05 December 2009

Ecology of Extinction

 Carolina Parakeet Photo: Hafner/LSU Museum of Natural Science

Extinction is a natural process. All species may by doomed to extinction, just as all born are doomed to death. Prehistoric people may have caused extinction of birds, especially on islands. Hawaii has a diverse fossil avifauna alive when Polynesians arrived (flightless ibis, goose, terrestrial owl). Why do people cause extinction? Basically the answer is ECOSYSTEM DISTURBANCE and maybe hunting. New Zealand had moas up to 12-15 feet tall. There are 27 species in the fossil record--they lived up to the 1500s.

A chronology of extinction looks like this: 1700-1775 (5 species extinct), 1800-1885 (1), 1825-1850 (10), 1850-1875 (13), 1875-1900 (12), 1900-1925 (11), 1925-1950 (4), 1970-1975 (1).

As tropical rainforests are denuded, we may expect this number to take a sharp rise in the near future.
About 55 species have gone extinct in last 200 years. Most extinction is on islands. Islands in pacific (40 species extinct),eastern and northern Pacific (4), south and central Pacific (15), Hawaii (13), New Zealand (8), Indian Ocean (6), Caribbean (2), Continents: North America (4), South America (1+), northeast Asia (1). The score = islands 48, continents 6. Islands usually lacked mammal competitors.
Causes of extinction: cats & rats--20 species (many island species were flightless), goats--11 species, diseases in Hawaii--8 species, human hunting--9 species, habitat destruction 5 species. GRAND TOTAL=42 species The causes of the remainder of extinction are unclear.

THERE IS ALWAYS A SLOW RATE OF EXTINCTION. Once a population is reduced to a certain level (for whatever reason) time will cause extinction: YOU DON'T HAVE TO SHOOT EVERY ONE. Once a population reaches a critically low level, it becomes vulnerable to density independent factors.

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