malagasy forest

       2.  Longleaf pine woodland habitat  loss in the southeastern US
             -Loss of longleaf pine forest
            -Converted to agriculture
            -Fire suppressed
            -Beaver exterminated

    C.  Overhunting
        1.  Extinction of Pleistocene megofauna
        2.  Extinction of Moas
            --Moaris arrived in New Zealand ~800 yrs ago
            --Initial Moa pop. Size = ~160,000
            --1000's of Moa remains at archeological sites
            --Moa demography and behavior led to rapid demise

    D.  Introduced species
        1.  Brown tree snake
            --Arrived to Guam from New Guinea
            --Has caused extinction of 12 bird species
            --Major efforts to prevent introduction to Hawaii

    E.  Climate  change and extinction
       -Examples include Golden Toad and Monteverde Harlequin frog

II.  Pathways to extinction
    A.  Carolina parakeet
        -- extinct from overhunting

        -Flourished in NC swamps and dense forest
        -Attacked agricultural fruits

    B.  Passenger pigeon
        1.  Once among the most abundant birds on earth
        2.  Nomadic and flocking behavior a response to nut production by trees
        3.  Suffered from forest loss
        4.  Railroad and telegraph accelerated hunt 

        5.  Ecosystem impacts include:
           - Physical damage to trees
           - Deposited large amounts of excrement at roosts
           - Selectively consuming red oak (promoting white oak dominance)

    C.  Heath Hen
        1.  Once common from New England to Virginia
        2.  1876, only on Martha’s Vineyard
        3.  1900, fewer than 100 survivors
        4.  1907, refuge established, 50 birds
        5.  1915, recovery, 2000 individuals
        6.  1916, catastrophic fire, followed by severe winter, 100+ individuals remain
        7.  1920, recovery 200+ individuals
        8.  1920, disease reduces pop. size to <100
        9.  1932, extinct, due to inbreeding depression??, too many males

    D.  The Extinction Vortex
        1.  A number of demographic and genetic factors can conspire to further reduce sizes of small populations
        2.  These include inbreeding, genetic drift, and random demographic factors
        3.  Further compounded by natural catastrophe and human impacts

III.  Conservation Approaches
    A.  Population Viability Analysis
        1.  Use population models to determine the most effective strategies for conservation
        2.  Can pinpoint years or stages of survivorship are most important

    B.  Example:  Should dams be breached for Chinook Salmon?
        1. Conducted population viability analysis
        2. Determined population growth rates under several conditions (fishing or not, dam breach or not)
        3. Found that improving migration mortality can not make λ > 1
        4. Instead, improving first year survival or estaurine survival would have greatest positive effect