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Keywords:

  • Bahamas;
  • climate change;
  • dynamic equilibrium;
  • extinction;
  • hurricane;
  • island biogeography;
  • metapopulation;
  • species turnover

ABSTRACT

Aim  To document long-term rates of immigration, extinction and turnover in insular floras and evaluate the relative impacts of recent hurricane activity and climate change.

Location  Three archipelagos of small islands, in the Exuma Cays, Andros and Abacos, Bahamas.

Methods  I surveyed the floras of 194 vegetated islands in three archipelagos over several multi-year periods, spanning up to 17 years. Changes in abundance (foliar cover) of persistent populations were measured on a subset of 14 islands in the Exuma Cays over a 9-year period.

Results  Rates of plant turnover were generally low compared with other organisms, but varied among archipelagos and time periods. Turnover rates were usually higher in the second decade of this study, and extinction rates were often dramatically higher than immigration rates in the second decade, resulting in overall decreases in species richness. Turnover did not differ significantly among island types based on generalized location and surrounding water depths, and extinctions were not more likely to occur on more exposed islands. The abundance (foliar cover) of populations that did not go extinct decreased steadily over the second decade of this study, indicating, along with higher extinction rates, a generalized decline in these insular floras.

Main conclusions  Although some islands may have been at or near a state of dynamic equilibrium in the first decade of this study, average species richness declined in all three archipelagos during the second decade, when extinctions greatly outnumbered immigrations. Four major hurricanes affected the study archipelagos in the second decade of this study, although the available evidence suggests that the hurricanes were not directly responsible for the declines. Indirect effects of hurricanes such as increased herbivory and possible decreased nutrient availability, along with a long-term (25 years) increase in temperature and decline in rainfall are likely contributing factors.