PARENT SESSION
Oral Session #71: Animal Population Ecology. Presiding: J. Dooley.
Thursday, August 9, 2001. 1:00 PM to 4:15 PM. Hall of Ideas J.
The effects of island area and latitude on species extinction rates.
Forsyth, David1, Duncan, Richard2, 1 2
ABSTRACT- The Theory of Island Biogeography models the number of species present on an island as a dynamic equilibrium between immigration and extinction rates. An important assumption of the Theory is that smaller islands support fewer species relative to larger islands because smaller islands suffer higher extinction rates. While many data are consistent with this hypothesis, there have been few direct tests. We tested if extinction rates decrease with increasing island area by collating information on the fates of 151 deliberate introductions of six mammal species (pigs, goats, sheep, rabbits, cats and possums) to 84 of New Zealand's offshore islands. The introductions occurred decades to centuries ago, and the islands varied in size from 0.4 - 175 000 ha. Extinction rates for all six species did decrease with increasing island area. However, extinction rates also decreased with decreasing latitude, and this effect was far stronger than that of island area. Our results therefore confirm that smaller islands do experience higher extinction rates, but also provide a mechanism for understanding the role of latitude in shaping species range sizes.
KEY WORDS: extinction rates, island biogeography, range size, latitudinal gradients